The present study was carried out at the Experimental Farm, Nubaria ResearchStation, Onion Research Department, Agricultural Research Center, Nubaria Region during the two winter seasons of 2018/2019 and 2019/2020 to study the effect of transplanting date on yield, quality and leaf diseases of the four onion cultivars. The two field experiments were laid out in a split-plot system in four replications in both seasons. The main plot was occupied by onion cultivars (Giza Red, Giza 6 Mohasen, Giza White and Giza 20), while the subplots were allocated by transplanting dates (1^st November, 20^th Novmber and 20^th December) in both seasons.





The obtained results showed there was a significant difference among the four onion varieties, where Giza 6 Mohassan recorded the highest yield and quality characters and gave the lowest % bolter, double bulbs and number of days to maturity. Transplanting date 20^th November or 20^th December recorded the highest values of yield and quality characters and gave the lowest % bolter, double bulbs and number of days to maturity. The interaction between planting dates and onion cultivars was significant on all the studied characters, where planting Giza Red or Giza 6 Mohassan at 20^th of November of December recorded the highest ones and gave the lowest % of a bolter, double bulbs and number of days to maturity in the two cropping seasons under the study conditions. The observation of stemphylium leaf blight showed that Giza red is the best variety to resist the disease compared with other varieties. In case of planting date, the best time for planting to reduce the disease is 20^th November and 20^th December.