The Effect of Silicon on Strawberry Plants and its Role in Reducing Infection by Podosphaera aphanis

Abstract

Podosphaera aphanis which causes powdery mildew of strawberry is of economic importance in strawberry production in United Kingdom as it affects yield and fruit quality. Silicon has been shown to reduce the severity of a number of plant diseases. In strawberry, the mechanism of suppression against powdery mildew remains uncertain. Therefore, it has been suggested that supplying silicon would help strawberry plants to absorb silicon and improve resistance against the pathogen. The silicon based wetter Omex SW7 was used and three different concentrations of silicon wetter were applied on the leaves of the strawberry plants (foliar application). Each treatment was applied at three different timings. Enhanced level of silicon was quantified by the Autoclave Induced Digestion (AID) method. Whilst the main study has used the variety Elsanta, other varieties have also been used. It was observed that the weekly application (total 5 sprays) of 3 different concentrations of Omex SW7 on leaves showed significantly (P<0.05) higher silicon concentrations compared to application 3 times in weeks 1, 3 and 5 or twice in weeks 1 and 5. Microscopic observations showed that weekly application of standard, high and very high concentrations of Omex SW7 significantly (P<0.05) increased the number and length of leaf hairs on both the upper and lower surfaces of strawberry leaves. The different varieties of strawberry used showed morphological changes in the leaves with regard to the density and length of leaf hairs. Untreated leaves from Rhapsody had no hairs on the upper leaf surface, but a low density of hairs was observed after treatment with the high concentration of Omex SW7. In this study, Omex SW7, a silicon based wetter was applied to the roots of strawberry plants (root application) and silicon accumulation and physical changes in leaves were assessed. Strawberry variety Elsanta was used in this experiment. Results revealed that weekly application (total 5 applications) of 2 different concentrations (standard and high) of Omex SW7 to roots showed significantly (P<0.05) higher silicon concentrations compared to application 3 times in weeks 1, 3 and 5 or twice in weeks 1 and 5. It was found that the weekly application of two different concentrations of Omex SW7 showed significantly higher (P<0.05) leaf hair numbers and significantly (P<0.05) longer leaf hair length on both the upper and lower surfaces of leaves compared to application 3 times in weeks 1, 3 and 5 or twice in weeks 1 and 5. The effect of foliar application of silicon and potassium carbonate to limit P. aphanis infection was examined in a field trial under polythene tunnel at Wisbech. Treatments were arranged in a randomised block design of 3 replicates. There were a total of 18 plots. There were six treatments and all treatments were applied to the strawberry variety Sonata. Results revealed that application of silicon based wetter Omex SW7 onto the leaf surface does result in accumulation of silicon in the leaves. The application of Omex SW7 has stimulated an increase in the number and length of leaf hairs in strawberry plants. Results showed that germinating ascospores and colonies were present in all plots before the trial was sprayed. Treatments with standard and high Omex SW7 significantly (P<0.05) reduced the number of germinating ascospores and colonies in this trial. However, Potassium carbonate alone gave some reduction in the number of colonies and germinating ascospores. Moreover, potassium carbonate mixed with silicon based wetter Omex SW7 significantly (P<0.05) reduced the number of germinating ascospores and colonies.