In vitro and in silico studies of salicylic acid on systemic induced resistance against bacterial leaf blight disease and enhancement of crop yield

Salicylic acid (SA) is an effective elicitor to promote plant defenses and growth.  This study aimed to investigate rice (Oryza sativa L.) cv. Khao Dawk Mali 105 treated with salicylic acid (SA)-Ricemate as an enhanced plant protection mechanism against bacterial leaf blight (BLB) disease caused by Xanthomonas oryzae pv. oryzae (Xoo).  Results indicated that the use of SA-Ricemate as a foliar spray at concentrations of more than 100 mg L^–1 can reduce the severity of BLB  by 71%.  SA-Ricemate treatment also increased the hydrogen peroxide (H₂O₂) content of rice leaf tissues over untreated samples by 39–61%.  Malondialdehyde (MDA) in rice leaves treated with SA-Ricemate also showed an increase of 50–65% when comparing to non-treated samples.  The differential development of these defense compounds was faster and distinct when the SA-Ricemate-treated rice was infected with Xoo, indicating plant-induced resistance.  Besides, SA-Ricemate elicitor at a concentration of 50–250 mg L^–1 was correlated with a substantial increase in the accumulation of total chlorophyll content at 2.53–2.73 mg g^–1 of fresh weight which suggests that plant growth is activated by SA-Ricemate.  The catalase- and aldehyde dehydrogenase-binding sites were searched for using the CASTp server, and the findings were compared to the template.  Chemsketch was used to design and optimize SA, which was then docked to the catalase and aldehyde dehydrogenase-binding domains of the enzymes using the GOLD 3.0.1 Software.  SA is shown in several docked conformations with the enzymes catalase and aldehyde dehydrogenase.  All three catalase amino acids (GLN7, VAL27, and GLU38) were discovered to be involved in the creation of a strong hydrogen bond with SA when SA was present.  In this mechanism, the aldehyde dehydrogenase amino acids LYS5, HIS6, and ASP2 were all implicated, and these amino acids created strong hydrogen bonds with SA.  In field conditions, SA-Ricemate significantly reduced disease severity by 78% and the total grain yield was significantly increased which was an increase of plant height, tiller per hill, and panicle in three field trials during Aug–Nov 2017 and 2018.  Therefore, SA-Ricemate can be used as an alternative elicitor on replacing harmful pesticides to control BLB disease with a high potential of increasing rice defenses, growth, and yield components.