Yongzhong Li

A two-year field experiment was conducted in Tengchong, Yunnan, to evaluate the effects of tobacco monoculture (TM) and maize relay intercropping with tobacco (TIM) on subsequent tobacco growth and the rhizosphere microenvironment. Results showed that TIM significantly increased plant height by 11.8% and maximum leaf length by 12.4% at the vigorous growth stage without reducing yield. Although leaf chloride content increased and the potassium-to-chloride ratio decreased, both remained within high-quality ranges. Relay-cropped silage maize yielded 4.86 t·hm⁻², adding 1.70 × 10⁴ CNY·hm⁻². TIM reduced nitrogen accumulation in aboveground tobacco and temporarily lowered soil organic matter and available potassium, while increasing acid phosphatase, peroxidase, and urease activities. Soil bacterial α-diversity increased, with enrichment of beneficial genera, including Candidatus Solibacter, Talaromyces, and Penicillium. Metabolomics identified 1043 metabolites, with upregulation of galactinol, N-acetyl-L-tryptophan, and 3-dehydroshikimic acid, enriched in cyanogenic amino acid and cysteine–methionine pathways. PLS-PM and Mantel analyses indicated that relay-cropped maize indirectly regulates nutrient availability via microbial and metabolic pathways. These results show that maize relay intercropping creates a soil “legacy effect,” shifting the system from direct nutrient competition to microbially mediated nutrient buffering.

Viruses deploy numerous strategies to infect plants, typically by forming complexes with another virus, leading to more efficient infection. However, the detailed plant responses to viral infection and the underlying mechanisms of co-infection remain unclear. Previously, we found that tomato spotted wilt orthotospovirus (TSWV) and Hippeastrum chlorotic ringspot orthotospovirus (HCRV) could infect plants in the field by forming a complex. In this study, we found that TSWV infected tobacco (Nicotiana benthamiana) plants in cooperation with HCRV, leading to a more efficient infection rate of both viruses. We then used the in-depth full-length transcriptome to analyze the responses of N. benthamiana to complex infection by TSWV–HCRV (TH). We found that infection with individual TSWV and HCRV triggered plant defense responses, including the jasmonic acid signaling pathway, autophagy, and secondary metabolism. However, TH co-infection could not trigger and even suppress some genes that are involved in these basal resistance responses, suggesting that co-infection is advantageous for the virus and not for the plants. Typically, the TH complex inhibits NbPR1 expression to suppress tobacco resistance. Moreover, the TH complex could alter the expression of microRNAs (miRNAs), especially novel-m0782-3p and miR1992-3p, which directly interact with NbSAM and NbWRKY6 and suppress their expression in tobacco, leading to downregulation of NbPR1 and loss of resistance in tobacco to TSWV and HCRV viruses. Overall, our results elucidated the co-infection mechanisms of TH in tobacco by deploying the miRNA of plants to suppress plant basal resistance and contributed to developing a novel strategy to control crop disease caused by this virus complex.

Boron (B) deficiency is a common phenomenon in most tobacco-planting areas in Yunnan, China. In 2020 and 2022, hydroponic experiments that contained B in a concentration gradient of 0.000, 0.125, 0.250, 0.750, 5.000, 10.000, 20.000, and 40.000 mmol L⁻¹ were conducted to investigate tobacco cultivar K326′s agronomic traits, photosynthetic performance, antioxidant enzymes, and boron and nicotine concentration. As B concentration increased, indices including leaves biomass and net photosynthetic rate (Pn) generally increased first and then decreased, which was in contrast to antioxidant enzymes, including superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT). With increasing B concentration, boron content in tobacco seedlings increased significantly by 24.00~96.44%, while decreased nicotine content by 21.60~82.03%. The highest biomass and photosynthetic performance were obtained within 0.75 and 5.00 mmol L⁻¹ treatments. The results of the sandy soil pot verification experiment were similar to the hydroponic experiment obtained. The beneficial mechanism of moderate B on tobacco seedlings is to maintain cell structure integrity, enhance photosynthetic capability, and promote root growth. Consequently, the optimum B concentration for tobacco seedlings is 0.75~5.00 mmol L⁻¹, and applying 0.25~0.50 B kg hm⁻¹ in soil under available B insufficiency could meet the needs of the growth of flue-cured tobacco.

Leaf samples were collected from four spider lily and tobacco plants with tospovirus‐like symptoms in Yunnan province. The nucleocapsid ORFs of the four isolates were obtained by RT‐PCR, cloning and sequencing of the amplified products. Nucleotide sequences of the obtained amplicons were more than 90% identical to that of Calla lily chlorotic spot virus (CCSV) isolates deposited in the GenBank database. The virus induced systematic leaf necrosis, chlorotic lesions, rugosity and deformation on mechanically inoculated experimental hosts. This is the first report of CCSV in mainland China, and also on spider lily and tobacco.