Microbial Plant Pathogens E-Book

Perumal Narayanasamy

• Herausgeber: John Wiley & Sons
• Kategorie: Fachliteratur
• Sprache: Englisch

Seitenzahl: 3097

Veröffentlichungsjahr: 2016

Beschreibung

Healthy seeds and propagules are the basic requirement for producing good grains, fruits and vegetables needed for human survival and perpetuation. Dispersal of microbial plant pathogens via seeds and propagules has assumed more importance than other modes of dispersal, as infected seeds and propagules have the potential to become the primary sources of carrying pathogen inoculum for subsequent crops. Several diseases transmitted through seeds and propagules have been shown to have the potential to damage economies as a result of huge quantitative and qualitative losses in numerous crops. Hence, it is essential to rapidly detect, identify and differentiate the microbial plant pathogens present in seeds and propagules precisely and reliably, using sensitive techniques.

Microbial Plant Pathogens: Detection and Management in Seeds and Propagules provides a comprehensive resource on seed-borne and propagule-borne pathogens. Information on the biology of microbial pathogens, including genetic diversity, infection process and survival mechanisms of pathogens and epidemiology of diseases caused by them, are discussed critically and in detail to highlight weak links in the life cycles of the pathogens.
Development of effective disease management systems, based on the principles of exclusion and eradication of pathogens and immunization of crop plants to enhance the levels of resistance of cultivars to diseases, has been effective to keep the pathogens at bay. The need for production of disease-free seeds/propagules has been emphasized to prevent the carryover of the inoculum to the next crop or introduction of the pathogens to other locations. Effectiveness of adopting simple cultural practices and development of cultivars resistant to diseases through traditional breeding methods or biotechnological approach have resulted in reducing the pathogen inoculum and disease incidence. Although application of different chemicals may reduce the disease incidence effectively, biological management of crop diseases, employing potential biological control agents have to be preferred to preserve the agroecosystems. Greater efforts have to be made to integrate compatible strategies to enhance the effectiveness of diseases management systems.
Protocols appended at the end of relevant chapters form a unique feature of this book to enable the researchers to fine-tune their projects.

This 2 volume set provides comprehensive and updated information about the economically-important groups of microbial plant pathogens carried by seed and propagules. Graduate students, researchers and teachers of plant pathology, plant protection, microbiology, plant breeding and genetics, agriculture and horticulture, as well as certification and quarantine personnel will find the information presented in this book useful.

Leseprobe

Table of Contents

Cover

Volume 1

Title Page

Preface

Acknowledgement

Volume 1: Pathogen Detection and Identification

1 Introduction

1.1 Concepts and Implications of Pathogen Infection of Seeds and Propagules

1.2 Economic Importance of Seed‐ and Propagule‐Borne Microbial Pathogens

1.3 Nature of Seed‐ and Propagule‐Borne Microbial Pathogens

1.4 Development of Crop Disease Management Systems

References

2 Detection and Identification of Fungal Pathogens

2.1 Detection and Differentiation of Fungal Pathogens in Seeds

2.2 Detection and Differentiation of Fungal Pathogens in Propagules

2.3 Appendix

References

3 Biology of Fungal Pathogens

3.1 Biological Characteristics

3.2 Physiological Characteristics of Fungal Pathogens

3.3 Genotypic Characteristics of Fungal Pathogens

3.4 Influence of Storage Conditions

3.5 Appendix

References

4 Process of Infection by Fungal Pathogens

4.1 Invasion Paths of Seedborne Fungal Pathogens

4.2 Invasion Paths of Propagule‐Borne Fungal Pathogens

References

5 Detection and Identification of Bacterial and Phytoplasmal Pathogens

5.1 Detection and Identification of Bacterial Pathogens

5.2 Detection of Bacterial Pathogens in Propagules

5.3 Detection of Phytoplasmal Pathogens

5.4 Appendix

References

6 Biology and Infection Process of Bacterial and Phytoplasmal Pathogens

6.1 Biology of Bacterial Pathogens

6.2 Disease Cycles of Seedborne Bacterial Pathogens

6.3 Disease Cycles of Propagule‐Borne Bacterial Pathogens

6.4 Biology of Phytoplasmal Pathogens

6.5 Disease Cycles of Phytoplasmal Pathogens

6.6 Appendix

References

7 Detection and Identification of Viruses and Viroids

7.1 Detection of Viruses in Seeds

7.2 Detection of Viruses in Propagules

7.3 Detection of Viroids in Seeds

7.4 Detection of Viroids in Propagules

7.5 Appendix

References

8 Biology and Infection Process of Viruses and Viroids

8.1 Characteristics of Plant Viruses

8.2 Biological Properties of Viruses

8.3 Infection Process of Plant Viruses

8.4 Characteristics of Viroids

8.5 Infection Process of Viroids

References

Index

Volume 2

Title Page

Preface

Acknowledgement

Volume 2: Epidemiology and Management of Crop Diseases

9 Epidemiology of Seed‐ and Propagule‐Borne Diseases

9.1 Epidemiology of Fungal Diseases

9.2 Epidemiology of Bacterial Diseases

9.3 Epidemioloy of Virus Diseases

References

10 Crop Disease Management: Exclusion of Pathogens

10.1 Health Status of Seeds and Propagules

10.2 Plant Quarantines for Preventing Entry of Microbial Pathogens

10.3 Production of Disease‐Free Seeds and Propagules

10.4 Appendix

References

11 Crop Disease Management: Reduction of Pathogen Inoculum

11.1 Reduction of Pathogen Inoculum by Cultural Practices

11.2 Reduction of Pathogen Inoculum by Physical Techniques

11.3 Reduction of Pathogen Inoculum by Chemical Techniques

References

12 Crop Disease Management

12.1 Types of Disease Resistance: Enhancement of Genetic Resistance of Crop Plants

12.2 Identfication of Sources of Resistance to Crop Diseases

12.3 Improvement of Disease Resistance Through Biotechnological Approaches

References

13 Crop Disease Management: Biological Management Strategies

13.1 Evaluation of Biotic Agents for Biological Control Potential

13.2 Evaluation of Abiotic Agents for Biological Control Potential

13.3 Methods of Application of Formulated Products of Biological Control Agents

13.4 Integration of Biological Control with Other Management Practices

References

14 Crop Disease Management: Chemical Application

14.1 Application of Fungicides

14.2 Application of Chemicals Against Bacterial Diseases

14.3 Application of Chemicals Against Virus Diseases

References

15 Crop Disease Management: Integration of Strategies

15.1 Development of Integrated Disease Management Systems

15.2 Management of Fungal Diseases

15.3 Management of Bacterial Diseases

15.4 Management of Virus Diseases

References

Index

End User License Agreement

List of Tables

Chapter 02

Table 2.1 Effect of alkali treatments on the colony diameter and sporulation of seedborne fungi associated with peanut seed lots* (Elwakil et al. 2007).

