Pine wilt disease (PWD) caused by Bursaphelenchus xylophilus is a major threat to pine forests worldwide. Induction of resistance is a promising and safe management option that should be investigated in relation to its possible influence on the pine tree ecosystem, including the surrounding microbial communities. In this study, two main resistance-inducing chemical elicitors, methyl salicylic acid (MeSA) and acibenzolar-s-methyl (ASM), were tested for their control efficiency against PWD and their influence on the rhizosphere microbial composition. Foliar treatment of pine seedlings with the chemical elicitors resulted in a reduction in PWD severity, with ASM showing better control efficacy, reaching up to 73% compared to the untreated control. Moreover, bacterial community analysis of the rhizosphere revealed significant changes in several microbial taxa that were present at low relative abundance. In particular, ASM treatment resulted in a significant increase in specific microbial taxa, including members of the Rhodanobacter, Devosia, Bradyrhizobium, Acidibacter, Mesorhizobium, and Hyphomicrobium genera, which are known to play ecological and plant growth-promoting roles. Furthermore, chitinolytic bacteria were shown to be reduced in response to treatment with both MeSA and ASM. Altogether, the present findings demonstrate the occurrence of significant alterations in several ecologically important microbial taxa after treatment with resistance-inducing chemicals. As compared to MeSA treatment, ASM treatment was more effective at suppressing PWD and resulted in more beneficial changes in rhizosphere microbial composition.

Bakanae disease is a fungal disease of rice (Oryza sativa L.) caused by the pathogen Gibberella fujikuroi (also known as Fusarium fujikuroi). This study was carried out to identify novel quantitative trait loci (QTLs) from an indica variety Zenith. We performed a QTL mapping using 180 F_2:9 recombinant inbred lines (RILs) derived from a cross between the resistant variety, Zenith, and the susceptible variety, Ilpum. A primary QTL study using the genotypes and phenotypes of the RILs indicated that the locus qBK1^z conferring bakanae disease resistance from the Zenith was located in a 2.8 Mb region bordered by the two RM (Rice Microsatellite) markers, RM1331 and RM3530 on chromosome 1. The log of odds (LOD) score of qBK1^z was 13.43, accounting for 30.9% of the total phenotypic variation. A finer localization of qBK1^z was delimited at an approximate 730 kb interval in the physical map between Chr01_1435908 (1.43 Mbp) and RM10116 (2.16 Mbp). Introducing qBK1^z or pyramiding with other previously identified QTLs could provide effective genetic control of bakanae disease in rice.

Bakanae disease is an important fungal disease caused by Gibberella fujikuroi. Incidence of rice bakanae disease creates serious problems in the foremost rice growing countries, and no rice variety has been found to be completely resistant to this disease. However, breeding rice varieties resistant to bakanae disease may be a cost-saving solution preferable to the application of fungicides. In this study, we aimed to determine the exact position and the candidate gene for qBK1, a major resistant quantitative trait locus (QTLs) for bakanae disease. The genotypes/phenotypes of recombinants selected from backcrossed recombinant inbred lines of two rice varieties, Shingwang (resistant) and Ilpum (susceptible), indicated that the locus qBK1, conferring resistance to bakanae disease in Shingwang, was delimited to a 35-kb interval delimited by InDel 18 (23.637 Mbp) and InDel 19–14 (23.672 Mbp). Sequence analysis of this 35-kb region revealed four candidate genes, LOC_Os01g41770, LOC_Os01g41780, LOC_Os01g41790, and LOC_Os01g41800. There were many non-synonymous SNPs in LOC_Os01g41770 and the transcript of LOC_Os01g41790 was early terminated in Shingwang, whereas there were no differences in both LOC_Os01g41780 and LOC_Os01g41800 sequences between Ilpum and Shingwang. Expression profiling of the four candidate genes showed the up-regulation of LOC_Os01g41770, LOC_Os01g41780, and LOC_Os01g41790 in Ilpum and of LOC_Os01g41800 in Shingwang after inoculation of G. fujikuroi. Utilization of marker-assisted selection (MAS) with a precise molecular marker on qBK1 could provide an effective tool for breeding rice varieties resistant to bakanae disease. To our knowledge, this is the first report on fine mapping and candidate gene approaches for identifying the gene for qBK1.

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.

The pinewood nematode (PWN) Bursaphelenchus xylophilus causes pine wilt disease, which results in substantial economic and environmental losses across pine forests worldwide. Although systemic acquired resistance (SAR) is effective in controlling PWN, the detailed mechanisms underlying the resistance to PWN are unclear. Here, we treated pine samples with two SAR elicitors, acibenzolar-S-methyl (ASM) and methyl salicylic acid (MeSA) and constructed an in vivo transcriptome of PWN-infected pines under SAR conditions. A total of 252 million clean reads were obtained and mapped onto the reference genome. Compared with untreated pines, 1091 and 1139 genes were differentially upregulated following the ASM and MeSA treatments, respectively. Among these, 650 genes showed co-expression patterns in response to both SAR elicitors. Analysis of these patterns indicated a functional linkage among photorespiration, peroxisome, and glycine metabolism, which may play a protective role against PWN infection-induced oxidative stress. Further, the biosynthesis of flavonoids, known to directly control parasitic nematodes, was commonly upregulated under SAR conditions. The ASM- and MeSA-specific expression patterns revealed functional branches for myricetin and quercetin production in flavonol biosynthesis. This study will enhance the understanding of the dynamic interactions between pine hosts and PWN under SAR conditions.

Rice (Oryzae sativa cv. dongjin) is a cornerstone of global food security; however, Burkholderia glumae BGR1, which is responsible for bacterial panicle blight (BPB), threatens its productive output, with dire consequences for rice and other crops. BPB is primarily caused by toxoflavin, a potent phytotoxin that disrupts plant growth at various developmental stages. Therefore, understanding the mechanisms through which toxoflavin and BPB affect rice plants is critical. Toxoflavin biosynthesis in B. glumae BGR1 relies on the toxABCDE operon, with ToxA playing a central role. In response to this threat, our study explores a metagenome-derived toxoflavin-degrading enzyme, TxeA, as a potential defense mechanism against toxoflavin’s destructive impact. TxeA-induced degradation of toxoflavin represents a potential strategy to mitigate crop damage. We introduce a groundbreaking approach: engineering transgenic rice plants to produce toxoflavin-degrading enzymes. These genetically modified plants, armed with TxeA, hold significant potential for combating toxoflavin-related crop losses. However, removal of toxoflavin, a major virulence factor in B. glumae BGR1, does not completely inhibit virulence. This innovative perspective offers a new shift from pathogen eradication to leveraging transgenic plants’ power, offering a beacon of hope for crop protection and disease management. Our study offers insights into the intricate interplay between toxoflavin, BPB, and TxeA, providing a promising avenue to safeguard rice crops, ensure food security, and potentially enhance the resilience of various agricultural crops to B. glumae BGR1-induced diseases.