Numerical taxonomic analysis and crossability of diploid Ipomoea species related to the sweet potato.

Abstract

The fifty-one diploid (2n=2x=30) Ipomoea strains, which have been named I. triloba. I. lacunosa and I. trifida in Kyoto University and Mie University, Japan, and I. triloba. I. lacunosa. I. ramoni and I. cordatotriloba (syn. I. trichocarpa) in the University of Georgia, USA, were studied for further identification by means of multivariate analyses. A total of forty-one characters distributed over various parts were used: (a) stems and leaves 10, (b) inflorescence 8, (c) corollas 10, (d) sepals 6, and (e) capsules and seeds 7. The initial data-base of 51 strains × 41 characters was subjected to the WVGM (weighted variable-group method) cluster analysis. Subsequently, the data-base of the same 51 strains with 25 characters was processed accordlng to principal components analysis. The 25 characters included one addltional root character but other 24 characters were selected from those used in the WVGM analysis. These two analyses represented that the 45 strains are divided into six phenetic groups, A1, A\2, B, C1, C2 and D. The other 6 strains including. I. trifida strain K221 remained ungrouped. Further, the result of analyses demonstrated that the I. trificla strain in question has the most phenetic similarity to group D and the next most similarity to group B. By making a morphological comparison between the phenetic group and taxonomically described species, three groups A1, A2 and B were identified as I. trlfloba L., C1 as I. lacunosa L. and D as I. cordatotriloba DENN. The intermediate position of group C2 in the taxonomic space suggested that the strains of this group are natural hybrlds, I. × leucantha JACQ. To clarify the interspecific relationships based on crossability within and between the phenetic groups, crossing studies have been carried out. Intragroup hybrldiza-tlon among the stralns In group B or group D showed various degrees of crossabllity, however, none of these strains produced hybrids in crosses with the I. trifida strain K221. The low crossability in intergroup hybridization between the strains of group D and one strain of A1 suggested the possible genetic divergence of these taxa, I. cordatotl'iloba and I. lacunosa. Crosses of the I. trifida strain K221 with four strains each from group A1, A2, C1 or C2 were also unsuccessful in obtaining hybrids. These results indicated the presence of a significant reproductive isolating barrier between diploid I. trifida and the other diploid lpomoea taxa studied.