الفهرس 
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Abstract
The study was conducted at the Experimental Farm of Toshka Research Center, Desert Research Center (DRC), Aswan Governorate, Egypt during 2008/2009 and 2009/2010 seasons to study the effect six planting dates (October 15th, November 1st and 15th, December 1st and 15th and January 1st) on growth and production of three cultivars of onion (Giza 20, Giza 9 and Giza 6) under Toshka conditions.
The experiment included 18 treatments, which were the combinations of six planting dates (October 15th, November 1st and 15th, December 1st and 15th and January 1st) and three cultivars (Giza 20, Giza 9 and Giza 6). The experiment was laid out in a split-plot design with
three replicates. The tested planting dates contributed as the main plot,
while cultivars were randomly distributed to the sub-plots. Experimental plots were consisted of 6 ridges each of 25 meters in length and 0.9 meter in width.
Healthy and uniform transplants of nearly sixty days old with the same characteristics (when they usually were 25 cm in height) were used for every planting date. Plants were transplanted on both sides of the drip line on both sides of the ridges at 10 cm between transplants.
Vegetative characteristics were recorded, i.e. plant height, number of leaves/plant and plant fresh and weights. Also, yield components were recorded. Finally, bulb quality characteristics, i.e. diameter of bulbs, neck diameter of bulbs, diameter-neck ratio, average bulb weight, total soluble solid (TSS) and dry matter of bulb were recorded.
All data were subjected to an analysis of variance with SAS statistical package. Means of main effects were separated using Duncan’s multiple range test. Means of interactions were separated using least significance difference (LSD) at P = 0.05.
The obtained results could be summarized as follows:
1. Effect of planting dates
All data recorded did not show a clear trend towards their response to different planting dates over the entire measuring period. At 60 days after planting dates, the highest significant value of vegetative growth
characteristics (plant height, number of leaves/plant, plant fresh and dry
weight) and bulb quality (neck, bulb diameter and bulb diameter-neck ratio) were obtained from planting on 15th December in both seasons, while plant fresh and dry weight and bulb diameter gave the highest significant values in the second season in planting 1st November and 1st December, respectively. At 90 days planting dates the highest significant value of vegetative growth characteristics were obtained from planting on 15th December in the first seasons, while plant height of onion plants did not significantly influence in the first season. However, the highest significant values of vegetative growth characteristics were obtained in planting on 1st December in the second season, while plant dry weight and
bulb diameter gave the highest significant value in 1st January. However, the highest significant value of bulb diameter-neck ratio was obtained in planting on November in both seasons. At 120 days after planting date, onion plants were planted late (1st December until 1st January) were significantly from the other planting dates in both seasons. At harvesting, onion plants planted on 1st December gave the highest significant plant fresh and dry weight in both seasons. However, the highest significant values of plant dry weight were obtained in planting on 15th October in the second season.
The highest significant value of average bulb weight was obtained in planting on 15th November in both seasons. However, plantings on 15th
December gave the highest significant values of the content of total soluble solids and dry matter of bulbs in both seasons. Concerning the effect of tested planting dates, no clear trend was observed for yield components (marketable and total bulb yields).
2. Effect of cultivars
Concerning the effect of tested cultivars, there was not a clear effect
of cultivar on the tested growth, yield and quality parameters although Giza 20 and/or Giza 9 performed better than Giza 6.
3. Effect of interaction between planting date and cultivar The interaction between planting date and cultivar did not significantly influence all studied characters over the entire data collection period in both seasons.