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-silk interaction, and kernel set in two hybrids grown in a greenhouse and 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 tissue) was delayed, compared with controls, when silk elongation was arrested by low psi(w) within 3 days after the first silks appeared (DAFS). A similar water deficit 5 DAFS, however, hastened silk senescence. The change in silk development had a direct effect on kernel set. Low silk psi(w) decreased set 20 to 40% 3 DAFS, and decreased set almost completely 5 DAFS. Pollen tubes were observed in > 90% of silks pollinated at psi(w) between - 1.0 and - 1.3 MPa, although there were fewer tubes 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 indicate that low psi(w) imposed < 4 DAFS limited kernel set primarily by causing developmental failure within the ovary, not loss of silk function. Low psi(w) imposed > 5 DAFS limited kernel set by hastening silk senescence. Thus, water deficits at anthesis can cause loss of silk receptivity in maize, but only when low silk psi(w) occurs > 5 d after silks emerge from the husks.