Studies on interaction of varieties, irrigation regimes and planting types on early blight disease of potato

The early blight disease caused by Alternaria alternata and A. solani with dominancy of A. alternata is one of the important diseases in the potato growing areas of Iran causing economic losses every year. Experiments were conducted during 2008-2009 to study the interactions of potato varieties، irrigation and planting types on the incidence and the severity of disease in Freidan area، Isfahan province، in a split split plot design on a susceptible potato variety، Agria. The severity of the early blight disease was assessed in 6 classes of infections and/or scoring scales: 0، 10، 25، 50، 75 and 100 at two growth stages; before and after flowering. The infection severity percentages and scoring scale of the disease were determined. The results indicated that، almost all the three factors had a very highly significant effect on the incidence and the severity of the early blight disease. The tested varieties showed significantly different reactions to the disease where disease severity in varieties Marfona and Agria was 12. 99 and 28. 31%، respectively. Also، Sprinkler and tip irrigation with 14. 48 and 16. 59% disease severity were significantly different general irrigation (30. 21%). No significant effect was observed between planting types since disease severity was 20. 61 and 20. 71% in single row and double row planting، respectively. The interactions of variety × irrigation، planting types × irrigation، and year had significant effect in disease severity (25. 74، 5. 62 and 13. 53% respectively). The interactions of the above factors also showed a very highly significant effect. The average yield of Agria and Marfona was 24. 03 and 23. 13 t/ha، respectively. Our results indicated that the severity and development of disease was more in general irrigation than in sprinkler and tip irrigation. The results indicate that resistant varieties can significantly reduce disease development and severity. However، a single-row and double-row planting had no significant effect on disease reduction.