Aggressiveness of eight Venturia inaequalis isolates virulent or avirulent to the major resistance gene Rvi6 on a non‐Rvi6 apple cultivar

For sustainable management of scab‐resistant apple cultivars, it is necessary to understand the role of aggressiveness in the adaptation of Venturia inaequalis populations and particularly the costs to the organism of acquiring additional virulence. The aims of the present study were (i) to identify the quantitative variables that are most important in determining the differences in aggressiveness among groups of V. inaequalis isolates, and (ii) to ascertain whether virulent and avirulent isolates of V. inaequalis differ significantly in aggressiveness. The aggressiveness of eight isolates that differed in their virulence to the major resistance gene Rvi6 was compared on the non‐Rvi6 apple cv. Gala. Three components of aggressiveness, namely lesion density, the number of spores per square centimetre of leaf area, and the number of spores per lesion, were evaluated 21 days after inoculation, and the kinetics of lesion density over time were analysed in terms of maximum lesion density, length of latent period and rate of lesion appearance. On the second youngest but fully developed leaf at the time of inoculation, maximum lesion density in the virulent group was 20% lower and the latent period 7% longer, than in the avirulent group. However, the alternative hypothesis, namely that isolates had adapted to quantitative resistance present in cv. Gala depending on their cultivar of origin, could not be rejected. The analysis of the kinetics of lesion density by a non‐linear mixed‐effect model proved useful in the assessment of aggressiveness.     

Late-blight epidemics on potato in Finland, 1933–2002; increased and earlier occurrence of epidemics associated with climate change and lack of rotation

Changes in the incidence and onset of potato late-blight epidemics in Finland were investigated and compared with possible changes in climate, presence of soil-borne inoculum, and aggressiveness of Phytophthora infestans populations. Datasets were constructed from leaf blight assessments in cultivar trials or fungicide tests carried out at eight experimental sites during the periods 1933–1962 and 1983–2002. Additional data were obtained from late-blight monitoring projects carried out from 1991 to 2002. From 1998 to 2002, the risk of blight outbreak was 17-fold higher compared with the periods 1933–62 and 1983–1997. Simultaneously, the outbreaks of the epidemics began 2–4 weeks earlier. The changes observed were associated with a climate more conducive to blight in the late 1990s. Lack of rotation also advanced blight epidemics by an average of 9 days in 1998–2002, but it did not have this effect in 1992–1997, suggesting that soil borne inoculum may not have been a significant threat to potato until the late 1990s. The aggressiveness of the P. infestans isolates seemed to have only minor effect on the onset of the epidemics after 1991, as the apparent infection rate remained unchanged despite weather conditions more favourable to late blight in the late 1990s. As a consequence of the more frequent and earlier epidemics, the sales of fungicides used against late blight in Finland increased 4-fold from the 1980s to 2002.     

Glomerella cingulata on camellia

Glomerella cingulata was shown to be associated with a leaf blotch, canker and dieback of imported camellia plants. It was particularly damaging on hybrids of Camellia saluenensis such as C. x williamsii cv. Donation. Pathogenicity tests, using whole plants and detached leaves of cv. Donation, distinguished between virulent and a virulent strains of the fungus. The virulent strain did not cause severe damage when inoculated into a range of other woody ornamentals. Conversely, Colletotrichum spp., including G. cingulata , isolated from other hosts were not virulent to Camellia cv. Donation. Apart from a loss of virulence associated with a mutation to paleness of colonies in culture, virulent isolates with dark-grey colony centres were morphologically identical to avirulent isolates from camellia, including tea plant ( Camellia sinensis ), and to some isolates from other hosts. A form of Colletotrichum acutatum isolated from camellia and readily distinguished from G. cingulata by bright pink colonies and conidial shape was shown to be avirulent on Camellia cv. Donation. It is proposed that the virulent form on ornamental camellia be described as Glomerella cingulata f.sp. camelliae.     

Genetic Variation and Virulence on Lr26 in Puccinia triticina

ABSTRACT The genetic relationships between isolates of Puccinia triticina virulent on wheat with the Lr26 resistance gene were studied. The diversity within and between isolates of P. triticina from Israel, Europe, and the United States was determined by virulence on near-isogenic Thatcher lines and by random amplified polymorphic DNA. According to the molecular markers, isolates that were virulent on Lr26 had diversity levels similar to those of Lr26 nonpathogenic isolates. Distances between subpopulations of isolates virulent and avirulent on Lr26 varied and were unrelated to the Lr26 virulence phenotype. Cluster analysis suggested four groups, three of which were closely associated with the geographical origin of the isolates-Israel, the United States, and Europe. All four groups included both Lr26 virulent and avirulent pathotypes. The results showed that Lr26 virulent rust pathotypes are as genetically dissimilar as the rest of the population. The cluster analysis showed that the rust population in Israel includes at least two different subpopulations, both of which contain Lr26 virulent and Lr26 avirulent isolates.     

