Antifungal Activity of Bacillus velezensis CE 100 against Anthracnose Disease (Colletotrichum gloeosporioides) and Growth Promotion of Walnut (Juglans regia L.) Trees

Abstract

Walnut anthracnose caused by <i>Colletotrichum gloeosporioides</i> is a deleterious disease that severely affects the production of walnut (<i>Juglans regia</i> L.). The aim of this study was to assess the antifungal and growth promotion activities of <i>Bacillus velezensis</i> CE 100 as an alternative to chemical use in walnut production. The crude enzyme from <i>B. velezensis</i> CE 100 exhibited chitinase, protease, and β-l,3-glucanase activity and degraded the cell wall of <i>C. gloeosporioides</i>, causing the inhibition of spore germination and mycelial growth by 99.3% and 33.6% at 100 µL/mL, respectively. The field application of <i>B. velezensis</i> 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, <i>B. velezensis</i> 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 <i>B. velezensis</i> 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 <i>B. velezensis</i> CE 100 is an effective biocontrol agent against anthracnose disease and a potential plant growth-promoting bacteria in walnut tree production.