The nature and role of metabolic leakage from root-knot nematode galls and infection by Rhizoctonia solani.

A severe root rot of tomato caused by Meloidogyne incognita and Rhizoctonia solani was associated with nutrient mobilization into gall tissue and root exudation. Root decay did not develop when root exudates were continuously removed by leaching. When leachates were collected from M. incognita-infected and control roots and applied to roots of tomatoes inoculated with R. solani alone, roots receiving leachates from M. incognita-infected roots developed a severe rot while roots receiving leachates from control roots were free of decay. During the fourth and fifth weeks following nematode infection, an increased mobilization of (1)C labelled compounds to nematode-infected roots occurred. Higher counts of water soluble nonvolatile (1)C labelled exudates leaked from nematode-infected roots than from control roots at each weekly sampling period. Higher concentrations of Ca, Mg, Na, K, Fe, and Cu were found in exudates from nematode-infected roots than from the control roots. During the first 14 days following nematode infection, carbohydrates were the major organic constituents in exudates leaking from nematode-infected roots. Fourteen days after nematode infection, nitrogenous compounds become the major organic constituents leaking from roots. Shifts in C/N ratio of root exudates from nematode-infected roots were associated with parasitic development of R. solani in tomato roots.