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1.
Differentiation of pathotypes of lettuce mosaic virus 总被引：2，自引：0，他引：2
Differential interactions between six crisphead cultivars of lettuce and five isolates of lettuce mosaic virus (LMV) have identified a novel resistance factor in the cultivar Ithaca. The LMV isolates could be grouped into three pathotypes, two of which have not been identified previously. One of these, pathotype III represented by an isolate from Spain, was virulent on all of the cultivars. There were differences in aggressiveness between isolates of the same pathotype. 相似文献
2.
We examined interactions between wheat (Triticum aestivum) and Mycosphaerella graminicola, causal agent of Septoria tritici blotch, to determine whether specific interactions occur between host and pathogen genotypes that could be involved in eroding resistance. The moderate resistance of the wheat cultivar Madsen has eroded significantly in the Willamette Valley of Oregon since its release in 1990. Foote is a replacement cultivar expressing moderate resistance and was released in 2000. Isolates of M. graminicola were collected from Foote and Madsen in 2004 and 2005 and tested on each cultivar in growth chamber and greenhouse experiments. There was a significant (P 相似文献
3.
Barley cultivars show various patterns of resistance against isolates of Magnaporthe oryzae and M. grisea. Genetic mechanisms of the resistance of five representative barley cultivars were examined using a highly susceptible barley cultivar, 'Nigrate', as a common parent of genetic crosses. The resistance of the five cultivars against Setaria, Oryza, Eleusine, and Triticum isolates of M. oryzae was all attributed to a single locus, designated as Rmo2. Nevertheless, the Rmo2 locus in each cultivar was effective against a different range of isolates. Genetic analyses of pathogenicity suggested that each cultivar carries an allele at the Rmo2 locus that recognizes a different range of avirulence genes. One allele, Rmo2.a, corresponded to PWT1, which conditioned the avirulence of Setaria and Oryza isolates on wheat, in a gene-for-gene manner. The other alleles, Rmo2.b, Rmo2.c, and Rmo2.d, corresponded to more than one avirulence gene. On the other hand, the resistance of those cultivars to another species, M. grisea, was conditioned by another locus, designated as Rmo3. These results suggest that Rmo2 is effective against a broad range of blast isolates but is specific to M. oryzae. Molecular mapping revealed that Rmo2 is located on the 7H chromosome. 相似文献
4.
ABSTRACT The selective effect of quantitative host resistance on pathogen aggressiveness is poorly understood. Because two previous experiments with a small number of bread wheat cultivars and isolates of Mycosphaerella graminicola had indicated that more susceptible hosts selected for more aggressive isolates, we conducted a larger experiment to test that hypothesis. In each of 2 years, six cultivars differing in their levels of partial resistance were planted in field plots, and isolates were collected from each cultivar early and late in the growing season. The isolates were inoculated as populations bulked by cultivar of origin, field replicate, and collection date on seedlings of the same six cultivars in the greenhouse. The selective impact of a cultivar on aggressiveness was measured as the difference in aggressiveness between early and late isolates from that cultivar. Regression of those differences on disease severity in the field yielded significance values of 0.0531 and 0.0037 for the 2 years, with moderately resistant cultivars selecting for more aggressive isolates. In a related experiment, the protectant fungicide chlorothalonil was applied to plots of two susceptible cultivars to retard epidemic development. When tested in the greenhouse, isolates of M. graminicola from those plots were significantly more aggressive than isolates from the same cultivars unprotected by fungicide. 相似文献
5.
The oilseed rape cultivar Cresor was resistant to 14 isolates of Peronospora parasitica derived from crops of Brassica napus in the UK. Segregation for resistance to one isolate among F2 plants and F3 progeny of crosses between Cresor and the susceptible cultivars Victor and Jet Neuf indicated that resistance was controlled by a single gene. There was evidence that genetic background and environment could influence the phenotypic expression of this resistance. Two sexual progeny isolates derived from a homothallic isolate of P. parasitica avirulent on Cresor were completely virulent on this cultivar. This suggested that the parental isolate was heterozygous at a matching locus or loci for avirulence and demonstrated the race-specific nature of the resistance. 相似文献
6.
