Tomato Yield and Aerial Pests Populations Affected by Grafting, Nitrogen Rate and Ratio of NO3-:NH4+ in Hydroponic Cultivation

Experiments were conducted using tomato cv. Belle, in hydroponic system during spring-summer of 2012 and 2013. In 2012, the effects of grafting (non-grafted and grafted on rootstock Arnold) and three N application rates (75, 140 and 205 mg/L) on fruit yield and population density of aerial pests (Bemisia tabaci and Tuta absoluta) were studied. The same variables were determined in 2013, but we included additional treatments (non-grafted and self-grafted tomato, and tomato grafted on rootstocks Arnold and He-Man) and three ratios of NO₃^-:NH₄⁺ ions (92:8, 85:15 and 70:30) in N reduced nutrient solution (140 mg/L N).

Grafting did not consistently affect marketable yield but affected populations of B. tabaci and T. absoluta in both experiments. In 2013, grafted plants provided higher number of marketable fruits (more than 10%) compared to non-grafted or self-grafted plants. Number of B. tabaci nymphs on grafted (rootstocks cv. Arnold or He-Man) was lower compared to those on self or non-grafted plants. The number of T. absoluta mines was the lowest on plants grafted on cv. Arnold. The influence of N rate and ratio on yield components and populations of aerial pests was observed in both experiments. In 2012, at the early yield, the highest number of fruits and the highest yield per plant were recorded on plants grown at 75 mg/L N. Plants at 75 mg/L N also had lowest total fruit weight. The lowest density of B. tabaci nymphs was found on ungrafted or grafted plants at 75 mg/L N. Nymphs population was lower at 140 mg/L N compared to 205 mg/L N. Morphological characteristics of pupal stage were least expressed on plants at 205 mg/L N. T. absoluta infestation was increased on plants grown at 140 and 205 mg/L N. In 2013, number of fruits and total marketable yield was higher on plants supplied with 8% NH₄⁺ compared to plants supplied with 30% NH₄⁺ in nutrient solution. The lowest B. tabaci nymphal population inhabited on plants supplied with 30% NH₄⁺. T. absoluta infestation was increased on plants supplied with 15% NH₄⁺ in 2013. Nitrogen application rate of 140 mg/L N provided higher tomato yield and lower B. tabaci density than standard of 205 mg/L N.