Study On Pollen Chromosome Doubling And Triploid Plants Breeding Of Citrus In Vietnam

Citrus fruit trees belong to the family of Rutaceae, subfamily Aurantioideae. Citrus fruit is one of the most important crops in the world. Seedless is a desirable horticultural attribute in Citrus and is positively associated with triploidy. Triploid seedless Citrus cultivar is one of the main objectives of Citrus breeding. In crop breeding, the frequency at which 2n gametes are formed is also very important, in that it may affect the rate of new polyploidy formation. Together with the endosperm,2n gametes have also been a major factor in the origin and evolution of polyploidy. The two main mechanisms of polyploid formation are somatic doubling of chromosomes in meristem tissues of sporophytes, zygotes, or embryo and meiotic nuclear restitution leading to 2n gamete production.Phuc Trach and Dien pummelo are local varieties in Vietnam, good quality but there are too much seeds that will affect their commercial value. This research has studied on biology characteristics and carried out experiments on pollen chromosome doubling. These researches showed the results that include five points as follows:(1) During the years of 2009-2010, the fruit quality of Phuc Trach and Dien pummelo were investigated, the results showed that:the weighted indexes of fruits in Phuc Trach pummelo are higher than Dien pummelo, but the seed number and fruit skin of Phuc Trach pummelo are higher than Dien pummelo. Therefore, the edible percentage of Dien pummelo is higher than Phuc Trach pummelo. There is a difference in fruit maturity between the two varieties, the Phuc Trach pummelo variety get mature in mid-September but the Dien pummelo variety get mature in late January.(2) The PMCs meiosis of Phuc Trach and Dien pummelo begins at February 7 and February 12 in Red River Delta, when the flower buds a diameter of 0.3-0.4cm and PMCs at meiotic prophase I, by tetrads stage, about 4 days after meiotic prophase I. The duration of prophase I is very long. The synchronization of meiosis were greatly different in different clones, floral branches from the same clones, male flowers from the same floral branches and even anthers of the same flower of Phuc Trach and Dien pummelo(3) At the meiotic prophase I, different concentrations of Colchicine were used, and successfully induced 2n pollen in Phuc Trach and Dien pummelo. The optimal concentration of Colchicine for treatment was 0.3%,0.5%. The highest average percentage of unreduced pollen by treating Phuc Trach and Dien pummelo flowers for 4 and 6 days with 0.3%,0.5% Colchicine was 12.35 and 10.01%, the highest proportion was 17.17 and 12.17%. (4) The 1n and 2n pollen can germinated, but 2n pollen germinated later and pollen tube grew slower than 1n pollen in vivo in Phuc Trach and Dien pummelo, suggesting that the fertilizing ability of 2n pollen was weaker than that of 1n pollen and 2n pollen was less competent than 1n pollen.(5) The developed small seeds and aborted seeds were rescued,26 seedlings of Phuc Trach pummelo and 324 seedlings of Dien pummelo were derived from these seeds with the aid of embryo rescue technique. Partec low cytometry analysis indicated that complex ploidy levels in these progenies, among which there were 3 triploid of Phuc Trach pummelo,4 triploid of Dien pummelo (triploid chromosome number is 2n=3x=27), and 1 tetraploid of Dien pummelo (tetraploid chromosome number is 2n=4x=36).