Manchanahally Shivanna Meera Manchanahally Byrappa Shivanna Koji Kageyama Mitsuro Hyakumachi 《European journal of plant pathology / European Foundation for Plant Pathology》1995,101(4):421-430
Initial experiment on the reactions of five Japanese cultivars of cucumber toColletotrichum orbiculare infection in the greenhouse revealed that cv Suyo and Gibai were susceptible and moderately susceptible, respectively, while cv Shogoin fushinari and Sagami hanjiro were resistant to infection byC. orbiculare; cv Ochiai fushinari was moderately resistant. The ability of 16 plant growth promoting fungi (some isolates belonged to species ofPhoma and some non-sporulating isolates) isolated from zoysiagrass rhizospheres to induce systemic resistance in the above five cucumber cultivars was tested by growing plants in potting medium infested with barley grain inocula of PGPF in the greenhouse. The second true leaves of 21-day-old plants were challenge inoculated withC. orbiculare and disease assessed. Nine, out of 16 isolates, caused significant reduction of disease caused byC. orbiculare in at least two cultivars.Phoma isolates (GS8-1 and GS8-2) and non-sporulating isolates (GU21-2, GU23-3, and GU24-3) significantly reduced the disease in all the five cultivars. The disease suppression in cucumber was due to the induction of systemic resistance, since the inducer(s) and the pathogen were separated spatially and that the inducer did not colonize aerial portions. The resistance induced by certain isolates in a susceptible cultivar was less than that in a resistant cultivar. Disease suppression caused by isolate GU21-2 was similar to theC. orbiculare induced control in certain cultivars. The average rate of expansion of lesion diameter on leaves due toC. orbiculare was slower due to induction with the selected plant growth promoting fungi compared to the uninduced control plants. Roots of four cultivars were colonized by only three isolates, however, roots of one cultivar (Suyo) was colonized by five isolates suggesting the cultivar-specific root colonization ability.Abbreviations cv
cultivar(s)
- PGPF
plant growth promoting fungal isolates
- PGPR
plant growth promoting rhizobacteria 相似文献
7.
The displacement in east Africa of the US-1 clonal lineage of Phytophthora infestans by 2_A1 clonal lineage has been very rapid. This study tested the hypothesis that dominance of 2_A1 could be due, at least in part, to the increased aggressiveness of 2_A1 over US-1, using both a detached leaf assay (DLA) and a tuber slice assay. The assays were conducted in Uganda and Kenya but US-1 was only assayed in Uganda, because isolates could not be moved across borders and no potato US-1 isolates were available in Kenya. All isolates were collected from potato and compared on two potato cultivars (Kachpot-1 and Sarpo Mira), with the 2_A1 isolates also tested on tomato cultivar Rio Grande. Additionally, a tuber slice assay was done to test whether the capacity to infect tubers differed between 2_A1 and US-1. The aggressiveness of the isolates in the DLA varied significantly both within and among isolates classified according to clonal lineage and for type of host. The 2_A1 isolates were significantly more aggressive than US-1 isolates on both potato varieties evaluated. There were no significant effects of clonal lineage or potato cultivar used in the tuber assay. No significant correlation between foliar and tuber pathogenicity was observed. The 2_A1 isolates were significantly more aggressive on potato than on tomato. An effect of location was also observed in the DLA, on both hosts. It can be concluded from this study that greater pathogenicity of 2_A1 is at least partly attributable to its increased aggressiveness on potato. 相似文献
8.