Table 2.2 Comparative effectiveness of treatments with electrolyzed water (AEW) or sodium hypochloride (NaOCl)

a

(Bonde et al. 2003).

Table 2.3 DNA contents (pg/µg plant DNA) of

Microdochium majus

and

M. nivale

in pooled historical grain samples of wheat and barley during (1957–2000) (Nielsen et al. 2013). From each period, the sample was pooled using one sample per year which was again pooled from four samples in the individual year.

Table 2.4 Quantification of

V. dahliae

using quantitative polymerase chain reaction (qPCR, mean ± standard deviation) in commercial spinach seed lots (Duressa et al. 2012).

Table 2.5 Variations in in vitro growth, in vitro levels of DON and zearalenone produced, and disease rating of four typed

Fusarium

isolates compared to the

F. graminearum

isolates collected in North Carolina (Walker et al. 2001).

Chapter 03

Table 3.1 Assessment of variability in pathogenic potential of fungal pathogens using differential cultivars/genotypes of crop plants.

Table 3.2 Average spread in wheat spikelets and toxin accumulation in inoculated spikelets in cultivar Norm after inoculation with NIV‐ or DON‐type isolates of

F. graminearum

clade from Lousiana (A) or NIV‐type isolates of

F. graminearum

and

F. asiaticum

from Louisiana (B) (Gale et al. 2011).

Chapter 04

Table 4.1 Invasion paths of seedborne fungal pathogens.

Table 4.2 Effects of

Fusarium graminearum

on disease incidence and mycotoxin accumulation (µg g

–1

) in grains of seven wheat cultivars (Yoshida and Nakajima 2010): A: Chikugoizumi; B: Norin 61; C: Shiroganekomugi; D: Minaminokaori; E: Saikai 165; and F: Sumai 3.

Chapter 05

Table 5.1 Comparative efficiency of three different laboratory methods in detecting

X. campestris

pv.

undulosa

in wheat seeds and influence of seed infestation on seedling infection (Frommel and Pazos 1994).

Table 5.2 Comparative efficacy of MC‐sELISA and ELISA formats in detecting

Acidovorax avenae

pv.

citrulli

in seeds of watermelon and cucumber from plants infected by the pathogen (Himananto et al. 2011).

Table 5.3 Colony formation of sorted

Cmm

cells labeled with Calcein AM, cFDA, PI or combinations of Calcein AM, cFDA with PI, after plating on GNA medium (Chitaara et al. 2006).

Table 5.4 Detection by PCR assays using different target sequences of seedborne bacterial plant pathogens.

Table 5.5 Detection of

Xylella fastidiosa

(

Xf

) by PCR and isolation of

Xf

in culture from sweet orange seedlings obtained from seeds extracted from CVC‐affected fruits (Li et al. 2003).

Table 5.6 Comparative sensitivity of PCR formats determined by using different CFUs of

Pseudomonas syringae

pv.

phaseolicola

(Schaad et al. 2007).

Table 5.7 Comparative efficacy of the BX‐S and Aac primer sets in IMS‐real‐time PCR assay for the detection of

Acidovorax avenae

ssp.

citrulli

(

Aac

) in seed lots of watermelon with different levels of infestation (Bahar et al. 2008).

Table 5.8 Comparative efficacy of ELISA, DIG‐labeled PCR, and nested PCR assays for the detection of

C. michiganensis

ssp.

sepedonicus

in seed tubers and stem samples of potato (Lee et al. 2001).

Table 5.9 Virulence characteristics of Idaho isolates of

Streptomyces

on radish in comparison to type strain of

S. scabiei

T

(ATCC 49173) (Wanner 2007).

Table 5.10 Detection of “

Ca.

Liberibacter asiaticus” in seedlings by qPCR assay at different time intervals between planting seed and DNA extraction and testing (Hartung et al. 2010). Total number of tests (1216) performed from January 2006 to December 2006.

Table 5.11 Influence of temperature range on zebra chip disease development in inoculated potato plants (Munyaneza et al. 2012).

Table 5.12 Comparative efficacy of diagnostic techniques in detecting

L. xyli

ssp.

xyli

infection in sugarcane leaf 5 (fourth leaf basal to leaf 1; fully expanded youngest leaf) of sugarcane stalks (7 month old) (Grisham et al. 2007).

Chapter 06

Table 6.1 Quantification of “

Ca

. Liberibacter asiaticus” genomes in DNA extracts of fruit tissues of huanglongbing (HLB‐) infected citrus plants using qPCR assay (Li et al. 2009a).

Table 6.2 Influence of temperature on development of ZC symptom and pathogen growth (potato plants inoculated with ZC pathogen and maintained in growth chamber at different temperatures) (Munyaneza et al. 2012).

Chapter 07

Table 7.1 Plant viruses belonging to different families, genera, and type species transmitted through seeds/propagules of infected plants (Mayo and Brunt 2007).

Table 7.2 Seed transmission of plant viruses in different host plant species, as revealed by immunoassays.

Table 7.3 Infectivity of RYMV in extracts from seeds of rice and wild host species as determined by ELISA at two stages (Allarangaye et al. 2006).

Table 7.4 Confirmation of ELISA results by vascular puncture inoculation of corn plants (Forster et al. 2001).

Table 7.5 Detection of

Plum pox virus

‐M in whole seeds and seed parts (Milusheva et al. 2008).

Table 7.6 Viruses detected in propagules of crops using immunoassays.

Table 7.7 Comparative efficiency of the polymerase chain reaction (PCR) and grafting for detection of geminiviruses in sweet potato plants (Li et al. 2004).

Table 7.8 Comparison of levels of sensitivity and specificity of methods for detection of

Plum pox virus

(Capote et al. 2009).

Table 7.9 Viroids belonging to different families and genera transmitted through seeds/propagules of infected plants (Mayo and Brunt 2007).

Chapter 10

Table 10.1 Effect of heat treatments on survival of strawberry plants infected by angular leaf spot disease under field conditions (Turechek and Peres 2009).

Chapter 14

Table 14.1 Effect of timings of fungicide application at anthesis on infection parameters and mycotoxin accumulation in wheat cultivar Norin 61 in 2006 (Yoshida et al. 2012).

Table 14.2 Effect of treatment with PA in combination with different seed drying temperatures on seed transmission of BFB in watermelon (Hopkins et al. 2003).

List of Illustrations

Chapter 02

Figure 2.1 Sorting of wheat kernels damaged by

Fusarium

spp., using high‐speed optical sorter (Scam Master II DE). Rapid separation of Fusarium damage kernels (FDK) with different concentrations of deoxynivalenol (DON).

