Isolation of Endophytic Actinomycetes From Leaves of Tomato Plants and Their Activities Against Bacterial Speck Disease

Abstract

The biological control agents of endophytic actinomycetes was investigated to determine whether control of bacterial speck of tomato, caused by Pseudomonas syringae pv. tomato (Pst). From natural infected tomato leaves showing bacterial speck disease symptoms, six isolates of Pst (Pst1, Pst2, Pst 3, Pst4, Pst5, and Pst DC3000) were isolated, it proved to be pathogenic and able to infect tomato plants under greenhouse condition, causing speck disease symptoms. From the eighty eight isolates of endophytic actinomycetes recovered from healthy tomato leaves plants, nine isolates were selected and tested for their potential inhibition against bacterial tomato speck disease in vitro and in vivo. According to16SrDNA analysis the isolates TR-24 and TR-26 of isolated actinomyces proved to be Streptomyces glaucescens. While the isolates TR-20, TR-32 and TR-34 were identified as Streptomyces graminisoli and isolates TR-25 identified as Streptomyces flavovirens as well as isolates TR-33 and TR-35 were identified as Streptomyces scabies. Finally isolate TR-36 was identified as Streptomyces roseochromogenus. Application of nine isolates of Streptomyces by spraying or drenching methods, all Streptomyces isolates were able to reduce disease severity of bacterial speck compared to infected control. Minutely, the spore suspensions of TR-24 and TR-26 isolates gave the highest reduction of the disease severity. However, the lowest reduction was achieved by isolate TR-35 compared with other Streptomyces isolates.