Genotyping and phenotyping heat tolerance in black raspberry (Rubus occidentalis L.)
The demand for fresh, locally grown fruit, including raspberry, is strong in the United States. However, production of this crop in the southeastern US is difficult, because cultivars are not well adapted to the warm climate, where daytime summer temperatures typically range from 30 to 35¶øC. Recent research extolling the health benefits of a polyphenolic-rich diet has led to a resurgence of interest and breeding efforts in black raspberry. In this study, two related full-sib black raspberry populations, designated ORUS 4304 (192 progeny) and ORUS 4305 (115 progeny), were evaluated in south-central North Carolina (elevation 191 m, harvest season daily highs/lows 31/20¶øC) using chlorophyll fluorescence (Fv/Fm) as a phenotypic measure of heat tolerance. Fv/Fm is a non-invasive measurement of thylakoid damage to photosystem II that has been used to quantify heat tolerance in many annual and perennial plants. Readings were taken thrice on fully expanded primocane (non-fruiting canes) leaves during August 2013. Data collected from the populations show a normal distribution for Fv/Fm. Further, Thirteen genotypes had Fv/Fm values higher than the parents, indicating that there was transgressive segregation for chlorophyll fluorescence as a measure of heat tolerance in the population. Pairwise correlation analyses between chlorophyll fluorescence and horticultural traits found ambient Fv/Fm was negatively correlated with floricane vigor and lateral length at p<0.0001, while critical Fv/Fm was negatively correlated with berry weights at p<0.05. Additional phenotyping will take place in upcoming years, and, using a forward genetics approach, we will determine quantitative trait loci for heat tolerance within black raspberry based on linkage map assembly of population 4304. Ultimately, we hope to gain a more complete understanding of heat tolerance in raspberry to make breeding commercial quality cultivars a possibility in the southeastern US.
Bradish, C.M., Bushakra, J.M., Dossett, M., Bassil, N.V., Finn, C.E. and Fernandez, G.E. (2016). Genotyping and phenotyping heat tolerance in black raspberry (Rubus occidentalis L.). Acta Hortic. 1127, 321-324
chlorophyll fluorescence ratio (Fv/Fm), heat stress, plant breeding