Field efficiency of Brassica napus specific resistance correlates with Leptosphaeria maculans population structure

Field experiments were conducted in Versailles, France, to assess blackleg resistance of Brassica napus cultivars Quinta and Glacier under natural infection conditions. Blackleg disease severity was assessed twice during growth of B. napus. Quinta resistance was highly expressed as only 13% to 18% of the plants exhibited leaf symptoms in December, whereas Glacier and other cultivars displayed more than 80% of infected plants. In June (harvest), 70% (first year) to 41.5% (second year) of Quinta plants were canker-free. In contrast, Glacier was as infected as the susceptible control cultivars, with more than 88% of plants displaying canker. The Leptosphaeria maculans population structure was examined in parallel. Based on soluble protein patterns, 9% of the 299 fungal isolates collected were characterized as Tox⁰ species, and belonged to the NA1 sub-group. All but two of Tox⁰ isolates were isolated from atypical dark necrotic leaf lesions, mainly occurring on Quinta. In contrast, the Tox⁺ isolates were recovered from typical leaf lesions. Following a cotyledon inoculation test on the differential set Westar, Quinta and Glacier, 92 to 95% of Tox⁺ isolates collected on susceptible cultivars were characterized as PG3 isolates, i.e. avirulent on Quinta. The remaining Tox⁺ isolates belong to PG4, i.e. virulent on the three cultivars. No PG2 isolate, i.e. avirulent on both Quinta and Glacier, was identified in the sampling. The present study suggests that specific resistance expressed at the cotyledon level can be efficient under field conditions where the corresponding avirulent races of the pathogen are prevalent.     

Antagonistic Interactions Between Strains of Xanthomonas oryzae pv. oryzae

ABSTRACT The ability of some phytopathogenic bacterial strains to inhibit the growth of others in mixed infections has been well documented. Here we report that such antagonistic interactions occur between several wild-type strains of the rice bacterial blight pathogen Xanthomonas oryzae pv. oryzae. In mixed inoculations, a wild-type Philippine strain was found to inhibit the growth of a wild-type Korean strain. Furthermore, a nonpathogenic mutant of the Philippine strain maintained these antagonistic properties. Growth curve analysis indicated that both the wild-type Philippine strain and its nonpathogenic mutant inhibited the growth of the Korean strain 2 days after infection and prior to the onset of disease symptoms. When mixed with the nonpathogenic mutant, 10 out of 18 diverse wild-type X. oryzae pv. oryzae strains did not cause disease. Conversely, three of the strains that were not affected by the nonpathogenic mutant were found to inhibit the growth of both the wild-type and mutant Philippine strains, indicating that antagonism is widespread and strain specific. The observed growth inhibition occurred only in planta and did not correlate with bacteriocin activity in vitro. Antagonistic interactions also were found to affect resistance (R) gene-mediated resistance. The R gene Xa21 was capable of protecting rice plants coinoculated with nonantagonistic virulent and avirulent strains; however, when avirulent strains were coinoculated with virulent antagonistic strains, disease ensued. Taken together, these results indicate that X. oryzae pv. oryzae has evolved strategies to compete with rival strains in a fashion that allows virulent strains to evade R gene-mediated protection even when avirulent strains are present in the inoculum.     

Specific Behaviour of French Aphanomyces Euteiches Drechs. Populations For Virulence and Aggressiveness on Pea, Related to Isolates from Europe, America and New Zealand

The pathogenic variability of Aphanomyces euteiches on pea was investigated using a collection of 88 pea-infecting isolates from France and 21 isolates from Denmark, Sweden, Norway, USA, Canada and New Zealand. Aggressiveness and virulence were assessed by scoring the root symptoms on a differential set of six pea genotypes. Eleven virulence types were characterised. The virulence type I, previously described as virulent on the whole set, was predominant and included the most aggressive isolates of all geographical origins. The other types were much less prevalent, existing as one to five isolates. Three virulence types (III, IV and V) contained no French isolates. The type III, avirulent on MN313, was composed of American isolates only, and resembled the major group recently described in the USA. A wide range of aggressiveness was found within the virulence type I, and the French isolates appeared globally more aggressive than the foreign isolates. These findings indicate that isolates from the virulence type I should be used as references in breeding programs, and that pea lines PI180693 and 552 may be the most interesting resistance sources to date, despite their only partial resistance.     

