WILTING DISEASE OF YOUNG AVOCADO TREES CAUSED BY Neonectria radicicola IN ISRAEL

Blighting and wilting of young avocado (Persea americana Mill.) trees accompanied by root rot were observed in the last three years in a few locations in Israel. Symptomatic trees were mostly vars. Pinkerton and Ardit, 2 – 5 years after planting in the orchard, heavily loaded with fruit. Isolations revealed a Cylindrocarpon sp. A survey was initiated in avocado nurseries for fungi, and Cylindrocarpon sp. was isolated from the roots of 10%-100% of the seedlings in all the surveyed nurseries, although the seedlings showed no wilting symptoms. Fungicides efficacy experiments in seedlings showed good control results only with Prochloraz formulations "Merag" and Sportak". Perithecia of the fungus were observed in the lab, first on roots and later on PDA medium. Single-conidium and single-ascospore isolates were obtained for morphological identification of this Cylindrocarpon / Neonectria species. Sequences of the small subunit mitochondrial rDNA, β-tubulin, and ITS region revealed homologies of 99.8%, 100%, and 94% respectively with Neonectria radicicola / Cylindrocarpon destructans complex. N. radicicola / C. destructans is a known agent of root rot disease in nurseries of raspberry, grapevine, ginseng and forest trees. This is the first report of Neonectria radicicola in Persea americana. The questions to discuss are: is this a new soil-borne pathogen in Israel, or an indigenous one. Have changes in avocado horticulture management, (water salinity, fertigation, heavy yield on young trees etc') increased the pathogenicity of the fungus?