Figure 2.2 Effectiveness of acidic electrolyzed water (AEW) and sodium hypochlorite (NaOCl) in eliminating the wheat kernel bunt pathogen

Tilletia indica

. Note the inhibition of development of the pathogen in the medium amended with seed washes obtained after treatment with AEW and NaOCl.

Figure 2.3 Detection of

Colletotrichum lindemuthianum

in infected bean seed powder containing different concentrations of the pathogen, using nested PCR assay. Lanes: M‐100‐bp DNA ladder; 1, 100%; 2, 80%; 3, 60%; 4, 40%; 5, 20%; 6, 10%; 7, 8%; 8, 6%; 9, 4%; 10, 2%; 11, 1%; 12, 0%; 13, anthracnose‐resistant genotype G2333; 14, negative control (water); and 15, positive control (pathogen DNA).

Figure 2.4 Estimation of biomass of

Septoria tritici

in inoculated wheat leaves, after different periods of incubation at 12°C and 18°C employing PCR/PicoGreen assay.

Figure 2.5 Detection of

Verticillium longisporum

in spinach seed predominantly infected by

V. dahliae.

Note the presence of 340 bp amplicon unique to

V. longisporum

detected by PCR assay. Lane 1: DNA template extracted from a pure culture of

V. longisporum

strain Bob 70; lane 2: DNA template of

V. longisporum

strain Bob 70 in seed DNA background; lane 3: DNA templates extracted from

V. dahliae

strain VdLs 16; lanes 4–18: templates expressed in seed lots; lane 19: negative control (water); lane L: DNA standards.

Figure 2.6 Assessment of DNA contents of

Sclerotinia sclerotiorum

present along with

Botrytis cinerea

in mixed populations using quantitative PCR assay. Bars indicate the standard errors of means.

Figure 2.7 Differentiation of isolates of

Fusarium graminearum

,

F. avenaceum

and

F. culmorum

based on random amplified polymorphic DNA (RAPD) profiles formed by Operon primer OPB15. Lane 1: Molecular standards; lane 2:

F. avinaceum

; lane 3:

F. culmorum

(R‐6565); Lanes 4 and 5:

F. graminearum

(R‐6914 and R‐6925) and lanes 6 to 29: isolates 1 to 24 of

F. graminearum

from North Carolina, USA.

Figure 2.8 Detection of

Tilletia indica, T. walkeri

and

T. horrida

by PCR assay using

T. indica

‐specific primer pairs Ti17M/M2 and Ti57M1/M2. Note products of similar size produced from DNA of

T. indica

and

T. walkeri

, but not from

T. horrida

. Lanes 1 and 14: Molecular ladder; lanes 2, 3, 6, 7, 10 and 11:

T. indica

; lanes 4, 8 and 12:

T. walkeri

and lanes 5, 9 and 13:

T. horrid

.

Figure 2.9 Differentiation of isolates of

T. indica, T. walkeri, T. horrida

and

T. barclayana

based on the sequence analysis of ITS region

Sca

I restriction enzyme digest of ITS, 5.8S and ITS ribosomal DNA PCR products differentiated by agarose gel electrophoresis. Lanes 1 and 20: DNA ladder; lanes 2–7:

T. indica

; lanes 8–13:

T. walkeri

; lanes 17–19:

T. barclayana.

Chapter 03

Figure 3.1 Determination of DNA contents of

Ramularia collo‐cygni

in different layers of leaves and ears of barley cultivar Lanark 2009 at different sampling dates, using quantitative assay.

Figure 3.2 Assessment of virulence and toxigenic potential of isolates representing genetic variation in

Fusarium graminearum

present in Louisiana State, USA. Gray columns: average spread in spikelets in point‐inoculated wheat spikes of susceptible cultivar Norm. Black columns: average trichothecene mycotoxins accumulation in ppm in inoculated spikelets; Fg:

Fusarium graminearum

; GC: Gulf coast population of

F. graminearum

; Fa:

F. asiaticum

; NIV: nivalenol; DON: deoxynivalenol.

Chapter 04

Figure 4.1 Response of chasmogamous (open‐flowering) and cleistogamous (closed‐flowering) barley to inoculation with

Fusarium graminearum

at different days after anthesis (daa). (a) Spikes at 2 daa; (b) spikes at 8 daa; (c) spikes at 10 daa; (d) view of ventral side of floret at 6 daa; and (e) 9 daa. Until 6 daa, anthers remained within closed florets; most anthers were partially extruded at 8 daa and anthers were entirely extruded at 10 daa. Arrows indicate extruded anthers.

Figure 4.2 Effects of inoculation of two barley cultivars (1) Nishinochikara and (2) Minorimuge on the appearance of mature grains, following inoculation with

Fusarium graminearum

at different days after anthesis (daa). (a) Unioculated; (b) inoculated at anthesis; (c) inoculated at 10 daa; and (d) inoculated at 20 daa. Mycotoxins contents (DON + NIV) ranged from 0.0 to 9.0 µg g

–1

in Nishinochikara samples and from 0 to 10.3 µg g

–1

in Minorimuge samples.

Figure 4.3 Visualization by light microscopy of pathogen invasion in floral parts of rice spikelets inoculated with

Ustilaginoidea virens

. Note infection of three special filaments located between ovary and lodicules near the lemma in semithin sections. (a, b) Floret filled with mass of dense pathogen hyphae; arrows show location of three infected filaments; and (c) shrunken uninfected filaments (F1) surrounded by dense hyphal mass.

Figure 4.4 Transmission electron microscopic visualization of infection process of

Ustilaginoidea virens

in infected rice lodicules. Note the presence of (a): pathogen hyphae (PH) in firm contact with lodicules; (b) and (d): intracellular colonization in the outer layers of cells of lodicules and (c): light microscopic examination showing hyphae (arrowed) extending into intracellular space, but not reaching the vascular tissues.

Chapter 05

Figure 5.1 Isolation of

Clavibacter michiganensis

subsp.

michiganensis

(

Cmm

) from tomato seed extracts on YPGA medium at different concentrations before and after immunomagnetic separation (IMS). Left: saprophytic bacterial populations at high levels and right: effective reduction of saprophytic bacterial population by IMS, favoring the development of

Cmm

.

Figure 5.2 Detection of

Xanthomonas campestris

pv.

vesicatoria

(

Xcv

) by immunogold electron microscopy using the monoclonal antibody MAB 4AD2 specific to the pathogen. Note the uniform distribution of immunospecific epitopes on the cell wall of

Xcv

.

