| Common scab is a disease of the potato tuber that results in reduced quality and subsequent market loss to growers. Despite what is known about the pathogen, there is no single and efficient method known to control the disease. Host plant resistance to scab is a favorable strategy for managing the disease in potato. Chapter one consists of a review of the literature on scab, and to a lesser extent, Verticillium wilt (VW) and cold-induced sweetening (CIS). Chapter two examines methods to reduce variability when screening for scab and Verticillium wilt (VW), another disease that requires labor-intensive phenotyping. The main objective of this research was to identify a sampling strategy which minimizes standard deviation and sample number. The sampling strategy which revealed the lowest variation for VW indicated that future collection of stems should include one stem from four plants in three blocks, totaling twelve stems per clone. For scab, five to eight plots per clone should be assayed. Chapter three focuses on QTL analysis and the effect of allelic substitution on resistance to scab, resistance to cold induced sweetening (CIS), vine maturity (maturity), plant vigor (vigor), percent dry matter (PDM), and average tuber weight (ATW). The F2, diploid mapped population had 98 individuals derived from two F1 clones of a cross between female S. tuberosum US-W4 and male S. chacoense 524-8. 524-8 was the source of resistance to scab and CIS, has late maturity, high vigor, and low tuber weight relative to US-W4. A significant QTL was identified on chromosome eleven for the scab phenotypes percent surface area and lesion type. The dominance ratio was 0.4 for PSA and 0.3 for LT. The source of dominance was susceptible grandparent US-W4. Two significant QTLs were identified for CIS, one on chromosome six (dominance ratio -0.5 and -0.6) and one on chromosome four (dominance ratio = 0.1). QTLs for maturity (dominance ratio = 0.2) and vigor (dominance ratio = 0.3) were identified at the same position on chromosome five. One QTL was identified for ATW on chromosome one and had a dominance ratio of 0.8 for large size. |
