Changes of yield and yield components of tomato (Solanum lycopersicum L.) under the effects of ultraviolet radiation and abscisic acid application in water deficit stress conditions

The use of low doses of ultraviolet radiation (< 50 kJ m-2 day-1), is one way to stimulate plant defense system that can increase cell metabolism, improve physiological processes and increase plant resistance to various environmental stresses. Accordingly, an experiment was conducted to investigate the effect of ultraviolet radiation (UV-AB, UV-C and natural light) and spraying of the abscisic acid hormone on the changes of agronomic traits and fruit yield of tomato plants under water deficit stress conditions during vegetative and reproductive stages.

In this two-years experiment was conducted out in the form of a compound factor analysis in a factorial using based on a randomized complete block design with four replications in 2014-15 and 2015-16 crop years. Experimental treatments include: (1) mild spectra of ultraviolet radiation (non-radiation (control), UV-AB and UV-C), (2) abscisic acid (non-application and application of abscisic acid hormone) and (3) irrigation factor (full irrigation during the whole growth period (control or non-water deficit stress), water deficit stress during vegetative stage and water deficit stress at reproductive stage).

The results of analysis of variance showed that the effects of mild ultraviolet radiation, abscisic acid hormone and irrigation factor on fruit yield of tomato and fresh weight of fruit were significant at 1% level, but the effect of the abscisic acid hormone was not significant on the number of fruit per plant and dry weight of fruit. The results indicated that during the first year ultraviolet radiation of UV-AB and UV-C reduced by 15.8 and 16.3% of the number of fruits per plant. But in the second year, there were notable changes, so that UV-AB radiation increased by 6.2% and UV-C radiation decreased by14.1% of the number of fruits per plant. The results showed that in full irrigation conditions, dry weight of fruit was generally higher than water deficit stress at vegetative and reproductive stages, however, the use of UV-AB and UV-C rays in the full irrigation and water deficit stress conditions, the dry weight of fruit is relatively less than the non-use of UV rays. The results of interaction of irrigation factor × application of abscisic acid showed that in all irrigation treatments including full irrigation, water deficit stress at vegetative and reproductive stages application of abscisic acid increased fruit yield per plant, 18.1, 11.5 and 7.8%, respectively. The results obtained for dry weight of fruit for the index of dry weight of fruit to fresh weight were also true. Thus, at all levels of water deficit and control, the index of dry weight of fruit to fresh weight in plants exposed to mild radiation of UV-AB was less than non-ultraviolet irradiation and mild radiation of UV-C. The results showed that the under full irrigation conditions, application of abscisic acid reduced the index of dry weight of fruit to fresh weight, while its application in water deficit stress at vegetative and reproductive stages increased by 5.1 and 6.5% of the above attributes, respectively.

Results showed that the treatment combination of application of abscisic acid × full irrigation × UV-AB was the best in terms of fruit yield per plant, number of fruit per plant, and fruit dry weight. Overall, it could be stated that the use of low doses of UV-AB radiation with application of abscisic acid can have a positive effect on fruit yield and yield components of tomato.