Vergara - 1976 - Physiological and morphological adaptability of ri

PHYTOTRONS IN AGRICULTURAL RESEARCH
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some perennial pasture plants. They may also be used to generate male sterility
in some crops, as low temperatures do in sorghum (Downes and Marshall.
1971). to aid hybridization programs. In cotton. phytotron conditions have
been used to assess the potential of two male-sterile lines for hybrid cotton
production in the field (Marshall et al,
1974). In both lines. the extent of male
sterility was greatly affected by temperature. and to a lesser degree by day length.
and was sufficient to insure hybridization tinlj; at yrery high temperatures. Thus,
only very restricted areas would be suitable for hybrid seed production.
Day length and temperature can also influence whether reproduction in several
grasses of Androptigtineae is sexual or apomictic. and it is therefore possible
that phytotrons could play a key role in the development of crops in which
hybrids in the field are apomictic and. as a result. fixed from generation to
generation in their heterosis, as may be possible in Sorghum bicolor.
Controlled environments have long been used to increase the number of life
cycles that can be traversed each year in breeding programs. and much effort has
been given to developing regimes for the most rapid reproduction of ‘various
crops. such as pearl millet (Hellmers and Burton, 1972).
The opportunity for manipulation of time of flowering. sexuality’. and fertility
of economic plants in phytotrons clearly constitutes one of their major roles in
agricultural research.
MODIFYING THE RANGE OF ADAPTATION
In their response to temperature. plants appear to be much more conserv-‘ative
than in their response to day length. While there are major differences among
plants in the optimum temperature for growth, and particularly in their ability
to grow at cool and hot extremes, many of these differences are associated with
taxonomic grouping. and races or eultivars ofa species do not differ nearly so
much in temperature response as in day length response. Nevertheless. what
differences there are between cultivars and races may be of considerable signif—
icance. both agriculturally and adaptively.
'l'he various processes that contribute to growth and development ofa particular
cultivar may respond to temperature in very different Way's, as Went (1957)
established for tomatoes and several other plants. Thus. the optimum temperature
represents the best compromise for all processes contributing to growth.
development and yield. and as such will vary with stage of development and
previous conditions. Moreover. optimum conditions for a community of plants
may be different from those for single plants.
In agriculture we are more often concenied with relative performance under
sub-optimal or extreme conditions. For example, the ability to grow at coo]
temperatures, say lO—l5°C, is often crucial to the early development 0f many
crops, and screening for seedling tolerance of cool temperatures has been an
important part of many’ pb_vtotron programs, such as those on cotton, peanuts,
and soybeans at Raleigh. Plants with the C. pathway of photosynthesis seem