اتيولوژي بيماري پوسيدگي قارچي ريشه نهال هاي تاغ در نهالستان هاي استان يزد

Etiology of Haloxylon Root Rot in Nurseries of Yazd Province

Saxuals (Haloxylon spp.) is one of the most important xerophytes and one of the best plant for sand stabilization in salty deserts. Insect pests, diseases and environmental factors restrict the reproduction and growth of saxual in nurseries of Yazd province, Iran. Surveys of 1998-2000 showed that damping off and root rot were the most destructive and prevalent diseases in saxual nurseries. In order to determine the causal agents of damping-off and root rot, several samples were taken from nurseries. Infected plants indicated symptoms on root and crown. Isolation were done by planting pieces of discolored root and crown tissues on PDA and WA media and 189 fungi isolates were identified belonging to following six species: Fusarium solani, F. oxysporum, F. culmorum, Pythium aphanidermatum, alternata alternata and Rhizoctonia fragariae. From a total of six species, the pathogenicity of four fungi,i.e. R. fragatae, F. solani, F. oxysporum, P. aphanidermatum were observed in greenhouse. Symptoms of disease appeared on root system of saxual seedlings 21 days after inoculation. The pathogenic fungi were re-isolated from the infected seedlings. The sauxal plant is reported as a new host (Matrix nova) for these fungi: R. fragariae, F. oxysporum., F. solani, and F. culmorum (55%) with 105 isolates were found to have the greatest frequency and distribution among the pathogenic fungi studied. Anastomoses groupe of R. fragariae was identified as AG-G. In this investigation, using fungicide on media to induce teleomorph production in R. fragatae, of the fungus was not produced.