Fine mapping and DNA fiber FISH analysis locates the tobamovirus resistance gene L3 of Capsicum chinense in a 400-kb region of R-like genes cluster embedded in highly repetitive sequences

The tobamovirus resistance gene L3 of Capsicum chinense was mapped using an intra-specific F2 population (2,016 individuals) of Capsicum annuum cultivars, into one of which had been introduced the C. chinenseL3 gene, and an inter-specific F2 population (3,391 individuals) between C. chinense and Capsicum frutescence. Analysis of a BAC library with an AFLP marker closely linked to L3-resistance revealed the presence of homologs of the tomato disease resistance gene I2. Partial or full-length coding sequences were cloned by degenerate PCR from 35 different pepper I2 homologs and 17 genetic markers were generated in the inter-specific combination. The L3 gene was mapped between I2 homolog marker IH1-04 and BAC-end marker 189D23M, and located within a region encompassing two different BAC contigs consisting of four and one clones, respectively. DNA fiber FISH analysis revealed that these two contigs are separated from each other by about 30 kb. DNA fiber FISH results and Southern blotting of the BAC clones suggested that the L3 locus-containing region is rich in highly repetitive sequences. Southern blot analysis indicated that the two BAC contigs contain more than ten copies of the I2 homologs. In contrast to the inter-specific F2 population, no recombinant progeny were identified to have a crossover point within two BAC contigs consisting of seven and two clones in the intra-specific F2 population. Moreover, distribution of the crossover points differed between the two populations, suggesting linkage disequilibrium in the region containing the L locus

Genomic and biological characterization of chiltepin yellow mosaic virus, a new tymovirus infecting Capsicum annuum var. aviculare in Mexico.

The characterization of viruses infecting wild plants is a key step towards understanding the ecology of plant viruses. In this work, the complete genomic nucleotide sequence of a new tymovirus species infecting chiltepin, the wild ancestor of Capsicum annuum pepper crops, in Mexico was determined, and its host range has been explored. The genome of 6,517 nucleotides has the three open reading frames described for tymoviruses, putatively encoding an RNA-dependent RNA polymerase, a movement protein and a coat protein. The 5′ and 3′ untranslated regions have structures with typical signatures of the tymoviruses. Phylogenetic analyses revealed that this new virus is closely related to the other tymoviruses isolated from solanaceous plants. Its host range is mainly limited to solanaceous species, which notably include cultivated Capsicum species. In the latter, infection resulted in a severe reduction of growth, indicating the potential of this virus to be a significant crop pathogen. The name of chiltepin yellow mosaic virus (ChiYMV) is proposed for this new tymovirus

The location and exploitation of genes for pest and disease resistance in European gene bank collections of horticultural brassicas

The objective of this project is to conduct a systematic evaluation of the distribution of diversity in Brassica oleracea with respect to resistance to three important parasites: Peronospora parasitica (downy mildew), Albugo candida (white blister) and Brevicoryne brassicae (cabbage aphid). A core collection of approximately 400 accessions representing the geographical, morphological and physiological diversity of the species has been selected for study. Protocols have been established to allow the rapid evaluation of phenotypic variation for response to all parasites and primary screening of the core collection is well advanced. Resistant individuals are being selected from within accessions expressing a high frequency of resistance. These are being crossed with a uniformly susceptible, self-compatible, rapid-cycling line to facilitate genetic characterisation and potentially easy gene-banking. Several putative new sources of resistance have been identified. Data will be linked to the European Brassica Database and together with seed will be made freely available to breeders and other researchers

Avaliação da resistência a tobamovirus em acessos de Capsicum spp. Evaluation of resistance of Capsicum spp. genotypes to tobamovirus

A resistência em Capsicum spp a tobamovírus é governada pelos genes L¹ a L4. Baseado na capacidade de alguns isolados suplantarem a resistência destes genes, os tobamovírus podem ser classificados nos patótipos P0, P1, P1-2 e P1-2-3. No Brasil, até o momento as três espécies de tobamovírus conhecidas são: Tobacco mosaic virus (TMV), Tomato mosaic virus (ToMV), pertencentes aos patótipos P0 e Pepper mild mottle virus (PMMoV) pertencente ao patótipo P1-2, respectivamente e podem infectar pimentas e pimentões. Oitenta e seis genótipos de pimentão e pimenta foram avaliados quanto à resistência a tobamovírus, sendo 62 de Capsicum annuum, 18 de C. baccatum e seis de C. chinense. Oito acessos de C. annuum, seis de C. baccatum e os acessos ICA #39, Pimenta de cheiro e PI 152225 de C. chinense apresentaram reação de hipersensibilidade ao ToMV, enquanto que o acesso Ancho de C. annuum foi considerado tolerante, permanecendo assintomático, porém permitindo a recuperação do vírus quando inoculado em Nicotiana glutinosa. Para o PMMoV patótipo P1,2 foram avaliados os acessos de pimentão e pimenta considerados resistentes ao ToMV. Somente o PI 152225 de C. chinense desencadeou reação de hipersensibilidade ao PMMoV, sendo fonte potencial de resistência para programas de melhoramento a este vírus no Brasil.<br>The resistance of Capsicum spp to tobamoviruses is conferred by the genes series L¹ to L4. Based on the ability of some isolates to overcome the resistance genes, the tobamovirus can be classificated in the pathotypes P0, P1, P1-2 and P1-2-3. In Brazil, at this moment there are three species of tobamovirus: Tobacco mosaic virus (TMV), Tomato mosaic virus (ToMV), belonging to pathotype P0 and Pepper mild mottle virus (PMMoV) belonging to pathotype P1-2 respectively, that can infect sweet and hot peppers. Eighty-six genotypes of sweet and hot pepper were evaluated for the resistance to tobamovirus. Eigth genotypes of C. annuum, five of C. baccatum and the three genotypes ICA #39, Pimenta de cheiro and PI 152225 of C. chinense reacted with hipersensibility to ToMV, while the genotype Ancho of C. annuum was considered tolerant to ToMV, remaining symptomless but allowing the multiplication of the virus. The genotypes considered resistant to ToMV, were evaluated for the reaction to P1,2 PMMoV. Only the PI 152225 of C. chinense reacted with hipersensibility to PMMoV, indicating that it could be used as a potential source of resistance in the breeding programs from Brazil