A Streptomyces rhizobacterium with antifungal properties against spadix rot in flamingo flowers

Abstract

Spadix rot is an emerging disease of flamingo flowers (Anthurium andraeanum) that limits their commercial production. The biological control of spadix rot by Streptomyces, a rhizosphere bacterium, is a possible method for controlling this disease instead of the excessive use of chemical fungicides. This research aimed to screen actinobacteria with antifungal ability against Lasiodiplodia theobromae. Five actinobacteria were tested against L. theobromae by dual-culture assays. Streptomyces TH23-7 was the most effective strain against L. theobromae, with a percentage inhibition of 79.04%. TH23-7 caused a change in the morphology of L. theobromae, as observed through a scanning electron microscope. GC/MS analysis of TH23–7 revealed the dominant volatile compound—[2,2-dimethyl-4-(3-methylbut-2-enyl)-6-methylidenecyclohexyl]methanol. Interestingly, Streptomyces TH23-7 is the first species in this genus to produce this volatile compound. The enzyme activities of chitinase and β-1,3-glucanase were investigated by enzyme assays in the cell-free culture filtrate (CF) of TH23-7 cells with activities of 0.025 and 0.66 U/mL, respectively, which were significantly higher than those observed with medium alone (control). An in vivo test showed that the application of TH23-7 spore suspension and cell-free CF limited lesion development in spadix flamingo flowers. The activities of chitinase and β-1,3-glucanase in the TH23-7-inoculated flamingo flowers at 7 days post inoculation were 0.032 and 0.861 U/mL, respectively, which were higher than that in the control (uninoculated plants) and was associated with host resistance to spadix rot. Based on the results of a biochemistry test, morphology and molecular properties, the TH23-7 strain was identified as Streptomyces angustmyceticus. This finding revealed that S. angustmyceticus strain TH23-7 displays antifungal activity against L. theobromae and has the potential to control spadix rot of flamingo flowers.