Figure 5.3 (a) Visualization of “

Candidatus

Liberibacter asiaticus” in the transverse sections of phloem sieve element in seed coat of grapefruit cultivar Conners using transmission electron microscopy (TEM). B: bacterial cells; SP: sieve plate, and M: mitochondria (b) Cross‐section of phloem sieve element showing large number of bacterial cells.

Figure 5.4 Detection of

Xanthomonas campestris

pv.

campestris

(

Xcc

) in

Brassica

seed using multiplex PCR assay targeting sequences of

hrpF

gene. (a) Multiplex reactions for amplification of pathogen‐specific 619 bp and 360 bp products from

Brassica

samples and (b) pathogen‐specific

hrpF

product of 619 bp amplified from

X. campestris

.

Figure 5.5 Detection of

Xylella fastidiosa

(

Xf

) in citrus fruits by polymerase chain reaction (PCR). Note the presence of pathogen‐specific 472 bp amplicon (arrow) in different fruit tissues. Lane 1: peduncle; lane 2: exocarp; lane 3: mesocarp; lane 4: endocarp; lane 5: septa; lane 6: central axis; lane 7:

Xf

strain 9a5c; lane 8: central axis of healthy fruit (negative control). DNA ladder (100 bp) is positioned at the extremities.

Figure 5.6 Detection of

Xylella fastidiosa

(

Xf

) by PCR assay in different seed tissues and emerging seedlings, as revealed by

Xf

‐specific product of 472 bp (arrow). DNA ladder (100 bp) is positioned at the extremities. Lane 1 and 11:

Xf

strain 9a5c DNA (positive controls); lane 2: seed coat; lanes 3 and 4: embryos; lanes 5–7: in vitro isolates from cultivars Valencia, Natal, and Pera; lanes 8–10: seedlings of cultivars Pera, Natal, and Valencia; lane 12: water (negative control).

Figure 5.7 Detection of “

Candidatus

Liberibacter asiaticus” in greenhouse‐grown sweet orange trees inoculated by bud grafting. Monitoring pathogen distribution by determining populations of pathogen (genomes) in bark tissues of stem and root at different positions by qPCR assays.

Figure 5.8 Determination of detection threshold of

Pseudomonas phaseolicola

pv.

phaseolicola

, using standard PCR and nested PCR formats. Nested PCR assay was more sensitive than standard PCR assay. Ethidium bromide‐stained bands (white on black background, upper panel) and bands detected by Southern hybridization (black bands on white background, lower panel) represent pathogen DNA concentrations in a descending order; two left lanes in each group correspond to duplicate PCR reactions with external primers and two right lanes to duplicate reactions with nested primers.

Figure 5.9 Detection of

Acidovorax avenae

subsp

. avenae

by nested PCR assay in spiked rice seed samples (a) without enrichment and (b) with enrichment in SP liquid medium. Note the presence of amplified product of 224 bp from pathogen DNA at different concentrations. Lane 1: (1–2) × 10

4

; lane 2: (1–2) × 10

3

; lane 3: (1–2) × 10

2

; lane 4: 10–20; lane 5: 1–2 CFU g

–1

of seeds; lane 6: uninoculated seed extract.

Figure 5.10 (a) Relationship between populations of pectolytic erwinias and seed germination (negative) and (b) relationship between erwinia populations and disease incidence (positive).

Figure 5.11 Comparative efficacies of nested PCR and DIG‐labeled PCR formats for the detection of

Clavibacter michiganensis

subsp.

sepedonicus

in field‐grown potato cultivars. (a) Nested PCR products on agarose gel (1%); Rus: Russet Burbank; Nor: Norchip; T1–T4: tuber samples; S1–S4: stem samples; lane S: DNA standard (1 kb) and C‐w: water control. (b) DIG‐labeled PCR products dot‐blotted on nylon membrane detected using NBT and BCIP. Row a: samples Rus T1–T3, Red T1, Red T2, and Nor T1; row b: samples Nor T2–T4 and Rus S1–S3; row c: samples Rus S4 and C‐w.

Figure 5.12 Assessment of genotypic diversity of eleven strains of

Xanthomonas citri

subsp.

citri

using BOX‐, ERIC‐, and rep‐PCR assays. M: molecular size standards. Genomic profiles were separated on agarose gels and stained with ethidium bromide.

Figure 5.13 Detection of

Clavibacter xyli

subsp.

xyli

(

Cxx

) in sugarcane vascular samples by PCR assay and Southern blotting. (a) PCR products were stained with ethidium bromide; lane 1: DNA standards; lane 2: cultured pathogen cells; lane 3: water control; lanes 4–23: sugarcane vascular samples. (b) Autoradiograph of gels in panel (a) probed with

32

P labeled L1/G1, primed PCR product from

Cxx

genomic DNA.

Figure 5.14 Detection and identification of Idaho

Streptomyces

isolates with three primer sets for amplification of the same set of DNA templates. (a) Primers ASE3/Scab2m producing 474 bp fragment; (b) primers ASE3/Aci2 producing 472 bp fragment; and (c) primers Aci1/Aci2 producing 1278 bp fragment. Lane M: DNA ladder; lane 1:

S. scabies

ATCC49173; lane 2: IDOI‐16c (

S.europaiscabiei

); lane 3:

S. acidiscabies

T

ATCC49003; lane 4:

S. acidscabies

ME02‐6987A; lane 5: IDOI‐6.2A; lane 6: IDOI‐12c; lane 7: ID03‐1A; lane 8: ID03‐2A; lane 9: ID03‐3A.

Figure 5.15 Detection of huanglongbing (HLB) infection by biological tests on sour orange seedlings S389, S433, and S391 from left, and healthy sour orange seedlings of the same age on the right.

Figure 5.16 Detection of two strains of

Ralstonia solanacearum

by PCR using two primer sets AKIF‐AKIR and 2IF‐2IR: (a) MAFF 211490 and (b) MAFF 211471. Lanes 1 and 2: 2.2 × 10

4

 CFU; lanes 3 and 4: 2 × 10

3

 CFU; lanes 5 and 6: 6.2 × 10

2

 CFU; lanes 9 and 10: 2 CFU; lane 11: control without template; lane m: DNA ladder marker (100 bp).

Figure 5.17 Detection of

Clavibacter michiganensis

subsp.

sepedonicus

by PCR assay performed at two melting temperatures of 85.5°C (positives) and 94.5°C (negatives). Left: DNA size standards; lanes 1–5: negative samples; lanes 6–8: positive samples generating a 152 bp amplicon.

Figure 5.18 Optimization of real‐time PCR assay with primer pair VM3/4 to illustrate sensitivity and linearity of the assay using 10‐fold serial dilutions of

Xanthomonas citri

pv.

aurantifolii

B DNA. (a) Sensitivity of the real‐time PCR assay; and (b) standard curve showing linear relationship between cycle number and pathogen concentration.

