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A Novel Method to Monitor Root Decomposition Demonstrates that Salt Stress Can Enhance the Rate of Tomato Root Decomposition

Rockefeller Foundation, P.O. Box 30721, Lilongwe 3, Malawi

^* Corresponding author.

This study quantified the effects of an abiotic stress, salinity, and a biotic stress, phytophthora root rot, on root mortality and decomposition in tomato (Lycopersicon esculentum Mill.). Rhizotron windows were used to measure root mortality rates in mature, container-grown plants. A novel assay was developed to monitor root decomposition by quantifying root-length disappearance over time using petri dishes in incubation chambers. Phytophthora root rot infection was induced by salt stress in the presence of Phytophthora parasitica Dastur inoculum; however, the moderate levels of disease induced had no effect on rates of root mortality or on root decomposition. Genotypic differences in root decomposition under salt stress were shown by the decomposition assay, the first report of intraspecific variation in root decomposition rates. High-salt UC82B had 50% higher root mortality and a threefold higher initial root decomposition rate than low-salt UC82B. In contrast, salinity did not enhance root mortality or decomposition in cv. CX8303. UC82B grown under salt stress had thin roots of high N concentration, whereas salt stress did not alter N concentration in CX8303 roots. On a plant by plant basis, root N concentration was correlated with initial rootlength loss in the degradation assay, whereas root diameter was not. The results indicate that an indirect consequence of salt stress could include rapid root decomposition.

Received for publication April 1, 1993.