Hybrids between the soybean, Glycine max (L.) Merrill, and the wild Glycine soja Sieb. and Zucc. exhibited marked differences in chromosome behaviour and fertility, depending on parentage of the hybrids and temperature of the culture. Meiosis in some F1 hybrids was regular, while in others the frequency of pollen mother cells (PMCs) with irregularities ranged up to 44%. Degeneration of pollen and seed was not, however, always proportional to meiotic irregularity. The results from glasshouse and controlled environment studies suggest that at least three factors were influencing chromosome behaviour and fertility. These factors were genotype, temperature, and genotype–temperature interaction. An aspect of practical significance arises where off-season nurseries are used to increase seed in which gene transfer is expected. If temperatures at the site are suboptimal for chromosome pairing and chiasmata formation, the operation may be selfdefeating. These results also have implications in studies in which the affinity of two taxa is being determined by chromosome behaviour of the hybrid between them. Unless crosses involve a number of parents with different genetic constitutions and are studied under a range of temperatures, the results may be misleading.
HE herbaceous legume Indigofera spicata Forsk. (pre-T viously Izdigofera eizdecaphylla Jacq.) (5) , also called creeping or trailing indigo, has features which, were it not for its toxic nature,would make it one of the foremost tropical forage legumes. Breeding work with the objective of obtaining a nontoxic strain of creeping indigo has been hampered by the difficulty and expense of experimenting directly on cattle with toxic materials. Since the original finding that creeping indigo was toxic to cattle (9; I O) , all attempts to identify the toxic substance have been with small test animals. Rosenberg and Zoebisch (11) showed that chicks would exhibit characteristic symptoms when fed creeping indigo. Evidence that the toxic chemical is 3-nitropropanoic acid has been brought forward by workers in Puerto Rico and Hawaii (2, 4, 8) u s i n g chicks as test 'Published with the approval of the Director of the Hawaii Agricultural Experiment Station as Technical Paper No. 626.
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