PCR amplification of the fas-1 gene for the detection of virulent strains of Rhodococcus fascians

Thirty-six isolates of the fasciation-inducing bacterium Rhodococcus fascians were evaluated for the presence and location of the fas-1 gene, which codes for an isopentenyl transferase, the committed step in cytokinin biosynthesis. The presence of fas-1 was determined by PCR using a set of primers to the most conserved regions of the gene and by Southern hybridization to genomic digests using the PCR fragment as a probe. Both methods revealed the presence of the gene in 18 virulent isolates and the absence of the gene in 18 avirulent isolates. Thus, there is a strong relationship between the presence of the gene and virulence of the organism. The location of fas-1 was determined by probing blots of linear and circular DNA. For most of the virulent isolates, the gene was localized to a 200 ± 10 kb linear plasmid. Three virulent isolates lacked a plasmid of this size, but contained fas-1 either on a linear plasmid of 130 kb or on a large circular plasmid.     

Cytochrome b gene sequence and structure of Pyrenophora teres and P. tritici-repentis and implications for QoI resistance

Resistance to QoI fungicides in Pyrenophora teres (Dreschsler) and P. tritici-repentis (Died.) Dreschsler was detected in 2003 in France and in Sweden and Denmark respectively. Molecular analysis revealed the presence of the F129L mutation in resistant isolates of both pathogens. In 2004, the frequency of the F129L mutation in populations of both pathogens further increased. The G143A mutation was also detected in a few isolates of P. tritici-repentis from Denmark and Germany. In 2005, the F129L mutation in P. teres increased in frequency and geographical distribution in France and the UK but remained below 2% in Germany, Switzerland, Belgium and Ireland. In P. tritici-repentis, both mutations were found in a significant proportion of the isolates from Sweden, Denmark and Germany. The G143A mutation conferred a significantly higher level of resistance (higher EC50 values) to Qo inhibitors (QoIs) than did the F129L mutation. In greenhouse trials, resistant isolates with G143A were not well controlled on plants sprayed with recommended field rates, whereas satisfactory control of isolates with F129L was achieved. For the F129L mutation, three different single nucleotide polymorphisms (SNPs), TTA, TTG and CTC, can code for L (leucine) in P. teres, whereas only the CTC codon was detected in P. tritici-repentis isolates. In two out of 250 isolates of P. tritici-repentis from 2005, a mutation at position 137 (G137R) was detected at very low frequency. This mutation conferred similar resistance levels to F129L. The structure of the cytochrome b gene of P. tritici-repentis is significantly different from that of P. teres: an intron directly after amino acid position 143 was detected in P. teres which is not present in P. tritici-repentis. This gene structure suggests that resistance based on the G143A mutation may not occur in P. teres because it is lethal. No G143A isolates were found in any P. teres populations. Although different mutations may evolve in P. tritici-repentis, the G143A mutation will have the strongest impact on field performance of QoI fungicides.     

南方根结线虫Me3毒性与非毒性群体对寄主趋向性和侵染能力的比较

 探究南方根结线虫Me3毒性与非毒性群体对抗感寄主趋向性和侵染能力,为揭示毒性群体致病机理及防治根结线虫策略提供理论依据。使用以水琼脂为介质的研究方法,通过对比分析辣椒抗病品种HDA149和感病品种茄门根尖附近聚集的2龄幼虫(J2)数量,来揭示南方根结线虫对抗感辣椒品种根尖的趋向性效应,并利用实时荧光定量 PCR 检测侵入到辣椒根系的毒性与非毒性线虫数量,对其侵染能力进行比较。J2 趋向性试验结果显示,在相同的时间点,HDA149 和茄门辣椒根尖处附近聚集的毒性群体 J2 数量总是显著多于非毒性群体的 J2数量;J2 对抗感辣椒的选择性结果表明,不论是毒性群体还是非毒性群体的 J2,在相同的时间点,茄门根尖附近聚集的线虫数量显著多于HDA149根尖附近的线虫数量;荧光定量 PCR 检测线虫侵染结果显示,毒性群体 J2侵入到辣椒根系的数量相对非毒性群体的 J2 更多。总之,相比南方根结线虫Me3非毒性群体,毒性群体的 J2 对寄主根系有较强的趋向性,并且侵染效率更高;相比于抗性寄主,Me3毒性群体和非毒性群体的 J2 对感病寄主有更强的选择性。     

