EVALUATION OF WEST INDIAN AVOCADO SEEDLINGS'S TOLERANCE - RESISTANCE TO PHYTOPHTH0RA CINNAMOMI RANDS COMPARED WITH CLONAL RESISTANT ROOTSTOCKS DUKE 7, THOMAS, AND TORO CANYON, UNDER FIELD CONDITIONS.

The aim of this research was to find West Indian avocado (Persea americana Mill.) germplasm resistant to Phytophthora cinnamomi Rands, as the West Indian race (WI) is well adapted to the Canary Islands conditions. The trial field selected was an old-established avocado plantation with a high degree of P. cinnamomi infection. After planting, symptom expressions of the clonal resistant rootstocks Thomas (TH), Duke 7 (D7), and Toro Canyon (TCY) were compared with those of WI seedlings and seedlings of Persea indica (L.) K. Spreng wild material (PI), the latter generally used as a susceptible tester for P. cinnamomi. A randomized block design was used for all plantings and the trial was carried out during three years. The recorded data include: height, trunk diameter, disease severity, and surviving plants. The results indicate that D7 and TH are, in our conditions, quite resistant to P. cinnamomi but TCY is not. Most of the PI seedlings died, but the surviving plants presented a high degree of resistance. Unselected WI seedlings seem to have a considerable natural resistance to P. cinnamomi when compared with the clonal rootstocks. This could be of great interest for commercial avocado plantations in countries where the WI race is the preferred rootstock.