Evaluation of the Potential of Agro-Industrial Waste-Based Composts to Control Botrytis Gray Mold and Soilborne Fungal Diseases in Lettuce

Cátia Santos,Piebiep Goufo,Isabel Cortez,Joana Monte,Natália Vilaça,João Fonseca,Henrique Trindade

doi:10.3390/pr9122231

Abstract

Composts are widely used in horticulture as organic amendments to improve the properties of soils. Composts have also been reported to enhance the disease suppressive potential of soils and, therefore, could be used as a strategy for managing plant diseases. The aim of this study was to test the ability of soils amended with four different agro-industrial waste-based composts (chestnut peels and shells, spent coffee grounds, grape marc, and olive leaves) to inhibit the growth and activity of Botrytis cinerea and several soilborne pathogens. First, the capacity of aqueous compost extracts to inhibit the growth of Botrytis cinerea and five soilborne fungi was evaluated in vitro using a broth macrodilution method. Second, lettuce plants were grown on soils amended with composts and inoculated either with B. cinerea or the soilborne fungus Fusarium oxysporum Schlechtendahl isolated from lamb’s lettuce. The determination of minimal inhibitory concentrations indicated that none of the composts inhibited the mycelium growth of the selected fungal pathogens. However, the pathogens did not cause any damage on plants grown on the chestnut- and olive-based composts. Lettuce yields were also highest for plants grown with composts made from chestnut and olive, irrespective of the amount of compost incorporated into soils (5% or 10%, weight basis). The grape-based compost also exhibited a fertilization effect, although the effect was associated with increased Fusarium wilt severity. Both N immobilization and symbiosis with the compost’s microflora were used to explain the pathogenicity of F. oxysporum Schlechtendahl in response to amendment with composts made from grape and coffee wastes. The beneficial effects of the chestnut- and olive-based composts reported in this study could be exploited in strategies aimed at reducing reliance on synthetic pesticides for the control of fungi in lettuce cultivation.

Highlights

A decline in soil fertility and health have been reported worldwide during the last decades; changes in soil quality have been largely attributed to an unreasonable application of agrochemicals in farms [1,2]
These Minimal inhibitory concentrations (MICs) values were within the ranges of those reported by other authors using the broth macrodilution method [38,39]
Bioactive compounds in several cases exhibit their activity via direct interaction with the pathogens: for example, by facilitating perforation of microbial cell walls, altering the activity of an enzyme or the expression of a gene [12]

Summary

Introduction

A decline in soil fertility and health have been reported worldwide during the last decades; changes in soil quality have been largely attributed to an unreasonable application of agrochemicals in farms [1,2]. Several solutions have been proposed to reduce the use of synthetic fertilizers/pesticides, improve soil properties, and create an ecosustainable and efficient agriculture. In this regard, the use of composts has been reported to be advantageous for both recycling of wastes and replenishing of soil fertility [3,4,5]. The final levels of heavy metals in composts, vary, depending on the raw material and composting conditions; as such, composts may introduce heavy metals into soils, on the one hand, and remediate soils by changing the mobility and bioavailability of such contaminants, on the other hand [9]. Most composts are considered safe for application to soils [11,12,13]

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