AER1, a Major Gene Conferring Resistance to Aphanomyces euteiches in Medicago truncatula

Aphanomyces euteiches is a major soilborne oomycete pathogen that infects various legume species, including pea and alfalfa. The model legume Medicago truncatula has recently emerged as a valuable genetic system for understanding the genetic basis of resistance to A. euteiches in leguminous crops. The objective of this study was to identify genetic determinants of resistance to a broad host-range pea-infecting strain of A. euteiches in M. truncatula. Two M. truncatula segregating populations of 178 F5 recombinant inbred lines and 200 F3 families from the cross F83005.5 (susceptible) × DZA045.5 (resistant) were screened for resistance to A. euteiches. Phenotypic distributions observed suggested a dominant monogenic control of resistance. A major locus associated with resistance to A. euteiches, namely AER1, was mapped by bulk segregant analysis to a terminal end of chromosome 3 in M. truncatula and explained 88% of the phenotypic variation. AER1 was identified in a resistance-gene-rich region, where resistance gene analogs and genes associated with disease resistance phenotypes have been identified. Discovery of AER1 opens up new prospects for improving resistance to A. euteiches in cultivated legumes using a comparative genomics approach.

The Sbm1 locus conferring resistance to Soil-borne cereal mosaic virus maps to a gene-rich region on 5DL in wheat

A mosaic disease caused by Soil-borne cereal mosaic virus (SBCMV) is becoming increasingly important, particularly in winter wheat in Europe. As there are currently no effective cultural practices or practical environmentally friendly chemicals for disease control, host plant resistance is an important objective in breeding programs. However, development of resistant cultivars is slow owing to difficulties in germplasm screening for resistance. Therefore, there is a need to identify molecular markers linked to SBCMV-resistance gene(s), so that quick and accurate laboratory-based marker-assisted selection rather than prolonged field-based screens for resistance can be used in developing resistant cultivars. We previously demonstrated that resistance to SBCMV in Triticum aestivum ‘Cadenza’ is controlled by a single locus. In this work, we used AFLP and microsatellite technology to map this resistance locus, with the proposed name Sbm1, to the distal end of chromosome 5DL. Interestingly, several expressed disease-resistance gene analogues also map to this gene-rich region on 5DL. Closely linked (~17 cM interval) markers, BARC110 and WMC765, RRES01 and BARC144, that flank Sbm1 will be very useful in breeding for selection of germplasm carrying Sbm1.