Plant disease resistance

About: Plant disease resistance is a research topic. Over the lifetime, 12952 publications have been published within this topic receiving 381820 citations. The topic is also known as: plant innate immunity.

Genome-wide survey of Arabidopsis natural variation in downy mildew resistance using combined association and linkage mapping

Abstract: The model plant Arabidopsis thaliana exhibits extensive natural variation in resistance to parasites. Immunity is often conferred by resistance (R) genes that permit recognition of specific races of a disease. The number of such R genes and their distribution are poorly understood. In this study, we investigated the basis for resistance to the downy mildew agent Hyaloperonospora arabidopsidis ex parasitica (Hpa) in a global sample of A. thaliana. We implemented a combined genome-wide mapping of resistance using populations of recombinant inbred lines and a collection of wild A. thaliana accessions. We tested the interaction between 96 host genotypes collected worldwide and five strains of Hpa. Then, a fraction of the species-wide resistance was genetically dissected using six recently constructed populations of recombinant inbred lines. We found that resistance is usually governed by single dominant R genes that are concentrated in four genomic regions only. We show that association genetics of resistance to diseases such as downy mildew enables increased mapping resolution from quantitative trait loci interval to candidate gene level. Association patterns in quantitative trait loci intervals indicate that the pool of A. thaliana resistance sources against the tested Hpa isolates may be predominantly confined to six RPP (Resistance to Hpa) loci isolated in previous studies. Our results suggest that combining association and linkage mapping could accelerate resistance gene discovery in plants.

Mapping of Ve in tomato: a gene conferring resistance to the broad-spectrum pathogen, Verticillium dahliae race 1

Abstract: The soil-borne fungi Verticillium spp. cause vascular wilt disease in a wide range of crop plants. In tomato, resistance to Verticillium dahliae race 1 is conferred by a single dominant gene, Ve. Previous efforts to map Ve in tomato have yielded confusing results, locating it on different chromosomes, which subsequently raised the possibility that Verticillium resistance may be controlled by a number of loci. We used three different mapping populations to obtain an unambiguous map location of Ve: a recombinant inbred (RI) line population; an F2 population segregating for Verticillium resistance; and a population of 50 introgression lines (IL). In all of the mapping populations Ve was positioned on the short arm of chromosome 9 tightly linked to the RFLP marker GP39. This linkage was confirmed by screening for GP39 in different breeding lines with known resistance or susceptibility to Verticillium. A perfect match was found between GP39 and the Verticillium response of the lines, indicating the potential of GP39 in the rapid detection of Verticillium resistance and as a starting point for map-based cloning of Ve. This approach is particularly relevant for Verticillium dahliae race 1, since in the present work we also show that the isolate that infects tomato is responsible for wilt disease in other important crop plants.

Independent deletions of a pathogen-resistance gene in Brassica and Arabidopsis

Abstract: Plant disease resistance (R) genes confer race-specific resistance to pathogens and are genetically defined on the basis of intra-specific functional polymorphism. Little is known about the evolutionary mechanisms that generate this polymorphism. Most R loci examined to date contain alternate alleles and/or linked homologs even in disease-susceptible plant genotypes. In contrast, the resistance to Pseudomonas syringae pathovar maculicola (RPM1) bacterial resistance gene is completely absent (rpm1-null) in 5/5 Arabidopsis thaliana accessions that lack RPM1 function. The rpm1-null locus contains a 98-bp segment of unknown origin in place of the RPM1 gene. We undertook comparative mapping of RPM1 and flanking genes in Brassica napus to determine the ancestral state of the RPM1 locus. We cloned two B. napus RPM1 homologs encoding hypothetical proteins with ≈81% amino acid identity to Arabidopsis RPM1. Collinearity of genes flanking RPM1 is conserved between B. napus and Arabidopsis. Surprisingly, we found four additional B. napus loci in which the flanking marker synteny is maintained but RPM1 is absent. These B. napus rpm1-null loci have no detectable nucleotide similarity to the Arabidopsis rpm1-null allele. We conclude that RPM1 evolved before the divergence of the Brassicaceae and has been deleted independently in the Brassica and Arabidopsis lineages. These results suggest that functional polymorphism at R gene loci can arise from gene deletions.