Host-pathogen relationship of geographically diverse isolates of Septoria tritici and wheat cultivars 总被引：1，自引：0，他引：1
Pathogenic variability of 14 Septoria tritici isolates from different locations in the USA (California, Oregon, and Texas) was determined on seedlings of two sets of geographically diverse wheat cultivars under greenhouse conditions. Significant isolate effects, cultivar effects, and isolate × cultivar interactions were found, and a substantial amount of variation was accounted for by the interaction terms compared with the main effects of isolate and cultivar. All isolates were pathogenic on the cultivars tested but the degree of virulence on the individual cultivars varied among isolates. Linear contrasts between all homologous combinations (isolate × cultivar combination of same geographic location) and all heterologous combinations (isolate × cultivar combination of different locations) indicated that homologous combinations produced significantly more disease than heterologous combinations. The results demonstrate location-specific adaptation of S. tritici. Implications of pathogenic variability and local adaptation in S. tritici are discussed. 相似文献
9.
Host-mediated interactions between pathogen genotypes 总被引：6，自引：4，他引：2
Barley c ltivars with different resistance genes were inoculated with various sequences of virulent and non-virulent isolates of Erysiphe graminis f.sp. hordei. The resistance induced in incompatible reactions decreased infection by virulent isolates while, conversely, the degree of susceptibility induced in compatible reactions was sufficient to increase the ability of normally non-virulent isolates to infect a resistant host. The net effect of interactions was always overall reduction of conidial production when compared with inoculation of a virulent isolate alone.
Each interaction between isolates was dependent on the host cultivar, the pathogen isolates used and on the inoculation sequence. Often, induced resistance was most obvious when a nonvirulent isolate was inoculated prior to a virulent isolate. Induced susceptibility was usually more apparent when the virulent isolate was inoculated first. However, on the cultivar Wing, induced susceptibility was more apparent following prior inoculation of a non-virulent isolate. On the cultivar Hassan, prior inoculation with a virulent isolate sometimes induced susceptibility, but in some cases more susceptibility was induced by prior inoculation with a non-virulent isolate. In the latter instances, although relatively little infection developed, the majority of the spores produced were those of the normally non-virulent isolate.
There was some evidence of non-virulent isolates acquiring the ability to infect normally incompatible hosts. This effect disappeared after several generations in the absence of the virulent isolate. 相似文献
Each interaction between isolates was dependent on the host cultivar, the pathogen isolates used and on the inoculation sequence. Often, induced resistance was most obvious when a nonvirulent isolate was inoculated prior to a virulent isolate. Induced susceptibility was usually more apparent when the virulent isolate was inoculated first. However, on the cultivar Wing, induced susceptibility was more apparent following prior inoculation of a non-virulent isolate. On the cultivar Hassan, prior inoculation with a virulent isolate sometimes induced susceptibility, but in some cases more susceptibility was induced by prior inoculation with a non-virulent isolate. In the latter instances, although relatively little infection developed, the majority of the spores produced were those of the normally non-virulent isolate.
There was some evidence of non-virulent isolates acquiring the ability to infect normally incompatible hosts. This effect disappeared after several generations in the absence of the virulent isolate. 相似文献
10.
尖孢镰刀菌黄瓜专化型(Fusarium oxysporum f. sp.cucumerinum,Foc)是引起黄瓜枯萎病的病原真菌,为了明确不同抗性黄瓜品种连作对枯萎病菌遗传分化的影响,本研究采用TEF1-α、H3基因片段对不同抗性黄瓜品种连作及对轮作后分离的枯萎病菌群体进行遗传分化分析。结果表明,感病品种连作及轮作后菌群分化程度较低(0.007ST<0.045);与种植抗病品种一茬后的菌群相比,连作三、五茬后的菌群均发生显著分化(FST> 0.050),其中连作三茬后的菌群遗传分化程度最高(FST> 0.300)。单倍型分析发现,抗、感病品种连作后部分菌株形成新的单倍型,且分离自抗病品种的病原菌群体分化产生的单倍型数量多于感病品种。主成分分析结果进一步证明,与感病品种连作及轮作相比,抗病品种连作后病原菌菌群呈现出更显著的菌群分化。综上所述,抗病品种连作能够加剧黄瓜枯萎病菌群体的遗传分化。 相似文献
11.
