2012 Annual Report
1a.Objectives (from AD-416):
In 2009, a new late blight strain US-22 was identified along the East coast and as far west as Wisconsin. This strain was virulent on potatoes and significantly impacted potato production in affected areas. There was greater variation in the strains identified in potato fields in the U.S. in 2010, however US-22 was again identified in WI along with US-23 and 24. Although not yet present in the USA, destructive and highly virulent strains of P. Infestans have spread through Europe (genotype Blue 13), and are present in Guatemala (currently uncharacterized). These new strains can be much more aggressive compared to the old populations. We need to be prepared with germplasm that is resistant to highly virulent strains.
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.
The second year of an inoculated field trial was conducted using a cocktail of isolates common to the United States and Michigan. This included the new US22, US23, and US24 strains of late blight. Sets of three progeny (Spunta-RB x susceptible; Spunta-RB x moderate resistance; Spunta-RB x resistant) were planted in a randomized complete block design with two replications. Visual ratings of percent defoliation due to late blight were recorded at least weekly after inoculation occurred and relative area under disease progress curve (RAUDPCs) were calculated 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. This study was conducted in 2010 and repeated in 2011. The 2011 data resulted in lower infection levels compared to the 2010 results. The results of both years suggest that combining the RB gene with current resistance genes in parents may lead to higher levels of late blight resistance. We selected 50 of the most resistant lines from these crosses that contain the RB gene. These will be further tested against more P. infestans isolates in 2012 and are candidates for effector testing.
This research relates to Objective 1, Develop adapted potato clones with enhanced resistance to major potato diseases.