Document Type

Thesis - University Access Only

Award Date


Degree Name

Doctor of Philosophy (PhD)

Department / School

Plant Science


Eight hard spring wheat lines Triticum aestivum L. of diverse origin were crossed in a diallel mating design. Yield trials of the parents and F2 Bulks were planted at three different planting dates in Cd. Obregon Mexico and Brookings, South Dakota USA. There was a continuous decrease in yield with late planting in Mexico with the second and third planting dates, yielding 75% and 44% respectively of the first planting date. In South Dakota, the yield of the second date of planting was reduced 65% of the first planting, but there was not further reduction from the second to the third. In Mexico, grains per spike was the yield parameter most affected. In South Dakota it was spikes per square meter. General combining ability (GCA) was significant for all traits. The rank of the parents per se was very similar to the rank by GCA. Fang 60 which had a high number of kernels per spike was the top yielding parent in Mexico and kernels per spike was the yield parameter that showed the greatest reduction with late planting in Mexico. SD305 6 showed good stability for high number of tillers per square meter. The eight parents were also evaluated in growth chamber experiments under controlled conditions under hot (35 0C) and cool (15 CC) temperatures. The effects of high temperature treatment were extreme with average reduction in yield over 75% from the cool to the hot chamber. There were highly significant differences among genotypes in the hot chamber for: yield, number of grains, kernel weight,_ biomass and SPAD number. For the physiological characters studied in the hot chamber there were reductions in total chlorophyll, chlorophyll a and chlorophyll b. The plants in general started to mature from the bottom to the top soon after they were moved inside of the hot chamber. The chlorophyll meter provided and objective measure of "stay green" character that has been reported to be correlated with yield. The heritability of yield components appear to be more stable than the heritability of yield. Genetic variability in regards to high temperature was evident in the cultivars used in this study and it was evident to see that high temperature tolerance has to be related to the growth stage in which the stress occurs. The first step of any breeding program should be to characterize the environment and to target the growth stages during which the heat stress is most likely to occur.

Library of Congress Subject Headings

Wheat -- Effect of temperature on



Number of Pages



South Dakota State University