We obtained 7 semidwarf strains with lodging resistance by irradiating dry Tartary buckwheat seeds with gamma rays and various ion beams. These strains were named IRBFT-6, 20, 38, 45, 63, 67 and 77. These plant types have not been previously observed among Tartary buckwheat genetic resources, so it seemed that they have new characteristics. The populations of F₂ from crosses between IRBFT-6, 20, 45 (semidwarf-mutant lines) and their original varieties fitted a 3:1 segregated ratio of wild type to semidwarf type, suggesting that the semidwarf trait in IRBFT-6, 20, 45 was controlled by a nuclear single recessive gene, respectively. Judging from the plant type (wild versus semidwarf) in F₁ and F₂ of half diallel cross, it was estimated that IRBFT-6, 20, 45 had a common semidwarf gene (sdA) and IRBFT-38, 63, 67, 77 had another semidwarf gene (sdB).

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Pre-harvest sprouting and high alpha-amylase activity of seeds are the most serious problems of wheat production in Hokkaido. There has been an increase in the frequency with which several days of continuous rain have occurred at the time of wheat harvest. In addition, low temperatures, i.e., below 15°C, combined with rainfall, accelerate the damage due to pre-harvest sprouting of wheat. Pre-harvest sprouting cannot be easily controlled using chemical or agricultural methods. The most effective means of controlling this damage is by breeding resistant cultivars. Resistance of hard red spring wheat to pre-harvest sprouting was evaluated among the following lines: OS38-5, OS68, OS70 and OS71 derived from OS21-5. The spring wheat OS21-5 has highly dormant seeds that are continuously selected through early generation for low-temperature ungerminability. The seeds of the OS-lines are highly dormant and highly resistant to pre-harvest sprouting at 15°C; further, a high falling number was maintained for 7 days during artificial continuous rain treatment at low temperatures. The embryo of OS38-5 was highly sensitive to abscisic acid (ABA) at 15°C. Genetic analysis for high dormancy of the seeds was conducted for progeny lines derived from crosses involving OS71 as the donor parent for seed dormancy. The effects of selection on seed dormancy in F₁ plants were found. Genetic segregation of seed dormancy was investigated using F₂ progeny derived from a cross between Kitakei-haru747/OS71 and 16S30/OS71. High dormancy of the seeds seemed to be controlled by several recessive genes. Heritability of seed dormancy in the case of Kitakei-haru747/OS71 and 16S30/OS71 was 0.66 and 0.19, respectively. Wheat of the OS-lines has the following characteristics: low yield, small grain, low lodging and scab resistance, and poor bread-making quality. Therefore, successive crosses between favorable progeny appear to be a promising approach.

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