Genetic and Quantitative Analysis of Red Raspberry (Rubus idaeus) for Heat Tolerance and Longer Chilling Requirement


Despite the high level of interest for growing red raspberries (Rubus ideaus) in the southeastern US, production is limited by the lack of adapted, high quality cultivars. Breeding efforts are underway for increasing cultivar availability for this region, however breeding improvements in Rubus are slow and time-consuming. In order to expedite the slow, but effective, breeding process, more molecular breeding tools should be developed. Cultivars adapted to the southeastern US need to tolerate warm summers, and winters with temperature fluctuations. To address this issue, we have developed a genetic linkage mapping population from a cross that segregates for the tolerance of both conditions, (R. parvifolius × ‘Tulameen’) × ‘Qualicum’. This population was used for the construction of a genetic linkage map and for quantitative trait loci (QTL) analysis of heat tolerance, and chilling requirement for tolerance to fluctuating winter temperatures. As expected, seven linkage groups were created and were similar to the already published map. Because heat tolerance is a difficult trait to measure, a protocol was developed using chlorophyll fluorescence to assess heat tolerance. This protocol was used to measure tolerance in the population, and after QTL analysis, 3 QTL explained ~35% of the variation. Chilling requirements in the population were estimated by measuring bud break under greenhouse conditions. Quantitative analysis was performed on these estimates, and 3 QTL were found in two separate season evaluations, and in most cases co-localization occurred in the same region on the map. These regions explained the majority of the variation in the trait (100-64.5%). In summary, this research has established a protocol that measures heat tolerance in red raspberry, without relying on visual assessment, and has mapped important QTL for further molecular studies. Future research should focus on these regions to develop closely linked molecular markers for marker assisted breeding.



Rubus, Rosaceae, heat tolerance, chilling requirement, chlorophyll fluorescence, genetic linkage map





Horticultural Science