Silicon sources on biochemical responses and Corynespora cassiicola control in cucumber plants

Target spot ( Corynespora cassiicola ) is an important leaf disease of cucumber, and studies on its alternative management are essential for the economic viability of the crop. The objective was to evaluate silicates in controlling target spot and its pathogen, as well as to characterize the biochemical responses of plants. Preventive spraying was performed three times, at weekly intervals, with K 2 SiO 3  + Cu and K 2 SiO 3 , at the concentrations 0, 28, 56, 84 and 112 mg L − 1 Si. Assessments included mycelial growth and germination in vitro ; disease severity; number and diameter of lesions; pathogen sporulation on leaves; activities of the enzymes peroxidase, polyphenol oxidase and β-1,3-glucanase, and leaf levels of phenolic compounds. Silicon had no effect in vitro , nor did it affect lesion diameter and sporulation. The lowest disease severity was observed at five days after inoculation at 56 and 84 mg L − 1 Si, while no control was detected after three and seven days. The lowest number of lesions was found for K 2 SiO 3  + Cu after five days of inoculation and for the concentration 56 mg L − 1 Si after seven days, while for K 2 SiO 3, the number of lesions was lowest at 56 and 112 mg L − 1 Si after five days and at 84 and 112 mg L − 1 Si after seven days. In general, there were no differences between silicates. Enzyme activities and phenolic compound levels were not influenced by Si. Thus, Si had almost no evident effect on target spot control, and no direct effect either on the pathogen or on the biochemical responses of plants.