Abstract
In this study, two bacterial strains, IRP7 and IRP8, were selected to induce resistance against pine wilt disease (PWD). Foliar application with these strains to nematode-inoculated pine seedlings significantly reduced PWD severity. The effect of nematode inoculation and bacterial treatment on the rhizosphere bacterial community was investigated. The results indicated that the rhizosphere of nematode-inoculated seedlings contained a lower relative abundance of beneficial microbes such as Paraburkholderia, Bradyrhizobium, Rhizobacter, Lysobacter, and Caballeronia. Bacterial treatment resulted in significant changes in the microbes that were represented in relatively low relative abundance. Treatment with IRP7 resulted in an increase in the relative abundance of Nitrospirillum, Bacillus, and Luteibacter, which might be useful for protection against infection. Treatment with IRP8 resulted in an increase in the relative abundance of obligate bacterial predators of the Bdellovibrio genus that were previously shown to control several bacterial phytopathogens and may have a role in the management of nematode-carried bacteria. The selected bacteria were identified as Pseudomonas koreensis IRP7 and Lysobacter enzymogenes IRP8 and are suggested as a potential treatment for induced resistance against PWD. To our knowledge, this is the first report on the effect of foliar treatment with resistance-inducing bacteria on the rhizosphere microbiota.
Highlights
Pine wilt disease (PWD) is a major threat to pine forests worldwide, causing huge economic and environmental losses due to widespread infections of pine trees [1]
These strains were stored at −80 ◦ C and cultured in tryptic soy agar (TSA) at 28 ◦ C for 48 h, and single colonies were transferred to tryptic soy broth (TSB) and incubated in a shaking incubator (150 rpm) at 28 ◦ C for 48 h
Consistent with the findings of previous studies, the bacterial strains used in this study significantly reduced PWD symptoms in pine seedlings
Summary
Pine wilt disease (PWD) is a major threat to pine forests worldwide, causing huge economic and environmental losses due to widespread infections of pine trees [1]. The disease is mainly caused by the pine wood nematode (PWN) Bursaphelenchus xylophilus, first reported in Japan in 1971, disease symptoms were observed as early as. In addition to PWN, there is evidence of the important roles of the pine sawyer longhorn Monochamus beetle vector, microbes carried by nematodes, and the associated ophiostomatoid blue stain fungi in disease development, which present PWD as a model for plant pathobiome studies [5]. Microorganisms 2021, 9, 688 spp., produce phytotoxins involved in the development of disease symptoms and browning of tissues [6,7,8,9]. It was reported that inoculation of pine trees with microbe-free axenic nematodes could not induce PWD symptoms [10]. Beneficial plantassociated microbes play key roles in supporting plant health and protecting trees against infection through many approaches including induction of resistance or direct nematocidal activity [11]
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