Reaction of Soybean Cultivars to Sclerotinia Stem Rot in Field, Greenhouse, and Laboratory Evaluations

Abstract: programs. Soybean cultivars have been evaluated for resistance to sclerotinia stem rot under field conditions Sclerotinia stem rot of soybean [Glycine max (L.) Merr.], caused and some with partial resistance to the disease have by the fungal pathogen Sclerotinia sclerotiorum (Lib.) de Bary, recently has increased in importance in the northern U.S. soybean pro- been identified (Grau et al., 1982; Boland and Hall, duction area. The objective of our study was to determine the effec- 1987; Nelson et al., 1991; Kim et al., 1999). Although tiveness of three different inoculation techniques in predicting the researchers have been successful in identifying partial field reactions of cultivars to sclerotinia stem rot. Eighteen soybean resistance using field evaluations, these evaluations are cultivars were field tested in six Michigan environments from 1994 to difficult because of the need for a cool, wet environment 1996 and tested in the greenhouse or laboratory with three inoculation for disease development and the high spatial variability methods. The cultivars were inoculated by placing infested oat (Avena of disease foci across fields. For these reasons, researchsativa L.) seed or mycelial plugs on cotyledons or by placing mycelial ers would benefit from having a controlled-environment plugs on detached leaves. There were significant (P , 0.05) differences screening method that accurately predicts the reaction in resistance to sclerotinia stem rot among cultivars at all but one of soybean germplasm in field environments. field environment and for all inoculation methods. The disease severity ratings based on the inoculations were significantly correlated with Both physiological resistance and escape mechanisms the field results, with the exception of one method. Disease severity contribute to differences in the reaction of cultivars to ratings for the three inoculation methods were significantly correlated sclerotinia stem rot in field trials. Escape mechanisms with only two exceptions. Cultivars such as Novartis S19-90 and Corsoy include early flowering and maturity, less lodging, and 79 consistently had the lowest disease severity ratings in the field tests an upright, open canopy. One or more of these mechaand for the inoculation methods. Similarly, a number of cultivars were nisms have been shown to be significantly associated rated as susceptible in all tests. Ratings for cultivars with intermediate with reduced levels of sclerotinia stem rot in several reactions were not consistent across tests. The inoculation methods studies (Boland and Hall, 1987; Nelson et al., 1991; Kim tested can provide some useful information on the resistance of soy

CaWRKY6 transcriptionally activates CaWRKY40, regulates Ralstonia solanacearum resistance, and confers high-temperature and high-humidity tolerance in pepper

Abstract: High temperature (HT), high humidity (HH), and pathogen infection often co-occur and negatively affect plant growth However, these stress factors and plant responses are generally studied in isolation The mechanisms of synergistic responses to combined stresses are poorly understood We isolated the subgroup IIb WRKY family member CaWRKY6 from Capsicum annuum and performed quantitative real-time PCR analysis CaWRKY6 expression was upregulated by individual or simultaneous treatment with HT, HH, combined HT and HH (HTHH), and Ralstonia solanacearum inoculation, and responded to exogenous application of jasmonic acid (JA), ethephon, and abscisic acid (ABA) Virus-induced gene silencing of CaWRKY6 enhanced pepper plant susceptibility to R solanacearum and HTHH, and downregulated the hypersensitive response (HR), JA-, ethylene (ET)-, and ABA-induced marker gene expression, and thermotolerance-associated expression of CaHSP24, ER-small CaSHP, and Chl-small CaHSP CaWRKY6 overexpression in pepper attenuated the HTHH-induced suppression of resistance to R solanacearum infection CaWRKY6 bound to and activated the CaWRKY40 promoter in planta, which is a pepper WRKY that regulates heat-stress tolerance and R solanacearum resistance CaWRKY40 silencing significantly blocked HR-induced cell death and reduced transcriptional expression of CaWRKY40 These data suggest that CaWRKY6 is a positive regulator of R solanacearum resistance and heat-stress tolerance, which occurs in part by activating CaWRKY40