Effects of combined application of potassium silicate and Streptomyces pctum bio-control agents on growth, yield and quality of strawberry under continuous cropping in greenhouse

Continuous cultivation of strawberry generally leads to stunted growth, yield loss and reduced fruit quality. These problems could be overcome by integrated management approaches such as combined biological, chemical and other control practices. In this study, the effects of single or combined application of potassium silicate (Si) and Streptomyces pctum (Act12) bio-control agents on the growth, yield and quality of strawberry (“Hongtaihou” variety) under continuous cropping in greenhouse conditions were evaluated. The experiment was conducted from Sep. 2008 to Apr. 2009 in greenhouse with continuously cropped strawberry. The results showed that combined Si and Act12 bio-control agents significantly enhanced strawberry health and growth under continuous cropping. The ratio of “I” growth-scale strawberry plant increased by 44.7% and that of “III” growth-scale decreased by 58.3% in the third year of continuous cropping. The death rate of strawberry reduced to almost 0% under Si+Act12 treatment in the fourth year of continuous cropping. Plant fresh weight, root fresh weight, leaf number and leaf fresh weight of strawberry in the third year of continuous cropping significantly (P < 0.05) increased by 73.7%, 71.3%, 11.1% and 38.7%, respectively. Continuous cropping strawberry for three consecutive years under Act12+Si treatment antedated blooming for 10 days compared with the control. The bud number was also significantly (P< 0.05) enhanced by 17.0% under Si+Act12 treatment. Fruit number, single fruit weight and per-plant yield under Si+Act12 treatment increased by 18.6%, 90.6% and 126.2%, respectively. Compared with the control, fruit contents of total soluble solid, sugar-to-acid ratio and vitamin C at full fruit stage increased by 21.7%, 36.2% and 27.0%, respectively. Leaf soluble protein increased by 67.4% and leaf PPO activity related with disease resistance at full fruit stage significantly (P< 0.05) increased by 101.0% under Act12+Si treatment. The combined application of Si+Act12 agents significantly improved single fruit weight and per-plant fruit yield of strawberry in the fourth year of continuous cropping by 194.7% and 359.1%, respectively. These results suggested that the combined application of Si and Act12 bio-control agents not only promoted strawberry growth and yield and quality of fruit, but also enhanced plant disease resistance. It was concluded that the application of Si+Act12 agents had the potential for alleviating the adverse effects of continuous cropping of strawberry in greenhouse conditions.