Host Status of Citrus and Citrus Relatives to Tylenchulus graminis

Studies were conducted on the host suitability of four citrus rootstocks--rough lemon (Citrus limon), sour orange (C. aurantium), trifoliate orange (Poncirus trifoliata cv. Argentina), and Swingle citrumelo (C. paradisi x P. trifoliata)--to Tylenchulus graminis which was previously considered a "grass" race of T. semipenetrans. In an uncultivated field, sour orange seedlings grown with T. graminis-infected broomsedge (Andropogon virginicus) were not infected with this nematode after 18-month's exposure to T. graminis population densities ranging from < 0.01 to 0.4 second-stage juveniles (J2)/cm(3) soil. In a greenhouse test, two T. graminis populations from two Florida locations did not infect sour orange seedlings grown for 2 years in soil naturally infested with 0.3 and 1.3 J2/cm(3). Rough lemon, trifoliate orange, and Swingle citrumelo seedlings suppressed T. graminis initial population densities of 7 to final values of < 0.1 J2/cm(3) soil. Final values of > 70.0 J2/cm(3) occurred in soil with broomsedge. These findings provide conclusive evidence that T. graminis is a specific parasite of grasses and does not infect citrus.