Dry matter and water dynamics of wheat grains in response to source reduction at different phases of grain filling

Agreement that wheat (Triticum aestivum L.) is scarcely limited by source of assimilates during grain fill has not been confirmed when source was drastically decrease in high yield potential environments. Dry matter (DM) and water dynamics of growing grains being possibly able to explain grain weight (GW) responses to source-sink ratios (S-S-ratios) in these conditions. Objectives were to evaluate response of GW to S-S-ratios at different phases during grain fill, and relationship between DM and grain water content in response to different S-S-ratios. Wheat was sown at field conditions during 20042005 and 2005-2006 growing seasons. Four S-S-ratios were assessed: Control without S-S-ratios modification (C), S-S-ratios from anthesis (At) + 12 d to physiological maturity (Sh(All)), S-S-ratios from At + 12 d to first half of grain fill (Sh(1st)) and from second half of grain fill to maturity (Sh(2nd)). Thousand grain weight (TGW), GW at individual positions (IGW), stabilized grain water content (SGWC) and grain filling rate (GFR) were measured. TGW sensitivity to S-S-ratios varied according to length of treatment and its timing, i.e. Sh(All), Sh(1st), and Sh(2nd) treatments reduced TGW by 48%, 26%, and 22%, respectively. These reductions were little higher when IGW were evaluated in Sh(All) (i.e. 53%) and Sh(1st) (i.e. 33%) treatments and lower in Sh(2nd) (i.e. 12%). SGWC sensitivity was lower than that of IGW across S-S-ratios (e.g. Sh(All) 27%, Sh(1st) 22%, and Sh(2nd) 5%). However, close association between IGW and SGWC (R-2 = 0.78, p <= 0.001) and between GFR and SGWC (R-2 = 0.98, p <= 0.001) was found regardless of S-S-ratios and seasons.