ABSTRACT
Tylenchulus semipenetrans Cobb was first recorded in the County of Los Angeles by J. R. Hodges in 1912. Cobb described this species and organized an international inquiry from which it resulted that this parasite was widespread throughout the world. He used this example of a parasitic plant nematode to draw attention to the scientific and economic importance of nematodes in agriculture and set up the first laboratory for nematology. The species of nematodes known to affect citrus plants totalled eight in 1949, 28 in 1959 and 189 belonging to 39 genera in 1968. This is a sedentary semi-endoparasitic nematode distributed throughout the citrus fruit growing areas. The females attach themselves to the radicle and secrete from their excretive pore a mucilaginous substance to which particles of soil become attached, so as to give the radicles a coral-like appearance. T. semipenetrans can survive for a number of years in ground not under citrus plants.
