Effect of GA3 and nitrogen on yield and marketability of lettuce (Lactuca sativa L.)

Abstract

In the present study the effect of both nitrogen application rate and gibberellic acid (GA3) on yield and earliness of production and marketability (plant height and leaf color) of lettuce was examined. Three commercial cultivars [cv. 'Kismy' and 'Marady' (loose-leaf types) and cv. 'Adranita' (romaine type)] were cultivated in an unheated plastic greenhouse for three consecutive growing periods. During cultivation, four nitrogen rates (0, 150, 300 and 450 mg L-1 of N) and two foliar sprayings with two concentrations of GA3 (0 and 50 mg L-1 for the first and second sowing and 0 and 25 mg L-1 for the third sowing) were applied. Total fresh and dry weight significantly decreased and increased, respectively, by GA3 application, especially in the second sowing date, whereas high nitrogen rates (300 and 450 mg L-1) resulted in higher fresh weight (by 11.2%) and lower dry weight (by 7.5%) respectively. Plant height was significantly increased by GA3 application, except for cv. 'Adranita' in the third sowing date, whereas nitrogen application did not affect plant height for all the cultivars studied. The application of GA3 and high nitrogen rates resulted in an increase of the total number of leaves per plant and a decrease of chlorophyll content of leaves during the first sowing date and third sowing date. In conclusion, nitrogen application could be beneficial for total yield and the total number of leaves, whereas medium GA3 concentration (25 mg L-1) should be applied during spring (third sowing date) as it results in plants with higher number of leaves, total fresh weight (cv 'Kismy') and marketable height.