Source/sink ratio and the relationship between maximum water content, maximum volume, and final dry weight of maize kernels

Final kernel weight (KW) is closely related to maximum kernel volume (KV) and maximum kernel water content (KWC). It is not clear, however, how changes in the reproductive sink capacity, assimilate availability during grain filling and physical restriction to kernel expansion affect the relationship between KW and KWC or between KW and KV. Three experiments were conducted at Balcarce, Argentina and Ames, USA. Defoliation, thinning, plant density, restricted pollination and volume restriction treatments were imposed to manipulate KV, sink and source capacity. KW varied from 111 to 436 mg across all hybrid–treatments combinations and was related to the source/sink ratio during grain filling (r2 = 0.85). Treatment variation in KW was related primarily to changes in kernel growth rate, except for the complete defoliated treatment, which also shortened the duration of grain filling. KW was correlated with maximum KWC (r2 = 0.77, p < 0.001) and with maximum KV (r2 = 0.91, p < 0.001). The developmental patterns for KW, KWC and KV during grain filling were not affected by the source/sink manipulations, except for severe defoliation. In the latter case, maximum KWC was not a good estimate of final KW. KV, however, was sensitive to reductions in carbohydrate supply during grain filling and was closely correlated to KW. Physical restriction to kernel expansion reduced kernel weight 13% relative to its control (p < 0.01). But restricting kernel expansion did not alter the general relationships between KW and KWC or between KW and KV, because kernel density was not affected.