Primary trisomics obtained from autotriploid by diploid reciprocal crosses in cucumber

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 F₁ 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.