Evaluating Rootstocks for Greenhouse Tomato Production

Grafting technique has been increasingly adopted in greenhouse tomato production especially with soilless cultural systems to achieve extended harvest and increased yield. This study was conducted in a passively-ventilated high-roof greenhouse to investigate the effects of rootstocks and rootstock-scion interactions on tomato yield and fruit quality. Two indeterminate greenhouse tomato cultivars ‘Compari’ and ‘Westland’ and a determinate field tomato cultivar ‘Tasti-Lee’ were grafted onto two popular rootstock cultivars including ‘Maxifort’ and ‘Beaufort’, using the splice grafting method. The six grafting combinations were compared with non-grafted scion plants in a randomized complete block design with four replications. After grafting and healing process, all the plants were transplanted on 10 September into 3-gal plastic pots filled with aged pine bark while nutrients were supplied by a computerized recycle system. Marketable yield varied significantly among tomato scion cultivars as reflected by differences in average fruit weight and fruit number. Rootstock effect was dependent on rootstock-scion combinations. In general, grafted tomato with ‘Maxifort’ exhibited enhanced growth vigor and improved productivity as compared with non-grafted controls, particularly in ‘Compari’ and ‘Tasti-Lee’ towards the mid to late growing season. Grafted tomato with ‘Beaufort’ demonstrated a significant reduction of early yield in ‘Compari’ and ‘Tasti-Lee’; however, it seemed to be ameliorated from mid to late harvests. Overall, fruit size was increased as a result of grafting. It was also observed that ‘Maxifort’ appeared to improve water uptake of tomato plants under low night temperatures. Leaf tissue analysis indicated great variations of macro- and micronutrient status in tomato plants as affected by rootstocks and rootstock-scion interactions. Interestingly, Na⁺ concentrations in tomato leaves were significantly lower in all the grafted treatments than that of the non-grafted plants, suggesting a unique mechanism of Na⁺ uptake by interspecific rootstocks and possible improvement of salt tolerance in grafted tomato. Analysis of fruit quality attributes revealed significant varietal differences with ‘Tasti-Lee’ having the highest levels of total soluble solids and lycopene, whereas grafting did not alter fruit quality from non-grafted tomatoes.