Growth, Development, and Yield of Spring Wheat in Artificial Climates

Abstract

Spring wheat was grown to maturity in three growth rooms providing: (a) 18 h of light at 20° C and 6 h of darkness at 15° C (hot long days, HL); (b) 18 h of light at 15° C and 6 h of darkness at 15° C (cold long days, CL); (c) 14 h light at 20° C and 10 h of darkness at 15° C (hot short days, HS). Plants were moved between environments at spikelet initiation and anthesis, so dividing the growth period into three. Mean lengths in days of these periods in the different environments were: Period 1: HL 16, CL 18, HS 25; Period 2: HL 42, CL and HS 61; Period3: HL 53, CL 83, HS 63. The length of periods 2 and 3 also depended on previous treatments. Grain dry weight was affected by environmental differences in all periods and effects in successive periods were additive. Compared with HL, CL or HS in period I before initiation increased grain yield by 6 per cent by increasing grain number per ear, HS in period 2 between initiation and anthesis decreased it by 24 per cent by decreasing the number of grains per spikelet and the proportion of spikelets that contained grain; CL in period 2 increased it by 21 per cent by increasing the number of ears; CL in period 3 after anthesis increased it by 16 per cent because leaves died later; HS in period 3 decreased it by 14 per cent because there was less radiation and hence less photosynthesis. Dry weight of shoot and root at maturity was increased by CL or HS in periods 1 or 2, and increased by CL and decreased by HS in period 3. The effects on final yield of treatment during periods 1 and 2 were the consequence of similar effects already produced at anthesis, and shoot and root dry weight changed little during period 3. The effects of environmental differences on grain dry weight could not be explained by differences in leaf-area duration after anthesis (D₃), except that CL in period 3 increased both yield and D₃ but not proportionately, so that, as with HS in the same period, grain: leaf ratio was decreased. Environmental differences in periods 1 and 2 appeared to affect grain weight by altering the capacity of the ear to accumulate carbohydrates, determined by the number of grains per ear, rather than by altering the supply of carbohydrates, determined by D₃. There were some interactions between environments in different periods which were usually small compared with the main effects.