Studies on seedlessness of loquat fruit as related to endogenous plant hormone.

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1. Six tetraploid loquats were obtained by applying amiprofos-methyl and colchicine for chromosome doubling agents to diploid loquat shoot apex.2. The ratios of triploid seedlings produced by reciprocal crossing between tetraploids and diploids ranged from 92% to 100%. There were no great differences among the reciprocal crosses.3. Leaf width and thickness, stomata length, maximal diameter of calyx, petal length and width, and pollen grain diameter in the dr-, tri- and tetraploid plants significantly increased with increasing polyploidy level in loquats. The pollen germination ratios were high at 95% in both the diploid and the tetraploid. However, it was markedly low at 8% in the triploid, and the fructification was also extremely low at 0.1%.4. When 1,000ppm-GA_3 plus 20ppm-CPPU was applied to flowers and fruits two times at bloom and about 60 days after bloom of triploid loquat, the percentage of fruit set at harvest was highest (92%). On the other hand, Set of fruit applied with CPPU or GA_3 alone was 31% and 53%, respectively. Fruit set and Size of seedless fruit in the applications of GA_3 plus CPPU increased linearly with increasing GA_3 concentration. However, brix decreased in the treatments including CPPU. This cause depended on decrease of sucrose content.5. GA-like substances were extracted from immature seeds of loquat. After it was fractionated by ODS-HPLC, each fraction was applied to flowers and fruits of diploid loquat. Seedless fruits were induced in treatment of five fractions, but the percentage of fruit set varied among fractions.6. When 1,000ppm-GA_3, 20ppm-CPPU, 100ppm-NAA, 1,000ppm-ABA and 400ppm-ethepnone were applied to diploid loquat fruits during 60 to 20 days before harvest, fruit size in GA_3 and CPPU treatments, and sugar content in ethephone, CPPU and GA_3 treatments increased. However, NAA application resulted in low sugar and high acid contents.