WATER DEFICIT AFFECTS RECEPTIVITY OF MAIZE SILKS

Drought during anthesis decreases seed set in maize (Zea mays L.) even if pollination occurs. To test whether low silk water potential (psi( w)) decreases silk receptivity, we examined silk development, pollen-s ilk interaction, and kernel set in two hybrids grown in a greenhouse a nd exposed to a brief water deficit after silks emerged from the husks . Low silk psi(w) directly affected silk development. Silk elongation was inhibited as silk psi(w) decreased, and no growth occurred at silk psi(w) below - 0.8 MPa. Silk senescence (collapse of basal silk tissu e) was delayed, compared with controls, when silk elongation was arres ted by low psi(w) within 3 days after the first silks appeared (DAFS). A similar water deficit 5 DAFS, however, hastened silk senescence. Th e change in silk development had a direct effect on kernel set. Low si lk psi(w) decreased set 20 to 40% 3 DAFS, and decreased set almost com pletely 5 DAFS. Pollen tubes were observed in > 90% of silks pollinate d at psi(w) between - 1.0 and - 1.3 MPa, although there were fewer tub es per silk. Tube growth was slow at low silk psi(w), but tubes failed to reach the ovary only after silks had senesced. These results indic ate that low psi(w) imposed < 4 DAFS limited kernel set primarily by c ausing developmental failure within the ovary, not loss of silk functi on. Low psi(w) imposed > 5 DAFS limited kernel set by hastening silk s enescence. Thus, water deficits at anthesis can cause loss of silk rec eptivity in maize, but only when low silk psi(w) occurs > 5 d after si lks emerge from the husks.