Morphological and Molecular Identification of Fusarium ipomoeae as the Causative Agent of Leaf Spot Disease in Tobacco from China.

Tobacco (Nicotiana tabacum L.), which creates jobs for 33 million people and contributes two trillion dollars' tax annually, is one of the most important economic plants globally. However, tobacco is seriously threatened by numerous diseases during production. Previously, the field survey of tobacco diseases was conducted in the Guizhou and Guangxi provinces, the two main tobacco-producing areas in China. A serious leaf spot disease, with a 22% to 35% incidence, was observed in farming plants. In order to determine the causal agents, we collected the disease samples and isolated the pathogenic fungi. The pathogen was identified as Fusariumipomoeae, based on the morphological characteristics and phylogenetic analysis. Pathogenicity tests showed that F. ipomoeae could induce tobacco leaf spot and blight. To our knowledge, this is the first report worldwide of F. ipomoeae causing leaf spots and stems on tobacco. Our study reveals the serious consequences of F. ipomoeae on tobacco filed production and provides information for future diagnosis and management of the Fusarium disease.

Tobacco Root Microbial Community Composition Significantly Associated With Root-Knot Nematode Infections: Dynamic Changes in Microbiota and Growth Stage.

The root-knot nematode (RKN) is an important pathogen that affects the growth of many crops. Exploring the interaction of biocontrol bacteria-pathogens-host root microbes is the theoretical basis for improving colonization and controlling the effect of biocontrol bacteria in the rhizosphere. Therefore, 16S and 18S rRNA sequencing technology was used to explore the microbial composition and diversity of tobacco roots (rhizosphere and endophytic) at different growth stages in typical tobacco RKN-infected areas for 2 consecutive years. We observed that RKN infection changed the α-diversity and microbial composition of root microorganisms and drove the transformation of microorganisms from bacteria to fungi. The abundance of Sphingomonas decreased significantly from 18% to less than 3%, while the abundance of Rhizobiaceae increased from 4 to 15% at the early growth stage during the first planting year, and it promoted the proliferation of Chryseobacterium at the late growth stage in rhizosphere microorganisms with the highest abundance of 17%. The overall trend of rhizosphere microorganisms changed in the early growth stage with increasing growth time. The specific results were as follows: (1) Rhizobiaceae and Chryseobacterium increased rapidly after 75 days, became the main abundant bacteria in the rhizosphere microorganisms. (2) The dominant flora in fungi were Fusarium and Setophoma. (3) Comparing the root microbes in 2017 and 2018, RKN infection significantly promoted the proliferation of Pseudomonas and Setophoma in both the rhizosphere and endophytes during the second year of continuous tobacco planting, increasing the relative abundance of Pseudomonas from 2 to 25%. Pseudomonas was determined to play an important role in plant pest control. Finally, a total of 32 strains of growth-promoting bacteria were screened from tobacco rhizosphere bacteria infected with RKN through a combination of 16S rRNA sequencing and life-promoting tests. The results of this research are helpful for analyzing the relationship between RKNs and bacteria in plants, providing reference data for elucidating the pathogenesis of RKNs and new ideas for the biological control of RKNs. GRAPHICAL ABSTRACT.

Identification of five small heat shock protein genes in Spodoptera frugiperda and expression analysis in response to different environmental stressors.

Spodoptera frugiperda (J. E. Smith) is a highly adaptable polyphagous migratory pest in tropical and subtropical regions. Small heat shock proteins (sHsps) are molecular chaperones that play important roles in the adaptation to various environment stressors. The present study aimed to clarify the response mechanisms of S. frugiperda to various environmental stressors. We obtained five S. furcifera sHsp genes (SfsHsp21.3, SfsHsp20, SfsHsp20.1, SfsHsp19.3, and SfsHsp29) via cloning. The putative proteins encoded by these genes contained a typical α-crystallin domain. The expression patterns of these genes during different developmental stages, in various tissues of male and female adults, as well as in response to extreme temperatures and UV-A stress were studied via real-time quantitative polymerase chain reaction. The results showed that the expression levels of all five SfsHsp genes differed among the developmental stages as well as among the different tissues of male and female adults. The expression levels of most SfsHsp genes under extreme temperatures and UV-A-induced stress were significantly upregulated in both male and female adults. In contrast, those of SfsHsp20.1 and SfsHsp19.3 were significantly downregulated under cold stress in male adults. Therefore, the different SfsHsp genes of S. frugiperda play unique regulatory roles during development as well as in response to various environmental stressors.