Effects of modifying the environment on flowering, fruiting, and biochemical composition of the snap bean (Phaseolus vulgaris L.)

Abstract

The effects of modifying air temperature, soil temperature, and soil moisture levels on flowering, fruiting, and chemical composition of Tendercrop snap beans were studied in experiments in the field and in the greenhouse during 1961, 1962, and 1963. High maximum temperatures of 95-105° F. during bloom reduced the percent set and number and weight of pods of bean plants. Plants appeared to be most sensitive to temperatures at six to eight days after first bloom. Air temperatures in the field were increased 8-10° F. above controls by use of clear polyethylene plastic cages. The carbohydrate content of leaves and stems of plants subjected to high temperatures was decreased with a greater relative reduction of starch than of other sugars. Air temperature appeared also to affect the protein metabolism since cystine was not detected in plants subjected- to high temperature. Furthermore, threonine was detected in plants exposed to high temperatures, but not in control plants. Soil temperatures ranging from 55° to 90° F. had a pronounced effect on growth, flowering, and yield of snap beans, with best growth of plants and highest number of flowers and pods and weight of pods being obtained at soil temperatures of 75° to 80° F. Diurnal fluctuation of soil temperature had no advantage over comparable constant mean soil temperature for growth of plants. An exception was at fluctuating soil temperatures of 50-60° F- compared to constant temperature of 55° F. Soil temperature did not affect levels of total sugar and reducing sugar, but the starch content was decreased with an increase in soil temperature. Sucrose content of plants at fluctuating soil temperatures tended to be higher than in plants grown at comparable constant mean temperatures. Dry weight of shoots and roots and P and K content of plants increased with increased soil temperature. Magnesium content tended to decrease with an increase of soil temperature while Ca content of plants was variable. Snap bean plants which received the highest amount and frequency of irrigation from planting to harvest had the highest dry weight of shoots, number of flowers, percent set, and yield of pods when compared to plants subjected to moisture stress, either before or after bloom, or during both periods. On a dry weight basis, the carbohydrate content of leaves and stems of plants was highest when amount and frequency of irrigation was highest, but on the fresh weight basis, the carbohydrate content decreased with an increase in soil moisture. The stems and leaves of plants at the high moisture treatments contained highest levels of P and K while N and Mg levels of the same plants were lowest. A higher concentration of arginine was found in plants at high moisture levels than at low moisture levels. Tyrosine was detected in plants grown at the higher moisture, but not in plants subjected to moisture stress. Data suggest that soil moisture levels affected protein metabolism. Sucrose sprays had no significant effect on production of pods and carbohydrate content of bean plants. When soil temperature and moisture levels were varied, significant correlation co-efficients were obtained between weight of plants and number of pods, and between weight of plants and weight of pods. Data suggest that for highest yield, environmental factors should favor production of a large vigorous plant, with large photosynthetic capacity for bearing flowers and fruits. Bean plants appear to be especially sensitive to adverse temperature and moisture conditions during the period of anthesis and early pod development. Although adverse effects of high temperature and of moisture stress on pollination and fertilization were not studied, per se, in the present investigations, these adverse conditions caused a lower production of pods, lower carbohydrates levels, and appeared also to affect protein metabolism in snap beans. Further research is needed, especially to elucidate the adverse effects of high temperatures and moisture stress on biochemical processes and constituents of the snap bean and the significant relationship of these to growth, flowering, and fruiting.