Quantifying the Effects of Daily Light Integral or Photoperiod on Maize Morphology across Developmental Stage

Maize breeding and product development practices with transgenic and genome edited events use horticultural practices and controlled environment facilities for year-round production. In winter months, when ambient light is limited in the northern regions of the United States, tassel barrenness (lacking anthers) can be problematic due to reduced pollen production. Our objective was to quantify the tassel morphology of two maize inbred lines in response to low daily light integral (DLI) at different growth stages and identify a DLI threshold for tassel quality. Inbreds A and B were analyzed after being transferred from a high DLI equivalent (23.7 mol·m −2 ·d −1 ) to a low DLI equivalent (9.3 mol·m −2 ·d −1 ) for 7 days starting at vegetative growth stages (V) V4, V5, V6, V7, V8, V9, V10, V11, or V12 then placed back in the high DLI environment. Data were collected to characterize tassel morphology and barrenness in response to the low DLI stress. Inbred A tassels were more barren under low DLI during V7. Tassels of Inbred B plants responded similarly to the low DLI during V6. These results indicate that low DLI stress impacts tassel morphology of the two inbred lines tested during specific growth stages for 7 days. To identify the number of days required to negatively affect tassels, at the low DLI treatment, plants were subjected to 9.3 mol·m −2 ·d −1 at V6 on Inbred B for 0, 1, 2, 3, 4, 5, 6, or 7 days. Tassel height was shorter (by 9.2, 11.8, or 11.8 cm) for plants that received 5, 6, or 7 days (respectively) of low DLI stress during the V6 developmental stage compared with the high DLI control. These results highlight the importance of providing supplemental lighting if the DLI falls below a critical threshold that is likely well below 23.7 mol·m −2 ·d −1 for more than 5 days during tassel development. Photoperiod manipulation to increase DLI was investigated as a tool to suppress tassel barrenness. Inbreds A and B were subjected to a 16, 20, or 22-hour photoperiod during vegetative or reproductive growth. A longer photoperiod during vegetative growth resulted in an elongated tassel height for Inbred A (by 4.3 cm). For Inbred B, tassel branch number was less (by 3.5 branches), and barren tassel length was shorter (by 19.1 cm). Only Inbred A tassel morphology responded to the longer photoperiod during reproductive growth stages compared with the control, with a 1.4 cm longer tassel height, from 16 to 20 hours, and a 4.8 cm shorter tassel height from 16 to 22 hours, and a 6.2 cm shorter tassel height from 20 to 22 hours. These results indicate that a longer photoperiod can alter the tassel morphology of the two inbred lines during either vegetative or reproductive growth stages. Increasing the photoperiod too much can decrease tassel quality, for example, tassel branch number and viable tassel length decreased (by 4.5 branches and 23.6 cm) for Inbred A plants as the vegetative photoperiod increased from 20 to 22 hours.