Genetic variation in seed dormancy in Digitaria milanjiana in relation to rainfall at the collection site.
According to the duration of dormancy, 3 different classes could be recognized among African accessions. Material originating in the low-rainfall tropics displayed long dormancy which could be broken by subjecting the caryopses to a temperature of 60°C for periods of up to several months. No dormancy was found in material from equatorial sites with abundant rainfall, but an ecotype from a low-rainfall equatorial site showed dormancy of intermediate duration which did not yield to heat treatment. Dormancy could be broken, in both types of material in which it occurred, by removing the glumes and lemmas from the caryopses. Analysis of dormancy in hybrids showed that, in the material from low-rainfall equatorial, though not low-rainfall tropical, sites, it is controlled by interaction between the embryo and the maternal genotype. There was evidence that hexaploids as a group are more dormant than tetraploids.