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. T o test this possibility, we examined the capacity of silks to support pollen germination, tube growth, and the passage of the tube to the ov ary as flowers aged. Plants were grown in the greenhouse and silks wer e pollinated by hand up to 14 d after emergence from the husks. Flower s in the mid-base region of the ear failed to set kernels when pollina ted 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, coin cident with the occurrence of silk senescence. During the first 24 to 36 h of senescence, pollen germination and tube growth proceeded norma lly. However, once the basal tissue collapsed, tube growth was restric ted and fertilization did not occur. These results indicate that kerne l set on an ear was closely related to the number of flowers having si lks that are not senesced at pollination. Silks of aging flowers lost receptivity initially because the base of the silk collapsed, and poll en tubes were blocked from reaching the ovary. Silk senescence is the primary cause for reproductive failure in maize if pollination does no t occur soon after silks emerge from the husk.