Figure 5.19 Detection of

Xanthomonas citri

(

Xc

) 3213 by real‐time PCR assay in herbarium samples collected in 1912. Lanes 1 and 2: A1 extract and DNA; lanes 3 and 4: A2 extract and DNA; lanes 5 and 6: F3 extract and DNA; lanes 7 and 8: F4 extract and DNA; lane 9: water control; lane 10: 10 ng of

Xc

3213 DNA; lanes 11–14: Kingsley’s primer pair PCR products; lane 11: A1 DNA; lane 12: A2 DNA; lane 13: F3 DNA; lane 14: F4 DNA; lane 15: water control; lane 16: 10 ng of

X. citri

pv.

citri

A DNA; lane M: DNA marker standards.

Figure 5.20 Detection of

Xanthomonas axonopodis

pv.

citri

(Xac) by isolation, standard PCR, and real‐time PCR assays in citrus fruit lesions. Bars represent percentages of positive detections by different detection methods.

Figure 5.21 Patterns of hybridization of DIG‐labeled PCR amplicons from

Erwinia carotovora

subsp.

atroseptica

(

Eca

),

E. chrysanthemi

(

Ec

), and

Clavibacter michiganensis

subsp. s

epedonicus

(

Cms

) on the oligonucleotides array. a:

Eca

strain 31; b:

Ec

strain 340; and c:

Cms

strain R3. Positive hybridization signals are seen as dark spots within template circles.

Figure 5.22 Patterns of hybridization of DIG‐labeled PCR amplicons from a mixture of

E. carotovora

subsp.

atroseptica

(

Eca

) and

E. chrysanthemi

(

Ec

) on the oligonucleotides array. (a) Mixture of

Eca

strain 31 and

Ec

strain 340; (b) DNA from

Eca

‐inoculated potato tuber tissues; and (c) DNA from potato tissue culture. Positive hybridization signals are observed as dark spots within template circles.

Figure 5.23 Amplification curves of fluorescent signals from different isolates of “

Candidatus Phytoplasma mali

” (AT1), “

Ca. P. prunorum

” (ESFY1and ESFY2), and “

Ca. P. pyri

” (PD1) following real‐time PCR. Top: qAP‐16S‐F/R primers; bottom: AP‐MGB probes at 64°C as hybridization temperature.

Figure 5.24 Differentiation of strains of Flavescence dorée (FD) phytoplasma in Serbia using restriction fragment length polymorphism analysis. (a) FD0f3/r2 amplicons; (b) rp(V)F2/rpR1 amplicons of FD‐infected Serbian sample (A10). Fragment sizes from top to bottom: 310, 281, 271, 234, 194, 118, and 72.

Figure 5.25 Detection of potato purple top phytoplasma by real‐time PCR assay. Eight potato plants showing positive reaction in nested PCR assay were analyzed along with a sample from healthy potato plants cultivar Shepody.

Figure 5.26 Patterns of RFLP obtained following digestion of amplicons from “

Ca. Phytoplasma mali

” isolates with (a)

Fau

I and (b)

Hpa

II restriction enzymes. (a) Isolates 246, 147, 230, T‐4, T‐11, 221, 239, 241, AP (AT‐1 subtype), T‐9, T‐16 (AP‐15 subtype), and T‐10 (AT‐2 subtype). (b) Pattern 1 isolates: 243, 244, 246, 45, 147, 230, T‐4, T‐11, 221, 241, and AP (AT‐1 subtype); pattern 2 isolates: T‐9, T‐16 (AP‐15 subtype), T‐10 (AT‐2 subtype), and AP (AT‐1 subtype). M: DNA size markers.

Figure 5.27 Comparative sensitivities of PCR assays using different primers amplifying different amplicons from the DNA of

Spiroplasma citri.

(a) Primer P89f/r producing 707 bp product; (b) primer P58‐6f/4r producing a 450 bp product; and (c) Sprialin‐f/r (Spln) producing 675 bp product. Lanes 1 and 9: DNA size standards; lanes 3–7: serial dilutions of

S. citri

DNA (10

–1

, 10

–2

, 10

–3

, 10

–4

, and 10

–5

); lane 8: water control.

Chapter 06

Figure 6.1 Detection of

Xanthomonas campestris

pv.

vitians

(

Xcv

) by isolation from stab‐inoculated lettuce and visualization of phloem and xylem from which the pathogen could be isolated. Isolation of

Xcv

from stem sections taken at different locations: (a) 2–4 cm at 4 h postinoculation (hpi); (b) 0–2 cm from point of inoculation at 12 hpi; (c) 4–6 cm from point of inoculation at 16 hpi; (d) 0–2 cm from uninoculated plant (control); (e) cross‐section of lettuce stem showing phloem and xylem under light microscope.

Figure 6.2 Relative populations of

Pseudomonas fuscovaginae

isolated from rice seeds with or without treatment with sodium hypochlorite (NaOCl). Populations of

P. fuscovaginae

expressed as CFU/100 seeds with different levels of seed discoloration in cultivar Amaroo.

Figure 6.3 Correlation between seed contamination levels and severity ratings of tomato bacterial canker disease. Contamination levels of tomato seeds by

Clavibacter michiganensis

subsp.

michiganensis

measured as CFU g

–1

of seed and number of diseased seedlings infected per 200 seeds show high positive relationship (

r

2

 = 0.9448).

Figure 6.4 Transmission of latent

Xanthomonas campestris

pv.

musacearum

(

Xcm

) in bunch tissues to subsequent generations up to F3 in banana cultivars Pisang Awak and Mbwazirume.

Figure 6.5 Detection of “

Candidatus

Liberibacter solanacearum” in potato plants exposed to liberibacter‐infective psyllids at 24–28°C by PCR assay. Lane 1: DNA standards; lanes 2–8: liberibacter‐inoculated plants maintained at 12–17°C; lanes 9–15: liberibacter‐inoculated plants maintained at 0–25°C; lanes 16–21: liberibacter‐inoculated plants maintained at 27–32°C; lanes 22–29: liberibacter‐inoculated plants maintained at 32–35°C; lanes 31–37: liberibacter‐inoculated plants maintained at 35–40°C; lane 38: negative control; and lanes 30 and 39: pathogen DNA (positive controls).

Figure 6.6 Symptoms of common scab disease caused by

Streptomyces scabiei

on potato tubers of cultivar Desiree at harvest, following inoculation at 13 and 18 days after tuber initiation.

Chapter 07

Figure 7.1 Detection of

Soybean mosaic virus

(SMV) by dot‐immunobinding assay (DIBA) and tissue‐print immunoassay (TPIA) using NBT/BCIP as substrate. (a) DIBA: F3: negative control; F5: positive control. (b) TPIA: A1 and B1: positive controls; H4: negative control. Development of color indicates the presence of SMV in sample extracts.

