Comparison of Field Resistance to Phytophthora cinnamomi in Twelve Avocado Rootstock

Abstract

Twelve avocado (Persea americana Mill.) rootstock selections were tip-grafted with a commercial scion, cv . Hass, and evaluated for their field resistance to Phytophthora cinnamomi Rands. Percentage difference in trunk cross-sectional area of the inoculated compared to uninoculated rootstock, the overall growth in trunk cross-sectional area, and visual rating of disease severity of the commercial scion were used to evaluate rootstock over 79 weeks. Avocado trees on the rootstock selections Thomas, Martin Grande (G75Sa, b, and c), Barr Duke, and D9 demonstrated the highest level of resistance to P. cinnamomi, whereas those on Topa Topa, Borchard, and G6 had the lowest levels. Trees on Duke 7, G1033, and Toro Canyon rootstock were intermediate in their levels of resistance. Among uninoculated rootstock, trees on Thomas and G6 exhibited the greatest growth in trunk cross-sectional area. whereas those on D9 showed the least.