Meiotic analyses of Cucumis hybrids and an evolutionary evaluation of the genus Cucumis ( Cucurbitaceae).

Meiosis in seven interspecific Cucumis hybrids has been analysed i.a. in C. metuliferus × C. zeyheri, where the parents belong to different sections. In the triploid hybrids a remarkably high number of trivalents has been found. Additional data from literature on geographical distribution, cucurbitacins, flavonoid patterns, isozymes, C-banding, genome size, DNA amount and chloroplast DNA are used to discuss species relationships and evolution. The African cross-compatible group is divided into the Myriocarpus subgroup with the diploid species C. africanus, C. myriocarpus subsp. leptodermis and subsp. myriocarpus, and the Anguria subgroup with C. anguria, C. dipsaceus, C. ficifolius, C. prophetarum, C. zeyheri and all polyploids (except C. heptadactylus). It is argued that the Asian subg. Melo with x = 7 is derived from the African subg. Cucumis with x = 12; the latter contains all the polyploid species and has the most common basic chromosome number of the Cucurbitaceae. This phylogenetic advance is interpreted with concepts of the quantum model of evolution. [ABSTRACT FROM AUTHOR]