Figure 7.2 Simultaneous detection of six viruses by tissue‐printing hybridization technique using nonisotopic polyprobe‐6. (a) Positive reactions are indicated by development of color in samples infected by

Cucumber mosaic virus

,

Pepino mosaic virus

,

Parietaria mottle virus

,

Potato virus Y

,

Tomato mosaic virus

, and

Tomato spotted wilt virus

; lack of reaction in healthy samples N‐INF1, N‐INF2, and N‐INF3. (b) Positive reactions are seen in field‐grown plant samples when infected by any one of the viruses with which polyprobe‐6 can hybridize.

Figure 7.3 Estimation of genomic RNA concentration of two strains of

Pea enation mosaic virus

EMV1 and PEMV2, using multiplex quantitative real‐time RT‐PCR assay in stipule, whole pea, seed coat, and embryo tissues. Genomic RNA concentrations are expressed as mean normalized accumulation (MNA).

Figure 7.4 Detection of grapevine leafroll viruses by immunosorbent electron microscopy (ISEM) using the bivalent reagent C

L

‐LR3. The bivalent antibody could trap (a) GLRaV‐1 or decorate (b) GLRaV‐7 and (c) GLRaV‐3; bar = 100 nm.

Figure 7.5 Detection of

Grapevine virus A

(GVA) in tissue prints and extracts of petiole tissues in

Vitis

spp. and hybrids. Tissue imprints: Columns A and B; Dot blots: Column C. Samples: 1: 110 Richter; 3: Kober 5BB; 5:

Vitis rupestris

; 7:

V. riparia

8‐ LN 33 (interspecific hybrids of different

Vitis

spp.); 28: Interspecific hybrid Prim (Palatina); 30:

V. vinifera

culitvar Guzal Kara; TA: positive grapevine cultivar Traminer, lower leaves; TB: positive grapevine cultivar Traminer, upper leaves; F10: plasmid.

Figure 7.6 Detection of sweet potato viruses by PCR assays in sweet potato using three different primer pairs: (a) PW285‐1/PW285‐24; (b) SPG1/SPG2; or (c) SPG3/SPG4. Lane 3: an uncharacterized Jamaican isolate infecting sweet potato; lane 4: an uncharacterized Puerto Rican isolate infecting sweet potato; lane 5:

Ipomoea leafcurl virus

; lane 6:

Tomato yellow leafcurl virus

; lane 7:

Tomato mottle virus

; lane 8:

Bean golden mosaic virus

; lane 9:

Cabbage leafcurl virus

; lane 10:

Squash leafcurl virus

; lane 11:

Cotton leaf crumple virus

; lane 12:

Beet curly top virus

; lane 13: a potyvirus infecting sweet potato (negative control); lane 14: water control.

Figure 7.7 Detection of purified

Potato virus Y

added directly at different concentrations to RT reaction mixture by RT‐DIAPOPS procedure. Four columns represent each dilution of PVY in four independent experiments.

Figure 7.8 Correlation between tuber infection by

Potato mop‐top virus

(PMTV) and incidence of spraing in Scottish seed potato tubers of cultivar Cara.

Figure 7.9 Detection of

Sweet potato leaf curl virus

(SPLCV) in in vitro plantlets of sweet potato accessions by real‐time PCR assay. Amplification plot from SPLCV: samples spiked with positive control crossed the cycle threshold; the DNA extract from PI 585052 also crossed the cycle threshold.

Figure 7.10 Detection of

Plum bark necrosis stem pitting‐associated virus

(PBNSPaV) by nested RT‐PCR assay using ASPn1/ASPn2 primer pair. M: molecular size standards; P: positive virus control; H: healthy plant control. (a) Lanes 1–16; (b) lanes 3–18, 11–14; 16: virus positives from symptomatic and asymptomatic plant samples.

Figure 7.11 Detection of

Potato yellow vein virus

(PYVV),

Tomato infectious chlorosis virus

(TICV), and

Tomato rattle virus

(TRV) by the multiplex PCR assay using serially diluted individual and mixed DNA templates. Lanes 1–7, 8–14, and 15–21: PYVV at original 1:10, 1:100, 1:500, 1:1000, 1:2000, and 1:4000. TICV: original, 1:10, 1:100, 1:200, 1:400, 1:800, and 1:1600. Lanes 22–29: serially diluted samples of three mixed cDNA species: original, 1:10, 1:100, 1:500, 1:1000, 1:2000, 1:4000, and 1:8000. M: molecular size standards (100 bp).

Figure 7.12 Comparative levels of sensitivity of DAS‐ELISA, IC‐PCR and IC‐PCR‐ELISA techniques for the detection of

Potato virus Y

. IC‐PCR‐ELISA was more sensitive than other two techniques tested.

Figure 7.13 Detection of

Plum pox virus

(PPV) by real‐time RT‐PCR with (a) SYBR Green and (b) TaqMan chemistries, employing four direct sample preparation methods–dilution, spot, tissue‐print, and squash methods–along with healthy GF305 peach seedlings as negative control. Dilution and spot real‐time RT‐PCR methods were slightly more sensitive than tissue‐print and squash methods.

Figure 7.14 Detection of (a) CEVd, (b) CBLVd, (c) HSVd, (d) CDVd, and (e) CBCVd in mixed infections in citrus plants by Northern hybridization with viroid‐specific probes. Lane 2: Fino lemon; lane 4: Common mandarin; lane 6: Tahiti lime; lane 8: Foster grapefruit; lane 10: sour orange; lanes 1, 3, 5, 7, and 9: corresponding healthy control.

Figure 7.15 Detection of six viroids in mixed infections by dot‐blot hybridization assay using DIG‐labeled probes in extracts of pome and stone fruit trees. A1–11: extracts from plants infected by

Apple scar skin viroid

(ASSVd); B1–11: extracts from plants infected by

Apple dimple fruit viroid

(ADFVd); C1–11: extracts from plants infected by

Pear blister canker viroid

(PBCVd); D1–11: extracts from plants infected by

Apple fruit crinkle viroid

(AFCVd); E1–11: extracts from plants infected by

Hop stunt viroid

(HSVd); F1–11: extracts from plants infected by

Peach latent mosaic viroid

(PLMVd); G1–11: extracts from healthy plants. Single probes tested: row 1 (ASSVd); row 2 (ADFVd); row 3 (PBCVd); row 4 (AFCVd); row 5 (HSVd); and row 6 (PLMVd). Polyprobes tested: poly2‐A (ASSVd and ADFVd, row 7); poly2‐B (PBCVd and AFCVd, row 8); poly2‐C (HSVd and PLMVd, row 9); poly4‐AB (ASSVd, ADFVd, PBCVd, and AFCVd, row 10) and poly6 (row 11).

