Abstract
Nonpathogenic tumor (“Intumescence” or “Oedema”) is a physiological disorder that may develop on tomato (Lycospericon esculentum) leaves. Although genotype and water congestion resulting from the imbalance between plant water use and uptake have been considered as the primary cause of the blister-like symptoms, initiation and process of the tumorous growth remains unclear. A wild tomato species Lycopersicon hirsutum is known for its susceptibility to intumescence formation, particularly in greenhouse. In a recent greenhouse study of grafted tomatoes, the rootstock ‘Maxifort’ (a hybrid derived from L. hirsutum) showed marked symptom of foliar oedema, indicating the possibility of genetic inheritance of intumescences. Tomato ‘Florida-47’ did not exhibit any tumorous growth in either non-grafted treatment or grafted treatment with ‘Maxifort’ as rootstock. The incidence of oedema on ‘Maxifort’ was further evaluated when it was grafted onto the unsusceptible ‘Florida-47’. Replacing the roots of ‘Maxifort’ with that from an unsusceptible tomato variety did not alter the overall susceptibility of ‘Maxifort’ to intumescences as the injury was present in all the grafted ‘Maxifort’ plants. Internal morphology of oedema-afflicted leaves of ‘Maxifort’ revealed evident cell enlargement, while the involvement of cell division in intumescence development needs to be further determined.
