Microecological mechanisms of red-leaf disease occurrence in Salvia miltiorrhiza Bge.

A comparative study was made on the nutrient content in rhizosphere soil and the micro- flora in rhizosphere soil and on rhizoplane of healthy and red-leaf diseased Salvia miltiorrhiza plants, aimed to approach the microecological mechanisms of red-leaf disease occurrence in S. milt- iorrhiza. The N, P, K, and Mn contents in the diseased plant leaves were significantly lower than those in the healthy plant leaves (P<0. 05). No significant difference was observed in the available P content in the rhizosphere soils of diseased and healthy S. miltiorrhiza, but the available N and K contents were significantly higher (P <0. 05) in the rhizosphere soil of diseased S. miltiorrhiza. These results indicated that the red-leaf disease occurrence in S. miltiorrhiza was related to plant P deficiency, but the lack of P in the plants was not caused by the insufficient soil P supply. As com- pared with those in healthy S. miltiorrhiza rhizosphere, the bacterial number in diseased S. miltior- rhiza rhizosphere soil decreased by 41. 3%, while the fungal and actinomycetes numbers increased by 156. 6% and 189. 5% (P<0. 05), respectively. Similar variations in the numbers of bacteria, fungi, and actinomycetes were observed on diseased S. miltiorrhiza rhizoplane. In the rhizosphere soil and on the rhizoplane of diseased S. miltiorrhiza, the predominant microbial species that might be harmful included six fungi (Fusarium solani, Myrothecium roridum, F. tricinctum, Aspergillus calidoustus, F. oxysporum, and Dothideomycetes sp. ), four actinomycetes (Streptomyces lateritius, Lentzea waywayandensis, S. stelliscabiei and S. collinus), and two bacteria (Bacillus aryabhattai and Piscinibacter aquaticus). These predominant soil microbes likely caused plant P deficiency via negatively affecting the growth of roots and their absorption of soil nutrients. It was suggested that the red-leaf disease occurrence in S. miltiorrhiza was closely related to the plant P deficiency caused by the abnormality of soil microflora in the rhizosphere soil and on the rhizoplane of S. milt- orrhiza. [ABSTRACT FROM AUTHOR]