Effect of salicylic acid on cotton yield and induced resistance against biological stress

Abstract

Background and objectives: Biotic stresses affect the yield and yield components of cotton. Alternaria leaf spot (caused by Alternaria alternata) is one of the most common foliar diseases of cotton (Gossypium spp.) and occurs in most cotton-growing regions of the world. Control of the disease through genetic resistance is not possible at present because no cotton cultivars with high levels of resistance to A. alternata are commercially available. In the past decade, the effectiveness of resistance-inducer salts against plant pathogens gives an environmentally friendly option for disease control. Therefore, the impact of salicylic acid on disease control, plant growth and some biochemical constituents of two cotton cultivars (Gossypium hirsutum L.), Golestan and Sahel under A. alternata stress, were evaluated. Materials and methods: Treatments, four levels salicylic acid (0, 0.05, 0.1 and 0.5 mM) and two level inoculation factor (control and pathogen) as a factorial experiment in a completely randomized design with four replications were studied in field condition. 20-day old cotton plants were sprayed with different concentrations of salicylic acid and the treatment were repeated two times at 14 days intervals. Effect of salicylic acid on the differences in growth traits (plant height and number of sympodial branch), yield and disease index in two cotton cultivars (Gossypium hirsutum L.), Golestan and Sahel, were evaluated. Also, changes of total phenol, peroxidase activity and malondialdehyde contents were measured by chlorometric analysis. Results: The results showed that the isolate of A. alternata tested in this experiment were pathogenic to cotton cultivars. Although, Golestan cultivar were more susceptible to alternaria leaf spot than Sahel cultivars. Foliar applications of salicylic acid have been shown to significantly affect yield, disease index, total phenol, peroxidase activity and malondialdehyde contents in two cotton cultivars. 5 mM salicylic acid by significant increasing total phenol contents and peroxidase activity, alleviated the malondialdehyde contents and oxidative stress lead to low disease severity in all cultivars. Yield and oxidative stress affected significantly in Sahel in comparison to Golestan cultivar. The relationship between disease index and yield and leaf phenol accumulation, peroxidase activity and malondialdehyde contents in relation to disease index in the presence of salicylic acid concentrations was described as regresional models. Conclusion: Overall, this research revealed that seedlings treatment with salicylic acid has provided most optimal performance against A. alternata infection and oxidative stress. Although, the effect was different in two cotton cultivars. Hence, using of salicylic acid as a biotechnologic approach be suggested for improve plant to alternaria leaf spot resistance.