Inheritance of Resistance to Ascochyta Blight in Lentil

Abstract

The inheritance of resistance to ascochyta blight in lentil (Lens culinaris Medik.) caused by Ascochyta fabae Speg. f. sp. lentis Gossen et al (Syn. A. lentis Vassil.) was studied using as parents the Canadian cultivars Eston (susceptible) and Laird (moderately resistant) and two resistant lines from ICARDA, ILL-5588 and ILL-5684. The F2, F2-derived Fa families and F2-derived F4 families of each cross were evaluated for ascochyta resistance under field conditions in an ascochyta nursery during 1987, 1988 and 1989, respectively. The parents and segregating populations were rated for ascochyta reaction on the basis of foliage symptoms, using a 1 to 9 disease rating scale, with plants rated 1 to 5 considered resistant and plants rated 7 to 9 considered susceptible. In addition percent seed-borne ascochyta infection was evaluated, using the seed plating technique. The cuItivar Eston was susceptible. Laird lentil was resistant to foliar infection by ascochyta, but its resistance breaks down in the late podding stage and under the wet conditions of the ascochyta nursery percent seed-borne ascochyta infection was even higher than in the susceptible cultivar Eston. The lines ILL-5588 and ILL-5684 were highly resistant with resistance persisting after maturity and the seed coats do not become infected and discolor materially even with prolonged exposure to wet weather at harvest. A chi-square test for goodness-of-fit of the F2 and F2- derived F3 families indicated that resistance to foliar infection by ascochyta in Laird lentil was conditioned by a single recessive gene, ral1• Results also indicated that the resistance to foliage and seed infection by ascochyta of ILL- 5588 and ILL-5684 was due to two - dominant genes,' Ral2 and Ral3. ILL-5588, but not ILL-5684, also carried the ral1 gene for resistance to foliar infection by ascochyta and is the better source of resistance to ascochyta. The high correlation between percent seed-borne ascochyta infection in Fz-derived F3 families and in F2-derived F4 families plus the medium to high heritability estimates (0.52 to 0.8l) indicate that it will be easy to select for ascochyta resistance in these crosses. An effective method of selecting for ascochyta resistance in lentil was developed. An ascochyta nursery is developed by spreading infected lentil straw between the lentil rows prior to flowering. This nursery is then sprinkled intermittently once or twice each day until about two weeks after maturity. The crop is permitted to dry naturally and selections made for ascochyta resistant F2 plants or replicated progeny rows in later generations. Ascochyta resistance is based on a low level of discolored seed (0 to 5%), reconfirmed by plating the seed to determine percent seed-borne ascochyta infection in replicated progeny rows. Only a few selections have a high level of clean bright seed and require seed planting. This technique is quick, easy, effective and efficient. Resulting selections are resistant to both foliar infection and seed infection by ascochyta.