Figure 7.16 Detection of (a)

Chrysanthemum stunt viroid

(CSVd) and (b)

Potato spindle tuber viroid

(PSTVd) by real‐time TaqMan assay using viroid‐specific probes. TaqMan amplification plots for specific detection of CSVd and PSTVd.

Figure 7.17 Comparative levels of sensitivities of electrophoresis, Southern blot hybridization, and RT‐PCR dot‐blot hybridization (DBH) for the detection of

Hop stunt viroid

(HSVd) and

Citrus exocortis viroid

(CEVd) in citrus. (a, b) electrophoresis; (b, e) Southern blot hybridization; (c, f) RT‐PCR‐DBH. Lanes: M: molecular standards (100 bp); 1–3: serially diluted positives (10–10

4

); 4: negative control without template; 5: RT product; 6: extracted RNA.

Figure 7.18 Detection of

Potato spindle tuber viroid

(PSTVd) in potato, tomato, and petunia by RT‐PCR assay. M: DNA size standards; lanes 1, 2, and 7: healthy tomato, petunia, and potato; lane 3: dry tomato infected with Cornell severe PSTVd strain; lane 4: freshly infected petunia; lanes 5 and 6: dry tomato infected with PSTVd‐S; lane 8: water control.

Figure 7.19 Comparative sensitivity of RT‐LAMP and Tsutsumi RT‐LAMP assays for detection of

Potato spindle tuber viroid

(PSTVd) using different dilutions of total potato plant RNA. Dilutions of total RNA: 1 × 10

–2

; 1 × 10

–3

; 1 × 10

–4

; control: water (without template).

Chapter 08

Figure 8.1 Influence of

Bean pod mottle virus

(BPMV),

Soybean mosaic virus

(SMV), and mixed infections on the percentage of seeds of soybean lines with mottling symptoms under field conditions in 2001. Mean percentages of mottled seeds (columns) followed by the same letter are not significantly different as per the Student’s test (

P

 = 0.05).

Figure 8.2 Differentiation of

Citrus tristeza virus

(CTV) isolates in individual and mixed infections of sweet orange plants based on SSCP profiles characteristic of

p18

gene. SSCP profiles of mild isolate T425, severe isolates T388 or T305, or a mixture of T425 and T388 or T425 and T305 in the extracts of inoculated plants determined at 3 years after challenge inoculation with T388 or T305 isolates.

Chapter 09

Figure 9.1 Influence of irrigation on development of

Phomopsis longicolla

(a) leaf, (b) stem, and (c) pod, represented by area under disease progress curve under nonirrigated (NI), post‐flower irrigation (PF), and pre‐ plus post‐flower irrigation (PPF) environments during 2003–2004. Means followed by the same letter within each irrigation environment are not significantly different (

P

 ≰ 0.05).

Figure 9.2 Effects of irrigation on percentage of recovery of

Phomopsis longicolla

from (a) infected seed, (b) seed germination percentage, and (c) seed hardiness in soybean crop grown in nonirrigated (NI), post‐flower irrigation (PF), and pre‐ plus post‐flower (PPF) irrigation environments. Means followed by the same letter within each irrigation environment are not significantly different (P ≰ 0.05).

Figure 9.3 Differential disease progress curves of late blight disease in pure stands of potato (a) cultivar Sante and (b) cultivar Cara and mixtures with Sante or Cara at three planting densities.

Chapter 10

Figure 10.1 Effectiveness of in vitro thermotherapy coupled with shoot‐tip grafting for elimination of

Indian citrus ringspot virus

(ICRSV) from citrus plantlets. Note the absence of ICRSV‐specific amplicons in treated plantlets. Lane M: DNA size standards; lanes 1 and 2: positive and negative controls, respectively; lanes 3–6: samples from treated citrus plantlets.

Figure 10.2 Efficiency of hot water treatment (HT) in eliminating

Xanthomonas fragariae

from strawberry plants. (a) Survival of plants (percentage) after different periods of heat treatment (min) at 44°C and 48°C; (b) average number of runners in survivors after HT; and (c) average number of flower trusses formed in plants exposed to HT.

Figure 10.3 Detection of sweet potato little leaf phytoplasma in in vitro shoot cultures by PCR assay after cryotherapy. (a, b) Lane M: DNA ladder; lane P: positive control; N: negative control; lanes 1–4: presence of c. 1.8 kb product in (a) and absence of this product from (b) indicating the effective elimination of the pathogen in cryotherapy‐treated shoot cultures.

Figure 10.4 (a) Visualization of sweet potato little leaf phytoplasma in TEM cross‐sections of shoot tips taken at different positions of leaf primordial of plantlets after cryotherapy. (b, e) Cross‐sections of leaf primordial closer to the apical dome (AD) show the elimination of the phytoplasma; (c, d, f) cross‐sections of leaf primordial away from AD show partial or lack of effectiveness of cryotherapy; and (c, d, f, g) phytoplasma cells are indicated by arrows.

Chapter 11

Figure 11.1 Development of potato black dot disease on stems, stolons, and roots of three potato cultivars with different levels of resistance in (a) England and (b) Scotland. Disease severity ratings measured on potato cultivar Maris Piper (■), Sante (Δ), and Saxo (X).

Figure 11.2 Effects of different rotation crops during 2000–2006 on incidence of Rhizoctonia canker, black scurf, and common scab diseases in potato. (a) Rhizoctonia canker; (b) black scurf; and (c) common scab. Two‐year rotational crops include barley (BA), canola (CN), millet/rapeseed (RP), green bean (GB), sweet corn (SC), soybean (SY), and potato (PP, control without rotation). Bars with the same letter are not significantly different as per Fischer’s protected least significant difference test (

P

 < 0.05).

Figure 11.3 Effectiveness of mulching with bicolor aluminized polyethylene before planting and application of chemicals provide additive effects by reducing disease severity. Unfilled bars: with chemical (Kocide 2000 + Neemguard) application and filled bars: without chemical application.

Chapter 12

Figure 12.1 Effects of low‐ and high‐titer of

Fusarium graminearum

conidia in combination with (a) point‐ and (b) spray‐inoculation with the pathogen on (c–d) means of spikes and ears infected by DON‐ and NIV‐producing isolates in spring wheat cultivar Mercia. (e–f) High‐titer inoculum produced greater disease severity; DON‐producing isolates spread rapidly, while NIV‐producing isolate was restricted to inoculated spikelets within the spike.

Figure 12.2 Evaluation of corn hybrids under inoculated conditions for resistance to Fusarium ear kernel rot disease. Assessment of disease severity by visual rating based on percentage (0–100%) of ears with symptoms in different corn hybrids.

