Abstract

Chile is one of the world's leading walnut producers, but the endoparasitic migratory nematode Pratylenchus vulnus considerably affects walnut plants and decreases crop yield. This study assessed the biological control effects of three selected native rhizobacteria species (Bacillus weihenstephanensis FB25M, Brevibacterium frigoritolerans FB37BR, and Oerskovia turbata FB55) against P. vulnus and its damage to walnut plants. The direct effect of the bacterial filtrates of the three species on population of P. vulnus was evaluated in vitro for 72 h at 20 degrees C and nematode mortality registered every 24 h. The antagonistic effect of a bacterial suspension was measured under greenhouse conditions using 3-month-old potted walnut plants. The growing substrate of the plants was inoculated with a suspension of 1 x 106 colony-forming units (CFU/ml) of each rhizobacteria strain or their mixture, followed by P. vulnus inoculation. As control treatments, two commercial products (chemical: cadusafos; and biological: rhizobacterial mix) and unbacterized plants with and without nematodes were used. Results under in vitro conditions showed that after 72 h exposure of P. vulnus to rhizobacterial filtrates, all bacterial treatments were effective in controlling the nematode (P < 0.01), reaching values between 98 and 100% and exhibiting nematicidal and nemastatic effects. The greenhouse experiments had consistent results; rhizobacteria-treated walnut plants exhibited the maximum biocontrol (mortality) values (67-77%) (P < 0.05). Similarly, rhizobacterial treatments demonstrated the highest root weight compared with the untreated and chemical control treatments (P < 0.05). The evaluated rhizobacterial species showed nematicidal and root growth-promoting effects, which can offer a potential alternative for controlling and protecting walnut plants from P. vulnus.