Etiology of Avocado Root-Rot in Thailand

Abstract

The symptomatology and morphology of the two causal fungi of Avocado root-rot were studied in detail. Infection was found in all stages of plant development, from the seedling to the mature producing tress. Primary infection was generally through the small absorption roots about 1-3 mm in diameter. In severe case of the disease the main roots and trunk of the tree also exhibited the disease symptoms. Visible symptoms of infected young plants included the yellowing of the leaves, reduction of leaf size, die-back of branches and general wilting of the plant.
From 27 isolates collected from diseased trees in the provinces of Nakhon Ratchasima, Chanthaburi, Tak and Chiang Rai, 26 contained Phytopthora cinnamomi Rands and one P.palmivora.
Koch’s postulate was carried out using seven day old seedlings grown in soil inoculated with various P. cinnamomi isolates, The seedling grown in inoculated soil showed wilting symptoms within 30 - 40 days, with some seedling dying about 10 days after the aerial symptoms were observed. Inoculation of stem components with P.cinnamomi resulted in the development of brown lesions resembling the canker symptoms of known diseased plants.