Developmental Basis of Maturity Differences in Spring Wheat¹

Abstract

Abstract Characterization of the developmental basis of maturity of spring wheat ( Triticum aestivum L. em Thell) was sought in studies of the range of vernalization and photoperiodic responses in a number of spring wheats. Vernalization responses of 12 spring wheat cultivars of Australian and overseas origin were evaluated as final leaf number of plants after cold treatment of germinated seedlings at 4 C for weekly intervals from 0 to 6 weeks. With the exception of the wheats ‘Bordan’ and the fixed crossbred ‘KB’ each genotype exhibited a marked response to cold treatment as decreased final leaf number; each appeared to attain its threshold response to cold within the 6‐week period of treatment. The behavior of two pairs of cultivars, ‘Insignia 49’ and ‘Early Summer Insignia 49’, and ‘Thatcher’ and ‘Winter Thatcher’, each pair believed to be near‐isogenic except for the presence and absence of vernalization response, indicated the likelihood that the possession of vernalization response, as such, was of no apparent significance in influencing final leaf number, spikelet number, and days to ear emergence under normal sowing times of spring wheat in southern Australia. Variation in photoperiodic response within and between genotypes was examined under two daylengths — that of a normal field sowing and that of an extended photoperiod (18‐hour). Photoperiodic response was shown to be likely of major significance in determining maturity of spring wheat grown in southern Australia. Reasonably high correlations were obtained between spikelet number and days to ear emergence under both the normal (r = +0.74**) and 18‐hour photoperiod (r = +0.67**). Wide differences in spikelet number between wheats of closely similar developmental patterns indicated the likely presence of a significant genetic component of spikelet number determination in wheat. It is postulated that in the absence of both photoperiod limitations and the need for vernalization, growth temperatures could differentially influence developmental rate among spring wheat genotypes.