Temperature-dependent germination traits in oilseed rape associated with 5'-anchored simple sequence repeat PCR polymorphisms

An experiment was conducted to test the hypothesis that phenotypes differin g in germination rate and the presence or absence of secondary dormancy at low temperature were not genetically different. Seed of oilseed rape was ge rminated at 4, 10 and 19 degreesC, where selections were made in the percen tile ranges 1-10 (early), 45-55 (intermediate) and 91-100 (late). Secondary dormancy occurred only in the late selections at the two lower temperature s. Thermal weighting of curves of cumulative germination on time gave circu mstantial evidence that early percentiles were similar at all three tempera tures and that seeds with secondary dormancy came largely from later percen tiles above the 50th, To test for genetic differentiation between phenotype s, 5'-anchored simple sequence repeat primers were used to generate DNA mar ker profiles of seedlings raised from seed from each category. Principal co ordinate analysis, and more detailed comparisons using the most discriminat ing markers, confirmed that the early germinators at the three temperatures were not associated with different banding profiles, but seeds entering se condary dormancy, particularly at 10 degreesC, were genetically distinct fr om germinators at the same temperature. Secondary dormant seeds at low temp erature appear to originate mainly from the late germinating seed at higher temperature. Effects of temperature history and the requirement for altern ating temperatures to break secondary dormancy were quantified. The results confirm the existence of genetically discrete sub-populations differing in ecologically significant traits.