A comparison of three methods for determining root-knot nematode infectionof cotton roots

Three methods for determining the extent of infection of cotton roots (Goss ypium hirsutum L.) by root-knot:nematode, Meloidogyne incognita (Kofoid and White) Chitwood, were compared. Root-knot nematode eggs were added to pots containing either sterilized soil or soil amended with rye, and cotton see dlings were planted. Cotton root systems were then assessed for infection/d amage after 14 and 28 days of exposure. At the 14-day sampling, the roots w ere stained, using the lactophenol acid fuchsin method and the juvenile nem atodes counted. At the 28-day samplings, the cotton roots were given a visu al rating for nematode-induced root galling (0-100), and the galls were cou nted. The number of stained juveniles counted in the roots at 14 days gave a poor indication of the number of galls that will ultimately develop. The visual raring and the gall counts gave similar results. In this study the v isual rating proved to be faster and more useful due to difficulties encoun tered obtaining a representative root sample for gall counts.