Expression of Vernalization Genes in Near-isogenic Wheat Lines : Effects of Night Temperature

Abstract

Four near-isogenic lines of wheat ( Triticum aestivum L.em Thell) were used to compare selected night temperatures for their effectiveness as vernalizing temperatures. All treatments (conducted within a phytotron) had a common day temperature of 20 °C for 12 h and night temperatures were 4, 7, 10, 13 and 20 °C. Interpretation of results for reproductive development was confounded by three interacting factors, their relative importance varying with genotype. Firstly, development rate was generally slower at lower night temperatures. Secondly, in contrast, there was a tendency for lower night temperatures to hasten development rate if vernalization requirements were satisfied. Thirdly, the lower night temperatures provided a more favourable environment for leaf production such that for some genotypes, vernalized plants had higher final leaf numbers than unvernalized plants. Only for the genotype with the strongest vernalization response (vrnl vrn2) did hastening of development due to vernalization override any delaying effects. For this genotype, 4, 7 and 10 °C were vernalizing temperatures. For the other three genotypes, any hastening of development due to vernalization was outweighed by delaying effects of lower night temperatures. Spikelet number and days to anthesis were positively correlated in three of the four genotypes. It appeared that differences in spikelet number were a direct result of night temperature influencing the duration of the spikelet phase and/or rate of spikelet initiation. Plant size at flowering was determined by the differential effects of night temperature on growth and development rates.