2017 ASHS Annual Conference

Maize (Zea mays L.) is a high-light requiring plant, and for year-round growth of high-quality maize in greenhouses there are no specific guidelines for light levels at critical developmental stages when grown in a greenhouse setting. During winter months in northern latitudes of North America, poor tassel development is observed. Poor tassel development is defined as shorter, less branched tassels that are partially to completely lacking anthers. The objective of this research was to determine which stages of corn development were most sensitive to low-light stress in relation to tassel development. Two maize inbreds, referred to as Genotype A and Genotype B, were sown in packs filled with a peat-based soilless substrate and placed in a greenhouse. After 3 wks, plants were transplanted into 22.8-cm-diameter plastic containers and transferred to a growth chamber. The day/night temperature set points were 29.1/21.1 °C and a day/night vapor pressure deficient (VPD) of 1.4/0.87 kPa. A 16-h photoperiod was maintained using metal halide lights as the sole light source providing a photosynthetic photon flux (PPF) 550 µmol^.m^-2.s^-1, resulting in a daily light integral (DLI) of 23.7 mol^.m^-2.d^-1. When plants reached a specific developmental stage (V4, V5, V6, or V7), plants were transferred to a second chamber with the same air temperature and VPD set points, but a PPF 210 µmol^.m^-2.s^-1 (9.3 mol^.m^-2.d^-1) for 7 d. An additional group of plants was grown the entire time in the high-light chamber to serve as the control. Tassel length, viable tassel length, and tassel branch number were recorded. Viable tassel length was shorter than untreated plants when plants were subjected to a low light stress for both genotypes, though the magnitude of effect varied with genotype. Genotype A plants receiving a low light stress at V6 or V7 had viable tassel lengths that were 46% or 41% shorter, respectively, compared to untreated plants (100.9 cm). Alternatively, Genotype B plants that received a low light stress treatment at V4 or V7 resulted in viable tassel lengths that were 26% or 24% shorter, respectively, than untreated plants (103.0 cm). This research indicates that light levels at specific stages of vegetative growth have a significant impact on tassel quality. Additionally the vegetative stages that are most susceptible to low-light stress on tassel development are dependent on the genotype.