Unreasonable cultivation methods and management measures have led to widespread obstacles in tobacco continuous cropping in planting areas, resulting in reduced tobacco yield and soil degradation. Therefore, intercropping tobacco with other crops is an effective strategy to improve continuous cropping barriers. In this study, flue-cured tobacco NC102 and conventional planting varieties of Salvia miltiorrhiza were used as materials, and four treatments of flue-cured tobacco monoculture (CK), flue-cured tobacco, and Salvia miltiorrhiza at a ratio of 1:1 (TS11), 2:2 (TS22), and 2:3 (TS23), respectively, were set up to study their effects on soil microorganisms, physical and chemical properties, and yield and quality of flue-cured tobacco. The results showed that intercropping Salvia miltiorrhiza increased the number of soil bacteria and actinomycetes, decreased the number of fungi, and increased the activity of urease and sucrase. The content of available nitrogen and available phosphorus in intercropping Salvia miltiorrhiza soil was significantly higher than that of the flue-cured tobacco monoculture, while the content of available potassium was lower than that of the flue-cured tobacco monoculture. The soil environment was more conducive to the growth of flue-cured tobacco. Compared with the flue-cured tobacco monoculture, the proportion of superior tobacco in intercropping Salvia miltiorrhiza increased by 2.2–3.4%, and the ratio of potassium to chlorine in leaves of different parts of flue-cured tobacco increased by 12.3–75.0%. The content of total sugar and soluble sugar in middle and upper leaves of intercropping flue-cured tobacco was higher than that of the flue-cured tobacco monoculture, which improved the quality of flue-cured tobacco. From the analysis of the chemical composition of tobacco leaves, TS11 (flue-cured tobacco and Salvia miltiorrhiza intercropping row ratio of 1:1) had the best treatment effect, potassium content, total sugar, reducing sugar content, and potassium chloride ratio of flue-cured tobacco were the highest, the chlorine content was the lowest, and the quality was better than other treatments. From the analysis of total output value, the total output value of TS22 (flue-cured tobacco and Salvia miltiorrhiza intercropping row ratio of 2:2) was higher than that of other intercropping treatments. In 2018 and 2019, the total output value increased by 21.3% and 22.4%, respectively, compared with the flue-cured tobacco monoculture. The intercropping advantage was obvious, and the treatment effect was the best.

Cigar tobacco, an economically important cash crop, holds a substantial role within the fiscal framework of the national economy. This crop, however, is characterized by a marked vulnerability to pathogenic bacteria, culminating in consequential financial loss throughout its cultivation phase. Plant growth-promoting rhizobacteria (PGPR), a salient class of advantageous bacterial flora, are recognized for their ability to enhance plant growth, inhibit deleterious pathogens, and synthesize compounds that either have a direct impact on plant morphogenesis or activate otherwise ineffectual soil components. Through these mechanisms, PGPR augments the soil’s nutritional profile, making it more receptive to plant uptake, thus stimulating vegetative growth. The Bacillus subtilis microbial fertilizer, the prime exemplar of PGPR, demonstrates not only a pathogen-suppressive effect but also an induction of the plant’s innate disease resistance mechanism. This bolsters the plant’s resilience to disease fosters a probiotic milieu within the soil, and catalyzes the formation of agglomerate structures, all of which contribute to enhanced soil fertility and moisture retention, increased soil friability, and the facilitation of root expansion. In this study, a controlled pot experiment was conducted to elucidate the mechanism through which inter-root probiotics rehabilitate the soil’s ecosystem and foster crop growth in cigar tobacco seedlings afflicted with root black rot bacteria. Four treatments were instituted, including CK: a blank control (no microbial application); A: probiotic only (Bacillus subtilis microbial fertilizer); B: both pathogenic and probiotic (the Bacillus subtilis microbial fertilizer together with root black rot pathogen); C: pathogenic only (the root black rot pathogen). Our empirical findings delineate that the presence of pathogenic bacteria deteriorates the soil environment, thereby constraining the transmutation of soil nutrients and their subsequent assimilation by plants. This severely impedes the vegetative development of cigar plants. By contrast, the application of a PGPR microbial fertilizer modified the soil microbial community structure, exhibiting an antagonistic interaction with the indigenous pathogenic bacterial species. Relative to the CK treatment, the application of the Bacillus subtilis microbial fertilizer was found to invigorate the catalytic conversion of soil enzymes, incrementing the peroxidase, acid phosphatase, urease, and sucrase activity by 12.98%, 19.55%, 13.57%, and 17.91%, respectively. Meanwhile, it was observed to ameliorate the soil’s physicochemical attributes, enhancing the available content of nitrogen, phosphorus, and potassium by 4.52%, 6.52%, and 15.14%, respectively, along with the augmentation of soil organic matter content by 17.33%. The fortification of soil physicochemical properties and the enrichment of soil fertility, as a result of the PGPR microbial fertilizer application, translated into a robust 57.23% enhancement of root vigor and a 60.47% extension of the root length of cigar tobacco seedlings. These soil amendments subsequently fueled an uptick in the growth parameters of cigar plants, including increases in plant height, stem girth, leaf count, maximal leaf dimensions, and both the fresh and dry weight of cigar tobacco.

Increasing shoot branch numbers of Chrysanthemum morifolium Ramat cv. Hangbaiju (Hangbaiju) is crucial for producing high flower yields. Pot experiments were designed to evaluate the effects of foliar application of 6-benzylaminopurine (6-BA) combined with prohexadione-Ca (Pro-Ca) on the yield and quality of Hangbaiju flowers. Foliar application of 6-BA combined with Pro-Ca typically increased leaf chlorophyll content and decreased leaf soluble sugar and soluble protein contents throughout the floral organ growth phase. At the bud formation phenophase stage (August), the contents of gibberellin (GA), indole-3-acetic acid (IAA), and zeatin (ZA) decreased (except for GA content in the 10 mg L⁻¹ 6-BA combined with 100 mg L⁻¹ Pro-Ca treatment), but abscisic acid (ABA) content increased. The yield of Hangbaiju flowers was found higher in plants treated with foliar application of 6-BA combined with Pro-Ca. Higher yields were found in the 6-BA₅ + Ca₁₀₀ and 6-BA₁₀ + Ca₁₀₀ treatments than in the 6-BA₅ + Ca₅₀ and 6-BA₁₀ + Ca₅₀ treatments, and the highest yield was observed in the 6-Ba₅ + Ca₁₀₀ treatment both in 2019 and 2020. Nutritional indices such as soluble sugar, soluble protein, total amino acid, and water extract increased, and medicinal indices such as flavonoid, total phenolics, chlorogenic acid, cynaroside, and 3,5-dicaffeoyl quinic acid slightly decreased after foliar application of 6-BA combined with Pro-Ca; however, they were all higher than the standards recorded in the Chinese Pharmacopeia. Overall, foliar application of 6-BA combined with Pro-Ca could increase the yield and nutritional quality of Hangbaiju flowers, enhancing its tea quality.