Possible role for wild genotypes of Pisum spp. to enhance ascochyta blight resistance in pea

Abstract

Summary. There are no cultivars with effective field resistance to ascochyta blight currently available in Australia but a number of wild genotypes of Pisum have been identified as possible sources of resistance and these were evaluated in crosses with a commercial cultivar. Pisum fulvum JI 1006, used as the pollen parent, was crossed with P. sativum cv. Wirrega using wild type P. sativum JI 252 as a bridging cross. JI 1006 and JI 252 both respond to Mycosphaerella pinodes infection by inducing a rapid hypersensitive response. All F₂ seedlings (17–20-day-old) from the cross Wirrega × (JI 252 × JI 1006) were screened for their responses to M. pinodes infection in a controlled environment and plants with the highest levels of resistance were then screened as F₃ progeny families in the field to determine their responses to natural M. pinodes infection. Nine percent of these families were significantly more resistant for both leaf and stem disease compared with Wirrega and among them were 9 lines which flowered at the same time or earlier than Wirrega. However, even the most resistant line had 30% of the foliage destroyed by disease, indicating disease control was insufficient. A second resistance mechanism which impeded M. pinodes hyphal penetration in leaves (P. sativum SA 1160) was combined with the hypersensitive response in the cross SA 1160 × (JI 252 × JI 1006). The level of resistance to disease was now significantly higher than any plant in the original F₃ population, despite the wild-type growth habit of these plants. It is suggested that breeding programs should focus first on maximising field resistance through isolation of some optimal combinations of resistance mechanisms in wild genotypes before turning to improving the agronomic performance through backcrossing to advanced breeding lines.