Field screening for heat tolerant common bean cultivars (Phaseolus vulgaris L.) by measuring of chlorophyll fluorescence induction parameters

The temperature induced changes in chlorophyll fluorescence induction parameters (F0, Fm, Fv and their ratios) measured by a PEA analyzer were used to screen for heat-tolerance 12 cultivars and lines of common bean (Phaseolus vulgaris L.) available in the germplasm collections of Maritsa Vegetable Crops Research Institute, Plovdiv, and Institute of Plant Genetic Resources, Sadovo, Bulgaria. The experiments were carried out in a selection field of Maritsa Institute. The measurements were made on six different dates during the bean reproductive period (in June–July) when the temperatures were approximately 26 °C in the morning to and 42 °C at noon. Two lines, known earlier as heat-tolerant were used as controls.We found that most of studied cultivars and lines were heat-sensitive because upon day-course increase of temperatures from 26 °C to 42 °C they revealed statistically significant increase in initial fluorescence (F0), simultaneous decreases in maximum fluorescence (Fm), and in Fv/F0 ratio. Only two cultivars: Ranit and Nerine RS like the heat-tolerant lines preserved F0, Fm and Fv values and Fv/F0 ratio at 42 °C similar to those values at 26 °C. We have considered these two cultivars as heat-tolerant. They have good productivity and been quality and will be used as parental lines in bean breeding program.