Pathotypic and genetic diversity in the population of Rhizoctonia solani AG1‐IA causing rice sheath blight in China

Sheath blight, caused by Rhizoctonia solani AG1‐IA, is one of the most serious diseases of rice. In this study, a total of 175 isolates of R. solani AG1‐IA were collected from five rice‐growing regions in China. Pathogenicity tests revealed that all isolates were virulent to five cultivars with different levels of resistance at the rice seedling stage in the greenhouse. There was considerable variation in aggressiveness, and the isolates were classified into three pathotypes based on disease severity, with moderately virulent isolates prevalent in the population. Forty‐three haplotypes were identified based on ITS sequencing, and 39 haplotypes were distinct among isolates. There were high levels of haplotype diversity and nucleotide diversity within the populations of R. solani AG1‐IA. High gene flow (Nm = 1·63–5·22) was detected, consistent with relatively low differentiation between pairs of populations. Five populations were divided into two distinct clusters by the unweighted pair group method with arithmetic mean (UPGMA), and no spatial population differentiation was discernible. The majority (97·8%) of genetic diversity was distributed among isolates within populations, with only 2·2% of the genetic diversity attributed to differences among populations. The star‐like shape of the haplotype network provided evidence of signatures of population expansion in recent history. No significant relationships were found between the genetic diversity and aggressiveness or geographic origin among populations of R. solani AG1‐IA. These results highlight that the population characteristics of R. solani AG1‐IA should be taken into account in evaluating the germplasm resistance of rice cultivars to sheath blight.     

Genetic Analysis of Avirulence/Virulence of an Isolate of Magnaporthe grisea from a Rice Field in Texas

ABSTRACT An isolate of Magnaporthe grisea, Tm4, from a rice field in Texas was crossed with a fertile laboratory strain, 70-6. The progenies showed segregation of avirulence/virulence on rice cvs. Newbonnet, Lemont, Lebonnet, Leah, and Katy. The avirulent/virulent segregation ratios were 29:6 on Newbonnet, Lemont, and Lebonnet; 28:7 on Leah; and 33:2 on Katy. There was cosegregation on the first three cultivars. Several avirulent progenies were backcrossed to virulent parent 70-6. Three generations of backcrossing avirulent progenies to 70-6 led to segregation ratios that suggested certain strains had only one avirulence gene. Strains avirulent only on cv. Katy or only on cvs. Newbonnet, Lemont, and Lebonnet were test crossed with virulent siblings. Strains that gave progeny ratios approximating 1 avirulent:1 virulent when crossed with virulent siblings were selected for further test crossing. Intercrosses between strains with possible single avirulence genes were made to determine whether these strains had the same or different avirulence genes. Many lines still segregated two genes for avirulence after three generations of backcrossing. This is based on the recovery of virulent progenies from crossing two avirulent siblings.     

Virulent and avirulent isolates of Pseudomonas syringae subsp. savastanoi as colonizers of olive leaves: evaluation of possible biological control of the olive knot pathogen1

The epiphytic survival of virulent and avirulent (indoleacetic acid-deficient mutants) isolates of Pseudomonas syringae subsp. savastanoi, and their ability to colonize the olive phylloplane, was monitored for up to 30 days after artificial inoculation of several olive cultivars. After an initial decrease in numbers, the virulent bacteria multiplied and established a potential inoculum on olive leaf surfaces. In contrast, the numbers of avirulent bacteria rapidly diminished, so that they were eventually no longer detectable. Under the conditions used in this study, none of the avirulent mutants (producers or non-producers of bacteriocins) were able to compete with or successfully to inhibit the virulent isolate in vivo. This was probably due to the lack of epiphytic multiplication of the avirulent mutants.     

