Burrowing Nematodes May Survive on Variants of ‘Milam’ Lemon

Abstract

Abstract ‘Milam’ is a lemon-type citrus rootstock of unknown parentage considered resistant to the burrowing nematode, Radopholus similis (Cobb) Thorne. R. similis causes a serious disease of citrus in Florida called spreading decline. ‘Milam’ was found in 1954 as the noninfected rootstock of a ‘Parson Brown’ orange tree in a burrowing nematode infested grove. In greenhouse tests of 9 months duration, ‘Milam’ consistently eliminated burrowing nematode populations from containers of infested soil by preventing the development of nematode eggs in the root cortex (3). After eight years in a rootstock trial planted in an infested site, no burowing nematodes were found in feeder roots of ‘Milam’ although nematodes were present in roots of adjacent rough lemon and sweet orange rootstocks (2). ‘Milam’ has also been tested as a biological barrier for four years in a soil tank 25 feet in length. Burrowing nematodes multiplied in one end of the tank have not migrated beyond the first ‘Milam’—a distance of two feet. Burrowing nematodes migrated 12 feet per year in a similar soil tank when susceptible rootstocks were used (1).