Allelopathic Effect of Glucosinolate-containing Plant Green Manure on Pythium sp. and Total Fungal Population in Soil

Abstract

Two Brassicaceae (Iberis amara L. selection ISCI14 and Rapistrum rugosum All. selection ISCI4) and a Capparidacea (Cleome hassleriana L. selection ISCI2) possessing glucosinolates whose degradation products exhibit high fungitoxic activity in vitro were assayed as biocidal plants in a green manure simulation. The trials were carried out in pots, using aboveground fresh plant tissues incorporated at a realistic field rate into soil naturally infected by Pythium sp. The effect of these plant tissues on total fungal populations and Pythium sp. were compared with Crambe abyssinica H. cv. Mario, a Brassicacea containing glucosinolates whose degradation products exhibit low fungitoxic activity in vitro, and a plant (Helianthus annuus L.) not containing glucosinolates. All green manure treatments induced increases in total fungi over a 10-week period, showing an enhanced microflora level compared with untreated soil. Pythium sp. was strongly suppressed by the C. hassleriana, I. amara, and R. rugosum selections, while sunflower and crambe treatments increased Pythium sp. in a manner similar to that observed for total fungal population. These findings indicate that the green manures assayed suppress Pythium sp. and also induced an increase in total soil microbial activity.