USE OF TRIFOLIATE ORANGE AS A COMPARATIVE STANDARD FOR ASSESSING THE RESISTANCE OF CITRUS ROOTSTOCKS TO CITRUS NEMATODE

Twenty-one citrus rootstocks were screened in a greenhouse for resistance to Tylenchulus semipenetrans. Parasitism by T. semipenetrans was confirmed by verifying the host suitabilities of rootstocks expected under California conditions to be resistant (C-35 citrange, Swingle citrumelo, and Poncirus trifoliata cv. Rubidoux) or susceptible (Citrus sinensis cv. Argentina and Carrizo citrange) to T semipenetrans. P. trifoliata cv. Rubidoux was the resistant standard for comparing the host suitabilities of individual rootstocks. Five previously unscreened rootstocks expressed greater resistance than P. trifoliata: 1452 citrumelo, Siamese pummelo x P. trifoliata, and three selections from crosses of C. sunki and P. trifoliata (C-54, C-57, and C-146). Rank correlation showed the relative host suitabilities of individual rootstocks were consistent between two experiments.