Identification of three potassium-solubilizing bacteria and their effects on yield and quality of flue-cured tobacco

【Objective】 To explore the effects of different potassium-solubilizing bacteria and their combined bacterial agents on the yield and quality of flue-cured tobacco， which could reveal the potential of potassium-solubilizing bacteria in enhancing the chemical quality of flue-cured tobacco， and provide theoretical basis for their application in flue-cured tobacco production. 【Method】 Combined with morphological observation， physiological， and biochemical and phylogenetic tree construction， three potassium-solubilizing bacteria GUSC5， GUSC13， and GUSC18 isolated from grape rhizosphere soil were identified， and their potassium-solubilizing efficiency was determined by H₂O₂ cooking method. A field plot experiment was conducted using the tobacco variety Yunyan 87 as the test material. With the water treatment as the control， single potassium-solubilizing bacteria GUSC5（T1）， GUSC13（T2）， GUSC18（T3） and composite potassium-solubilizing bacteria GUSC5 and GUSC13（T4）， GUSC5 and GUSC18（T5）， GUSC13 and GUSC18（T6）， GUSC5， GUSC13 and GUSC18（T7）， all mixed in equal proportions were applied for root irrigation. The nutrient contents in the soil around the tobacco roots and the potassium content of the tobacco leaves at the 45^th， 70^th， and 95^th d after transplantation were measured. The economic traits of the cured tobacco leaves were statistically analyzed， and the main chemical component contents of the upper orange two （B2F）， middle orange three （C3F）， and lower orange two （X2F） tobacco leaves were determined. 【Result】 The results showed that the potassium-solubilizing efficiency of GUSC5 was Bacillus velezensis， GUSC13 was Bacillus subtilis， and GUSC18 was Bacillus licheniformis respectively， and the potassium-solubilizing efficiency was 129.28%， 158.95%， and 131.39% respectively. On the 95^th d after transplanting， the content of soil organic matter was significantly increased by the single potassium-solubilizing bacteria treatment （P<0.05， the same below）， and T2，T3， and T4 significantly increased the soil effective phosphorus content. On the 70^th and 95^th d after transplanting， the soil available potassium content was significantly increased by single potassium-solubilizing bacteria and two-pair compound potassium-solubilizing bacteria treatments. At the 45^th， 70^th and 95^th d after transplanting， the content of soil alkali-hydrolyzable nitrogen was significantly increased by T2 and T7. T5 significantly increased the potassium content of flue-cured tobacco and the medium and superior smoke rate at the 95^th d after transplanting was the highest （91.07%）. T7 improved the chemical composition and coordination of B2F grade tobacco leaves； the chemical composition and coordination of C3F grade tobacco leaves treated with T1 reached the demand of superior tobacco leaves， and the chemical composition and coordination of X2F grade tobacco leaves under T5 reached the demand of high-quality tobacco leaves. 【Conclusion】 Both single potassium-solubilizing bacteria treatment and composite potassium-solubilizing bacteria treatment can improve the soil nutrient conditions， as well as enhance the economic traits， chemical composition and coordination of tobacco leaves. Among them， the composite potassium-solubilizing bacteria GUSC5 and GUSC18 treatments have better effects in increasing the potassium content of fresh tobacco leaves， increasing the proportion of medium and superior grade tobacco leaves after curing， and improving the chemical composition and coordination of X2F grade tobacco leaves. The single potassium-solubilizing bacteria GUSC5 treatment has better effects in increasing the output value of tobacco and improving the chemical composition and coordination of C3F grade tobacco leaves.