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United States Department of Agriculture

Agricultural Research Service

Research Project: Resources for the Genetic Improvement of Potato

Location: Vegetable Crops Research Unit

2013 Annual Report


1a.Objectives (from AD-416):
Objective 1: Identify adapted interspecific hybrids with Verticillium wilt resistance, and introgress resistance into breeding lines. Develop and test molecular markers within a Ve resistance gene ortholog. Characterize the effect of Verticillium wilt resistance on stem-end chip defect. Objective 2: Identify lines carrying genes for resistance to early blight and late blight. Incorporate resistance into parental lines that will be released for use by breeders. Determine the physiological and genetic interactions between host and pathogen for these diseases. Objective 3: Genotype diploid and tetraploid populations segregating for resistance to common scab and cold-induced sweetening. Map the resistance genes, and identify markers useful to breeders.


1b.Approach (from AD-416):
Objective 1: We will design PCR primers for the isolation of Ve orthologs. Place candidate genes in an Agrobacterium vector and transiently co-express candidate genes with the V. dahliae Ave effector gene. Inoculate transgenic plants and score for Verticillium wilt. We will inoculate Verticillium wilt resistant and susceptible accessions of wild Solanum species and measure V. dahliae infection in stems by quantitative PCR. We will look for a Race 2 strain of V. dahliae in sap from stems resistant clones showing anomalously high amounts of V. dahliae. We will evaluate gene expression differences in resistant and susceptible clones following exposure to V. dahliae or the toxin produced by V. dahliae using RNA-seq. We will use a segregating population to evaluate stem-end defect in tubers from Verticillium-infested and fumigated fields. Objective 2: We will use microscopic observations to compare Alternaria solani spore germination and mycelial growth on inoculated leaves of two sources of early blight resistance. We will carry out a genetic study of early blight resistance in a segregating population and test potential DNA markers. We will combine two sources of early blight resistance and look for pyramiding effects. We will determine whether plant vigor is maintained when resistance to early blight and late blight are combined. Objective 3: We will map genes for resistance to cold-induced sweetening and identify markers useful to breeders. We will evaluate levels of vacuolar acid invertase activity in a diploid F2 population following cold storage. Use SNP markers to identify quantitative trait loci controlling resistance to cold-induced sweetening and common scab. Determine the usefulness of markers developed for these traits. We will release parental lines with resistance to cold-induced sweetening and scab, along with molecular markers to accompany the germplasm.


3.Progress Report:
Progress relates to objective 3 (Genotype diploid and tetraploid populations segregating for resistance to common scab and cold-induced sweetening. Map the resistance genes, and identify markers useful to breeders). We have mapped genes for resistance to common scab. We have completed a project to identify quantitative trait loci (QTL) for resistance to common scab, cold-induced sweetening, plant vigor, tuber size, and plant maturity in an interspecific diploid F2 population. Major QTLs were found and work is underway to identify markers for use in breeding.

Progress relates to objective 2 (Identify lines carrying genes for resistance to early blight and late blight. Incorporate resistance into parental lines that will be released for use by breeders). We have incorporated late blight resistance into parental lines. We have completed development of a population from a cross between late blight resistant K41 and early blight resistant +297. These individuals have been screened for resistance to late blight and clones with strong resistance have been identified and are being prepared for field trials.

Progress relates to objective 1 (Identify adapted interspecific hybrids with Verticillium wilt resistance, and introgress resistance into breeding lines. Develop and test molecular markers within a Ve resistance gene ortholog. Characterize the effect of Verticillium wilt resistance on stem-end chip defect). We have identified genes associated with Verticillium wilt resistance. Using a combination of targeted amplification of genomic deoxyribonucleic acid (DNA) and whole genome sequencing, we have identified two Ve genes within resistant potato hybrids. We have successfully amplified portions of both genes and isolation of full length coding sequences is currently underway.

Progress relates to objective 1 (Identify adapted interspecific hybrids with Verticillium wilt resistance, and introgress resistance into breeding lines. Develop and test molecular markers within a Ve resistance gene ortholog. Characterize the effect of Verticillium wilt resistance on stem-end chip defect). We have identified sources of Verticillium wilt resistance. Sixteen accessions of wild potato have been screened for resistance to Verticillium dahliae in the greenhouse and both resistant and susceptible individuals have been chosen for sequence analysis of the Ve gene locus.


Last Modified: 10/25/2014
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