Resistance to high tempeRatuRe stRess of vaRious bean (Phaseolus vulgaris L.) cuLtivaRs and Lines

The high temperature stress-induced changes in chlorophyll a fluorescence parameters were used to study heat tolerance in nine accessions of common bean (Phaseolus vulgaris L.) received from the germplasm collection of “Maritsa” Vegetable Crops Research Institute and the Invstitute for Introduction and Plant Genetic Resources. The bean plants were treated for 2h at two temperatures, 23oC and 45oC in controlled conditions. We found that most of the studied cultivars and lines did not show a significant decrease in the maximal PS2 quantum yield (Fv/Fm) below values reflecting reduced structural stability of PS2, except for lines 83201007 and RRR46. Simultaneously, a statistically significant increase in the initial fluorescence (F0) was measured in these lines. A decrease in the maximum fluorescence (Fm) after heat treatment was observed in most of the cultivars and lines studied, except for line RRR46. Despite the significant decrease in the Fv/Fm ratio, both lines 83201007 and RRR46 should not be considered as heat sensitive because of their plastic response to high temperature treatment. Similarly to other lines and cultivars, the lines 83201007 and RRR46 showed a well-expressed recovery 4h after treatment. Thus, such a flexible response of bean parental lines to high temperature can be used in future breeding programs when seeking a better response to conditions like a sudden jump to higher temperatures.