Sclerotinia sclerotiorum causes white mold and severe yield losses of pea. 484 accessions from the Pisum core collection were screened for resistance using a mini-agar plug technique. 49, 41, and 13 accessions were identified with partial resistance based on lesion expansion inhibition (LEI), nodal transmission inhibition (NTI), and both traits combined, respectively. A genetic linkage map based on F2 DNA from the cross, Lifter/PI240515, was developed with 78 markers on 9 linkage groups (LG) spanning 734 cM. Two quantitative trait loci (QTL) were identified based on phenotypic data from F2:3 and F3:4 families. A single QTL on LGIII explained 34.1% of the phenotypic variation for LEI, while a second QTL on LGII(b) explained 2.5% of the phenotypic variation for NTI. This is the first report of QTL for S. sclerotiorum resistance in pea which will be useful in development of resistant pea varieties.

Graduation date: 1996

[Truncated abstract] Field pea (Pisum sativum) has many benefits when included in the crop rotation system in broadacre grain farming. These benefits include a disease break and improved weed control for cereals and less dependence on nitrogenous fertilisers due to the leguminous nature of pea. Currently, field pea adoption in Australia is low because the crop is susceptible to the fungal disease `black spot’ (Mycosphaerella pinodes) and has low stem strength and a lodged canopy. Black spot causes yield losses averaging 10-15% per year. Lodging results in difficult and costly harvesting, increased disease pressure and increased wind erosion from exposed soil surface when stems break at the basal nodes. This project aimed to address these problems through breeding, and through the application of quantitative genetics theory to a recurrent selection program. A quantitative measurement of relative stem strength was developed which could be used effectively in the field on single plants. Accurate laboratory measurements of stem strength were closely correlated with the field measure of compressed stem thickness in the basal node region. A diallel analysis of stem strength of the progeny of crosses among a range of pea lines with different values of compressed stem thickness concluded that the genetic control of stem strength was additive, with no maternal inheritance or dominance or epistasis effects.