The Relationship of Host Range, Physiology, and Genotype to Virulence on Cantaloupe in Pseudomonas syringae from Cantaloupe Blight Epidemics in France

ABSTRACT In 1993, a bacterial blight caused important losses of cantaloupe (Cucumis melo var. cantalupensis) in southwestern France and has now been reported in all cantaloupe-growing regions of France. The causal agent of this blight is Pseudomonas syringae, although on a worldwide basis this bacterium has not been a major pathogen of melon for over 50 years. To identify the pathovar of the cantaloupe pathogen, we employed biochemical tests, plasmid and chromosomal profiling, and host range studies for 23 strains from cantaloupe and 47 reference strains of 14 pathovars of P. syringae. Numerical analysis of 119 traits, serological typing, syringomycin production, and BOX-polymerase chain reaction profiles did not allow us to differentiate among pathovars related to P. syringae pv. syringae. Host range studies of cantaloupe and references strains on 18 plant species showed that virulence to sugar beet was a common feature of strains virulent on cantaloupe, but was not common to strains avirulent on cantaloupe. Virulence to other species of plants varied among strains, but the overall extent of the host range was proportional to aggressiveness to cantaloupe. We propose that the strains attacking cantaloupe in France be considered P. syringae pv. aptata and that adequate host range testing may reveal that this pathovar is the cause of cantaloupe blight reported in other parts of the world.     

Durability of natural and transgenic resistances in rice to <Emphasis Type="Italic">Rice yellow mottle virus</Emphasis>

A monogenic recessive resistance to Rice yellow mottle virus (RYMV) found in the Oryza sativa indica cultivar Gigante and in a few Oryza glaberrima cultivars provided a higher level of resistance than either a polygenic partial resistance found in some japonica cultivars which delayed symptom expression or transgenic resistances which were partial and temporary. This high resistance was overcome by several isolates, but the percentage of such virulent isolates in the fields was low. There was no relationship between the virulence of an isolate towards the high resistance and its aggressiveness in other cultivars. Isolates with either of the two components of pathogenicity – virulence and aggressiveness – were found in each strain and in all regions of Africa, in both wild and cultivated grass species. There was no loss of fitness of resistance-breaking (RB) isolates as they were not counter-selected, impaired or outperformed after serial passages in susceptible cultivars, even in mixture with avirulent quasi-isogenic wild type isolates. Resistance breaking was highly dependent on the amount of virus inoculated and on the mode of transmission. Implications of these results for the durability of the resistances to RYMV and for the development of integrated disease management strategies are discussed.     

侵染优质稻美香占2号的稻瘟病菌生理小种鉴定及无毒基因分析

为明确优质稻种美香占2号的抗瘟性,并为其合理布局以及与不同品种的轮换种植提供科学依据,利用7个中国鉴别品种和11个抗稻瘟病单基因系,对2013—2017年自广东省美香占2号品种上分离获得的50株稻瘟病菌Magnaporthe oryzae菌株进行生理小种鉴定和无毒基因型分析。结果显示,50株稻瘟病菌菌株被鉴定为11个生理小种,其中优势小种分别为C13、B13、B01、B05和C05;50株稻瘟病菌菌株对IRBLkh-K3(仅含Pik-h基因)、NIL-e1(仅含Pi50基因)、IRBL9-W(仅含Pi9基因)和IRBLzt-T(仅含Piz-t基因)4个抗稻瘟病单基因系表现出极低的毒性,频率分别为4%、6%、6%和8%;对IRBLz-Fu(仅含Piz基因)、IRBLkp-K60(仅含Pik-p基因)和IRBLi-F5(仅含Pii基因)3个抗稻瘟病单基因系表现出相对较高的毒性,频率分别为88%、86%和80%;自美香占2号以及其它4个主栽品种上获得的70株稻瘟病菌菌株被聚为不同类群;2003—2007年供试菌株中无毒基因AvrPi9、AvrPiz-t、AvrPi50和AvrPik-h的出现频率较高,无毒基因AvrPi1、AvrPita2、AvrPi2和AvrPish的出现频率中等,无毒基因AvrPii、AvrPik-p和AvrPiz的出现频率较低。     

The reproductive potential of the root-knot nematode <Emphasis Type="Italic">Meloidogyne incognita</Emphasis> is affected by selection for virulence against major resistance genes from tomato and pepper

