The Potential for Breeding for Stemphylium Blight Resistance in the Genus Lens

Stemphylium blight (SB) caused by Stemphylium botryosum Wallr. is a widespread fungal disease and is becoming a serious threat of lentil in most of the lentil growing areas of the world including the temperate northern prairies of North America. It causes significant leaf damage with severe yield loss of lentil. The overall aim of this research was to identify sources of resistance to stemphylium blight and to determine the inheritance of resistance in recombinant inbred populations (RILs) for potential use in lentil breeding. Experiments were conducted to evaluate disease resistance of germplasm accessions selected from seven Lens spp. and in intraspecific and interspecific RIL population. Growth chamber, greenhouse and field trials in Saskatoon and Bangladesh were conducted. Seventy accessions selected from all wild species of the Lens genus were screened for SB resistance. An F₇-derived Lens culinaris intraspecific (‘Eston’ x PI 320937) RIL population (LR-39) with 96 lines along with checks was screened for SB resistance in the field at the University of Saskatchewan and at the field of Pulses Research Centre (PRC), Ishurdi, Bangladesh. An F₇- derived interspecific RIL population from the cross between resistant parents Lens culinaris cv. ‘Eston’ x Lens ervoides IG 72815, consisting of 123 lines was evaluated in greenhouse facilities at University of Saskatchewan using the highly aggressive S. botryosum isolate SB-19, and under field conditions of PRC, Ishurdi, Bangladesh. Most of the L. culinaris accessions were susceptible to SB, whereas more than 70% of the wild lentil accessions had disease severity scores equal to or significantly lower than that of the SB resistant check ’Eston’. The highest frequency of resistance to SB was observed in L. lamottei followed by L. ervoides of the secondary gene pool. These sources can potentially be used to develop new commercial cultivars with multiple disease resistance. A number of lines from both RIL populations showed consistent disease reaction, either resistant or susceptible, in the two environments with a significant variation in each environment. A continuous frequency distribution indicated quantitative inheritance of resistance in both RILs with some transgressive segregates for resistant disease reaction in the Bangladesh environment for LR-39, and for LR-26 compared to the resistant L. culinaris parent ‘Eston’ under Saskatoon and Bangladesh field conditions, respectively. Fifty-seven or 33% of RILs from the intraspecific LR-39 population showed resistance to SB in comparison to ‘Eston’. For the interspecific population LR-26, 60% and 68% of RILs had either resistant or very resistant disease reactions, respectively, under natural inoculation pressure in the field in Bangladesh and under greenhouse conditions when inoculated with isolate SB-19 at Saskatoon. The genotype × location interaction variance was higher than the genotype variance, indicating a substantial influence of the environment on the expression of resistance. Selected resistant RILs from both environments can be given priority for incorporation in the breeding program, and gene pyramiding might be helpful to develop new cultivars with resistance to multiple diseases including SB in the future. A high proportion of interspecific breeding lines with consistent resistant reaction to SB should prove useful for future breeding strategies. This extensive study of SB resistance inheritance pattern will provide a base for identification of potential SB resistance genes or interspecific origin through marker assisted breeding