Microsporogenesis and pollen abortion in Bruce plum (Prunus salicina x P. augustifolia)

Abstract

Investigations were undertaken to determine the causes of high rate of pollen abortion in Bruce plum (Prunus salicina x P. angustifolia). Microspore and pollen development in the pollen-fertile Methley plum (P. salicina x P. cerasifera) was compared with the same process in Bruce plum. Difficulties in the pairing of homologous chromosomes in the microspore mother cell of Bruce plum and the abnormality in the subsequent meiotic mechanism such as irregular orientation of chromosomes at the metaphase plate during division I and unequal distribution and disorganized condition of haploid chromosomes during division II, appear to be the prime cause of the high rate of pollen abortion. This situation appears to be inherent to the Bruce plum variety which suggests that the P. salicina and P. angustifolia cross producing Bruce plum was a wide one. Occasionally, the nucleus of the microspore mother cell of Bruce plum showed an eccentric development of pachytene loops causing some chromatin material to remain outside the nuclear membrane. This irregularity in the behavior of meiotic chromosomes probably contributed to a lesser extent to the high rate of pollen abortion in the Bruce plum. Application of plant growth regulators under the conditions of the experiment failed to correct the defective meiotic mechanism in the Bruce plum anther. Moreover, gibberellic acid application, either singly or in combination with kinetin, accelerated the growth of tapetum cells. In some cases the tapetum cells occupied almost the entire space in the locule leaving no room for the development of microspores or pollen grains.