Interspecific Hybridization in the Genus Desmoduim

Chow, Kuan-Hon
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Three species, Desmodium sandwicense E. Mey., Desmodium uncinatum (Jack.) D. C., and Desmodium intortum (Mill.) Urb., were used for interspecific hybridization studies. D. sandwicense is insensitive to daylength and flowers all year round in Hawaii, whereas D. uncinatum and D. intortum flower only in the short-day season. The percentage of pod formation through cross pollination was low, 9.2 percent for crossing two species and 4.9 percent for crossing two interspecific hybrids. Temperature greatly affected the percentage of pod formation, with increasing temperatures, the percentage of pod formation decreased. Hybrids between D. sandwicense and D. uncinatum were lower in percentage of pollen abortion than hybrids between D. sandwicense and D. intortum. Percentage of pod formation in the three species was negatively correlated with percentage of pollen abortion. Stem color of the three species was controlled by a single pair of genes, with colored as dominant and green as recessive. The genetic behavior of internode length of Desmodium plants was controlled by multiple genes. In leaflet size, the large leaflet of D. intortum appears to be dominant to the small leaflet of D. sandwicense. In contrast to this, the large leaflet of D. uncinatum appears to be recessive to the small leaflet of D. sandwicense. Leaflet marking on the midrib was controlled by a single pair of genes, with dominance for the marked and recessive for the non-marked. Rugose leaflet plants were found only in the three-species hybrids. It was assumed that the character was controlled by complementary genes. One thousand-seed weights for D. sandwicense, D. intortum, and D. uncinatum were respectively 3.53, 1.84, and 4.03 grams. Results obtained from F2 seeds indicated that seed size of Desmodium plants were governed by quantitative inheritance characteristics for its behavior. Five esterase patterns were found among the fifteen parental clones of the three species. All the esterase zones occurring in D. uncinatum also occur in D. sandwicense. This is a good indication of a closer relationship between these two species than between D. sandwicense and D. intortum. The electrophoretic peroxidase zones were classified into four groups. The third group is identical to all the fifteen parental clones. This indicates close relationships among the three species. The results of yield comparison showed that D. intortum had the highest green weight, and D. sandwicense, the lowest, among the three species. In F1 hybrids, the clone of the highest green weight was an intraspecific hybrid of D. intortum clones, I13xI33.
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