Abstract
Present study investigated the development and suppression of grapevine black foot using a highly virulent strain of Ilyonectria radicicola during 2010-2012 after its widespread outbreak in Duhok - Iraq since 2008. Inoculated roots showed distinctive symptoms of sunken necrotic lesions with internal black streaking of rootstocks. Production of mycelial mass (in vitro) was higher at pH 5.0 resulting in 57% severity of foot rot compared to 46.16% at pH 7.0. In general, Kamali cv. was the most susceptible cultivar with 59.29% of stubby root growth affected compared to 53.32% and 40.83% on Rashmew and Taefi cvs. respectively. Wounding roots of a susceptible cultivar developed the conspicuous symptoms of black foot rot with a severity of 90%. Increasing the conidial inoculum was essential for severe infection development to more than 62%, whereas interaction between inoculation and wounding of roots increased lesion severity to 80.09%. However, acidic pH significantly enhanced disease progression on inoculated vine cuttings to 84.41% compared to 40% at neutral pH. Unfortunately, inoculum of Ilyonectria radicicola was not suppressed significantly even with fungicide application and continued its damage on Rashmew cv. Resulting in disease severity of 23.70% . More than 25% of the inoculated vines grown in amendments of Trichoderma harzianum and farmyard manures were infected compared to 14.80% and 20.73% of the non-inoculated. Exclusion of fungal inoculum improved the plant vigours as measured by dry weight and shoot growth, whereas significant stimulation of root growth were evidenced in the amended treatments particularly those with farmyard manures and fungicides.
Highlights
Investigation of affected rootstock nurseries and older grapevines (2-8 years old) in Iraq revealed black discoloration and brown to dark streaks mainly at the basal end (Black foot) (Haleem, 2010; Haleem et al, 2012) and the diseases was caused by Ilyonectria radicicola
Tissue sections from border between healthy and rotted tissues were surface sterilized by immersion in 1% NaOCl for 2min. followed by two rinses in sterile water, blotted on sterile filter paper and transformed to Potato Dextrose Agar (PDA) with 0.25 mg/ml chloramphenicol
Spore suspension was prepared from one month old culture grown on PDA at 25°C, by flooding the agar surface with 10 ml of sterile distilled water (SDW) and scraping with a spatula
Summary
Investigation of affected rootstock nurseries and older grapevines (2-8 years old) in Iraq revealed black discoloration and brown to dark streaks mainly at the basal end (Black foot) (Haleem, 2010; Haleem et al, 2012) and the diseases was caused by Ilyonectria radicicola The symptoms included a reduction in the root biomass (plant vigour) with small-sized trunks, shortened internodes, sparse foliage and small leaves with interveinal chlorosis and necrosis (Rego et al, 2000; Halleen et al, 2006). Typical black foot symptoms on rotted cuttings including sunken, necrotic root lesions, vascular black discoloration and necrosis developed within two months (Rego et al, 2001) with reduction in plant vigor (Hallen et al, 2004).
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