Application of leaf extracts of Ambrosia artemisiifolia to control Spilocaea oleagina the causal agent of olive leaf spot disease on olive trees

Abstract

Olive leaf spot caused by the fungus Spilocaea oleagina is one of the most common diseases attacking olive trees all over the world. The disease causes severe premature defoliation of the leaves resulting in severe loses in yield. Control of the disease is achieved by application of copper containing fungicides which might not be always feasible due to negative impacts on human health and environment. The use of plant extract against plant diseases is considered a safe alternative to harmful fungicides. Ambrosia artemisiifolia is an invasive plant with allelopathic properties. The aim of this work is to 2 study the efficacy of A. artemisiifolia leaf extract on inhibition of germination of the olive leaf spot spores isolated from different regions in Palestine. Specific primers 18SF forward and 18SR reverse were used to confirm the identity of S. oleagina isolates. Box PCR using the Box REPAIR primer was used to discriminate between isolates. Aqueous extract (10% w/v) from A.artemisiifolia dried leaves was prepared in water and different concentrations (0.5, 1.0, 1.5, 2.0, 2.5, 5.0 and 10%) were tested against spore germination. The chemical fungicide Fungran was used in combination with the extract to study the efficacy of integrated control of the fungus. The PCR products revealed a 750 bp bands using the 18SF and 18SR specific primers.PCR identification of the isolated fungal stains confirmed that our isolates belong to S. oleagina. BLASTn analysis revealed 92-99% similarities with that the isolated fungal strains were to S. oleagina (Accession #. AF338393.1).The results showed that the extract could inhibit conidial germination at all concentrations. While maximum germination (80.33%) was obtained in control untreated spores, the germination rate of the spores was reduced significantly with increasing plant extract. Complete inhibition of spore germination was recorded in 10% plant extract. The lowest germination percent (2.8%) was achieved at 5% concentration. Interestingly, at low extract concentrations (0.5%), the germination rate did not exceed 50% of the control. The results showed also that combination of fungicide and plant extract (1:1 v/v) reduced the germination rate of spores to less than 5% of the control. Up to our knowledge, this work is the first of its kind that tested the efficacy of A. artemisiifolia leaf extract in combination with fungicides against the olive leaf spot disease. Further experiments are needed to produce a suitable formulation for use against the disease under field conditions.