Fei Xu Long Yang Jing Zhang Xiaoping Guo Xianlong Zhang Guoqing Li 《Phytoparasitica》2012,40(4):319-327
Three defoliating (D) pathotype isolates and five nondefoliating (ND) pathotype isolates of Verticillium dahliae from cotton in central China were tested for adaptation to various temperatures in conidial germination on water agar (10?C33°C), mycelial growth on potato dextrose agar (10?C33°C) and infection of cotton seedlings (Gossypium hirsutum cvs. ??E Mian 24?? and ??Yin Rui 361??) (25?C33°C). Results showed that the D-pathotype isolates adapted better than the ND-pathotype isolates to 30°C for conidial germination and mycelial growth, although the isolates of the two pathotypes had the same optimum temperature of 25°C. Under day/night temperatures of 25/25, 27/27 and 30/25°C for 20 and 25?days, the D-pathotype isolates induced the defoliation syndrome on seedlings of the two upland cotton cultivars, whereas the ND-pathotype isolates did not induce defoliation syndrome. The values for the areas under the disease progress curve (AUDPC) and the vascular discoloration index (VDI) were higher for the D-pathotype isolates than those for the ND-pathotype isolates in each temperature treatment. Under 30/30 or 33/27°C, at least two of the three D-pathotype isolates still had higher AUDPC values and/or VDI values than all the ND-pathotype isolates on E Mian 24. Therefore, the D-pathotype isolates appear more aggressive than the ND-pathotype isolates in infection of cotton. Results also showed that the cotton cultivar Yin Rui 361 was more tolerant than the cotton cultivar E Mian 24 to infection by both pathotypes of V. dahliae. This study suggests that the D-pathotype isolates can well adapt to high temperature and heavily infect cotton under 25?C30°C, and these features might be responsible for the rapid spread of this pathotype in central China. 相似文献
12.
ABSTRACT The Brassica napus-B. juncea recombinant line (MX), resistant to Leptosphaeria maculans, was produced by interspecific crosses and bears one gene (Jlm1) from the B. juncea B genome. We investigated whether this new resistance was race specific by characterizing protection against a large sample of L. maculans isolates. The pathogenicity of 119 isolates of L. maculans comprising 105 A-group isolates and 14 B-group isolates was studied at the cotyledon stage under controlled conditions using the MX line, the susceptible B. napus cultivar Westar, and the resistant B. juncea cultivar Picra. All but one of the isolates were pathogenic on 'Westar'. Only 3 of the 105 A-group isolates caused very mild symptoms on 'Picra'. Two of these strains were isolated from the MX line and the other from Sinapis arvensis. The other 102 strains caused hypersensitive-type responses. Most B-group isolates were pathogenic on 'Picra'. There were differences in pathogenicity among A-group isolates tested on the MX line, whereas all B-group isolates were pathogenic on this line. A-group isolates obtained from the MX line were more frequently pathogenic on the MX line than those obtained from B. napus cultivars. One isolate from S. arvensis infected the MX line. These results suggest that the resistance of the MX line is unlikely to be durable. Thus, the new resistance gene Jlm1 should probably be used in association with other sources of resistance, in plant breeding schemes, to prevent the breakdown of this resistance. 相似文献
13.
Identification of isolate-specific and partial resistance to septoria tritici blotch in 238 European wheat cultivars and breeding lines 总被引：2，自引：0，他引：2
From a total of 238 European cultivars and breeding lines screened for isolate-specific resistance to septoria tritici blotch (STB) with eight Mycosphaerella graminicola isolates from five different countries, 142 lines were resistant to Ethiopian isolate IPO88004, and 43 lines were specifically resistant to IPO323, with little or no leaf area bearing pycnidia of M. graminicola . These lines probably all have the resistance gene Stb6 . Specific resistances to isolates CA30JI, IPO001, IPO89011, IPO92006 and ISR398 were less common. Seventy-three per cent of the lines were specifically resistant to at least one isolate and 36 lines were resistant to more than one isolate. The line with the greatest number of specific resistances was the spring cultivar Raffles, with five. The most resistant line in which no specific resistance was identified was the Italian landrace Rieti, an ancestor of many modern European wheat cultivars. There was also a wide range of partial resistance among the lines tested, expressed in detached seedling leaves. Information about the resistance of wheat lines to M. graminicola isolates will assist breeders to choose parents of crosses from which progeny with superior resistance to STB may be selected. 相似文献
14.
