Xenia effects in maize with normal endosperm : II. Kernel growth and enzyme activities during grain filling

Xenia can be defined as the effect of the pollen genes on the development of the fruit or the seeds. In maize ( Zea mays L) with normal endosperm, the relative advantage in weight of cross‐fertilized to self‐fertilized kernels can reach 13% when inbred lines are used as females. To improve our understanding of the physiological bases of such a phenomenon in this species, we studied the accumulation of carbohydrate and the activities of starch‐synthesizing enzymes during the grain filling period in kernels from self and cross fertilization on independent ears from the same female inbred line. With one inbred line as female, selfed and crossed to an unrelated male, kernel growth was studied at 14, 21, 28, 39, and 74 d after pollination (DAP). The cross‐fertilization effect on kernel dry weight was maximum at 14 DAP and then decreased about 10%. Male effects on enzyme activities and carbohydrate content were studied at 14 and 28 DAP in a 3‐by‐3 diallel from inbred lines. At 14 DAP, the advantage of cross‐fertilization on average was 28.8% for starch content, 24.8% for ADP‐glucose‐pyrophosphorylase (EC 2.7.7.27) activity, and 24.1% for neutral invertase (EC 3.2.1.26) activity. The advantage depended on the cross for sucrose content, acid invertase activity, and sucrose synthase (EC 2.4.1.13) activity. At 28 DAP, cross‐fertilization advantage was not significant for enzyme activities or carbohydrate content but was still significant for kernel dry weight (+7.8%). At both stages, there was no correspondence between male and female effects, when both were significant. The data tend to show that differences in male effects for enzyme activities are expressed early after fertilization but are insufficient to explain male effects at the level of kernel weight.