Figure 12.3 Disease severity induced by

Streptomyces scabiei

in resistant clone 65A and susceptible parent Iwa.

Figure 12.4 Reactions of transgenic carrot plants expressing chitinase

CHIT36

gene to the fungal pathogens

Alternaria dauci

,

A. radicina

, and

Botrytis cinerea

following inoculation of detached leaflets and petioles. Values represent the percentage of nontransgenic “Koral” control for transgenic line 96‐183. N176 and N184: the nontransgenic clones not expressing

CHIT36

; D.c.c:

Dacus carota

ssp.

Commutatus

; YEL: yellow leaf mutant; bar: standard error; star: clones with significantly lower values than the control based on Dunnett’s test at

P

 = 0.05 for

A. dauci

and

P

 = 0.01 for

A. radicina

and

B. cinerea

.

Figure 12.5 Northern blot analysis revealing transcription of

xa21

gene of rice in

Citrus sinensis

cultivars (a) Hamlin; (b) Pera; (c) Natal; and (d) Valencia leaves. Lanes 1–8: transgenic lines expressing

xa21

mRNA; lane C: nontransgenic plant (control).

Chapter 13

Figure 13.1 Induction of resistance to tomato late blight by application of

Pseudomonas fluorescens

SS101 or massetolide A to leaves of tomato cultivar Moneymaker and its transgenic derivative

nahG

. Effect on (a) lesion area (mm

2

) and (b) disease severity (%) determined at 7 days postinoculation with

Phytophthora infestans

; asterisk (*) indicates significant reduction in disease severity relative to control (

P

 < 0.05); filled columns: control; blank columns: SS101 strain; lined columns: massetolide A.

Figure 13.2 Effect of BABA application on the development of defense responses in potato cultivars challenged with

Phytophthora infestans

. Note hypersensitive response (HR‐) like lesions formation in leaves treated with BABA, irrespective of infection at all intervals after inoculation; i: idioblast; m: mesophyll cells; HR: HR‐like lesions in BABA‐treated potato cultivar Ovatio at 48 h postinoculation.

Chapter 14

Figure 14.1 Positive correlation between the percentages of necrotic leaf surface on wheat cultivar Maxyl and the copy numbers of tubulin gene (DNA contents) determined by qPCR assay (

F

 = 0.95). Note the disease progress is proportional to the pathogen development.

Figure 14.2 Comparative abilities of Boscalid‐resistant (BR) mutants and their parental isolates in producing sclerotia on PDA medium at 40 days after inoculation. (a–c) Parental isolates; (d–h) BR mutants.

Figure 14.3 Baseline sensitivity frequency distribution of strains of

Xanthomonas oryzae

pv.

oryzae

to zinc thiazole.

Figure 14.4 Effect of application of penicillin G (P) or streptomycin (S) individually or in combination (PS) on populations (cells g

–1

of plant tissue) in huanglongbing (HB‐) affected citrus seedlings under greenhouse conditions. Penicillin applied at 1 g L

–1

and streptomycin at 100 mg L

–1

; CK: control (water).

Figure 14.5 Effect of application as trunk injection of combination of penicillin and streptomycin (PS) at different ratios on bacterial pathogen titers (cells g

–1

of plant tissues) in huanglongbing (HB‐) affected citrus plants under field conditions. PS‐5: penicillin 5 g + streptomycin 0.5 g/100 mL; PS‐10: penicillin 10 g + streptomycin g/100 mL; PS‐0: water control.

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Volume 1

Microbial Plant Pathogens

Detection and Management in Seeds and Propagules

Volume 1

P. Narayanasamy

Former Professor and Head

Department of Plant Pathology

Tamil Nadu Agricultural University

Coimbatore, India

This edition first published 2017 © 2017 John Wiley & Sons, Ltd.

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Library of Congress Cataloging‐in‐Publication Data

Names: Narayanasamy, P., 1937– author. Title: Microbial plant pathogens : detection and management in seeds and propagules / P. Narayanasamy. Description: Hoboken : John Wiley & Sons, 2017. | Includes bibliographical references and index. Identifiers: LCCN 2016036177 (print) | LCCN 2016037345 (ebook) | ISBN 9781119195771 (cloth) | ISBN 9781119195788 (pdf) | ISBN 9781119195795 (epub) Subjects: LCSH: Seed‐borne phytopathogens. | Seed‐borne plant diseases. Classification: LCC SB732.8 .N27 2017 (print) | LCC SB732.8 (ebook) | DDC 632/.3–dc23 LC record available at https://lccn.loc.gov/2016036177

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Dedicated to the memory of my parents for their love and affection

Preface

Agricultural and horticultural crops are raised by using seeds or propagules whose health status has to be ensured for healthy and high‐quality produce to satisfy the needs of human and animal populations. From time immemorial, seeds and propagules were obtained from selected plants growing in the wild environment, saved to grow plants of subsequent generations. In doing so, the improvement of quality parameters such as appearance, color, aroma, and taste was achieved by selecting plants with desired characteristics. However, due importance was not allocated to select plants with resistance to diseases caused by microbial plant pathogens, resulting in progressive increase in the susceptibility of plants to diseases and phenomenal crop losses which were considered responsible for dreadful famines and untold human suffering. Several diseases transmitted through seeds/propagules have been found to be highly destructive, with the potential to ruin the economy of certain countries. Such critical conditions were primarily ascribed to the failure to select disease‐free seeds and propagules for future generations of crops.

Early detection and precise identification of the pathogen(s) present in seeds/propagules which are involved in a disease(s) occurring at a geographical location constitute the basic strategy for development of effective disease management systems suitable for various agroecosystems. Studies of pathogen biology, the infection process, and epidemiology of crop diseases have highlighted the weak links in the life cycles of microbial pathogens in order to disrupt pathogen development and the progress of disease under field conditions. The principles of crop disease management are essentially based on exclusion, eradication, and immunization and various disease management strategies emerge from these principles. The need to produce disease‐free seeds and propagules to restrict the introduction of pathogens into fields/new locations and subsequent disease spread has been clearly indicated by different investigations. The role of quarantines and certification programs in excluding the introduction of new diseases into a country where the pathogen may be absent or less important has been well realized. The effectiveness of adoption of simple cultural practices in restricting disease incidence and further spread has been indicated in some pathosystems. The development of crop cultivars with built‐in resistance to diseases, the most economical disease management strategy, has been achieved through traditional breeding methods or biotechnological approach and has been shown to be instrumental in keeping many diseases under check. Employing biological control agents is advantageous, since this strategy has been demonstrated to be effective not only in restricting the disease incidence and spread but also in preserving the ecological environments. The application of