WATER-DEFICIT, ROOT DEMOGRAPHY, AND THE CAUSES OF INTERNAL BLACKENINGIN FIELD-GROWN TOMATOES (LYCOPERSICON-ESCULENTUM MILL)

An internal blackening disorder may cause substantial losses in the va lue of tomatoes grown for processing. The disorder resembles an intern al form of blossom-end rot and appears to be more common in dry season s. In an experiment to test whether the internal blackening is caused by water deficit and whether it is indeed blossom-end rot, plots of cv . Cannery Row were irrigated to keep the soil moisture deficit <50 mm and others were sheltered from rain and not irrigated from early flowe ring onwards. Shoot growth (total and fruit dry mass) was measured des tructively at intervals, and root growth and death nondestructively us ing minirhizotrons. There was a greater incidence of internal blackeni ng and blossom-end rot, and lower Ca concentrations, in the fruit of n on-irrigated plants. Root growth and root death were accelerated in th ese plants around the time that internally-blackened fruit were set. A lthough the internal blackening syndrome shared some features with blo ssom-end rot some differences were apparent in this experiment. It is suggested that internal blackening could have resulted from increased root competition for photosynthate, leading to abnormal seed developme nt. Root turnover was appreciable (30-40% of the roots survived less t han or equal to 28 days). This suggests there may be substantial error s in contemporary models of dry matter partitioning in tomato crops.