[Show abstract][Hide abstract] ABSTRACT: To understand the correlation between chromosomes behavior and fertility in autotriploid cucumber (Cucumis sativus L.), microsporogenesis in pollen mother cells (PMCs) and male gametophyte development were studied using improved staining
and chromosome preparation techniques. Meanwhile, for more efficient selection of trisomics from the progeny of autotriploid-diploid
crosses, fertilization rates of ovules from reciprocal crosses were counted to observe the transfer rate of gametes in the
autotriploid cucumber. Variable chromosome configurations, e.g. multivalents, quadrivalents, trivalents, bivalents and univalents
were observed in the most PMCs of the autotriploids at metaphase I. Chromosome lagging and bridges at anaphase in both meiotic
divisions resulted from irregular chromosome separation and asynchronization was frequently observed as well, which led to
formation of micronuclei and inviable gametes. The frequency of normal PMCs in autotriploids at the stage of tetrad was only
40.6%. Among those normal microspores, most of them (91.2%) could develop into normal gametophytes with 2 cells and 3 germ
pores. Stainability and germination rate of pollen grains were only 18.8 and 13.5%, respectively. However, chromosomes separated
to form gametes with 8 chromosomes at anaphase I, suggesting a possible method for the production of primary trisomics from
the progeny of autotriploid-diploid crosses. Fruit set of 3n×2n and 2n×3n were 80 and 70%, respectively. It obtained an average of 6.2 plump seeds per fruit in 3n×2n, while 4.9 in 2n×3n crosses. Transfer rates of gametes through the gastrula or the pollen in autotriploids were 13.4 and 10.4%, respectively.
Some aneuploid gametes (n+1=8, n+2=9) also have capability of setting seed and sexual reproduction besides normal gametes containing whole chromosome
sets (n=7, 2n=14). Further, some primary trisomic plants were selected from the progeny of autotriploid-diploid crosses. Based on the
results obtained we suggest that abnormal meiosis in PMCs was the cytogenetic reason for low fertility of autotriploid cucumber
pollen. 3n×2n cross was more efficient for selecting primary trisomic plants in cucumber.
Preview · Article · May 2009 · Plant Systematics and Evolution
[Show abstract][Hide abstract] ABSTRACT: To promote cytogenetical studies on cucumber (Cucumis sativus L., 2n = 2x = 14), the reciprocal crosses were made between autotriploid and diploid for selecting the primary trisomics. Meanwhile, chromosome behavior during meiosis in autotriploid cucumber was investigated to look for cytological evidences for origin of primary trisomics. Many viable F(1) seeds were obtained from reciprocal crosses between autotriploid and diploid. The number of chromosomes of 56 surviving progenies varied from 14 to 28, with plants having 2n = 15 occurring at the highest frequency (51.8%). Primary trisomics were firstly obtained in this study. Four types of primary trisomics were isolated and they could be distinguished from each other, as well as diploid. Variable chromosome configurations, e.g. univalent, bivalents and trivalents were observed in many pollen mother cells of the autotriploid at metaphase I. Binomial chromosome distribution was observed at anaphase I and frequency of 8/13 was 6.25%. The meiosis of autotriploid, especially the class of gametes with eight chromosomes, gave the cytological evidence of producing 2x + 1 type gamete and could be induced into primary trisomic plants from progeny of autotriploid-diploid crosses. These studies have established a ground work for selecting a series of primary trisomics, and further using them for associating linkage groups with specific chromosomes in cucumber.
Preview · Article · Mar 2009 · Sexual Plant Reproduction