engleski

Mapping of quantitative trait loci for resistance to Orobanche crenata in pea

Orobanche crenata (crenate broomrape) is a root parasite that represents the major constraint to pea production in Mediterranean areas (Rubiales et al., 1999). Only incomplete levels of resistance to broomrape have been identified in pea germplasm so far, suggesting that it is a polygenic trait. Higher levels of resistance have been found in nonadapted accessions of pea (Rubiales et al., 1999 ; 2005 ; Pérez de Luque et al., 2005). Thus, knowledge of the genomic location and linkage to molecular markers of these genes would facilitate gene transfer to pea cultivars through marker- assisted selection (MAS). A population consisting of 111 RILs (Recombinant Inbred Lines) derived from a cross between an accession of Pisum sativum spp. syriacum, which is partially resistant to O. crenata, and the susceptible pea cv. Messire have been analysed and a linkage map has been developed. These RILs were evaluated against broomrape under field conditions in Córdoba (Spain). Resistance to O. crenata was scored as the final number of emerged O. crenata shoots per pea plant per RIL. Simple regression was carried out using the score of vigour of each RIL family as an independent variable and the O. crenata score as a dependent variable. The regression corrected values (residuals) were used to correct for the possible differences in vigour. Regression residuals, considered as the O. crenata index, were multiplied by – 1 in order to assign greater values to the more resistant plants and a constant (10) was added in order to avoid negative values. The genetic map developed covers 1214 cM and contains three morphological, one isozyme, six STSs, six ESTs and 230 RAPD markers distributed in nine linkage groups. Of these, six groups have been assigned to chromosomes using markers common with the consensus pea map. A LOD of minimum 5.0 and a maximum recombination fraction of 0.3 (corresponding to a maximum Kosambi distance of 34.66 cM) were established as thresholds for grouping markers. Mean intermarker distance was 5.84 cM. The parental lines showed substantial differences in broomrape resistance. The female parent (P. sativum spp. syriacum) displayed a resistant index of 11.6 corresponding to 0.42 O. crenata shoots per pea plant, while the male parent (cv. Messire) showed an index value of 5 corresponding to 11 O. crenata shoots per plant. The resistance indices of the RILs ranged between 3.5 and 13, with 10 being the average value. This index was successfully applied in the detection of one QTL involved in the resistance to this parasite. This QTL is located in chromosome IV. The peak value of LOD was 3.86. This putative QTL explained 19 % of phenotypic variation of this trait and showed additive genetic effect of 0.749. Future research will be focused on studying the stability of this QTL in different environments and with different populations of the parasite. In addition, more accurate screening methods under controlled conditions might help to locate new QTL acting at different stages of the infestation process.

Pisum sativum L.; broomrapes; resistance; genetic mapping; QTLs

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