Utilization of chlorination and soilless media for management of Pythium aphanidermatum (Edson) Fitzp. in greenhouse production of Capsicum annuum L. in a closed soilless system

Water sanitation by chlorination was evaluated in growth chamber and greenhouse studies for management of Pythium aphanidermatum (Edson) Fitzp. in recycled effluent used for production of ‘Legionnaire’ bell pepper (Capsicum annum L.) in pine bark, sand, and perlite. Results of growth chamber studies supported that chlorination (source: 5.25% sodium hypochlorite) rates as low as 2 mg/L resulted in reduced plant growth in all media. Shoot growth and plant height were less affected in plants growing in pine bark relative to plants growing in sand. This was likely a result of the organic pine bark reacting with the chlorine. In greenhouse experiments conducted in spring and summer of 2007, plant growth such as height and shoot and root fresh weights decreased linearly as chlorination rate of nutrient solution increased from 0 to 4 ppm. In greenhouse experiments in fall 2007 and spring 2008, plants chlorinated and grown in pine bark had greater height and shoot fresh weight relative to those chlorinated and grown in perlite. Effects of inoculation were similar to the previous studies in that reduction in growth variables such as plant height and shoot and root fresh weights were a result of P. aphanidermatum infection. In spring 2007, the marketable number of fruit per square meter decreased with increasing chlorine concentration. In fall 2007, plants grown in pine bark that were chlorinated had greater marketable fruit weight relative to plants grown in perlite, treated by chlorination. The pathogen was isolated from roots in chlorinated and nonchlorinated plots indicating the pathogen was not eliminated via the chlorination treatment in addition to causing reduced yield. In spring 2008, plants grown in pine bark had greater marketable fruit numbers and weight relative to plants grown in perlite. Overall the pine bark would be the better choice for soilless media which can reduce phytotoxic effects from chlorination as compared to inorganic sand and perlite. ‘Legionnaire’ peppers are sensitive to chlorination rates as low as 2 mg/L and the use of an organic media such as pine bark can be beneficial in limiting phytotoxic effects and also has some pathogen suppressive characteristics.