ABSTRACT Alternaria spp. were sampled from brown spot lesions in several geographically separated citrus groves and different grapefruit and tangerine x grapefruit hybrid cultivars in Florida and screened for variation at 16 putative random amplified polymorphic DNA loci. Populations of the pathogen on two hybrids, Minneola and Orlando, in five locations throughout Florida were moderately differentiated (Nei's coefficient of gene differentiation [G(ST)] = 0.12) among locations. The hypothesis that host-specialized forms of Alternaria spp. cause brown spot on different Citrus spp. and cultivars was tested by estimating genetic differentiation among isolates sampled from different hosts and by pathogenicity assays. Isolates sampled from grapefruit and the hybrid cv. Nova were genetically distinct from isolates sampled from other hybrid cultivars including Robinson, Sunburst, Minneola, Orlando, and Murcott. No differentiation could be detected among isolates sampled from this latter group of hybrids. Quantitative pathogenicity assays on leaves using spray inoculation revealed that 'Nova' isolates were not significantly more pathogenic on 'Nova' compared with isolates from 'Minneola' and 'Orlando'. Similarly, grapefruit isolates were not significantly more pathogenic on grapefruit compared with isolates from 'Minneola'. Isolates from all hosts had similar disease rankings on each inoculated cultivar, with 'Minneola' the most susceptible, followed in decreasing order of susceptibility by 'Orlando', 'Sunburst', 'Nova', and 'Duncan' grapefruit. Rough lemon was generally immune to all isolates tested; however, occasional brown spot lesions were observed on leaves of this host with isolates from grapefruit. No evidence was found to support the hypothesis that unique genotypes of the pathogen, which are more virulent on 'Sunburst' or grapefruit, have been introduced to Florida. Populations of Alternaria spp. causing brown spot of citrus on grapefruit and 'Nova' in Florida are genetically distinct from isolates on other cultivars, and we speculate that these populations are in the early stages of adaptation to and possible speciation on these hosts. 相似文献
15.
Deanna L. Funnell-Harris Scott E. Sattler Jeffrey F. Pedersen 《European journal of plant pathology / European Foundation for Plant Pathology》2013,136(3):469-481
Sorghum is used as bioenergy feedstock, animal feed, and food. Economical methods for disease prevention and control are valuable for producers. Fluorescent Pseudomonas spp. were isolated from sorghum roots and surrounding soil with the goal of finding isolates that significantly inhibited sorghum fungal pathogens. Fluorescent pseudomonads were collected from seedlings of sorghum cultivars RTx433 and Redlan and wheat cultivar Lewjain, grown in two soils. Lewjain is known to support growth of producers of the antibiotic, 2,4-diacetylphloroglucinol (2,4-DAPG). Isolates from all three plants were assessed for hydrogen cyanide (HCN) and extracellular protease production, and for a 2,4-DAPG gene, phlD. Both soil type and plant type affected HCN- and protease-production, but phlD was not affected. Subsets of phlD + isolates were chosen to determine phlD genotypes and to conduct in vitro inhibition assays against sorghum pathogens. Most isolates from sorghum and wheat were genotype D, previously associated with superior root colonization. phlD + sorghum isolates were co-cultured with five sorghum pathogens. One isolate from each sorghum line exhibited inhibition to all five pathogens but more Redlan isolates were inhibitory to the virulent pathogen, Fusarium thapsinum, than RTx433 isolates. Nearly all inhibitory isolates from either sorghum cultivar were from one soil type. This is consistent with what had been previously observed in field studies: that soil type played a significant role in determining characteristics of fluorescent Pseudomonas spp. isolated from roots or soil, but sorghum genotype also had a considerable effect. 相似文献
16.
