Objective: Tomato is one of the most important greenhouse vegetables, and due to its content of lycopene, ascorbic acid, tocopherol, and organic acids, it plays a significant role in human health. Improving crop yield and quality is one of the main objectives of modern agriculture and greenhouse cultivation, which can be achieved through advanced techniques such as plant grafting and stem number management. Optimal management of the stem number plays an important role in balancing vegetative and reproductive growth and in the final yield.

Method: To investigate the effect of different rootstocks, stem number on growth, physiological characteristics, and yield of tomato, a factorial experiment was conducted in a completely randomized design with four replications during the years 2022 and 2023 in the greenhouse complex of Parsabad City.In this study, the effect of the rootstock type (non-grafted, wild tomato, King Kong and Imperador) and number of stem (single-stem and double-stem) on the vegetative characteristics and yield of greenhouse tomatoes of the Jonathan variety was investigated. In this experiment, traits such as leaf fresh and dry weight, number of leaves, plant height, stem diameter, total chlorophyll content, carotenoids, leaf stomatal conductivity, number of clusters, number of fruits, fruit weight, and fruit post-harvest life were investigated.

Results: The results showed the rootstock had a significant effect on plant height, leaf number, and stem diameter at 30, 60, 90, 120, 150, 180, and 210 days after transplanting, with the greatest plant height, number of leaves, and stem diameter observed on the ‘Emperor’ rootstock. The ‘Emperador’ and ‘King Kong’ rootstocks significantly increased leaf fresh and dry weight, number of clusters, number of fruits, leaf carotenoid content, and stomatal conductance. Plants trained with double stems produced higher leaf fresh and dry weight, more clusters, more fruits, and higher carotenoid content compared to single-stem plants. Fruit yield on the ‘Emperador’ rootstock was approximately 105% higher than that of non-grafted plants, and the highest fruit weight was obtained from two-stem grafted plants, particularly those on ‘Emperador’ and ‘King Kong’ rootstocks. In contrast, the lowest fruit weight occurred in the non-grafted control and wild rootstocks trained with a single stem. Also, the grafting rootstocks, by improving the plant’s physiological status (increasing photosynthetic pigment content and stomatal conductance), significantly increased shelf life.

Conclusions: The findings indicate that using vigorous rootstocks such as ‘Emperador’ and ‘King Kong’, combined with proper stem number management, can substantially enhance vegetative growth and yield of greenhouse tomato.