2n GAMETES IN DIPLOID SOLANUM: FREQUENCY AND TYPES OF SPINDLE ABNORMALITIES

Cytological disturbances resulting in 2n pollen were examined in four clones of diploid (2x = 24) Solanum phureja Juz. and Buk.; two (148-17 and 127-14) were variable and two (154-1 and B2-11) were consistently high in 2n pollen production. Three types of abnormal spindle orientation were observed at the second meiotic division: fused, tripolar, and parallel spindles (fs, tps, and ps, respectively). All four genotypes had fs. Three had tps, and ps was least frequent, occuring in two genotypes only. Cross-sections of buds revealed that all three abnormalities can occur in adjacent cells of a locule. In all genotypes, fs predominated at high levels of expression of 2n gametes. At lower levels of expression (i.e. less than 60%, which occurred only in 148-17 and 127-14), however, the frequencies of tps and ps increased. In general, there was little evidence for localization of dyads (resulting from fs or ps) or tetrads (resulting from normal divisions) within cross sections of locules, but 52.4% of all tetrads which occurred in a single locule of genotype 127-14 were found in 25% of the locular area. Cross-sections of buds revealed variation in frequency of 2n gametes among anthers (61.7 vs. 5.6% in 148-17) and between locules of an anther (73.1 vs. 90.0% in B2-11). Implications of the anatomical study were applied to current genetic theory regarding the development of 2n gametes in potato species.