Author : Siar, Simeona V.

Summary : The chromosome behaviour during microsporogenesis in Carica papaya, Carica cauliflora and their interspecific hybrids was studied to elucidate the observed sterility in the interspecific hybrids. Floral bud sampling for cytological studies was done at 11:30 am on a bright sunny day for both C. papaya and C. cauliflora. For interspecific hyrbrids, meiotic activity was at its peak at 12:30-1:30 pm for field grown plants and 1:30-2:30 pm for greenhouose grown plants. Meiosis in the parents was normal. The chromosomes showed regular pairing with nine bivalents at diakinesis and separated synchronously to each pole. At telephase II, tetrads of uniform size were produced. The chromosome number in both parents was consistent at 2n=18. Pollen fertility was high. An average of 96 percent and 94 percent fertility was recorded for C. papaya and C. cauliflora, respectively. The chromosomes of the interspecific hybrids showed very little to non-homology with the chromosomes of the two parents. Variable chromosome counts, presence of univalents, chromosome elimination and marked meiotic aberrations characterized the meiotic behaviour of the interspecific hybrids. These meiotic irregularities lead to the formation of non-functional pollen, thus very low pollen fertility was recorded for the interspecific hybrids.