In order to develop a simplified method of selection for ripening ability in paddy rice, the relationship between the ratoon volume at the ripening stage and the percentage of ripened grains was investigated for certain levels of fertilizer application and at some ripening stages using a large number of cultivars. Cultivar differences in the percentage of ripened grains varied considerably depending on the year and level of fertilizer and a large number of years and fertilizer levels were required to estimate the ripening ability. Cultivar differences in the ratoon volume varied largely depending on the ripening stages and appeared clearly at the early and late stages every year or at the intermediate stage in certain years. Cultivar differences in the ratoon volume at these ripening stages appeared clearly for every year and every level of fertilizer application, unlike the percentage of ripened grains. In each experiment at the early, late and intermediate ripening stages, correlation coefficients between the ratoon volume and the percentage of ripened grains for different fertilizer levels were generally low or high without clear or with clear cultivar differences in the percentage of ripened grains and the correlation coefficient for the level at which cultivar differences were most clearly revealed, was higher than +0.7 in each experiment. Furthermore, the correlation coefficients between the ratoon volume for fertilizer levels at which cultivar differences in the percentage of ripened grains could not be revealed and the percentage of ripened grains for fertilizer levels at which cultivar differrences were most clearly revealed, were higher than +0.7 in most of the cases. Based on these results, it was considered that the ripening ability could be easily selected based on ratoon volume at the ripening stage even for low fertilizer levels at which cultivar differences in the percentage of ripened grains did not appear clearly. Secondly, using F₃ pedigree lines derived from the crossing of two cultivars, a selection experiment for ripening ability based on the ratoon volume at the early ripening stage was conducted for 2 generations at a low fertilizer level. Inter-line differences in the ratoon volume and percentage of ripened grains were both significantly large and the correlation coefficient between the two characteristics was significantly high in the F₅ selected lines. Based on these results, it was considered that the simplified method of selection for ripening ability based on the ratoon volume was effective in rice breeding.

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Twelve genotypes of geranium (Pelargonium × hortorum Bailey) were grown in a greenhouse. Experiments were conducted to identify the response of the geraniums to high-temperature stress in order to develop a method of selection for high-temperature stress tolerance. All of the accessions showed a decrease in chlorophyll content under high-temperature treatments. A significant difference was found in the SPAD ratio I (treatment / no treatment) (SPAD-RI) in twelve accessions. Variation was found in high-temperature stress tolerance among accessions, and one wild species and four hybrid accessions showed a high-temperature stress tolerance. Moreover, a significant correlation was found between leaves and flowers in the value of high-temperature stress tolerance assessment (r = 0.806^**), between SPAD-R I and high-temperature stress tolerance assessment value (HTSTAV) of leaves (r = 0.963^***), and between SPAD-RI and HTSTAV of flowers (r = 0.747^**). Some characters were assessed and rated on a score of one to five. Flower quality was assessed for each accession under high-temperature conditions in August. High-temperature stress tolerance was found in four hybrid accessions. However, there was no significant correlation between the SPAD ratio II (August / no treatment in May)(SPAD-RII) and the value of flower quality assessment. A negative correlation was found between the leaf temperature and SPAD-RII (r = −0.721 ^**), but it unlike between the leaf temperature and flowering characters. A significant correlation was found between HTSTAV of flowers and the value of flower quality assessment (r = 0.630^*). These results suggest that high-temperature stress-tolerant varieties could be selected by high-temperature treatment during the optimum growth period (May in Japan) and then by comparison of certain characters under high-temperature conditions and optimum growth conditions within one year.

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Melon production in Hokkaido has been severely hampered since Fusarium wilt of melon caused by Fusarium oxysporum f.sp. melonis race 1,2y was first reported there in 1993. We immediately initiated a rootstock breeding project for race 1,2y resistance to meet farmers’ demand. Diallel analysis of race 1,2y resistance was performed using six netted melon (C. melo var. reticulatus Naud.) varieties and one oriental pickling melon (C. melo var. conomon Makino) variety. At 11 days after seeding, seedlings were inoculated by dipping their roots in a conidial suspension (10⁵ per ml) of the race 1,2y. Each seedling was transplanted individually in a 25 ml pot containing perlite. The inoculation test was arranged in a randomized block design with two blocks: 16 individuals (pots) of each parental or F₁ line were provided for a block of the test. The disease severity index (0-no symptoms; 1-chlorosis of cotyledon; 2-moderate wilt with chlorosis; 3-severe wilt with chlorosis; 4-death of plant) was recorded at 10 or 11 days after inoculation, and the degree of disease severity (Σ (100 × disease severity index / maximum disease severity index × No. of individuals inoculated)) was calculated. The disease severity of the parental varieties ranged from 1.3 to 71.5. Since the netted melon variety “Charentais” showed a reciprocal difference in disease severity, 6 × 6 subdiallel analysis was performed, by excluding “Charentais” and its F₁s. The 6 × 6 diallel analysis failed to reveal either a reciprocal difference or epistasis of the genes. Resistance was partially dominant over non-resistance and controlled by additive effects of genes. The dominant effect was also statistically significant. Heritability values in broad and narrow sense were 0.96 and 0.81, respectively. The (Wr + Vr) / Pr graph suggested that the oriental pickling melon variety “Tokyo wase (maruba)” displayed recessive resistance gene(s) to the race 1,2y.

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