Race identity, pathogenicity and damage threshold of Tylenchulus semipenetrans on sour orange in Jordan


  • T. K. Al-Azzeh
  • W. I. Abu-Gharbieh


Three populations of Tylenchulus semipenetrans, collected from Northern, Southern, and Central Jordan Valley, were differentiated on 'Valencia' sweet orange, 'Troyer citrange', 'Pomeroy' and 'Rubidoux' Poncirus tn/oliata, 'Thompson seedless' grape, and 'Manzanillo' olive. The three populations did not infect olive or P. tri/oliata, and consequently were identified as the 'Mediterranean' race. Pathogenicity tests showed that inoculation of 500 juveniles/pot (kg soil) did not affect the growth of sour orange seedlings. However, initial population densities (Pi) of 1,000 to 20,000 juveniles/pot progressively reduced vegetative growth by 9.1 to 30.3% and root weight by 9.7 to 30.9%. Also, Pi exceeding 5,000 juveniles/pot resulted in severe decline symptoms.  Plant growth was not adversely affected as long as the resulting nematode infestation stayed below certain critical levels, i.e., 2,450 juveniles/lOO em} soil; 1,250 eggs, 3,700 juveniles, 590 females, or 5,540 total developmental stages/g root. These levels of infestation represent damage thresholds of this nematode on sour orange seedlings under growth chamber conditions.