Phaseolus acutifolius A. Gray is More Heat Tolerant than P. vulgaris L. in the Absence of Water Stress

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Abstract
Field observations suggest that Phaseolus acutifolius A. Gray is more heat and drought tolerant than P. vulgaris L. Since high temperature stress and water stress are difficult to separate in field experiments, we do not know if P. acutifolius is more high temperature tolerant than P. vulgaris. The goal of our research was to determine whether P. acutifolius is more heat tolerant than P. vulgaris in the absence of water stress. Plants grown at 25°C for 13 d in controlled environment chambers were separated into two groups; one group was maintained at 25°C for 8 d and the other at 32°C for 8 d. Air vapor pressure deficit at the two temperatures was maintained at 1.1 kPa. Phaseolus vulgaris growth was significantly decreased at 32°C compared with growth at 25°C. The decrease included total leaf area, total dry weight, root weight, and net assimilation rate. Phaseolus acutifolius grew similarly at both temperatures. Separate experiments investigated the effects of temperature on seed germination and early seedling growth. Seed germination of both species was reduced by about 11% at 32°C compared with germination at 25°C. Initial P. vulgaris radical growth was inhibited at 32°C whereas radical growth of P. acutifolius was not affected. Our results indicate that at the tissue level P. acutifolius is more heat tolerant than P. vulgaris.

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