A Polyhaploid Plant of Solanum polytrichon Rydb.

Abstract

S. polytrichon Rydb. and S. stoloniferum Schlechtd. are two related tetraploid species, 2n = 48, in the Longipedicellata group of tuberous Solanums. Using the former as female parent, Dodds (unpublished work) obtained a good seed set in a cross between them; but only one seed germinated. This plant had the chromosome number 2n = 24, suggesting that it might be a polyhaploid of S. polytrichon, having arisen by haploid parthenogenesis. The plant was chlorotic and this fact is evidence in support of a parthenogenetic origin, as the parental plant of S. polytrichon (Commonwealth Potato Collection No. 2330.1) used was known to be heterozygous for a single recessive gene for chlorosis (Dodds, unpublished work). The polyhaploid was also smaller and slower growing than the normal plant. Table 1 shows the terminal leaflet index and stomatal length of the polyhaploid compared with those of S. polytrichon (C.P.C. 2330.1) and its normal and chlorotic segregates. A least-squares analysis of the data in Table 1 showed the reduction in both the leaflet index and stomatal length of the polyhaploid to be significant, and to be a direct consequence of the halved chromosome number and not of the fact that the plant was chlorotic. Similar reductions in leaf index and stomatal length were observed in polyhaploid S. demissum Lindl. by Howard and Swaminathan¹, and also in the 24-chromosome plant, supposedly haploid, from the cross S. chaucha 2n = 36 × S. tuberosum 2n = 48, Lamm². Narrow leaflets (low leaf index) seem to be a valuable morphological character for distinguishing Solanum polyhaploids.