Variation in growth rates and aggressiveness of naturally occurring self‐fertile and self‐sterile isolates of the wilt pathogen Ceratocystis albifundus 
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下载免费PDF全文 Ceratocystis albifundus is the most important fungal pathogen of black wattle (Acacia mearnsii) grown in plantations in southern and eastern Africa. It is a homothallic fungus but also undergoes unidirectional mating type switching. As a result, the ascospore progeny can be either self‐fertile or self‐sterile. The only apparent difference between these mating types is the deletion of the MAT1‐2‐1 gene in self‐sterile isolates. There is some evidence suggesting that self‐sterile isolates grow more slowly than self‐fertile isolates, but this has not been tested rigorously. The aim of this study was to determine whether self‐sterile isolates are less fit by examining growth rate, relative germination rate and pathogenicity. Five self‐sterile isolates were generated from each of five self‐fertile isolates of C. albifundus and these 30 isolates were compared. The results showed that the self‐sterile isolates grew consistently slower and were less pathogenic than the self‐fertile isolates. The germination ratio of self‐fertile to self‐sterile isolates from single ascospores collected from the ascomata of five self‐fertile isolates was on average 7:3. This could be a consequence of the self‐sterile isolates having a lower germination rate. This observation, and the lower growth and pathogenicity levels, suggests that self‐sterile isolates are not likely to compete effectively in nature, raising intriguing questions regarding their role and value to C. albifundus and other fungi having a similar mating system. 相似文献
17.
Colonization of roots, stolons, tubers and stems of various potato (Solanum tuberosum) cultivars by the black-dot fungus Colletotrichum coccodes 总被引：1，自引：0，他引：1
In an attempt to better understand the importance of tuber-borne inoculum in black dot development, several potato cultivars were inoculated with various Colletotrichum coccodes isolates. Symptoms developed first on underground organs (starting 2 weeks after inoculation on roots, and later on stolons and tubers) of inoculated plants; stem infections developed only after 7–10 weeks, depending on the cultivar. Infection with C. coccodes resulted in a reduction in numbers of stolons and tubers in cv. Bintje, but not in the later maturing cv. Roseval. Significant isolate by cultivar interactions were detected from the analysis of root symptoms after inoculation of three potato cultivars (Bintje, Spunta and Desiree) with five C. coccodes isolates. Such an interaction was also detected for stolon/tuber symptoms at the latest scoring date (98 days after inoculation), but not at earlier dates (58, 70 and 84 days after inoculation). These results suggest that protocols based on root colonization might be used for investigating cultivar response to black dot and pathogenicity of C. coccodes isolates, and that some specificity exists in the reaction of potato genotypes to this pathogenic fungus. 相似文献
18.
Variation in the early development of Bremia lactucae on lettuce cultivars with different levels of field resistance 总被引：1，自引：1，他引：0
The early stages of development of Bremia lactucae (lettuce downy mildew) were examined on lettuce cultivars possessing high (Iceberg and Regina di Maggio) and low (Great Lakes and Plenos) levels of field resistance. Germ tubes, appressoria, penetration, primary and secondary vesicles, intercellular hyphae and haustoria were observed 3. 6 and 24 h after inoculation of cotyledons and of leaf discs from adult plants. Differences were observed between cv. Iceberg and susceptible genotypes in the percentage of spores germinating and the incidence and speed of development of infection structures. Secondary vesicles were first observed 24 h and 6 h after inoculation in Iceberg and susceptible genotypes, respectively. The lowest incidence of secondary vesicle formation 24 h after inoculation (48 and/or 43%) was recorded in Iceberg and Regina di Maggio, and the highest incidence (68%) occurred in Plenos. The formation of intercellular hyphae and haustoria was not observed in cv. Iceberg some 24 h after inoculation. There were significant differences in the lengths of germ tubes formed on different cultivars. Those on cv. Iceberg were longer than those formed on susceptible cultivars. The results indicate that the field resistance of B. lactucae may result from mechanisms which are effective in the early stages of infection. 相似文献
19.
