Development of a genetic linkage map of broccoli and identification of QTL associated with glucosinolate variability

This study consists of three experiments dealing with the genetics of glucosinolates, a class of secondary metabolites in broccoli whose hydrolyzed breakdown products have demonstrated utility in both the prevention of tumor initiation and in reduced tumor promotion and progress. The study also details the development of a broccoli genetic linkage map and demonstrates how it can be utilized to identify genetic factors associated with both health promoting compounds and commercially important horticultural traits associated with broccoli production.; The first experiment details a survey of ten broccoli genotypes grown in four environments to estimate the heritability of glucosinolates, identify sources of variation associated with glucosinolates, and determining the stability of these compounds over multiple environments. Significant differences in genetic variability were identified for aliphatic glucosinolates, but not for the other major class indole glucosinolates. The percentage of glucosinolate variability attributed to genetic variation for individual glucosinolate compounds ranged from 12.0% to 71.0%. This demonstrated that expectations for successfully breeding for increased or altered levels of glucosinolates depended on the type of glucosinolate. Both qualitative and quantitative differences in glucosinolates were detected among the cultivars included in the survey, and two cultivars were then selected and used as parents to develop a segregating F2:3 population of broccoli.; The second experiment details the development of this population and describes the screening of 216 PCR based DNA markers and the placement of 62 polymorphic loci into ten genetic linkage groups spanning a distance of 468 cM with an average interval width of 9.4 cM. Finally, this chapter demonstrates the utility of the broccoli genetic linkage map by identifying four QTL associated with 55.6% of the phenotypic variation associated with broccoli days to harvest maturity in the first year of the experiment.; The third experiment then demonstrates how the broccoli genetic linkage map can be used to identify genetic factors affecting qualitative and quantitative differences in health promoting compounds. QTL analysis in this experiment identified seven QTL on six linkage groups associated with the variability of individual and/or total glucosinolate content at or above an LOD score of 3.0.