| 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.
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