Occurrence of Biotypes in Radopholus citrophilus

Two morphologically and karyotypically identical populations of the citrus burrowing nematode, Radopholus citrophilus, differed in their ability to damage and reproduce in roots of citrus rootstocks previously identified as either resistant or tolerant. These populations are considered to be biotypes, and their occurrence may explain the appearance of spreading decline symptoms in plantings of rootstocks previously considered resistant.