Reduction of Stromatinia cepivora inocula and control of white rot disease in onion and garlic crops by repeated soil applications with sclerotial germination stimulants

Ibrahim E Elshahawy,Ahmed A Morsy,Farid Abd-El-Kareem,Nehal M Saied

doi:10.1016/j.heliyon.2019.e01168

Abstract

The effect of soil-applied Allium crop products on the Stromatinia cepivora viability and the incidence of white rot in subsequent onion and garlic crops were evaluated in this work. The tested products were onion powder, garlic powder, onion oil, garlic oil and Allium waste (onion and garlic) that are described as sclerotial germination stimulants. Under in vitro conditions, data revealed that more than 80% of the sclerotia died in the soil treated with sclerotial germination stimulants. Under greenhouse conditions, soil-artificially infested with sclerotia of S. cepivora and treated with sclerotial germination stimulants for 6-months before cultivation, significantly reduced the incidence of white rot on onion and garlic. Onion oil, garlic oil and Allium waste were the most effective treatments, decreasing disease incidence by 78.6% in onion and 80.0% in garlic. Under field conditions, sclerotial germination stimulants were incorporated into the soil in commercial fields naturally infested with S. cepivora. Two fields were chosen based on differential sclerotial density. Within 6 months after treatment, more than 70% of the sclerotia died in the plots treated with sclerotial germination stimulants. In subsequent onion and garlic crops planted approximately one year after soil treatment, sclerotial germination stimulants were more effective than the control in reducing white rot symptoms coupled with low inoculum density (45.9 sclerotia/kg of soil). Reduction of white rot disease was accompanied by increased of growth and bulbs yield of onion and garlic plants. Despite the efficacy of sclerotial germination stimulants to reduce populations of viable sclerotia in soil with a high inoculum density (594.7 sclerotia/kg of soil), the pathogen caused substantial white rot and yield losses in subsequent onion and garlic crops planted approximately one year after soil treatment.

Highlights

Onion (Allium cepa L.) and garlic (Allium sativum L.) are among the most important vegetable crops in Egypt for local consumption and exportation
White rot disease caused by the soil borne fungus Stromatinia cepivora (Berk.) Whetzel is a serious threat to onions and garlic worldwide and is a major limiting factor in the production of both crops in Egypt (Hunger et al, 2002; Metcalf et al, 2004; Elshahawy et al, 2017a,b,c; Elshahawy et al, 2018a,b)
Few sclerotia can result in great crop losses; for example, economic losses due to white rot can occur at inoculum densities as low as 0.1 sclerotium/L of soil and populations above 10 sclerotia/liter of soil may cause near total crop loss

Summary

Introduction

Onion (Allium cepa L.) and garlic (Allium sativum L.) are among the most important vegetable crops in Egypt for local consumption and exportation. White rot disease caused by the soil borne fungus Stromatinia cepivora (Berk.) Whetzel is a serious threat to onions and garlic worldwide and is a major limiting factor in the production of both crops in Egypt (Hunger et al, 2002; Metcalf et al, 2004; Elshahawy et al, 2017a,b,c; Elshahawy et al, 2018a,b). The severity of white rot is usually related directly to the number of sclerotia in the soil at planting (Crowe et al, 1980). Few sclerotia can result in great crop losses; for example, economic losses due to white rot can occur at inoculum densities as low as 0.1 sclerotium/L of soil and populations above 10 sclerotia/liter of soil may cause near total crop loss. Populations near 1 sclerotium/L of soil may cause crop losses between 30 and 60% (Crowe et al 1980). When a sclerotium germinates and infects an Allium root, mycelia grow upward towards the bulb, eventually destroying it

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