ABSTRACT
Sustainable food production is necessary to meet the demand of the incessantly growing human population. Phytopathogens pose a major constraint in food production, and the use of conventional fungicides to manage them is under the purview of criticism due to their numerous setbacks. In the present study, essential oil-grafted copper nanoparticles (EGC) were generated, characterized, and evaluated against the maize fungal pathogens, viz., Bipolaris maydis, Rhizoctonia solani f. sp. sasakii, Macrophomina phaseolina, Fusarium verticillioides, and Sclerotium rolfsii. The ED50 for the fungi under study ranged from 43 to 56 µg ml-1, and a significant inhibition was observed at a low dose of 20 µg ml-1 under in vitro conditions. Under net house conditions, seed treatment + foliar spray at 250 and 500 mg L-1 of EGC performed remarkably against maydis leaf blight (MLB), with reduced percent disease index (PDI) by 27.116 and 25.292%, respectively, in two Kharif seasons (May-Sep, 2021, 2022). The activity of enzymatic antioxidants, viz., ß-1, 3-glucanase, PAL, POX, and PPO, and a non-enzymatic antioxidant (total phenolics) was increased in treated maize plants, indicating host defense was triggered. The optimum concentrations of EGC (250 mg L-1 and 500 mg L-1) exhibited improved physiological characteristics such as photosynthetic activity, shoot biomass, plant height, germination percentage, vigor index, and root system traits. However, higher concentrations of 1,000 mg L-1 rendered phytotoxicity, reducing growth, biomass, and copper bioaccumulation to high toxic levels, mainly in the foliar-sprayed maize leaves. In addition, EGC and copper nanoparticles (CuNPs) at 1,000 mg L-1 reduced the absorption and concentration of manganese and zinc indicating a negative correlation between Cu and Mn/Zn. Our study proposes that the CuNPs combined with EO (Clove oil) exhibit astounding synergistic efficacy against maize fungal pathogens and optimized concentrations can be used as an alternative to commercial fungicides without any serious impact on environmental health.
ABSTRACT
Indian mustard (Brassica juncea L.) is an important edible oilseed crop in India. Low productivity is the major concern which is adversely affected by biotic stresses. Alternaria blight (Alternaria brassicae) is one among major diseases that has no resistant cultivar until now. Keeping in view, an experiment was conducted for isolation of Alternaria blight-tolerant mutants in Indian mustard using gamma radiation and EMS mutagens during four consecutive years in Rabi (winter season). Furthermore, the morphologically and economically superior mutants of Brassica juncea were screened artificially at cotyledonary and adult stage against Alternaria blight. Tolerance to Alternaria blight is observed in DRMR-M-163 (11.7%), DRMR-M-158 (13.1%), DRMR-M-174 (13.8%) and DRMR-M-177 (18.6%) with minimum conidia in infected cotyledons. Mutant DRMR-M-178 (19.8%) had the highest radical scavenging activity, while DRMR-M-162 (104.9 mg/g AAE), DRMR-M-169 (96.9) and DRMR-M-161 (96.9) had higher antioxidant capacity that appears to act as defence to pathogen. DRMR-M-168 (8.4%), DRMR-M-173 (8.3), DRMR-M-171 (7.9), DRMR-M-165 (7.4), DRMR-M-175 (7.2) and DRMR-M-172 (6.9) had higher phenol content which may be responsive for resistance, although DRMR-M-161 (192.7 mg/g), DRMR-M-163 (187.7 mg/g), DRMR-M-164 (132.7 mg/g), DRMR-M-167 (149.3 mg/g), DRMR-M-173 (196.0 mg/g) and DRMR-M-178 (192.7 mg/g) mutants are found to contain low levels of total soluble sugar compared with susceptible Rohini (379.3). Based on biochemical parameter's similarity, mutants are grouped in 4 major clusters. Cluster 4 contained significantly different mutant DRMR-M-172. Relative expression of mitogen-activated protein kinase 3 (MAPK3) gene was found highest in DRMR-M-177, DRMR-M-174, DRMR-M-175, DRMR-M-178, DRMR-M-170, DRMR-M-176, DRMR-M-172 and DRMR-M-173 which resulted the better response to AB stress. Based on biochemical analysis, realtime PCR and cluster analysis, DRMR-M-172 mutant appears more tolerant to Alternaria. DRMR-M-178, DRMR-M-167 and DRMR-M-177 mutants seem tolerant and could be utilized for further breeding programme.
