Biological control of Peacock spot disease caused by Spilocaea oleagina on Olive using bacteria.

Abstract

The olive leaf spot disease caused by the fungus Spilocaea oleagina (Cast.) Hughes (syn. Cycloconium oleagina) is one of the most destructive diseases on olive trees causing losses that may reach 20% of the yield. The disease is controlled by the application of chemical fungicides which is not always feasible in providing proper protection against the pathogen. In this work we report the efficacy of Pseudomonas fluorescenc isolate ORS3 and Bascillus atrophaeus isolate Bat in controlling the disease under field conditions. An Olive field in, Tulkarm governorate, Palestine was selected. The olive trees were 5-10 years old and were highly infected with the olive leaf spot. Trees were sprayed with bacteria formulated in oil. Control trees were sprayed with water. For evaluation of bacterial efficacy against the disease, olive leaves were collected before and after application of the bacteria. Germination of conidia latent infection and severity were determined. In addition to that, bacterial viability was assessed. Results of the work revealed that the bacteria were able to inhibit conidial germination of the fungus. The percent of reduction in conidial germination (85.8 and 70.2%) in the presence of P. fluorescenc isolate ORS and B. atrophaeus isolate Bat, respectively was significantly lower than that in the control or in leaves sprayed with 10% oil (69.1 and 56.1%, respectively). After two weeks of spraying, the percent of latent infectoin (figure 4) was significantly (p<0.05) lower on leaves sprayed with P. fluorescenc isolate ORS3 and B. atrophaeus isolate BAT (5.1 and 3.8% latent infection, respectively). However, bacterial shelf life on the surface of olive leaves was reduced after three days of spraying (i.e no bacteria were re-isolated). The results indicated that the bacteria can be used for control of the leaf spot disease. Further studies are required to evaluate the efficacy of the bacteria under different environmental conditions.