Three methods for determining the extent of infection of cotton roots (Gossypium 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 seedlings were planted. Cotton root systems were then assessed for infection/damage after 14 and 28 days of exposure. At the 14-day sampling, the roots were stained, using the lactophenol acid fuchsin method and the juvenile nematodes counted. At the 28-day samplings, the cotton roots were given a visual rating for nematode-induced root galling (0-100), and the galls were counted. 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 rating and the gall counts gave similar results. In this study the visual rating proved to be faster and more useful due to difficulties encountered obtaining a representative root sample for gall counts.
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