Impact of Planting Date on Growing Degree Units, Grain Yield and Growth Traits of Some Egyptian Yellow Maize Inbred Lines

This study was conducted in 2021 to study the impact of planting date on maize inbred lines and determine their accumulated growing degree units (GDU).The experiment was held at three agriculture research stations (Gemmeiza, Ismaelia and Sids) with RCBD of four replications. It was planned to provide also some insights to optimize maize production and mitigate the impact of climatic changes to all researchers in the scientific community. Three planting dates i.e. April 20th (early), May20th (optimal) and June 20th (moderately late) were applied to investigate their effect on number of days to 50% tasselling and silking, plant height and grain yield of 16 Egyptian yellow maize inbred lines. In addition, to determine accumulated growing degree units (GDU) from planting to 50% silking. Results revealed highly significant differences among tested inbreds for all studied traits at the three planting dates indicating presence of genetic diversity among tested inbreds. Also, the same trend was found for differences among locations and inbreds x location indicating climatic variability among the three testing locations and that inbreds behaved differently at different locations due to differences in climatic conditions among locations and also genetic diversity among inbreds. Number of days to 50% tasselling and silking was reduced from April to June planting as a result of increased temperatures during plant development. Longest plant heights were obtained in April planting as a result of prolonged vegetative growth due to cool - moderate temperatures prevailing at early vegetative growth. Grain yield of all tested inbreds was reduced, with few exceptions, in June 20th planting as a result of high temperatures prevailing at time of tasselling and silking which resulted in pollen, stigma or fertilization abortion and caused poor seed setting. Highest yield of studied inbreds was obtained at Gemmeize location in April 20th planting and it is recommended as a suitable production location for inbreds. Inbred Sakha 3 was the best performing under variable planting dates. Also, inbreds Sakha 1, Sakha 11, Gz 639 and Gm 1021 performed well on certain planting dates. Determination of accumulated growing degree units for tested inbreds revealed big variation among them as a result of genetic diversity of inbreds and matched well with variation present in their silking dates and specified earliness or lateness of tested inbreds. Results of GDU would help in expectation of timing for many agricultural practices such beginning of detasselling process and harvest time in hybrid breeding programs.