Comparison of Rapid Methods for Evaluating Resistance to Phytophthora cinnamomi in Avocado Rootstocks. B. K. Gabor, Graduate Research Assistant, Department of Plant Pathology, University of California, Riverside 92521-0122. M. D. Coffey, Professor, Department of Plant Pathology, University of California, Riverside 92521-0122. Plant Dis. 75:118-120. Accepted for publication 12 July 1990. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/PD-75-0118.

The clonally propagated avocado rootstock selections Thomas, Duke 7, Barr Duke, and Topa Topa (Persea americana); UCR 2007, UCR 2008, and UCR 2053 (P. schiedeana); Martin Grande (G755a, b, and c), UCR 2022, and UCR 2023 (P. americana × P. schiedeana); and UCR 2066 (P. steyermarkii) were evaluated for resistance to Phytophthora cinnamomi in excised etiolated shoots, excised roots, and intact root systems grown in vermiculite. Resistance reactions were similar in etiolated shoots and intact root systems with the P. schiedeana, P. americana × P. schiedeana, and P. steyermarkii selections. With the P. americana selections, in contrast, the etiolated shoot and intact root system reactions differed. Screening of excised avocado roots for differences in electrolyte leakage gave variable results and did not differentiate among some resistant and susceptible rootstocks. In general, screening of intact root systems grown in vermiculite gave the best results, with comparative resistance responses similar to those determined under field conditions.