Reproduction of a Florida Population of Tylenchulus semipenetrans on Resistant Citrus Rootstocks. L. W. DUNCAN, University of Florida, IFAS, Citrus Research and Education Center, 700 Experiment Station Road, Lake Alfred 33850. R. N. INSERR A and J. H. O'BANNON, Florida Department of Agriculture and Consumer Services, Division of Plant Industry, Nematology Section, Gainesville 32614-7100; and M. M. EL-MORSHEDY, Central Agricultural Pesticide Laboratory, Dokki, Giza, Egypt 12618. Plant Dis. 78:1067-1071. Accepted for publication 23 August 1994. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/PD-78-1067.

Tylenchulus semipenetrans was detected at moderately high population density on seedlings of the hybrid rootstock Swingle citrumelo growing in a Florida citrus nursery. This rootstock is considered resistant to populations of T. semipenetrans in Florida. Seedlings of the nematode-resislant rootstocks Poncirus trifoliata (PT) and Swingle citrumelo (SC), and the susceptible rootstock rough lemon (RL) were planted in the nursery and in an orchard of mature citrus trees growing on RL. rootstock infected by T. semipenetrans. After 5 mo, the numbers of adult females per gram of root in the nursery were smaller on PT than on RL, but densities of females on SC and RL were not different. The numbers of second-stage juvenile nematodes (J2) per gram of root were not different on any rootstock seedling. In the orchard, RL supported higher numbers of both juveniles and females per gram of root than did either PT or SC. In greenhouse trials using the nursery population of T. semipenetrans and a population from an orchard, no differences in development of nematodes from the nursery were detected among RL, SC, or PT. All life stages of T. semipenetrans from the orchard were supported at higher densities on RL than on SC or PT. We conclude that a population of T. semipenetrans capable of circumventing resistance in PT and SC now occurs in Florida.

Keyword(s): biotype, citrus nematode. Citrus spp.