1a.Objectives (from AD-416):
The objective of this project is to characterize the genetic inheritance of partial resistance to Sclerotinia sclerotiorum in pea (Pisum sativum L.) and exploit this resistance in the development of improved varieties. White mold, caused by S. sclerotiorum (Lib.) de Bary, is an important fungal pathogen of many crop plants and can cause significant crop loss to peas when environmental conditions are suitable. Pea germplasm demonstrating partial resistance has recently been identified and will be incorporated in improved agronomically adapted cultivars. The resistant sources show three distinct mechanisms of resistance and these mechanisms will be pyramided in single adapted backgrounds in an effort to extend the durability of resistance.
1b.Approach (from AD-416):
A classical breeding and genetic approach will be used to study the inheritance of partial resistance to S. sclerotiorum in pea and develop improved cultivars. Four accessions of pea germplasm have been identified representing three distinct mechanisms of resistance. These accessions have been hybridized with adapted germplasm to develop large mapping populations. The adapted parents used in this project are currently being characterized in complementary mapping projects. Common parents among the populations allow maps generated in different populations to be combined readily based on common genetic markers. Recombinant inbred line populations will be developed using single seed descent to the F7. Initial resistance data generated based on F3 and F4 families will be mapped using F2 genotypes. Individual replicate plants will be inoculated at 15 days of age with agar plugs containing mycelium of S. sclerotiorum and placed in a humidity chamber for 3 days, at which time the white mold lesions will be measured. Plants will then be placed in a growth chamber at 25ºC for one weeks and individual plants will be scored for survival and nodal resistance (prevention of lesion movement through a node). Genetic maps will be developed using JoinMap 4.0, MapManager and MapMaker software packages and QTL data will be mapped using QTL Cartographer for Windows v. 2.5.
This project was initiated on June 1, 2009, research is ongoing, and the overall objective is the identification of genetic factors (QTL) controlling partial resistance to white mold in pea.
A genetic linkage map based on F2 DNA from the cross, Lifter/PI240515 (PRIL-17), was developed with 78 markers on nine 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 lesion expansion interval, while a second QTL on LGII(b) explained 2.5% of the phenotypic variation for nodal transmission inhibition. Several areas were identified for potential improvement in phenotypic evaluation.In addition to developing a map based on the PRIL-17 mapping population, the PI core collection was screened for resistance to Sclerotinia sclerotiorum. Many of the accessions previously identified with partial resistance were confirmed from his evaluations. Eight additional accessions were also identified with partial resistance and these accessions will serve as potential new sources of resistance for breeding programs. This research has established the initial basis for development of white mold resistant peas.