PR-proteins Mediated Disease Resistance in Cotton Genotypes against Cotton Leaf Curl Disease Upon Pretreatment with Salicylic Acid and β-aminobutyric Acid

Cotton leaf curl disease, caused by the Geminivirus and transmitted by whitefly, is a major concern for cotton growers. This study observed the effect of resistance-inducing chemicals (RICs); salicylic acid (SA) and β-aminobutyric acid (BABA), on pathogen-related proteins, total soluble protein, disease incidence, and disease index. Both elicitors were applied @ 250 μM using two methods: seed priming (once) and foliar spray (thrice at 5, 19, and 33 days after germination) on three cotton cultivars showing differential responses: F1378 (susceptible), LH2076 (moderately resistant), and FDK124 (resistant). The activities of proteins such as chitinase (PR-3), β-1,3-glucanase (PR-2), peroxidase (PR-9), and total soluble protein were estimated at 7, 21, and 35 days after germination. These resistance-inducing chemicals work via systemic acquired resistance, an eco-safe technique providing long-term protection. Our results revealed that SA and BABA significantly increased PR-proteins’ activities viz. chitinase, β-1,3-glucanase, peroxidase and total soluble protein content compared to the controls. Furthermore, treated plants showed a remarkable reduction in cotton leaf curl disease incidence and index compared to untreated plants. The higher activity of PR-proteins might be responsible for the decreased disease incidence and index in cotton cultivars. In addition, β-1,3-glucanase and chitinase negatively correlated with disease incidence and index, strongly indicating PR-proteins' role in the plant defense mechanism. A comparison between modes of elicitor treatment indicates seed priming to be the most effective as seed treatment given once sustained its effect up to 35 DAG whereas foliar spray in general gave better results. Although both elicitors seemed at par in their effectiveness, economy-wise SA will be the preferred elicitor. Therefore, SA treatment is suggested as an effective and eco-safe method to induce resistance against cotton leaf curl disease.