MS Exit Seminar - Nancy Huarachi Morejon
Genetic and Environmental Factors Affecting Improvement of Rootstocks for Tomato
Grafting to rootstocks is becoming popular in annual vegetable production to control soil borne diseases, replace fumigation, and impart vigor. Previous research indicates that inconsistent seed quality and lack of information about rootstock-scion compatibility inhibits adoption of the technology. The main goals of the research were to address limitations in seed quality of tomato rootstock and the efficiency of graft success between scion and rootstock. A total of 110 rootstocks were developed through pollination of 10 cultivated (Solanum Lycopersicum) parental lines as female plants and 11 accessions of wild species as male parents. Environmental and genetic effects on seed quality were evaluated during two seed production seasons and by harvesting fruit at different maturation stages. Seed quality was assessed based on seed size and germination rates. The failure of the graft to form due to excess callus, brittle joints, or stunted scions is often referred to as “incompatibility”. To improve graft success, the use of adhesives was investigated for nine different rootstocks which were grafted using both the traditional tube method and using cyanoacrylate glue. Finally, to identify the genetic basis of graft incompatibility, molecular markers were exploited for QTL analysis in two different populations. An advanced backcross population (BC3S4) derived from the elite lines H7998 (displaying a high rate of incompatible grafts) and OH88119 and an F2 population derived from H7998 and Ohio MR13 were developed. Seed size was influenced more by parental genetics than environment. Seed germination was influenced by genetics and environmental factors. Using seed weight as selection criterion in breeding might allow early selection for high quality rootstock. Grafting using adhesives resulted in higher success. Finally, I identified potential QTL for graft incompatibility on chromosome 9, and two QTLs for scion height on chromosome 2 and 4. In all cases, the negative effects (incompatible grafts or stunted scions) were linked to alleles from H7998. I was not able to independently validate QTL due to the lack of overlapping markers across the two populations. Further work would be necessary to confirm these results. In conclusion, I identified key selection points in the breeding of new tomato rootstock cultivars; demonstrated the importance of environmental conditions to obtain high quality seed from wide-cross hybrids; confirmed that grafting success can be increased using adhesives; and demonstrated that grafting success may have a genetic basis, with failure associated with alleles from H7998.
Friday, August 9
9:00 AM - 10:00 AM