2011 Annual Report
1a.Objectives (from AD-416)
A new late blight isolate, called blue 13 with fungicide resistance has recently taken a dominant position in Phytophthora populations in the United Kingdom, the Netherlands, Germany, and France. These new isolates are more aggressive compared to the old population. While this new isolate is not yet present in the United States, we need to be prepared with germplasm that is resistant to highly virulent strains.
Our specific objectives are to:
1. Conduct transformations with candidate sequences of a putative S. microdontum R-gene.
2. Identify functional orthologs of the late blight R-gene RB from disease resistant wild germplasm and test the functionality of these genes using a transient expression assay.
3. Evaluate the late blight resistant potato advanced breeding lines including the varieties 'Defender' and 'Jacqueline Lee' for resistance to Blue 13 and identify the presence of genes that recognize P. infestans effectors.
4. Evaluate the effect of pyramiding the RB with conventionally bred late blight resistant lines.
1b.Approach (from AD-416)
Stable transformation of LB susceptible potato with candidate resistance genes. Transgenic plants will be evaluated for resistance to LB. Crossing transgenic plants containing the RB gene or the newly discovered gene with conventionally bred LB resistant varieties will also be done.
An inoculated field trial was conducted at the Muck Soils Research Farm using a cocktail of isolates common to the United States (U.S.) and Michigan. Sets of three progeny (Spunta-RB x susceptible; Spunta-RB x moderate resistance; Spunta-RB x resistance) were planted in a randomized complete block design with two replications. The progeny were separated in RB+ vs RB- progeny by cross. Visual ratings of percent defoliation due to late blight were recorded at least weekly after inoculation occurred and disease progress was evaluated for each line. The RB+ progeny from all three crosses had, on average, lower levels of late blight infection. Secondly, the most resistant progeny were found in the crosses to parents with late blight resistance, while the most susceptible progeny were observed within the RB- progeny. The results suggest that combining the RB gene with current resistance genes in parents may lead to higher levels of late blight resistance. The project is monitored through in person discussions, phone calls, and e-mail exchanges.