Ethylene Production around Silking in Maize: Response of Two Hybrids with Contrasting Tolerance to Increased Stand Density.

Ethylene production has been associated with different responses to abiotic and biotic stress conditions in several crops. In maize there are reports of ethylene synthesis by endosperm and embryo tissues, and of their differential sensitivity to ethylene production. The production in maize kernels increases under light stress (e.g. increased stand density), but there is no comparative study addressing ethylene production of vegetative (leaves) and reproductive (earshoot) tissues during the critical period for kernel number determination (i.e. around silking). We determined ethylene production of these tissues along a 20-day period centered at silking. Two hybrids of contrasting sensitivity to light stress (AX886 >AX852) promoted by increased stand density (SD) were evaluated at two SDs: (i) 10 pl m^-2, which is near optimum for maximum grain yield, and (ii) 15 pl m^-2, which is considered supra-optimum and should promote significant plant barrenness. Ethylene production (in nL h g^-1) along the presilking period was significantly (P<0.05) larger for the earshoot (5.02 nL h g^-1 for AX 852 and 8.88 nL h g^-1 for AX886, averaged across SDs) than for the leaf tissues (0.63 nL h g^-1, averaged across treatments). From silking until R2, all tested tissues exhibited low levels of ethylene production (0.825 nL h g^-1 for leaves and 0.822 nL h g^-1 for ears without husks).