Self-incompatibility in pummelo [citrus grandis (L.) Osbeck] with focus on Vietnamese cultivars with or without parthenocarpy

Effect of pollination and non-pollination on fruit and seed set was examined in terms of ability of selfincompatibility and parthenocarpy with five-year-old trees of five Vietnamese pummelo cultivars grown in orchard locating at Thai Nguyen, Vietnam. Pollination of 'Phuc Trach' pummelo with different pummelo cultivars resulted in different rates of fruit set and number of seeds per fruit. The highest fruit-set rates of 29.1% in 2009 and 34.0% in 2010 were obtained from a cross of 'Phuc Trach' X 'Dien' pummelo, whereas the lowest fruit set rates of 0.6% in 2009 and 0.9% in 2010 were derived from self-pollination of 'Phuc Trach' pummelo. Number of seeds was ranged from 0 for self-pollination to 123 seeds for a cross with 'Dien' pummelo. Observation of pollen tube growth in self-pollinated styles of 'Phuc Trach' pummelo showed that pollen tubes were arrested in the style and fertilization did not occur. These results suggest that self-incompatibility and lack of parthenocarpy are the causes of the flower drop in 'Phuc Trach' pummelo. The similar results as those of 'Phuc Trach' pummelo were obtained in 'Dien' and 'Red Pummelo'. Thus, pollinizers are necessary for fruit set and enlargement of fruit in these three cultivars. On the other hand, 'Da Xanh' and 'Nam Roi' pummelos had highly vegetative parthenocarpy to produce large-sized seedless fruit without pollination. Solid planting is important for these two cultivars to produce seedless fruit.