2010 Annual Report 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 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 25°C 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 MapManager and MapMaker software packages and QTL data will be mapped using QTL Cartographer for Windows v. 2.5. 3.Progress Report 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. ADODR monitoring activities to evaluate research progress included phone calls, meetings with the cooperator, and an annual meeting held each year in January. Characterization of the genetic basis for partial resistance to Sclerotinia sclerotiorum in pea: Sclerotinia sclerotiorum is an important disease pest of many crops including pea (Pisum sativum L.) and crop losses have been significant when environmental conditions were conducive to disease development. Limitation regarding available germplasm with resistance has hampered development of resistant pea cultivars. The recent description of partial genetic resistance to S. sclerotiorum among pea accessions provides an opportunity to study the genetic control of resistance. Four sources of resistance, PI 103709, PI 169603, PI 240515 and ICI 1204-3 represent two distinct mechanisms of resistance (inhibited lesion expansion and nodal resistance). Genetic mapping populations involving these resistant sources are in development and will be used to place the genetic factors controlling resistance on the pea map. DNA markers associated with the resistance will be made available to breeding programs to aid selection of resistant progeny. In addition, hybridizations aimed at combining the resistance mechanisms will be made to provide an increased level of durable resistance. Results from this project will reduce the economic impact of the white mold pathogen in pea through. 1)the identification of genetic factors (QTL) controlling partial resistance to white mold on the pea map and. 2)the pyramiding of available mechanisms of resistance in an effort to develop durable resistance.