Genetic & Environmental Influences on Head Rice Yield 82

Genetic and Environmental Influences
on Head Rice Yield-82

Project Leader and Principal UC Investigators

Shu Geng, Department of Agronomy and Range Science, University of California, Davis

The objective of the project to determine genetic and environmental infuences on head rice yield is to analyze statewide records available from California rice mills to determine the effects on head yield of such factors as the variety, location where grown, time of harvest, grain moisture content, crop yields, and local climate conditions. Records were obtained for the three years 1979 to 1981 from the Rice Growers Association in Sacramento and the Butte County Rice Growers Association. Climatic records were obtained from weather stations in the Sacramento Valley.

Conclusions reached from a statistical analysis of nearly 5,000 grain lots were as follows:

Plant height is not a factor of importance in influencing head o rice.
The replacement of tall varieties by short-statured varieties did not affect the overall head yield.
Greatest differences in head rice yields were among maturity groups.
Late varieties averaged about 10 percent higher head yield than very early varieties and about 5 percent higher than early , varieties.

M7 and Calrose 76 were stable and uniformly high in head yield in different environments. Calrose, M5, M9 and S6 were unstable but had good head yield. M-101 was unstable and had poor head yield. S 201, Colusa, and Earlirose were highly unstable and location specific. These results suggest that in addition to maturity, there are diverse genetic backgrounds in head. yield that respond to different environments.

These differences were found in all rice growing areas. An analysis of temperatures at harvesting time indicated only 3 percent of the very early varieties were harvested at temperatures above 95°F. Similar distributions were found for late maturing cultivars. Consequently, differences in head rice between maturity groups appears to be a genetic characteristic that is linked with maturity.

The stability of head rice yields was analyzed for each variety grown over several years and in several areas. From the ranges in head rice yields, the varieties were classified as stable, unstable or highly unstable, if the ranges were less than 2 percent, between 5 and 9 percent, or above' 9 percent respectively. M7 and Calrose 76 were stable and uniformly high in head yield in different environments. Calrose, M5, M9 and S6 were unstable but had good head yield. M-101 was unstable and had poor head yield. S-201, Colusa, and Earlirose were highly unstable and location specific. These results suggest that in addition to maturity, there are diverse genetic backgrounds in head yield that respond to different environments. Analyses of the data from the Butte County Rice Growers Association show that grain yield was correlated with head yield. When yields increased, head yield increased.

Temperatures above 95°F during. maturation adversely affected head yield. Cold units (below 65°F) at the 10-day period prior to flowering had little effect on head yield but significantly reduced grain yield.

Variability in head yield increased when rice was harvested at lower moisture levels. Moisture curves were developed for ten commonly grown varieties from 1979 to 1981. The optimal moisture content at harvest for good head yields was 29 percent for very early varieties, 27 percent for early varieties and 25 percent for late maturing varieties. A study of the results from the 1982 crop year could further substantiate the validity of the results from 1979 through 1981.