Leaf Tip Die- Back of Yucca elephantipes by Lasidiplodia theobromae Pat. and Production of Phytotoxin in Filtrate and Infected Leaves

Abstract

Aims: Leaf tip die-back is a foliar disease of Yucca elephantipes that significantly reduces its aesthetic value. Investigations were carried out on the pathogenicity of the causal organism.  Methodology: A Bioassay of the isolated phytotoxin produced by the pathogen was carried out on yucca, jatropha, cowpea and  maize. The isolated fungus was grown on Czapek- Dox liquid medium and mycelia were harvested by filtration at 7-day intervals for 49 days.  The filtrate was applied on leaves of test plants growing in pots arranged in Complete Randomized Design with four replicates. Results: Lasiodiplodia theobromae was identified as responsible for the leaf tip die- back disease of yucca. Results of the pathogenicity test showed significant (p=.05) increase in the rate of development of necrosis and chlorosis with time. Significant increase in the necrotic and chlorotic lesions (p=.05) were observed among the test plants inoculated with 28, 35, 42, and 49 day old culture filtrate of Lasidioplodia theobromae. Extracts from infected leaves induced necrotic spots surrounded by a chlorotic halo ranging from 0.2- 1.2 cm. Evidence from this study demonstrated that L. theobromae is the causal organism of yucca leaf tip die back. The toxic principle can be isolated from 28 day-old cultures while the extract from infected yucca leaves produced all the symptoms as did the pathogen.