Water deficit, root demography, and the causes of internal blackening in field‐grown tomatoes:( Lycopersicon esculentum Mill.)

Summary. An internal blackening disorder may cause substantial losses in the value of tomatoes grown for processing. The disorder resembles an internal form of blossom‐end rot and appears to be more common in dry seasons. 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 flowering onwards. Shoot growth (total and fruit dry mass) was measured destructively at intervals, and root growth and death nondestructively using minirhizotrons. There was a greater incidence of internal blackening and blossom‐end rot, and lower Ca concentrations, in the fruit of non‐irrigated plants. Root growth and root death were accelerated in these plants around the time that internally‐blackened fruit were set. Although the internal blackening syndrome shared some features with blossom‐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 development. Root turnover was appreciable (30–40% of the roots survived 28 days). This suggests there may be substantial errors in contemporary models of dry matter partitioning in tomato crops.