Proc. of Second World Avocado Congress 1992 p. 141

In Vitro Screening of Tolerance to Phytophthora cinnamomi in Avocado Rootstocks

T. Botha

Westfalia Estate, P.O. Box 14, Duivelskloff 0835, Republic of South Africa

 

F.C. Wehner and J.M. Kotzé

Department of Microbiology and Plant Pathology, University of Pretoria, Pretoria 0001, Republic of South Africa

Abstract. New, existing and modified techniques were compared quantitatively for the in vitro screening of tolerance to Phytophthora cinnamomi in four avocado root-stock selections. Attraction of P. cinnamomi zoospores by exudates from excised avocado roots diffusing through a dialysis membrane accurately reflected known tolerance or susceptibility and eliminated the need for laborious processing of roots for microscopy. Similarly, lesion development on detached roots after inoculation with the pathogen correlated well with field performance of the various rootstocks, yet the technique was simple to perform. Suspending detached roots on glass rods in the culture medium reduced contamination and improved reliability of the root lesion technique.