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A comprehensive study was conducted on the prevalence of grapevine trunk diseases in Greece, focusing specifically on contamination of grapevine propagation material by Phaeomoniella chlamydospora and black foot disease‐related species. Additionally, detection of esca pathogen Fomitiporia mediterranea, causing white rot in grapevine and other woody hosts, was assessed using a new PCR‐based assay that distinguishes F. mediterranea from F. punctata. Development of a nested PCR assay, combined with a cost‐effective DNA extraction protocol, revealed a high percentage of infection by P. chlamydospora (51%) and Ilyonectria species associated with black foot disease (28%) in different types of grapevine propagation material (dormant cuttings, field‐rooted benchgrafts and green‐growing plants). Interestingly, black foot disease‐related pathogens were more prevalent in nursery plants grown in the field for 6 months (57%) than in other types of propagation material and compared with P. chlamydospora (43%), indicating increased infection of propagation material during growth in the nursery field. The cost‐effective molecular method developed in this study could be used in mass inspections of propagation material for phytosanitary purposes. Finally, using primers specific for F. mediterranea and F. puncata developed in this study, combined with the universal ITS4 primer, a collection of Fomitiporia isolates from mature grapevine and other woody hosts from Greece and Italy (southern Europe) were characterized as F. mediterranea, whereas German and Swedish isolates from forest plants (central Europe) were classified as F. punctata. The developed primers can discriminate between the two Fomitiporia species, which are indistinguishable based on culture and morphological characteristics alone. [ABSTRACT FROM AUTHOR]

Lettuce downy mildew caused by Bremia lactucae is the most important disease of lettuce worldwide. Breeding for resistance to this disease is a major priority for most lettuce breeding programs. Many genes and factors for resistance to B. lactucae have been reported by multiple researchers over the past ~50 years. Their nomenclature has not been coordinated, resulting in duplications and gaps in nominations. We have reviewed the available information and rationalized it into 51 resistance genes and factors and 15 quantitative trait loci along with supporting documentation as well as genetic and molecular information. This involved multiple rounds of consultation with many of the original authors. This paper provides the foundation for naming additional genes for resistance to B. lactucae in the future as well as for deploying genes to provide more durable resistance. [ABSTRACT FROM AUTHOR]

Genome-wide motif searches identified 1134 genes in the lettuce reference genome of cv. Salinas that are potentially involved in pathogen recognition, of which 385 were predicted to encode nucleotide binding-leucine rich repeat receptor (NLR) proteins. Using a maximum-likelihood approach, we grouped the NLRs into 25 multigene families and 17 singletons. Forty-one percent of these NLR-encoding genes belong to three families, the largest being RGC16 with 62 genes in cv. Salinas. The majority of NLRencoding genes are located in five major resistance clusters (MRCs) on chromosomes 1, 2, 3, 4, and 8 and cosegregate with multiple disease resistance phenotypes. Most MRCs contain primarily members of a single NLR gene family but a few are more complex. MRC2 spans 73 Mb and contains 61 NLRs of six different gene families that cosegregate with nine disease resistance phenotypes. MRC3, which is 25 Mb, contains 22 RGC21 genes and colocates with Dm13. A library of 33 transgenic RNA interference tester stocks was generated for functional analysis of NLR-encoding genes that cosegregated with disease resistance phenotypes in each of the MRCs. Members of four NLR-encoding families, RGC1, RGC2, RGC21, and RGC12 were shown to be required for 16 disease resistance phenotypes in lettuce. The general composition of MRCs is conserved across different genotypes; however, the specific repertoire of NLRencoding genes varied particularly of the rapidly evolving Type I genes. These tester stocks are valuable resources for future analyses of additional resistance phenotypes. [ABSTRACT FROM AUTHOR]

Studies on resistance gene function and evolution lie at the confluence of structural and molecular biology, genetics, and plant breeding. How-ever, knowledge from these disparate fields has yet to be extensively integrated. This review draws on ideas and information from these dif-ferent fields to elucidate the influences driving the evolution of different types of resistance genes in plants and the concurrent evolution of vir-ulence in pathogens. It provides an overview of the factors shaping the evolution of recognition, signaling, and response genes in the context of emerging functional information along with a consideration of the new opportunities for durable resistance enabled by high-throughput DNA sequencing technologies. [ABSTRACT FROM AUTHOR]