Occurrence and cytological mechanism of 2n pollen formation in Chinese Diospyros spp. (Ebenaceae) staminate germplasm

Some Diospyros spp. (Ebenaceae) staminate germplasm (2n = 6x = 90) recently found in Hubei Province, China, was of potential value for breeding. This study evaluated the natural rate of occurrence and cytological mechanism responsible for the formation of 2n pollen in this staminate germplasm. The frequencies of giant pollen, dyads, and triads detected in all accessions were 0 - 2.3%, 0.8 - 2.2%, and 2.3 - 4.3%, respectively. The correlation coefficient (r = 0.98**; P < 0.01) between the frequency of giant pollen and those of dyads and triads was highly significant, which strongly suggests that the giant pollen was 2n pollen. Cytological analysis of pollen mother cell meiosis showed that the main cytological mechanisms responsible for the formation of 2n pollen were tripolar spindles and fused spindles, instead of parallel spindles and vertical spindles. In addition, an abnormal disintegration of sister chromatids, which also produced 2n pollen in the end, was occasionally found at metaphase II. Diploid (2n) pollen produced by tripolar spindles and fused spindles was equivalent to first division restitution (FDR) gametes. Therefore, this Diospyros spp. staminate germplasm may have value for sexual polyploidisation in breeding programmes of Japanese persimmon.