Application of some natural compounds for management of potato late and early blights

Abstract

The effect of natural compounds to control foliar potato late (Phytophthora infestans) and early (Alternaria solani) blights was investigated. The natural compounds were 1.0 and 2.5 mM antioxidants (mannitol, oxalic acid, citric acid and ascorbic acid), 1mM polyamines spermine, ornithine and 1 % antitranspirants (bio-Film, nu-Film and kaolin). Evaluation under artificial infection in greenhouse conditions indicated that all natural compounds were effective against both pathogens. Furthermore, all natural compounds were active under natural infested in field experiments during 2004/ 2005 and 2005/2006 seasons. Twice applications of these compounds at 3-4-leaf growth stage and at 10-leaf growth stage on Sponta cv. of potato plants markedly decreased disease severity, Area Under the Disease Progress Curve (AUDPC) and sporulation of both late blight in winter season and early blight in summer season. Spraying these compounds increased the chlorophyll-a, chlorophyll-b and carotenoid pigment contents in leaves of treated plants compared with untreated control. All tested treatments showed positive effect on plant growth and tuber yield. Different induction of oxidative enzymes as peroxidase, polyphenoloxidase, polyamine oxidase, chitinases and β-1,3-glucanase as well as free and conjugated phenols was obtained as a result of polyamine and antioxidant sprays. The highest effective compound was spermine that decreased the incidence of both diseases, sporulation and gave two- to four-fold increase in oxidative enzyme activities as well as increased tuber yield. Oxalic acid and ascorbic acid gave best results. Kaolin as antitranspirant was also effective in this respect. The study demonstrated that these natural compounds not only inhibit the blight pathogens but also have an effect in improving the growth and tuber yield of potato plants.