Cold irrigation water (60° F) is used for cold water gradient screening of the 72 lines in county yield trials.

Basic Studies to Advance Rice Breeding Methods

Male sterile lines are being developed to convert rice from a normally self-pollinated plant to at least a partially cross-pollinated plant. By using these male sterile lines, it will be possible to do large-scale crossing among diverse lines to concentrate genes from many sources into locally adapted materials.

Chinese reports of 12 million acres of F₁ hybrid rice have greatly stimulated research on hybrid rice in other rice growing areas of the world. We are in the midst of studies to find out if hybrid rice is feasible for mechanized rice production in the United States. Chinese hybrid rice has high labor requirements. In order to grow hybrid rice in the United States commercially, it is necessary to develop suitable male sterility systems, to establish proof that hybrid rice yields are large enough to make them worthwhile, and to greatly improve grain quality. Solutions to these problems will require a number of years. In 1982 we obtained the Chinese cytoplasmic male sterility system. Lines from this system must be converted to cold-tolerant backgrounds before they can be properly evaluated. Obtaining good grain quality will be a major problem for United States hybrid rice production.

The use of tissue culture is also being studied as a possible new breeding method. Tissue culture is the regeneration of whole plants from small parts of a plant. It would allow new plants to be developed in the laboratory and would eliminate the need to maintain large field nurseries.

Current studies are limited to devising methods for regenerating plants from the vegetative tissue of young roots. There are many difficulties and to date, only six plants have been regenerated from vegetative tissue of a single line SD7. If the problem of regeneration can be solved, cell lines of rice could be selected in the laboratory after screening them for tolerance to herbicides. In the meantime, we are screening irradiated seedling populations for tolerance to Bolero using conventional methods, with early indications of some success.

Male sterile lines are being developed to convert rice from a normally self pollinated plant to at least a partially cross-pollinated plant. By using these male sterile lines, it will be possible to do large-scale crossing among diverse lines to concentrate genes from many sources into locally adapted materials.

Development of Germplasm for Breeding and Physiological Studies

Dr. J.N. Rutger and assistants examine plots of a weedy rice species which Rutger and Dr. R.K. Webster have found to be a source of stem rot resistance.

Earlier studies have strongly indicated the possibility that rice plants grown in California could produce more grain weight than the panicles now are able to hold. We are trying to prove this by developing strains with more grains and larger grains. Forty-seven lines were compared with three check varieties in 1982. Very large differences were found for grains per panicle and for individual grain weights. These will be tested again in 1983 to determine if increasing grain size and numbers can increase yields.

We are making crosses between California rice varieties and various related rice species to develop new cytoplasmic male sterility systems that may be more suitable for California. Fertile F₁ plants were obtained from five interspecific crosses in 1982. They will be further tested in 1983.

Floral characteristics were studied on 50 rice varieties from Egypt, the U.S. and elsewhere to find out if they might affect outcrossing rates in hybrid rice production. Differences were found in anther length and width, stigma length, pollen size, and number of pollen grains per anther. Work was continued on producing elongated mesocotyles on short statured rice varieties. This characteristic might be useful in improving stand establishment. Other studies were conducted for producing marker genes to identify new varieties from otherwise similar appearing older varieties. Work also continues in an effort to find better resistance to stem rot and sheath blight by interspecific hybrids.