Abstract
Half of the Sphagnum peat lots used as the substrate significantly reduced or inhibited damping-off caused by Alternaria brassicicola Wiltshire, Plenodomus lingam (Tode ex Fr.) Höhnel and Rhizoctonia solani Kühn on cauliflowers. New peat slowed down the spread of Fusarium oxysporum Schl. f. sp. lycopersici (Sacc.) Snyder & Hansen from infected tomato plants to healthy ones and development of the disease on infected seedlings in comparison to disinfected peat. When new peat was added to disinfected peat the suppressing effect was regained. The most common microbes in the peat were bacteria, Streptomyces spp., followed by fungi, Penicillium spp., Mortierella spp. and Trichoderma viride Pers. ex Fr. Strepromyces spp. and T. viride effectively inhibited the growth of a number of soil and seedborne fungi on a nutrient medium. Treating the peat or seeds with T. viride and Streptomyces spp, isolates inhibited or reduced damping-off caused by A. brassicicola, P. lingam and R. solani on cauliflower growing on the peat substrate.
Highlights
Light-coloured Sphagnum fuscum peat is the most common substrate used in greenhouse cultivation in Finland
In the tests carried out in 1975, the peat lots obtained from Leivonmäki and Metsämaa effectively suppressed dampingoff caused by Rhizoctonia solani Kiitin and Plenodomus lingam (Tode ex Fr.) Höhnel on cauliflower in comparison to the other peat lots (Fig. 1)
Capacity of the peat used as the substrate for the tomato plants to suppress fungal pathogens increased so strongly that the incidence of damping-off caused by A. brassicicola was only 13 % and that of damping-off caused by R. solani 30 %
Summary
Light-coloured Sphagnum fuscum peat is the most common substrate used in greenhouse cultivation in Finland. The high level of microbial activity in fertilized and limed peat, as well as the presence of certain chemical compounds such as phenols, are presumably the main reason for the ability of peat to suppress fungal pathogens. It has been known for a long time that mineral soil is capable of suppressing fungal pathogens (BAKER and COOK 1974, BAKER 1981), but the information about peat in this respect is sparse and partly contradictory (WATSON and FORD 1972, CHINN 1967)
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