Effect of low gamma irradiation doses on growth and productivity of green bean

The field experiment was conducted within the two successive growing seasons of 2007/2008 and 2008/2009 to study the effect of low gamma irradiation doses (0, 10,20,30,40,50 and 60Gy) on growth and productivity of green bean cv. Bronco with 3 sowing dates 8, 18 and 28th of October in the first season and 30th of September, 10 and 20th of October in the second season The results of laboratory determinations showed that gamma irradiation doses did not affect the germination percent but slightly affected germination rate and electrical conductivity. Concerning field experiment, data revealed that green bean plant vegetative growth, i.e plant height, fresh and dry weight, leaf number and leaf area, at 45 days after planting (DAP) and shoot number at 30, 45 DAP recorded significantly the highest values at the first sowing date in both seasons.With respect of gamma irradiation doses, all the previously mentioned parameters of plant vegetative growth recorded the highest values with 40 Gy at 15,30, and 45 DAP except number of leaves which recorded the highest value with 30Gy at 15,30 and 45 DAP. Concerning shoot number there was no significant difference among several doses at 30 DAP in the first season but in the second season it was 20 Gy and at 45 DAP compared with the control. Also the first sowing date in both seasons gave the highest pod length, fresh and dry weight, plant yield, number of pods per plant, marketable yield per plot and total yield per feddan. Whereas ,the second sowing date led to the lowest pod thickness. In addition, 20Gy of gamma irradiation doses recorded the highest value of pod length. The 30 Gy dose showed the highest value of pod fresh and dry weight, plant yield and total yield per feddan. In addition ,the 20 and 30 Gy doses led to the highest pod number per plant and marketable yield, concerning pod thickness there was slight difference only in the second season between several doses.The second sowing date in the first season and the third sowing date in the second season positively increased total sugars in leaves, and the first sowing date increased the total chlorophyll reading in leaves and protein in green pods, the second sowing date in first season and the third sowing date in second season led to the lowest percentage of fibers in green pods and there was no significant difference between the second and the third sowing date in the second season. Gamma irradiation at 20 Gy dose recorded the highest values of protein in green pods and 60 Gy dose increased total sugars and total chlorophyll reading in leaves whereas 20,30,40,50 and 60 Gy doses led to the highest percent of fibers in green pods and the control scored the lowest.