Use of isozyme markers to select for resistance to Ascochyta blight in lentil
The possible linkages of isozyme loci with genes for resistance to Ascochyta blight, caused by Ascochyta fabae f. sp. lentis Gossen et al., was investigated in lentil (Lens culinaris Medikus). The F2 seeds of five crosses, their parents and five lentil lines (DuPuy, Laird, PI 339283, PI 374118 and PR 86-360) were space planted with a susceptible check, Spanish Brown lentil. Disease inoculation was performed by spreading Ascochyta infected lentil debris and providing mist irrigation to enhance disease development. Gel electrophoresis was· used to resolve eight isozyme loci using leaf tissue of F2 plants in three gel and electrode buffer systems. Resistance to Ascochyta is due to a dominant gene (Rai1) in ILL 5588 lentil, and a recessive gene (ral2) in Indianhead lentil. Significant contingency chi-squared values occurred between the Ral 1 gene and the isozyme locus Aat-p (29 eM) and between the ral2 gene and the isozyme locus Pgd-p (28 eM). These markers are useless in selecting for resistance to Ascochyta due to the large map distance from the genes for resistance. Thus, markers more closely linked with these genes are required. More powerful molecular markers, such as RAPD, can be used in this endeavour. Two RAPD markers, tightly linked with Ral1 and ral2 genes, respectively, will greatly facilitate "pyramiding" of these two genes into one lentil line and thus, produce a stable genetic resistance to Ascochyta.
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