Chromosomal Pairing and Pollen Viability in Rhizophora mangle and Rhizophora stylosa Hybrids

Two prominent mangrove species of Fiji, Rhizophora mangle, Linn. Rhizophora stylosa Griff and their puative hyubrid (R x selala) were analysed for chromosome number and pairing. Both parental species and their hybrid possess a diploid number of (2n) = 36 chromosomes. Regular 18 bivalents were observed in two species but the hybrid lacked proper chromosome pairing during meiosis. Analysis of tetrads showed normal tetrad and microspores development in parental species but very high abnormality in the hybrid. Pollen fertility determined by staining technique and pollen germination technique showed very high pollen viability in both parental species but very low pollen viability in the putative hybrid. Lack of chromosomal homology appears to be contributing to high percentage of non-viable pollen resulting in complete sterility in the putative hybrid. 1 General Introduction Mangroves have very special place in the lives of Pacific islanders. These trees provide wood for fire, fuel, furniture and artifact making. Their fruits (propagules) are eaten when there is shortage of food. Mangroves protect seashore from degradation and also provide sanctuary for young crustaceans. Two species of these mangroves cross in nature and produce sterile hybrids. Hybrids normally grow faster and produce better quality timber. In the present investigation two parental species and their hybrids were studied for chromosome pairing and pollen viability. This study determined the cause of sterility in hybrids, which in turn will be helpful to propagate these hybrids by making them fertile using method of chromosome doubling.