In Vitro and Greenhouse Evaluation for Resistance to Early Blight of Potato Isolated from Alternaria alternata

Early blight of potato is caused by the fungus Alternaria alternata, one of the most destructive foliar diseases, especially in hot climates under irrigation. It usually causes leaf spots and tuber blight on potatoes. Potato resistance to early blight is a quantitative trait, and obtaining successful resistant cultivars is not simple. Some studies have shown that resistance to early blight is age-related: early-maturing cultivars are more susceptible than late-maturing cultivars.

In this study, the virus free potato seedlings were obtained from the National Plant Gene Bank of Iran during 2008-2009 and were inoculated in vitro with a culture filtrate of A. alternate. Seven cultivars (Ells, Picasso, Maradona, Marfona, Delta, Casmos and Desiree) were conducted that were propagated through nodal cutting every three month and kept in growth chamber at 25˚C ± 1˚C light with a period of 16 h light and 8 h dark. The leaflets received a 1000-μl droplet of the A. alternata culture filtrate and were inoculated by spraying with a suspension of 10⁵ conidia/ml of isolate A. alternata in the greenhouse method. And disease severity assessments were taken every 2 days beginning at 3 day until 21 day. The experimental design was a completely randomized design (CRD) with three replications and seven genotypes, which had been infected with the two leaves of each iteration. In vitro selection of fungal isolates of A. alternata, chlorotic and necrotic symptoms began 1 to 2 days after inoculation, but the assessment of greenhouse symptoms appeared 6-10 days after inoculation. The area under the disease progress curve values were presented by analysis of variance (ANOVA), and they were compared using Duncan’s test (a = 0.01%).

In both methods, there was a significant difference between the potato genotypes (P < 0.01). For In vitro selection and evaluation greenhouse, the results showed that Casmos was the most sensitive cultivar and Marfona was the most tolerance cultivar.

Article by Hamid Reza Mirkarimi, et al, from Iran.

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