Cytological Analysis on Seed Abortion of Psidium guava Ruby

Objective Seed-abortion mechanism in the fruit development of seedless Ruby guava was studied based on the cellular observations to aid the breeding and cultivating the unique variety.

Method Seedless Psidium guava Ruby and Watermelon Guava were compared on flower morphology, pollen germination, hybrid pollination, embryonic blastocyst paraffin section examination, and ovule pollination and fertilization.

Result The floral organs of Ruby Guava developed fully without apparent defects. The anthers were filled with pollen grains which germinated at a rate of 72.66%, mostly with normal pollen tubes and fertility. In a cross-pollination test, all Ruby fruits were emasculated and not pollinated, indicating an inability to set seeds unisexually. Its diploid chromosomal ploidy was normal, and so was the ovule shown by the regular structure of the ovary and embryo sac. From the day of flowering to the 5^th day afterward, the embryo sac developed normally, turning from a spherical to heart shape. Then, a torpedo-like structure appeared with a hollowing core. After the sperms entered the embryo sac in pollination, some ovules began to die in 7d. The lasting absence of sperm-egg fusion invariably caused the polar nucleus to degrade by the 11^th day with disappearing funicles, disintegrating ovules, emptying embryos, and eventual death of most ovules.

Conclusion The stimulating parthenogenesis type of fertilization of Ruby Guava required successful pollination to form the seedless fruits. Failure to inseminate the eggs invariably led to the seed abortion that started in 7d and ended in ovule death in 11d after pollination.