Effect of Osmotic and Matric Potentials on Sclerotinia minor and Sclerotinia sclerotiorum Virulence on Peanut

Ahmed Abd-Elmagid,Hassan Melouk,Ho-Jong Ju,Robert Hunger,Mark Payton,Carla Garzón

doi:10.33687/phytopath.004.03.1469

Abstract

The effect of osmotic and matric potentials on mycelial growth, sclerotia production, germination, and virulence of two isolates of Sclerotinia sclerotiorum, and one isolate of S. minor were studied on potato dextrose agar (PDA) media adjusted with KCl, glycerol, or agar. Osmotic potentials created by KCl and glycerol significantly reduced vegetative growth of the three isolates. On matrically adjusted PDA, vegetative growth of the three isolates was not negatively affected by matric stress up to -3.5 MPa. When KCl was the osmoticum, sclerotia number did not follow a consistent pattern. However, sclerotia number decreased when osmotic stress created by glycerol was increased. Matric stress was not a consistent factor affecting sclerotia production by both species. However, the highest levels of matric stress -3.0 and -3.5 MPa significantly reduced sclerotia production by both species. In general, there was a trend toward lower sclerotial germination with increasing osmotic and matric stress. Pathogenicity of S. minor and S. sclerotiorum on the peanut cultivar (Okrun) was reduced by high concentrations of KCl. Mycelia of both species produced at high matric potential -3.5 MPa did not differ in pathogenicity on Okrun compared with mycelia grown on non-amended PDA. In water-stressed-Okrun, induced by polyethylene glycol 8000, the Area under Disease Progress Curve (AUDPC) was significantly decreased. The relevance of these results to the behavior of S. minor and S. sclerotiorum, and their pathogenicity on peanut is discussed.

Highlights

Sclerotinia blight of peanut (Arachis hypogaea L.) caused by the soilborne fungi Sclerotinia minor Jagger and S. sclerotiorum (Lib.) de Bary was first reported in the United States in Virginia in 1971 (Kokalis-Burelle et al 1997)
The objectives of this study were to: 1) study the effect of water potential on the vegetative growth and sclerotia production of S. minor and S. sclerotiorum, 2) determine germination success of sclerotia produced on nutrient media at various water potentials, 3) study the pathogenicity of S. minor and S. sclerotiorum produced on media at various matric and osmotic potentials, and 4) determine the impact of water stress on the infection rate of peanut with S. minor and S. sclerotiorum
Mycelial growth of Sclerotinia isolates on SPDA with various water potentials: In osmotic potential experiments, mycelial growth response of Sclerotinia isolates to was similar for the two osmotica (Table 2)

Summary

Introduction

Sclerotinia blight of peanut (Arachis hypogaea L.) caused by the soilborne fungi Sclerotinia minor Jagger and S. sclerotiorum (Lib.) de Bary was first reported in the United States in Virginia in 1971 (Kokalis-Burelle et al 1997). S. minor and S. sclerotiorum survive in soil mainly by producing sclerotia on infected plants (Wu et al 2008). Most research on the effect of water potential on S. minor and S. sclerotiorum was performed on isolates infecting lettuce under environmental factors significantly different from those found in peanut fields. Mycelial growth and sclerotia production on nutrient medium: Petri dishes containing 15 ml of nutrient medium were each inoculated in the center with a 3-mm -dia mycelial disc taken from the periphery of 2-day-old cultures of S. minor and S. sclerotiorum grown on SPDA. Pathogenicity of mycelia produced on media at various water potentials: Plant inoculations were performed on six-to-eight-weeks old peanut plants (Faske et al, 2006). The effect of water stress on the infection of peanut by S. minor and S. sclerotiorum: Total number of plants in the experiment was 72, representing 9 treatments and 8 replicates. Six-to-eight week old plants were prepared for inoculation as described by Faske et al (2006)

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Conclusion