The effect of daylength on apical development and grain production in barley cultivars

Abstract

Differences in the magnitude of the response to daylength (8h S.D. and 16h L.D.) of a large number of two-row spring barley genotypes were found in both final spikelet number (100 cultivars, glasshouse) and in apical development (five cultivars, growth rooms). Apical growth and development of all genotypes was accelerated in L.D. compared with S.D. treatment and two physiological groups could be distinguished on the basis of the magnitude of this response. Group one cultivars (Clipper and Spartan) showed a more marked acceleration of apical development in long days compared with group two cultivars (Domen, Golden Promise and Ymer) and this was reflected in rapid spikelet primordium production resulting in a reduced maximum spikelet primordium number. A high spikelet primordium maximum was reflected in a high spikelet number. Apical growth and development, and spikelet primordium production were similarly accelerated by late sowing treatment in the field, both in 1976 (14 cultivars) and in 1977 (five cultivars), and cultivars differed in the magnitude of this response. Two physiological groups could again be distinguished and these corresponded to the two groups distinguished on the basis of their apical response to daylength. Because of the similarities in the apical response to daylength (growth room) and to sowing date (field) it is suggested that daylength is an important environmental factor influencing apical development in the field. A high spikelet primordium maximum was again reflected in high spikelet and grain numbers. Grain yield per plant was decreased by late sowing and this reduction was associated with grain number per plant (both ear number per plant and grain number per ear) rather than 1000 grain weight. This indicated the importance of the sink capacity of the plant in determining final grain yield. Photoperiod studies (using both Night interruption and Day extension treatments) indicated that cultivars which were very sensitive to long days (e.g. Clipper) responded to both the photoperiodic and radiation components of daylength whereas cultivars which were less responsive to daylength treatment (e.g. Golden Promise) were only responsive to the light energy available for photosynthesis. Movement of 14C-labelled assimilates to the main shoot apex was increased in both L.D. and D.E. treatments compared with short days for Clipper but, in contrast, was increased only in L.D. compared with D.E. and S.D. conditions for Golden Promise. This indicated that daylength, through the light energy available for photosynthesis, may control the absolute amount of assimilate available for transport to the apex, while superimposed on this, is the effect of photoperiod on apical development which, in turn, may alter the distribution pattern of assimilate movement to the apex. The implications of these physiological studies to plant breeding, with particular reference to Scottish growing conditions, is discussed.