Hideki OGISO Masashi FUJINAGA Hideki SAITO Toshiaki TAKEHARA Shigeru YAMANAKA 《Journal of General Plant Pathology》2002,68(4):292-299
One hundred and sixteen isolates of Fusarium oxysporum f. sp. lactucae obtained from 85 fields in three crisphead lettuce-producing areas in Nagano Prefecture, Japan were typed for races using
differential cultivars Patriot, Banchu Red Fire and Costa Rica No. 4. They were also grouped into vegetative compatibility
groups (VCGs) using complementation tests with nitrate non-utilizing (nit) mutants. Two California strains reported as F. oxysporum f. sp. lactucum, a type culture of F. oxysporum f. sp. lactucae, and 28 avirulent isolates of F. oxysporum obtained from crisphead lettuce were included for comparison. Among Nagano isolates, 66 isolates were identified as race 1,
and 50 as race 2. Race 1 strains derived from Shiojiri and Komoro cities and race 2 from Kawakami village and Komoro city.
All isolates of race 2 were biotin auxotrophs, and the race could be distinguished based on its requirement for biotin on
minimal nitrate agar medium (MM). Pathogenic isolates were classified into two VCGs and three heterokaryon self-incompatible
isolates. Strong correlations were found between race and VCG. All the race 1 strains were assigned to VCG 1 except self-incompatible
isolates, and all the race 2 strains to VCG 2. The 28 avirulent isolates of F. oxysporum were incompatible with VCG 1 and VCG 2. California strains was vegetatively compatible with VCG 1, and they were assigned
to race 1. Based on vegetative compatibility, these two races of F. oxysporum f. sp. lactucae may be genetically distinct, and F. oxysporum f. sp. lactucae race 1 is identical to F. oxysporum f. sp. lactucum.
Received 7 May 2002/ Accepted in revised form 6 September 2002 相似文献
20.
ABSTRACT Thirty isolates of P. griseacollected from rice during a blast epidemic in 1995 in the high (1,800 to 2,600 m) and middle (1,200 to 1,800 m) elevations of Bhutan and 80 isolates collected from one rice cultivar from two high- and two mid-elevation sites in 1996 were analyzed for virulence. Differential varieties were indica CO39, with five near-isogenic lines (NILs) for resistance genes in the genetic background of CO39, and japonica Lijiangxintuanheigu (LTH), with five NILs for LTH. Twelve selected Bhutanese landraces also were studied. In addition, 10 blast nurseries consisting of the NIL sets, important local landraces, and representatives of international differential groups were established in the 1996 and 1997 growing seasons in the mid- and high-elevation agroecological zones. The 110 isolates were differentiated into 53 pathotypes based on the 2 NIL sets. Thirteen isolates were avirulent on all of the NILs but were compatible with some landraces. Several isolates were able to attack one of the NILs of CO39 but not CO39. These results strongly suggest that both CO39 and LTH possess previously unidentified resistance. The landraces were not uniform in their reactions to the isolates. When a reaction index taking into account all individual plant reactions was used, isolates that had been assigned to the same pathotype could be further differentiated, indicating that the NIL sets could not completely discriminate virulences in Bhutanese P. grisea populations. In the trap nurseries, disease was always present in the middle elevations, but disease was very low during July 1996 in the high elevations and only present during August and September 1997. Almost all varietal groups were more frequently attacked in the middle than in the high elevations, indicating that the virulence spectrum is wider and the conduciveness of the environment is greater in the middle elevations. Landraces from the high elevations were most susceptible, followed by international differential groups 7 and 8. The results suggest that selection has yielded landraces with more complete and complex resistance in the more disease-conducive mid-elevation environment. At the same time, the pathogen population also possesses a wider virulence spectrum in that environment. 相似文献