2019 ASHS Annual Conference

To support research efforts within Corteva Agriscience maize plants are grown in a greenhouse in Johnston, Iowa during all 12 months of the year. Historically, during the summer months, kernel set has been below the desired standard. It had been thought that heat stress was a major factor due to the limited cooling capacity in the greenhouses from June through August. However, the exact parameters that influenced the observed poor kernel set was unknown. The objective of this study was to determine if temporary heat stress at different developmental stages had a negative effect on pollen or silk viability.

Maize plants from two different inbred lines were grown at day/night temperature set points of 78/68 °F. Plants were subjected to a heat stress treatment at 10 different developmental stages (V5, V6, V7, V8, V9, V10, V11, V12, R1, or R2) for a period of 7-d. The heat treatment was applied in a growth chamber with day/night temperature setpoints of 95/79 °F (average daily temp = 89.6 °F) and a 16-hr photoperiod. The experiment was replicated twice over two growth chambers with five single plant replicates per treatment in each treatment replicate. An untreated control was also included. After exposure to the heat stress treatment, plants were placed back into a greenhouse at the original setpoints.

To determine pollen viability, the pollen from treated plants was used to pollinate plants that did not experience a heat stress (untreated silk donors). To determine silk viability, treated plants were pollinated using pollen from untreated plants (untreated pollen donors). First silk emergence, first pollen shed and pollination dates were recorded for each plant. At the end of the study kernel count was estimated.

There was a clear trend for both genotypes that pollen viability is negatively affected when plants are heat stressed for 7 consecutive days at the temperatures tested. Kernel set for both inbreds was negatively affected when stressed at developmental stages V9-V12. Silk viability for only one of the inbreds significantly affected kernel set when heat stressed at developmental stages V9 and V10.