The emergence of virulent root-knot nematode populations, able to overcome the resistance conferred by some of the resistance genes (R-genes) in Solanaceous crops, i.e., Mi(s) in tomato, Me(s) in pepper, may constitute a severe limitation to their use in the field. Research has been conducted to evaluate the durability of these R-genes, by comparing the reproduction of several laboratory-selected and wild virulent Meloidogyne incognita isolates, on both susceptible and resistant tomatoes and peppers. We first show that the Me1 R-gene in pepper behaves as a robust R-gene controlling avirulent and virulent Me3, Me7 or Mi-1 isolates. Although the reproductive potential of the virulent isolates was highly variable on susceptible and resistant plants, we also confirm that virulence is highly specific to a determined R-gene on which selection has occurred. Another significant experimental result is the observation that a reproductive fitness cost is associated with nematode virulence against Mi-1 in tomato and Me3 and Me7 in pepper. The adaptative significance of trade-offs between selected characters and fitness-related traits, suggests that, although the resistance can be broken, it may be preserved in some conditions if the virulent nematodes are counter-selected in susceptible plants. All these results have important consequences for the management of plant resistance in the field.     

Evidence for a Minor Gene-for-Minor Gene Interaction Explaining Nonhypersensitive Polygenic Partial Disease Resistance

ABSTRACT Partial resistance is a quantitative type of resistance that, by definition of Parlevliet, is not based on hypersensitivity. It is largely pathotype nonspecific, although some minor isolate-specific responses have been reported. In order to elucidate the isolate specificity of individual genes for partial resistance, three barley recombinant inbred line mapping populations were analyzed for resistance to the leaf rust fungus Puccinia hordei. The mapping populations were inoculated with one isolate avirulent and two isolates virulent to resistance gene Rph7g. Six significant quantitative trait loci (QTLs) were detected. Of these, two (Rphq3 and Rphq11) were detected with only the avirulent isolate (1.2.1.) and one (Rphq18) only with both virulent isolates (CO-04 and 28.1). The effectiveness of these QTLs was tested with 14 isolates, using a tester set of genotypes containing alleles for resistance or susceptibility for these QTLs. QTL Rphq18 was effective to only two isolates, CO-04 and 28.1, whereas Rphq3 and Rphq11 were ineffective to CO-04 and 28.1 but effective to all other isolates, except one. This resulted in a significant Person's differential interaction, which is a hallmark of a gene-for-gene interaction. The minor gene-for-minor gene interaction is not based on hypersensitivity and there is no evidence that the resistance is based on genes belonging to the nucleotide-binding leucine-rich repeat class.     

Inheritance of virulence in Bremia lactucae to match several resistance factors in lettuce

A 1∶1 mixture of spores of the physiologic races NL5 and NL6 ofBremia lactucae was sprayed on leaf discs of the lettuce cultivar Olof. The resulting oospores were allowed to germinate on seedlings after a two-month ripening period. Monospore lines of 49 of the 79 recovered isolates were tested on cotyledons and leaf discs of a differential series for virulence to 11 resistance factors. All monospore lines were also tested for the mating type factor. A backcross of a progeny line, line H, with NL5 was made and 41 isolates tested on the differential series. Results indicated complex inheritance based on more than one locus each for virulence to R2 and R11. Vilulence to match the resistance factor R4 seems to be based on a dominant factor or on a combination of a dominant and a recessive factor. Virulence to factors R5, R8 and R10 are recessive and possibly interchangeable. Inheritance of virulence to factors R3, R6 and R9 must be studied further before definite conclusions can be drawn. Virulence to R7 resulted in many incomplete reactions, but all showed significantly less sporulation than the virulent parent. Variations in necrosis in intermediate reactions indicate the presence of minor genes affecting these symptoms. Many of the avirulent loci in the parent lines proved to be heterozygous. Mating type segregation fits a 1∶1 ratio, indicating that this factor is controlled by a single gene. Selfing, mutation and somatic crossing-over can affect the ratios of recovered progeny and so our conclusions concerning the inheritance of virulence.     

Studies on red light-induced resistance of broad bean to Botrytis cinerea: I. Possible production of suppressor and elicitor by germinating spores of pathogen

When detached broad bean leaves were preinoculated with virulent strain B304 of Botrytis cinerea 24 h before a challenge inoculation with strain B304, lesion formation by B304 was significantly inhibited in red light but not in the dark. In leaves that were preinoculated with avirulent strain 021 and then challenged by B304, however, lesion formation was not inhibited even under red light. Such differences in lesion formation after the challenge inoculation with an avirulent strain were also observed with lesions caused by Alternaria alternata, a nonpathogen of broad bean and by avirulent strain 021R in the presence of germination fluid from spores of strains B304 and 021R. These results suggest the possibility that virulent B. cinerea produced a suppressor involved in induced susceptibility and an elicitor involved in resistance induced by red light during spore germination.