Endophytes are facultative or obligate symbiotic microorganisms that live in apparently healthy internal plant tissues, without causing disease 17. Among them, the use of plant endophytes has more advantages compared to other microorganisms in plant disease control, therefore it is one of the current hot spots in biological control research 14,15,16,17. Using biological control methods based on microbes or their derivatives has become an important direction in plant disease control. However, these conventional control agents are now recognized to produce adverse residue and environmental problems, as well as having decreased effectiveness due to emerging pesticide resistance 10,12,13. The management of walnut bacterial blight has to date mainly relied on chemical pesticides such as copper-based compounds and streptomycin-dominated antibiotics 10,11. It causes early defoliation, fruit blackening and decay, immature dropping, kernel drying, oil and yield reducing, then serious walnut productivity losing and quality decreasing 9. Walnut bacterial blight negatively affects almost all walnut crown tissues. The disease has sparked international concern and has been added to CABI (Centre for Agriculture and Bioscience International) invasive species list 8. Currently, the disease is the most important bacterial disease affecting walnut production. juglandis ( Xaj) is also spreading around the world 6,7. With the walnut planting area increasing substantially, walnut bacterial blight caused by Xanthomonas arboricola pv. The harvest area and production of China accounting for 33.65% and 43.31%, respectively of global totals. China alone has harvested an area of 390 224 ha with production 1 586 367 tonnes 5. In 2018, the global walnut harvest area was 1159484 ha with production 3 662 507 tonnes. Walnut planting areas have increased sharply over the past several decades, particularly in Asia. Walnuts are widely spread both natively and commercially in Europe, Asia, and part of the United States 4. So walnuts have both nutritional and medicinal benefits 3. Walnut oil may even serve as a helpful natural remedy for hyperlipidemic patients with type 2 diabetes 2. Walnut kernels are composed largely of polyunsaturated fatty acid, alpha-linolenic acid, which gives them anti-atherogenic properties and brain health benefits. It is an important edible nut, wood oil crop, and valuable timber tree species 1. Furthermore, the two strains BME17 and OFE17 can suppress multiple plant fungal pathogens and bacterial pathogens on plates.Įnglish walnut or Persian walnut ( Juglans regia L) belongs to the Juglandaceae family Juglans genus. It turns out that all four strains were identified as Bacillus sp. Subsequently, the four endophytic bacteria were identified by morphology, Gram staining, Microbial Identification System (fatty acid methyl ester analysis), as well as 16S rDNA and gyrB sequencing. These indicated they have good biocontrol potential for walnut bacterial blight. The inhibition ratios of ATE18, BME17, CIE18, and OFE17 against Xaj on plates were 1.5, 1.6, 1.3, and 1.6, respectively.
Through dual-culture method screening, we obtained four antagonistic bacteria, ATE17, BME17, CIE17, and OFE17 which were isolated from Amaranthus tricolor, Bambusa multiplex, Canna indica, and Osmanthus fragrans plants respectively.
To seek biocontrol agents against Xaj, we screened 152 endophytic bacteria isolated from 87 plants. juglandis (Xaj) is the most important bacterial disease in walnut production worldwide. Walnut blight caused by Xanthomonas arboricola pv.
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