Increasing Assimilate Reserves Does Not Prevent Kernel Abortion at Low Water Potential in Maize

Abstract

Water deficits during anthesis cause maize (Zea mays L.) kernels to abort soon after fertilization. Inhibition of photosynthesis accounts for much of the kernel loss, but lack of assimilate reserves might also limit kernel development. We tested whether varying the level of C and N reserves prior to anthesis affected kernel set of plants pollinated at low water potential (Ψv). Plants were grown in sand/soil media in pots in the field under one of three light environments: Control, 75‐cm rows, 4.3 plants m−2; Shade, same as Control except under 55% shade cloth from V6 until maturity; or Isolated, 122‐cm rows, 0.7 plants m−2. These treatments produced a 3.3‐fold range in total extractable carbohydrate (TEC) and a 1.7‐fold range in total Kjeldahl nitrogen (TKN) per plant at silk emergence. Water was withheld at silk emergence and plants were pollinated by hand with excess pollen 4 d later when silk Ψw was = −1.1 MPa, leaf Ψw was = −1.8 MPa, and photosynthesis was completely inhibited. Plants were rewatered 2 d after pollination and remained well watered until physiological maturity. The brief water deficit decreased kernels per ear by 45% in the Controls, 72% in the Shade treatment, and 49% in the Isolated treatment. Lower kernel set in the Shade treatment was associated with low levels of TEC and TKN in the vegetative stalk, leaves, and reproductive stalk, compared with Control plants. However, accumulation of TEC and TKN in excess of Control values in the Isolated plants did not prevent kernel loss. Kernel set in all three treatments was more closely related to the rate of photosynthesis prior to imposing the water deficit than to the level of reserves accumulated prior to flowering. These results suggest that selection for high levels of reserves at pollination will not improve kernel set at low Ψw in maize.