Genetic basis of rate-temperature characteristics for germination in oilseed rape

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Abstract
Genetic control of germination time in oilseed rape might enable some cultivars to adapt locally as a volunteer weed or a feral plant. The heritability of within-population germination characteristics was therefore investigated for the oilseed rape cultivar Martina. Two groups of seed were selected from a batch of seeds germinated at 5°C: those germinating up to about the 20th percentile, termed early germinators, and those above the 80th percentile, viable non-germinators, which did not germinate at 5°C but did so subsequently when moved to a higher temperature. The groups of seeds were isolated, grown to flowering and the plants self-pollinated. Germination of the new seed from the two groups was then compared with seed from the original population at temperatures between 4°C and 19°C on a thermal plate. Differences between seed lots were small at 19°C, but large below 10°C. The differences in spread of time were analysed by fitting exponential curves to the non-linear relation of 1/time on temperature for each of five percentiles, 10, 20 50, 80, and 90. The fitting procedure tested the extent to which variation within and between seed lots was caused by variation in the base temperature, the curvature of the relation and a parameter for scaling the curve between percentiles. Progeny of the early seed germinated much more rapidly than the original, and germinated completely even at low temperature. The more rapid germination was attributed to a lower extrapolated base temperature of −2.3°C, compared to −0.7°C for the original, and slightly greater curvature. Progeny of non-germinator seed contained a higher proportion of viable non-germinating seed (for example, 20% germination at 4°C, compared to 50% for the original), but the germinating seed differed only slightly from the original in time to germination. Among the germinating percentiles, both types of progeny displayed less spread in time to germination than the original seed. It was concluded that the cultivar had the potential to give rise to genetically distinct populations able to exploit different seasonal opportunities.

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