Is barley yield in the UK sink limited? II. Factors affecting potential grain size

In the absence of serious post-anthesis stress, the potential supply of assimilates for grain filling in barley appears to exceed the storage (sink) capacity of the grains. The sink capacity is a function of the number of grains per unit land area and their potential size. In order to investigate the contribution of pre and early post-anthesis factors in the control of potential grain weight, regression analysis has been used to analyse data from field experiments conducted on winter barley crops cv. Pearl grown at six sites across the UK between 2002 and 2004. Crops were grown under a comparable husbandry regime with a full crop protection, growth regulator and fertilizer programme. The mean grain weight (MGW) varied from 35 to 46 mg at 100% dry matter over 17 site/year combinations. The variation in MGW between site/years was associated with differences in the rate rather than the duration of grain filling. MGW did not relate well to any measure of above ground growth or crop structure at ear emergence (Zadoks GS59). There was a significant positive linear relationship between MGW and the amount of radiation (PAR) intercepted per unit grain number between ear emergence and the start of rapid grain filling (r(2) = 0.32, P = 0.023), but not over the whole grain filling period. This is consistent with the view that MGW is determined by potential grain size. A multiple regression model comprising five explanatory variables accounted for a much larger proportion of the total variation in MGW (r(2) = 0.72, P = 0.013) than PAR interception on its own. There were significant positive associations of MGW with post-anthesis radiation use efficiency and PAR intercepted from GS59 to the start of rapid grain growth (RGG), and significant negative associations with the shoot number per plant, mean air temperature from GS39-59 and mean daily rainfall from GS59-RGG. The results suggest that both pre and post-anthesis conditions operate in concert to determine the potential grain weight of barley in temperate climates. The dry weight and water content of grains and ears followed a common pattern during grain growth for all site/years when the percentage moisture content was used as an index to normalise different rates of development. Use of the above data for predicting potential grain weight of barley prior to harvest is discussed. (c) 2006 Elsevier B.V. All rights reserved.