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Abstract
Induction of resistance to downy mildew caused by Plasmopara halstedii in sunflower was studied after treatment with β-amino butyric acid (BABA). Treatment of sunflower seeds with 50 mM BABA resulted in decreased disease severity and offered 47 and 50% protection under greenhouse and field conditions, respectively. The induction of resistance to P. halstedii by BABA was accompanied by the accumulation of various host defense related enzymes in susceptible sunflower seedlings. Enhanced activation of catalase, phenylalanine ammonia-lyase (PAL), chitinase (Pr3), peroxidase (POX), and polyphenol oxidase (PPO) was evident at 6 h, 9 h, 12 h, 12 h and 12 h post-inoculation, respectively in sunflower seedlings raised from seeds treated with BABA. Northern hybridisation analysis revealed increased levels of transcripts for five known defense-response genes, viz chalcone synthase, Pr-1a, peroxidase, β-1,3-glucanase and chitinase in these seedlings. This enhanced and early activation of defense related responses in the susceptible cultivar after treatment with BABA was comparable to that in the resistant cultivar. The results indicate that BABA-induced resistance against P. halstedii in sunflower is mediated through enhanced expression of genes for defense related proteins.