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. ADODR monitoring activities to evaluate research progress included phone calls, meetings with the cooperator, and an annual meeting held each year in January.
The mapping populations that we are working with have been advanced to the F6 and F7. Development of PRIL-17 is complete and it is currently being grown in the field as F7-derived lines for bulk seed increase. Seed from this increase will be evaluated in the fall of 2011 for resistance to Sclerotinia via the ARS-developedscreening method (Dr. Lyndon Porter; Prosser, WA). Results of this screening are corroborating previous results and are expected to identify additional individual lines from the more resistant PI accessions that can be used in breeding. PRIL-19 is in the F6 and will be advanced to the F7 in the fall of 2011. Bulk seed increase will follow. More than 50 polymorphic markers for PRIL-17 have been screened against the F2 DNA to develop an F2-based genetic map. Generation of a skeletal genetic map is in progress. F3 and F4 family seed from the two segregating populations, PRIL-17 and PRIL-19, were screened previously by ARS-Prosser and the data will be combined with the genetic marker data to establish initial placement of the genes for resistance on the genetic map. 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.