Nitrate/ammonium ratio effect on the growth, yield and foliar anatomy of grafted tomato plants

The vigorous behaviour of a rootstock modifies the growth and yield of a plant variety or hybrid, altering the plant nutritional requirements. The purpose of this work was to study four ratios of NO3-/NH4+ (100/0, 92/8, 85/15 and 80/20%) over the growth, leaf anatomy and yield of grafted and ungrafted tomato plants. We used a fully randomised experimental block design with factorial arrangement of 2 × 4 (grafted and ungrafted plants and four ratios of NO3-/NH4+), on eight treatments in total with four replicates each, using Tukey's mean comparison test (P ≤ 0.05). The rootstock was 'Silex' by Fito Seeds, with the 'El Arrojado' graft (variety) by Gene Seeds. The graft produced an increase in growth, dry biomass production, stomatal density, trichome number, epidermal cell density, fruits per plant, average fruit weight, fruit size and total soluble solids, in comparison with the ungrafted tomato plants. In most of the assessed variables, the grafted tomato plants gave their best response at an 85/15% NO3-/NH4+ ratio; while the ungrafted plants performed better at a 92/8% NO3-/NH4+ ratio. The response of the grafted plants to the different NO3-/NH4+ ratios suggests that grafting induces tolerance to NH4+.