Migration, colonization and seedling growth of rhizobia with matrine treatment in alfalfa (Medicago sativa L.)

Purpose: The purposes of this study were to determine the effect of matrine on the migration and the colonization dynamics of the two fluorescent-tagged rhizobia in Gannong No.5 alfalfa (Medicago sativa L. Gannong No. 5) tissues, and also to determine the effect of the combination treatments on alfalfa seedlings' growth.Materials and methods: 0, 100, 200, 300 and 400 mg L-1 matrine levels were added into two cyan fluorescent protein (CFP)-tagged rhizobia; Ensifer meliloti LZgn5f (gn5f) and Ensifer meliloti 12531f (12531f), respectively; and drenched the alfalfa root with the inoculants. Then the migration and colonization of the two rhizobia in alfalfa on D7, D14, D21 and D28, and subsequently seedling growth were investigated.Results: The results showed that the optimum matrine level enhanced the colonization of both fluorescent-tagged rhizobia in alfalfa roots and the highest colonization densities of log 6.31 cfu g(-1) and log 5.87 cfu g(-1) were achieved by adding 300 mg L-1 matrine into 12531f and adding 100 mg L-1 matrine into gn5f, respectively. They could migrate to the aerial tissues and most colonize stems through the application of adding 300 mg L-1 matrine into 12531f and 100 mg L-1 matrine into gn5f, respectively. No fluorescent-tagged rhizobia were detected in the control treatment. Alfalfa seedling growth parameters like leaf chlorophyll content, seedling growth rate, root length, seedling biomass and total N percentage also increased the most when 300 mg L-1 matrine was added into 12531f and 100 mg L-1 matrine added into gn5f treatments.Conclusions: Our results suggest that 300 mg L-1 matrine added into 12531f and 100 mg L-1 matrine added into gn5f might be exploited to promote the colonization of rhizobia in alfalfa tissue and positively impact growth and yield, indicating possible benefits for plant cultivation.