Polyploid distribution and seed dormancy in relation to provenance rainfall in the Digitaria milanjiana complex [African pasture grass]
1988
Hacker, J.B. (Commonwealth Scientific and Industrial Research Organization, St Lucia (Australia). Div. of Tropical Crops and Pastures)
Chromosome numbers were counted in 72 accessions in the Digitaria milanjiana complex and two of D.macroblephara from contrasting climates in Africa; 18 were diploids, 38 tetraploids, and 18 hexaploids. For 29 accessions, seed was treated at alternating temperatures of 30-25degC or 60degC for 0, 2, 6, 10 or 16 weeks and then germinated. Percentage germination increased over time but germination was markedly lower in accessions from low-rainfall (14 percent) than high-rainfall (33 percent at 16 weeks) provenances. Similarly, percentage germination was lower in hexaploids (16 percent) than tetraploids (26 percent) and lower in tetraploids than diploids (38 percent at 16 weeks). High temperature treatment increased germination percentage but the effect was only marked in accessions with comparatively high levels of germination at low temperatures. Percentage dormancy was significantly and negatively correlated with rainfall of provenance. It was concluded that seed dormancy in D.milanjiana is related both to polyploidy and rainfall of provenance and that genetic adaptation to arid regions has been associated with polyploidisation and increasing dormancy.
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