Morphogenetic effects induced by pathogenic and non pathogenic Rhizoctonia solani Kühn strains on tomato roots

The effects of two Rhizoctonia solani Kühn isolates on root colonization and morphology of in vitro grown tomato plants were compared. Pathogenic hyphae (R1556) penetrated and filled all the parenchyma cells of the cortex and of the central cylinder; the vessel elements underwent a significant degradation. Several brownish sclerotia and cushion formations were observed. Roots colonized by the non-pathogenic strain showed phytoplane non-pathogenic growth: hyphae occurred in the external root portion and in a few cortical parenchyma cells; a number of hyphal tips grew along the ridges of adjacent epidermal cells or in the intercellular spaces. Morphometric values were significantly lower in the roots of plants infected by the pathogenic isolate than in those infected by the non-pathogenic one compared to the controls. Root growth was described by a logistic model in infected plants and by a linear one in the controls.