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Meiosis and pollen fertility in Prunus avium L. cv. Lambert and irradiation propagates of Lambert Whelan, Ernest David Pratt

Abstract

The meiotic behaviour and pollen fertility of Lambert sweet cherry (Prunus avium L.) and irradiation propagates of Lambert were investigated. Chromosome clumping, due to associations between the centromere region of non-homologous chromosomes, characterized early meiotic stages in Lambert. While the associations, which were evident as chromatic centers, complicated interpretation of pachynema, the pachytene morphology of the eight chromosomes was described. Except for small chromatic areas delimiting the centromere, all chromosomes were basically achromatic. Three chromosomes had an additional one or two chromatic regions, which in all cases were in the short arm. One chromosome, designated number 3, had a major heterozygous interstitial deletion in the short arm. Marked repulsion between the homologous chromosomes during diplonema resulted in a diffuse stage. The single pair of univalents, occasionally observed throughout meiosis and considered to be of desynaptic origin, were first detected in diplonema. Subsequent meiotic stages were usually normal, and the incidence of abnormal meiosis and tetrad stages containing micronuclei were estimated to be 9-62 per cent and 3.24 per cent respectively. Meiosis was characterized by synchronous division within the anther locules. Cytoplasmic connections were evident between neighbouring meiocytes during meiosis I, and cytomictic phenomena were observed occasionally. Abortion of 50 per cent of the developing microspores occurred prior to the first mitotic division of the spore nucleus, and was attributed to the heterozygous deletion in chromosome 3. Pollen abortion at anthesis was estimated to be about 42 per cent. Annual or regional effects on the incidence of abnormal meiosis or pollen abortion were not evident. Forcing of blossom buds at 15°C did not appear to affect meiotic behaviour. Twelve irradiation propagates of Lambert were investigated. Of these, seven had pollen fertility similar to the parental Lambert clone, and their meiotic behaviour also was comparable. The remaining five propagates had reduced pollen fertility. One propagate was found to have a greatly increased incidence of the single pair of univalents, as compared to parental Lambert; two propagates contained a reciprocal translocation; and two contained a paracentric inversion. The extent of pollen abortion was predictable from the meiotic behaviour in only one of the latter five propagates. Pollen studies revealed significant annual variation among the 12 irradiation propagates, some varying more than others. With one exception, forcing of blossom buds at 15°C did not appear to affect meiotic behaviour.

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