Vergara - 1976 - Physiological and morphological adaptability of ri

GENETIC VstRlOLlSNESS IN CLIAIAIIC ADAPTATION I09
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DISCUSSION
STANSEL (Chairman): How many here while reading through the literature have come across
passages such as. “Observations were incomplete due to high temperature“? Or this: “Low
temperatures and excessive rainfall may have influenced the results." with no definition of these
climatic factors. How many times do we see these references to climatic variables in the literature
without definition? Everyone recognizes the impact of climatic variables but too few report
them. This is the problem our participants faced in accumulating the reported observations
from the literature. Have you been guilty of this practice?
Breeding for the illusive climatic adaptability can be a hazardous endeavor. Gains in some
characteristics can ofien be at the detriment of other characters. How often does our search for
climatic adaptability result in a narrowing of climatic response in the plant? For example, we
discussed earlier the development of US. varieties which were adapted to increased utilization
of available sunlight. resulting in increased yield. Yes, yields have been significantly increased.
but for a price. These very early maturing varieties also require a very high level of cultural
control. Water management of these varieties is critical due to the short basic vegetative phase.
Both timing and rate of fertilizer is critical for high yields. Weed control has caused producer
problems due to inability to compete with moderate weed infestations. Yields are so dependent
on climatic conditions. These varieties then have specific or limited climatic adaptability.
While they do well in Texas. they are not adapted elsewhere. How often do you hear. “We
have developed resistance to a particular disease; however. yields under disease-tree conditions
do not match the yields of local varieties"? Yes, too often we arc etfcctive in developing yield
resistance because of a restrictive climatic adaptability‘. ls the climate in your locality the same
year afier year‘? How often do you Iiear. “There is no such thing as a normal year"? Normality
is the exception to the rule. Plant breeders, more than any other group. are constantly trying to
measure climatic response. The program here at IRRI has shown there are eFfective ways to
develop climatic adaptability.
I wish to reiterate the observations discussed earlier by Dr. Chang because there is a message
here for all stibject-matter areas of agricultural research. Disruptive seasonal selection is