|Genetic and Physiological Determinants
of Yield and Quality-80
Project Leader and Principal UC Investigators
J.N. Rutger,USDA, UC Davis
M.L. Peterson, Dept. of Agronomy and Range Science, UC Davis
R.K. Webster, Dept. of Plant Pathology, UC Davis
The variety improvement program has been multi-faceted. USDA and UCD
scientists have provided basic research findings and "tools" including the
discovery of a source of stem rot in wild rice species - for the plant
breeders and pathologist at the Rice Experiment Station. Below is a brief
report of the added contributions of each group in 1980.
Progress to Develop Stem Rot Resistance
The objectives of this USDA-UC research were: 1) to determine if the tolerance of the wild Oryza species is due to morphological and/or anatomical characteristics; 2) to accelerate genetic studies on transfer of stem rot tolerance from Oryza rufipogon; and 3) to introduce from the International Rice Research Institute other rice wild species known to have stem rot resistance.
From the cross M-101 X O. rufipogon A100912 (the resistant O. rufipogon parent had a nonproductive plant type], several F3 lines with fairly good plant type were recovered and supplied to the Rice Experiment Station breeding program. Evaluations of F1, F2 and F3 generations of this cross indicate that stem rot resistance is due to dominant gene action involving more than one gene.
Although agronomic characters such as late flowering and high sterility seem to provide small degrees of resistance, it appears that there also must be a true genetic basis for stem rot resistance in O. rufipogon. Additional Oryza species introduced in 1980 as possible new sourcs of disease resistance included five entries of O. rufipogon, four of O. nivara, and five of O. spontanea.
Progress on Improving Hybrid Rice, Grain Quality and Yield Factors
Some of the basic studies on effects of temperature extremes on sterility were discontinued following the departure from UCD of Dr. I.E. Board. A genetic study on recombining the cold tolerance of the California variety M-101 and the long grain quality of Southern varieties was continued.
Basic research on factors to raise current yield levels showed that highest yields presently are obtained by short-stature, intermediate-maturity varieties. Grain size studies indicate that larger grains will increase yields. In general it appears that prospects for raising yield levels of rice by increasing the individual components of yield (grain size, grains/panicle, and panicles/m2) are promising and that this line of investigation should be vigorously pursued.
In hybrid rice studies, a fourth genetic element to facilitate hybrid rice production - a recessive tall gene - was identified by the Rice Experiment Station, analyzed genetically by the USDA, and a system for using this recessive tall character was proposed. In 1980, tall pollinators produced an average of 41 percent seed set on short-stature male steriles, while short-statured pollinators produced an average of 35 percent seed set. Both values are encouraging, but much basic research on the outcrossing mechanism needs to be done before hybrid rice can become a reality. Even assuming that the seed production mechanics are solved, hybrid seeds will be expensive, creating a need for lower seeding rates. However, 1980 results indicated that yields of current genotypes will be lowered by reducing seeding rates to 50 pounds per acre. Therefore, increased tillering ability may have to be incorporated into hybrid rice models.
A genetic study on amylose content showed that this character, an important determinant of long-grain cooking quality, was controlled by one or two genes, depending on the cross. Another determinant of cooking ' quality, alkali spreading score, was controlled by one gene in one cross, but inheritance was unclear in another cross. The single genetic control of these two important quality factors means that they are relatively easy to transfer from one line to another. To date, a search for high amylose mutants in adapted California varieties has not been successful.