No abstract

Japanese pear has a genetically controlled self-incompatibility system, but both the pollen-tube growth in a semi in vivo assay and fruit set after self-pollination differ considerably among cultivars. The percentage of styles in which pollen tubes have reached the base ranges from 0 to 36 %, a value determined by culture of styles in vitro, and fruit set ranges from 0.6 to 15.2 %. Based on these data, we have assigned a value for the self-incompatibility weakness to each cultivar. Here, we showed that pollen factors control the degree of self-incompatibility. When the pollen-tube growth of 13 cultivars was compared in a completely compatible 'Hougetsu' (S (1) S (7)) style, it differed a fair amount among cultivars and showed a significantly positive relation to self-incompatibility weakness (r = 0.707). The degree of self-incompatibility of pear is, therefore, determined by pollen factor(s) unrelated to the S-locus. Although the fruit set and fruit growth of 'Hougetsu' were not affected by the pollen donor, a positive relationship was also observed between seed number and self-incompatibility weakness (r = 0.972). However, in a style with no S-RNase production (genotype: S (4) (sm) S (4) (sm) ), the relationship disappeared (r = 0.341) and pollen-tube growth was promoted by 12-36 % except in one cultivar. These results suggest that S-RNase functions as a cytotoxin on compatible pollen in a cultivar-dependent manner, and that the degree of inhibition is determined by pollen factor(s) unrelated to the S-locus. The pollen factor also functions on S-RNase in incompatible styles, resulting in a different degree of self-incompatibility.

The production of yellow-skinned apples has increased in recent years; however, they are less acceptable to consumers than red-skinned apples. Therefore, the production of high-quality fruit is essential. In the present study, we applied a girdling treatment at 1) different times (June or August), and 2) different widths (2 cm, 5 cm, and 8 cm). We compared the effect on tree growth, flower bud formation and fruit quality over a 4-year field trial using vigorous yellow-skinned 'Koukou' apple trees. The August girdling reduced the shoot growth by about 6 to 10 cm per shoot and this reduction also restricted secondary extension of the shoots. The August treatment improved the fruit quality parameters, including the soluble solids content and skin color index, more effectively than the June treatment. Compared with the girdling timing, the effect of girdling widths in August was less obvious, but even the 2 cm treatment in August was enough to reduce tree vigor and improve fruit quality. Apical flower bud formation was accelerated by the August girdling in both the treatment year and the following year. Regardless of the girdling width, the August girdling improved the fruit quality parameters: e.g. flesh firmness, soluble solids content, and skin color index. The August girding fruit also had higher sorbitol and sucrose concentrations than the control. Moreover, both the girdling treatments accelerated the incidence of watercore, which is a preferred condition for the Asian market. In conclusion, we found that all widths of girdling in August improved the harvested fruit qualities, including the sugar (sucrose) content, as well as watercore development in the treatment year and effectively controlled tree vigor, increased flower bud formation and increased yields.

Since both artificial pollination and fruit thinning are necessary for marketable fruit production of Japanese pears (Pyrus pyrifolia (burm. f.) Nakai) in Japan, about a 20% fruit set is ideal without pollination because only 5% of flowers are actually subjected to fruit production. In this study, copper (Cu

A new red-fleshed apple cultivar, 'HFF33', which has superior taste and storability compared with 'Kurenainoyume,' was bred at Hirosaki University. Genotype analysis using SSR markers revealed that 'HFF33' could be obtained from a combination of 'Toko' × "Red-fleshed apple strain Parent A". The fruit has a conic shape, the peel develops a bright striped blush similar to 'Senshu,' and the flesh develops a crimson color on maturation. The tree had a branched shape, and the shoot growth was not so strong like 'Orin', although the branches were easily broken because of their thickness. At our experimental site, the suitable harvest time for this cultivar was the middle of November, and the fruit weighs 400 g, has a 13.4% soluble solid content, and around 0.6% titratable acidity. Fruit-bagging treatment completely prevented the development of cork spot-like physiological disorders and improved the skin blush: the color became brighter, and the stripe developed more distinctly than in non-bagged fruit. 'HFF33' exhibited long storability and could be stored under cold conditions for 180 days after harvest. Moreover, 1-MCP treatment was effective in preventing the loss of firmness. We registered 'HFF33' commercially with the trademark MIKU. Using this trademark, we will ensure quality control and establish the brand value.