Using Endophytic Actinomycetes to Induce Leaf Disease Resistance of Strawberry by Tissue Culture Techniques

Abstract

Diagnosis of strawberry leaf diseases, leaf spot and leaf blight were caused by Colletotrichum sp. and Pestalotia sp., respectively. Antagonistic endophytic actinomycetes were studied for controlling the pathogens. A total of 102 isolates were obtained from herbs and Rosaceae after isolations on IMA-2 medium. All of the isolates were used to determine efficiency in controlling of the pathogens using Dual Culture method. Six isolates were selected including ERY2, MET4, POL4, DUC2, PRU2 and ROS7 which showed highly inhibitory effects more than 70% of Percent Inhibition of Radial Growth (PIRG) on both pathogens. The highest percentages inhibition against Colletotrichum sp. and Pestalotia sp. at 92.50% and 87.50% were obtained from the testing with isolates MET4 and PRU2, respectively. Colonization tests in strawberry tissue culture plantlets of the selected isolates were performed in order to induce the leaf diseases resistance of the strawberry tissue culture plantlets. The endophytic actinomycete cell suspensions were inoculated by dropping on the strawberry tissue culture plantlets. Re-isolation for the ability to colonize in strawberry tissue culture plantlets of each selected isolate was done after incubated for 14 days. Percentage of recovery for each isolate from the inoculated plant parts were 96, 56, 70, 100, 100 and 93 percents, respectively. The majority was colonized in leaves. Induction of leaf diseases resistances in vitro were evaluated. The plantlets was colonized with the endophytic actinomycete for a certain period of 21 days before the pathogens were separately inoculated. Disease severity levels were scored comparing with the control treatments, pathogen treated plantlets with non-colonization of the antagonistic isolate. The results revealed that, the antagonistic colonized trials reduced average disease severity levels between 0.44-1.88 which statistically different from control treatment which were 3.78 to 4.00 of disease severity level. The best induced resistance isolate was MET4 for both pathogenic fungi.