Hormonal changes caused by the xenia effect during grain filling of normal corn and high-oil corn crosses
The xenia effect results from the cross-fertilization of nonrelated lines of crops, which causes a grain to produce a germ or embryo that is much larger than average. It is a significant genetic component in TopCross grain production systems, which can affect grain yield and quality. This study measured hormone variations during grain filling of normal corn (Zea mays L.) hybrids, and normal corn crossed with a high-oil corn. Two normal corn hybrids, Nongda 108 (ND108) and Liaoyu 20 (LY20), were used as the females. A high-oil corn hybrid, HOC115, was used as the male. Compared with self-fertilization, the cross between ND108 and HOC115 resulted in higher yield, while the cross of LY20 with HOC115 had lower yield. The changes in grain yield were mainly due to grain weight. Both hormone levels and endosperm cell division rates increased rapidly during the early stage of grain development, and then declined gradually until maturity. The levels of indole-3-acetic acid, gibberellin (GA3), zeatin riboside, and abscisic acid at an early developmental stage were closely related to the grain weight at maturity. Higher endosperm cell division rates and cell numbers were associated with lower levels of GA3, and higher filling rates were associated with higher GA3. The xenia effect was mainly mediated through changes of hormone contents, which affected endosperm cell division, grain sink strength, and, therefore, changed grain weight and grain yield.