Rice Genetics-87
 

 

 

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Project Leader and Principal UC Investigators

Neil Rutger, USDA-ARS

 

 Twelve germplasm lines were released jointly with the California Cooperative Rice Research Foundation, making them available to other public and private rice breeders. The lines with improved stem rot resistance and improved water weevil tolerance are among the most useful in this release.

Hybrid Rice Potential Explored

Basic research continues on genetic mechanisms that might make large-scale hybrid seed production easier.

A study attempting to understand the behavior of a photosensitive genetic male sterile line of Calrose 76 identified last year produced inclusive results. Data seem to support the hypothesis that fertility is enhanced by short day length. However, a 16.7 percent seed set was noted under long day length conditions where little or no seed set was expected.

Two new putative photosensitive male steriles were discovered from mutations of M-101 and M-201.

Promising Sterile Male

Work with male sterile lines needed for natural crossing to produce hybrid rice focused on understanding the process of male sterility and identifying sterile lines with the best outcrossing properties.

Current and previous studies have shown that male sterility is inherited as a single recessive gene character, but it was not known whether one or many different genes were involved. To date 47 of some 300 crosses between plants of different sterile sources have been evaluated. Many more of the crosses will have to be evaluated, but preliminary findings indicate that each male sterile gene is different. Thus, many different genes are probably involved in male sterility.

Outcrossing studies have identified M-201 NP (no pollen) as a useful male sterile germplasm source for future studies. A radiation induced mutant of M-101 identified as a useful germplasm source in previous population improvement schemes also continued to show desirable characteristics.

Resistance to Herbicides Sought

Tissue culture and mutagenized seed selections for herbicide resistance are continuing.

Two regenerated plants of M-202 that resulted from evaluating tissue cultures of 2,000 mature embryos of five rice varieties last year did not produce resistant progenies.

Promising plants from mutagenized seed selections have been identified and will be grown to the flowering stage and crossed with M-102 and other tester strains to determine their inheritance of tolerance.

Six surviving seedlings from a screening involving 200,000 M2 seeds are growing in the greenhouse, and their progeny will be tested for the level and inheritance of tolerance.

Tissue Culture Studies Seek Breeding Improvements

Anther culture, which could produce "instant" pure lines and shorten variety development cycles by two or three years is being explored. More than 28,000 anthers have been planted onto agar and, so far, 140 plants have been regenerated for further study and analysis.

Another study is under way to compare mutants induced through the tissue culture process with those induced by radiation and chemicals.

Asexual Seed Production Sought

Discovery and successful application of apomixis, a form of asexual seed production, in rice would permit production of true-breeding F1 hybrids with permanent heterosis (increased vigor associated with crossbreeding).

Twinning in seedlings can be an indicator of apomixis. Four highfrequency twinning lines from China show a rate of twinning ranging from six to 32 percent, compared with less than 0.1 percent twinning in ordinary rice. Studies are under way to determine exact origins of the twins and the inheritance of twinning.

 

Mutant Genes Prove Elusive

Chance plays a role in the work of any scientist, but perhaps most of all in the tedious, time-consuming chores of a geneticist. Project leader J. Neil Rutger knows this well.

Initial research into developing an herbicide-tolerant rice strain is a case in point. "There's a great need to find non-polluting herbicides that can still control weeds in rice fields," the USDA-ARS researcher said. While commercial chemists experiment with promising compounds that may meet that need, Rutger's team is in the midst of its second year of identifying the elusive mutant gene that might eventually be incorporated into commercial cultivars. The first year proved to be a disappointment, but Rutger is cautiously optimistic about findings from 1987. "1 think we have mutants, but we don't have confirmation yet," he said.

J. Neil Rutger leads the USDA-ARS research team that looks for methods of integrating conventional and molecular genetics of rice.

Persistence did pay off in 1987 when the geneticists were able to release to plant breeders germplasm with improved stem rot resistance and water weevil tolerance.

Another objective is to find the genetic tools that will make the plant breeder's job easier, such as use of male sterile lines to facilitate crosses and anther culture to shorten breeding cycles. But the "ultimate" plant breeder's tool, one that would go a long way toward true hybrid development, is asexual seed production. "It'd be phenomenally useful," Rutger said.

Thus far, Rutger's search for apomixis in rice has been unyielding. "This has the highest risk of all our research," Rutger said. "There's a 99 percent chance it won't work. But the payoff would be worth it."

Rutger's team cooperates in its research with the USDA's Western Regional Research Center in Albany, Calif. Their goal is to combine conventional and molecular genetics of rice to develop germplasm and breeding methods useful to the California rice industry.

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