Cytological studies of 2n male gamete formation in sugarcane, Saccharum L.

Abstract

The germplasm for modern sugarcane cultivars (Saccharum spp. hybrids)has been derived principally from S. officinarum (2n = 80), and S. spontaneum (2n = 40 to 128). Diploid gamete formation has been significant in developing cultivated sugarcane, but the cytological basis for the processes involved is not clearly understood. This research investigated microsporogenesis in nine clones of Saccharum spp. Hybrids and in S. officinarum and S. spontaneum. Diploid gamete formation occurred in all 11 lines, but was least frequent in S. spontaneum and S. officinarum which produced 0.5% and 0.8%2n gametes, respectively. In the hybrid lines, 2n gametes were formed infrequencies ranging from 0.9% to 4.4%. Cytological evidence was obtained for dyad and triad formation during microsporogenesis. Detailed analysis of chromosome behaviour at meiosis indicated that 2n male gamete formation is probably attributable to the absence of cytokinesis rather than a combination of asynchrony and non-disjunction. The clones were ranked on the basis of the frequencies with which they formed 4 × 1n microspores and the data were analysed using χ 2 tests for homogeneity. These established that theSaccharum spp. hybrids could be designated as either ‘high’ or ‘low’ frequency haploid gamete producers. Conversely, the latter group, which formed diploid gametes most frequently (2.2%–4.4%), can be described as high frequency diploid gamete producers. The identification of clones most frequently forming diploid gametes may facilitate the more rapid recovery of desirable sugarcane genotypes because such clones could be selected for preferential use in clonal improvement.