Aims: To explore the effects of light quality on the physiology and pathogenicity of Colletotrichum acutatum, we analysed the morphological traits, melanin production and virulence of the pathogen under different light wavelengths. Methods and Results: The influence of light wavelength on the mycelial growth and conidial germination of C. acutatum was investigated using red, green, blue and white light sources. Red and green light reduced the mycelial growth in comparison with blue and white light, and dark conditions. The least percentage of conidial germination was observed under blue light, while the germination rate among white, red and green light, as well as in the dark, was insignificant. In comparison with its influence on mycelial growth and conidial germination, light wavelength significantly affected the pathogen's virulence towards hot pepper fruits. The highest disease severity was observed under blue light, which was at least a twofold increase compared with the disease severity under other light conditions. To elucidate the effect of light on the disparity in virulence, scytalone was assayed by HPLC, and scd1 gene expression was examined with real-time PCR. The highest and lowest scytalone production was observed in the cultures incubated under blue (10Á9 mAU) and green light (1Á5 mAU), respectively. Higher scd1 gene expression (~40-fold increase) was observed in cultures incubated under blue and white light in comparison with those incubated in the dark. Conclusions: This study revealed that light affects the growth, colonial morphology and virulence of C. acutatum. The pathogen needs light for its active melanin production and also to attain higher virulence. Significance and Impact of the Study: This is the first report on the effect of light quality on the virulence of C. acutatum. The findings of this study will broaden our knowledge of the influence of light on physiological responses of fungal pathogens.

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Volatile compounds from rhizobacteria are known to elicit and regulate plant growth and defense against various biotic and abiotic stresses. In the present study, we elucidated the biological role of volatiles from Alcaligenes faecalis strain JBCS1294 on the growth performance of Arabidopsis thaliana under salt stress. JBCS1294 volatiles promoted gains in fresh weight and shoot length of Arabidopsis Col-0 under salt stress by 61.5 and 45.8 %, respectively. Hexanedioic acid and butanoic acid were identified as major volatiles emitted from JBCS1294. However, volatiles from JBCS1294 were unable to induce salt tolerance in eir1 and gai-1 mutant lines of A. thaliana, or in auxin and gibberellin inhibitortreated Col-0 plants. On the other hand, a significant increase of growth in cytokinin-, brassinosteroid-, and ethylene-defective mutant lines, or in respective inhibitortreated Col-0, led us to conclude that the auxin and gibberellin pathways are mediators which confer salt tolerance in Arabidopsis upon introduction of JBCS1294 volatiles. Exposure to JBCS1294 volatiles did not alter proline content in gai-1 and gibberellin inhibitor-treated lines. Additionally, AtNHX1, AtHKT1, AtSOS1, AtAVP1, auxin and brassinosteroid pathway genes were upregulated in the roots after exposure of salt-stressed seedlings to JBCS1294 volatiles, suggesting tissue-specific remodeling of gene expression.

Aims: Many physiological and microbial characteristics influence the biocontrol performance of the biological control agents (BCAs) in agricultural fields. To implement effective biocontrol, the contribution of specific genes, mechanisms and traits to the biocontrol performance of BCAs need to be characterized and explored in greater detail. Methods and results: In this study, a transposon (Tn) mutant library using the BCA Pseudomonas fluorescens NBC275 (Pf275) was generated to explore genes and bacterial characteristics involved in antifungal activity and biocontrol performance. Among the Tn mutants, 205 strains showing variations in antifungal activity compared to wild-type (WT) were selected and further analysed for biocontrol efficacy against gray mold in pepper fruits. The genes involved in pyoverdine biosynthesis (pvdI and pvdD) and chitin-binding protein (gbpA) played essential roles in the antifungal activity and biocontrol capacity of Pf275. In addition, a mutation in phlD completely abolished the antifungal activity and significantly suppressed the biocontrol ability of the strain. Genes affecting antifungal activity of Pf275 significantly influenced swimming motility, which was identified as an important trait for the biocontrol ability of the bacterial strain. Conclusions: Overall, our results suggest that antifungal compound production, siderophore biosynthesis and swimming motility synergistically contribute to Pf275 biocontrol performance. The utility of this library was demonstrated by identifying genes for antagonism and biocontrol ability in this BCA strain. The functional roles of many genes identified as contributing to antagonism and in vivo biocontrol activity require further study. Significance and Impact of this Study: Genes contributing to antifungal activity and biocontrol performance of P. fluorescens were identified and highlighted by Tn mutagenesis, which will give insight to improve the biocontrol performance of this BCA.