Abstract
Walnut anthracnose caused by Colletotrichum gloeosporioides is a deleterious disease that severely affects the production of walnut (Juglans regia L.). The aim of this study was to assess the antifungal and growth promotion activities of Bacillus velezensis CE 100 as an alternative to chemical use in walnut production. The crude enzyme from B. velezensis CE 100 exhibited chitinase, protease, and β-l,3-glucanase activity and degraded the cell wall of C. gloeosporioides, causing the inhibition of spore germination and mycelial growth by 99.3% and 33.6% at 100 µL/mL, respectively. The field application of B. velezensis CE 100 culture broth resulted in a 1.3-fold and 6.9-fold decrease in anthracnose disease severity compared to the conventional and control groups, respectively. Moreover, B. velezensis CE 100 produced indole-3-acetic acid (up to 1.4 µg/mL) and exhibited the potential for ammonium production and phosphate solubilization to enhance the availability of essential nutrients. Thus, field inoculation of B. velezensis CE 100 improved walnut root development, increased nutrient uptake, enhanced chlorophyll content, and consequently improved total biomass by 1.5-fold and 2.0-fold compared to the conventional and control groups, respectively. These results demonstrate that B. velezensis CE 100 is an effective biocontrol agent against anthracnose disease and a potential plant growth-promoting bacteria in walnut tree production.
Highlights
Walnut (Juglans regia L.) is the oldest cultivated fruit tree in Asia and has gained popularity around the world for edible oil production [1]
The cell growth of B. velezensis CE 100 increased to a peak value of 4.4 × 107 colonyforming units (CFU)/mL after 7 days of incubation and declined (Figure 2)
Chitinase activity in the cell-free culture broth of B. velezensis CE 100 increased in two phases, with an initial increase 3 days after inoculation followed by a slight decline 5 days after inoculation
Summary
Walnut (Juglans regia L.) is the oldest cultivated fruit tree in Asia and has gained popularity around the world for edible oil production [1]. Besides the production of edible oil, walnuts are consumed as dry fruits and are valuable raw materials for confectionary, as well as bakery products, due to their health benefits [3,4]. Walnut trees are among the most valuable sources of high-quality wood, for multiple uses, and products, such as veneers, furniture and interior designs, carving, gun stocks, and fore-ends [5]. Walnut production can be adversely affected by diseases caused by phytopathogenic fungi, which reduce their yield and marketability by limiting tree growth and reducing the quality and edible size of nuts as well as their organoleptic properties [7,8]
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