Abstract
Phytophthora root and crown rot is a plant disease responsible for important economic losses in protected pepper crops. A greenhouse experiment was carried out in a temperate climate region (northern Spain) to assess the effects of repeated biodisinfection after three consecutive crop seasons with different organic amendments (a non-composted mixture of sheep manure and chicken litter, a semicomposted mixture of horse manure and chicken litter, Brassica carinata dehydrated pellets plus Sinapis alba fresh green manure) on disease incidence, crop yield and soil quality. Biodisinfection treatments were found to improve soil water properties through reduction in soil bulk density and increased water infiltration. Biodisinfested soils showed higher values of physicochemical and microbial properties than control (untreated) and plastic-mulched soils. In plots treated with the non-composted or semicomposted mixture, the observed higher levels of microbial activity were strongly related with an increase in soil microbial biomass. Brassica-Sinapis treatment had a weaker effect on soil properties than animal manure-based treatments. However, highest counts of total bacteria, actinomycetes and Pseudomonas spp. were found in Brassica-Sinapis-treated soils. It was concluded that repeated biodisinfection for the control of Phytophthora root and crown rot in protected pepper crops located in temperate climate regions can improve soil quality and suppressiveness, as well as allow for a reduction in the dose of organic amendment needed for biodisinfection. Among the studied organic amendments, the semicomposted amendment was the best option in terms of reduction in disease incidence.
Highlights
In northern Spain, Phytophthora root and crown rot, most frequently caused by the oomycete Phytophthora capsici, is a plant disease responsible for important economic losses in protected pepper crops
A 25% of P. capsici oospores survived after 70 days in sterile moistened soil subjected to controlled conditions of daily cycling of 5 h at 35 °C and 19 h at 30 °C, under a temperature regime that closely reproduced common temperature profiles observed in solarization assays carried out in greenhouses in northern Spain (Etxeberria et al, 2011a,b)
Biodisinfection appears a good alternative to chemical soil disinfection, even when soil temperatures reached during treatments are not high enough to thermally inactivate plant pathogens (Núñez-Zofío et al, 2011)
Summary
In northern Spain, Phytophthora root and crown rot, most frequently caused by the oomycete Phytophthora capsici, is a plant disease responsible for important economic losses in protected pepper crops. Control of this disease in our region has traditionally been carried out by means of pre-plant chemical fumigation and post-plant application of fungicides during crop development. Soil biodisinfection through the application of organic amendments in combination with soil solarization (plastic mulching) (Gamliel et al, 2000) appears promising for the control of soilborne plant pathogens in temperate climate areas, such as northern Spain, where solarization is a priori not a good option (Coelho et al, 1999). Biodisinfection with organic amendments can control soilborne pathogens through: increase in soil temperature, accumulation of toxic volatile compounds (e.g., ammonia) generated during organic matter (OM) decomposition, creation of anaerobic conditions in soil, and increase in soil suppressiveness due to higher levels of soil microbial activity (Gamliel et al, 2000)
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