SENESCENCE AND RECEPTIVITY OF MAIZE SILKS

Ears of maize (Zea mays L.) fail to produce kernals if pollination is delayed more than a few days after silks emerge. Reproductive failure in aging flowers could be due to loss of silk receptivity to pollen. To test this possibility, we examined the capacity of silks to support pollen germination, tube growth, and the passage of the tube to the ovary as flowers aged. Plants were grown in the greenhouse and silks were pollinated by hand up to 14 d after emergence from the husks. Flowers in the mid-base region of the ear failed to set kernels when pollinated 7 or more days after their silks emerged. This corresponded to the day the base of the silks began to collapse (senesce). The remaining flowers on the ear failed to set kernels in acropetal succession, coincident with the occurrence of silk senescence. During the first 24 to 36 h of senescence, pollen germination and tube growth proceeded normally. However, once the basal tissue collapsed, tube growth was restricted and fertilization did not occur. These results indicate that kernel set on an ear was closely related to the number of flowers having silks that are not senesced at pollination. Silks of aging flowers lost receptivity initially because the base of the silk collapsed, and pollen tubes were blocked from reaching the ovary. Silk senescence is the primary cause for reproductive failure in maize if pollination does not occur soon after silks emerge from the husk.