Xanthomonas spp. cause severe bacterial diseases.  However, effective strategies for prevention and management of these diseases are scarce.  Thus, it is necessary to improve the efficiency of control of diseases caused by Xanthomonas.  In this study, Xanthomonas oryzae pv. oryzae (Xoo), which causes rice bacterial leaf blight, has been studied as a representative.  A transposon insertion library of Xoo, comprising approximately 200,000 individual insertion mutants, was generated.  Transposon sequencing data indicated that the mariner C9 transposase mapped at 35.7–36.4% of all potential insertion sites, revealing 491 essential genes required for the growth of Xoo in rich media.  The results show that, compared to the functions of essential genes of other bacteria, the functions of some essential genes of Xoo are unknown, 25 genes might be dangerous for the Xanthomonas group, and 3 are specific to Xanthomonas.  High-priority candidates for developing broad-spectrum, Xanthomonas-specific, and environment-friendly bactericides were identified in this study.  In addition, this study revealed the possible targets of dioctyldiethylenetriamine using surface plasmon resonance (SPR) in combination with high performance liquid chromatography–mass spectrometry (HPLC–MS).  The study also provided references for the research of some certain bactericides with unknown anti-bacterial mode of action.  In conclusion, this study urged a better understanding of Xanthomonas, provided meaningful data for the management of bacterial leaf blight, and disclosed selected targets of a novel bactericide.

Southern corn leaf blight (SCLB) caused by Cochlibolus heterostrophus, is a widespread foliar disease that has a substantial impact on maize yield in the Huanghuaihai region of China. Pydiflumetofen (Pyd), a new succinate dehydrogenase inhibitor (SDHI), has been found as a promising fungicide for the efficient control of SCLB, however, resistance of C. heterostrophus to Pyd has not been studied well. Here, five Pyd-resistant mutants were generated through fungicide adaptation. Sequence alignment analysis revealed that these mutants primarily mutated in ChSdhB and ChSdhD, with 3 genotypes: ChSdhB^H277Y, ChSdhB^I279T and ChSdhD^H133Y, exhibiting two distinct categories of resistance: high resistance (HR) and moderate resistance (MR), which resistance factors (RF) is 214.22 and 44.33-53.67, respectively. These mutants were more pathogenic than the wild-type parental strains, but there was a significant reduction in mycelial growth rate and sporulation in the resistant mutants, indicating a significant fitness cost associated with resistance to Pyd. In addition, this study revealed a positive cross-resistance between Pyd and another SDHI fungicide cyclobutrifluram. However, no cross-resistance was found between Pyd and other classes of fungicide, including prochloraz, fludioxonil, iprodioneand pyraclostrobin. Homology modeling and molecular docking further confirmed that point mutation of ChSdhB^H277Y, ChSdhB^I279T, and ChSdhD^H133Y could reduce binding affinity between Pyd and its target subunits from −74.07, −74.07, −152.52 kcal mol^-1 to −3.90, −4.95, −9.93 kcal/mol, respectively. These findings not only provided valuable insights for managing SCLB caused by C. heterostrophus, but also enhanced our understanding of molecular mechanism underlying plant pathogen resistance to Pyd.

Rice bakanae disease (RBD) is a devastating plant disease caused by Fusarium fujikuroi. This study aimed to evaluate the potential of cyclobutrifluram, a novel succinate dehydrogenase inhibitor (SDHI), to control RBD, and determine the risk and mechanism of resistance to cyclobutrifluram in F. fujikuroi. In vitro experiments showed that cyclobutrifluram significantly inhibited mycelial growth and spore germination, and altered the morphology of mycelia and conidia. Treatment with cyclobutrifluram significantly decreased mycotoxin production and increased cell membrane permeability in F. fujikuroi. The baseline sensitivity of 72 F. fujikuroi isolates to cyclobutrifluram was determined using mycelial growth and spore germination inhibition assays, which revealed EC₅₀ values of 0.0114 – 0.1304 μg mL^-1 and 0.0012 – 0.016 μg mL^-1, with mean EC₅₀ values of 0.0410 ± 0.0470 μg mL^-1 and 0.0038 ± 0.0015 μg mL^-1, respectively. Pot experiments demonstrated that the protective effect of cyclobutrifluram against F. fujikuroi was more significant than that of phenamacril and azoxystrobin, indicating that cyclobutrifluram is a promising antifungal agent for the control of RBD. Six cyclobutrifluram-resistant mutants of F. fujikuroi were obtained via fungicide adaptation. Moreover, these mutants exhibited weaker fitness than their parental isolate and positive cross-resistance with other SDHI fungicides, including pydiflumetofen and penflufen; however, no cross-resistance was detected with other classes of fungicides, including phenamacril, fludioxonil, prochloraz, or azoxystrobin. These results indicated that the resistance risk of F. fujikuroi to cyclobutrifluram might be moderate. Sequencing analysis revealed that mutations, including H248D in FfSdhB, A83V in FfSdhC₂, and S106F and E166K in FfSdhD, contributed to resistance, which was confirmed by molecular docking and homologous replacement experiments. The results suggest a high potential for cyclobutrifluram to control RBD and a moderate resistance risk of F. fujikuroi to cyclobutrifluram, which are meaningful findings for the scientific application of cyclobutrifluram.

The velvet protein family plays a key factor in coordinating development and secondary metabolism in many pathogenic fungi. However, no previous research has investigated the function of the velvet protein family in Fusarium oxysporum f. sp. Niveum (FON), which causes a highly destructive disease on watermelon. In this study, ∆fovel1 and ∆folae1 deletion mutants and ∆fovel1-C and ∆folae1-C corresponding complementation mutants of FON were confirmed. Meanwhile, effects of phenotype, biochemistry and virulence of the deletion mutants were protected. Compared with the wild-type strains, the ∆fovel1 and ∆folae1 mutants showed different mycelia phenotype, depressed of conidiation and reduced production of bikaverin and fusaric acid. Moreover, their virulence on watermelon plant roots was significant decreased. In addition, all of these alterations in mutants were restored in corresponding complementation strains. Importantly, yeast two hybrid results indicated an interaction relationship between FoVel1 and FoLae1. The results of this study indicated that FoVEL1 and FoLAE1 play critical roles in secondary metabolisms, conidiation, and virulence in FON. These information will deepen our understanding on the genetic and functional roles of the VEL1 and LAE1 in pathogenic fungi.