Epidemiological Characterization of Lettuce Drop and Biophysical Features of the Host Identify Soft Stem as a Susceptibility Factor to Sclerotinia minor

The soilborne fungus Sclerotinia minor was not known to produce sclerotia in the stems of infected and uncollapsed Lactuca standing intact until our observation in a greenhouse in 2017. We investigated lettuce–environment–S. minor interactions in two tolerant and four susceptible Lactuca genotypes to determine putative risk factors and targets for disease control. Symptomatological, pathophysiological, developmental, basal stem biophysical, and microclimate responses (27 variables) of the genotypes were determined under field and/or greenhouse conditions. Distinct patterns of infection responses were observed between modern cultivars and their primitive/wild relatives. The modern cultivars were susceptible to rapid basal stem and root degradations by S. minor. The oil-seed lettuce PI 251246 and the wild L. serriola 11-G99 were resilient to degradations and significantly deterred mycelium emergence and symptom development, but sclerotia formed to a significantly higher height in their stems. Photosynthetic efficiency declined rapidly within 1-day postinoculation (dpi) in susceptible plants but remained intact ~5–6 dpi in the tolerant 11-G99. Stomatal conductance spiked rapidly in 11-G99 plants within 1–3 dpi, coinciding with the emergence of fungal mycelia at the crown. A strong negative correlation detected between basal stem degradation severity/collapse and stem mechanical strength indicated that stem strength-mediated genetic factors determine the outcome of Sclerotinia infections of the host. Soft stem is a prominent lettuce drop susceptibility factor that could be targeted in resistance breeding. It also provides the prelude for the analysis of the biological basis of plant architecture-mediated resistance to Sclerotinia spp. in lettuce and other hosts.

Effect of low temperature culture on the biological characteristics and aggressiveness of Sclerotinia sclerotiorum and Sclerotinia minor

Sunflower White Mold caused by Sclerotinia sclerotiorum and Sclerotinia minor is a devastating disease worldwide. To investigate the effect of low temperature (4 °C) on biological characteristics and aggressiveness of isolates of the two species, which were collected from the same field in Baiyinchagan, Inner Mongolia, their mycelial growth rate, oxalic acid secretion level and polygalacturonase activity were compared under normal culture temperature (23 °C) and low temperature (4 °C). Aggressiveness was also evaluated on detached leaves by inoculating the isolates produced in both temperatures. The results suggested that culture of isolates at 4 °C not only promoted mycelial growth, but also enhanced secretion of oxalic acid and polygalacturonase activity of both S. sclerotiorum and S. minor isolates compared to that cultured at 23 °C. Additionally, the corresponding aggressiveness of tested isolates of the two species also increased after culture at 4 °C. However, S. sclerotiorum always showed faster mycelial growth, higher oxalic acid levels and greater polygalacturonase activity than S. minor at both 23 °C and 4 °C, indicating that S. sclerotiorum is generally the more aggressive species than S. minor.

Author Correction: Dimethyl disulfide exerts antifungal activity against Sclerotinia minor by damaging its membrane and induces systemic resistance in host plants

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Dimethyl disulfide exerts antifungal activity against Sclerotinia minor by damaging its membrane and induces systemic resistance in host plants

Microbial volatile compounds (MVCs) significantly influence the growth of plants and phytopathogens. However, the practical application of MVCs at the field level is limited by the fact that the concentrations at which these compounds antagonize the pathogens are often toxic for the plants. In this study, we investigated the effect of dimethyl disulfide (DMDS), one of the MVCs produced by microorganisms, on the fitness of tomato plants and its fungicidal potential against a fungal phytopathogen, Sclerotinia minor. DMDS showed strong fungicidal and plant growth promoting activities with regard to the inhibition of mycelial growth, sclerotia formation, and germination, and reduction of disease symptoms in tomato plants infected with S. minor. DMDS exposure significantly upregulated the expression of genes related to growth and defense against the pathogen in tomato. Especially, the overexpression of PR1 and PR5 suggested the involvement of the salicylic acid pathway in the induction of systemic resistance. Several morphological and ultrastructural changes were observed in the cell membrane of S. minor and the expression of ergosterol biosynthesis gene was significantly downregulated, suggesting that DMDS damaged the membrane, thereby affecting the growth and pathogenicity of the fungus. In conclusion, the tripartite interaction studies among pathogenic fungus, DMDS, and tomato revealed that DMDS played roles in antagonizing pathogen as well as improving the growth and disease resistance of tomato. Our findings provide new insights into the potential of volatile DMDS as an effective tool against sclerotial rot disease.

Screening of the Argentinean INTA peanut core collection with a molecular marker associated with resistance to Sclerotinia minor Jaggar

ABSTRACT Cultivated peanut, the third most important oilseed in the world, is consistently threatened by various diseases and pests. Sclerotinia minor Jagger (S. minor), the causal agent of Sclerotinia blight, is a major threat to peanut production in many countries and can reduce yield by up to 50% in severely infested fields. Host plant resistance will provide the most effective solution to managing Sclerotinia blight, but limited sources of resistance to the disease are available for use in breeding programs. Peanut germplasm collections are available for exploration and identification of new sources of resistance, but traditionally the process is lengthy, requiring years of field testing before those potential sources can be identified. Molecular markers associated with phenotypic traits can speed up the screening of germplasm accessions. The objective of this study was to genotype the peanut core collection of the Instituto Nacional de Tecnología Agropecuaria (INTA) Manfredi, Argentina, with a molecular marker associated with Sclerotinia blight resistance. One hundred and fifty-four (154) accessions from the collection were available and genotyped using the Simple Sequence Repeat (SSR) marker. Accessions from each botanical variety type represented in the core collection were identified as new potential sources of resistance and targeted for further evaluation in field tests for Sclerotinia blight resistance.

Effect of biocontrol and promotion of peanut growth by inoculating Trichoderma harzianum and Bacillus subtilis under controlled conditions and field

<p>La producción de maní en Argentina sufre severas fluctuaciones debido principalmente al daño provocado por enfermedades fúngicas; su control con productos sintéticos es ineficiente, siendo el control biológico una alternativa de manejo que contribuiría a la sustentabilidad del sistema de producción. El objetivo de este estudio fue evaluar el efecto de biocontrol y promoción de crecimiento en maní al inocular <em>Trichoderma harzianum</em> CT306 y <em>Bacillus subtilis</em> CT104, en condiciones controladas y campo. Los ensayos se realizaron en macetas con condiciones controladas (25 °C, 12 h luz) con semillas de maní Var. Granoleico infectadas con <em>Aspergillus</em> <em>flavus</em>, <em>Fusarium</em> sp., <em>Sclerotinia minor</em> y <em>Thecaphora frezzi</em>. En plantas crecidas hasta los 60 DDS, se observó ausencia de <em>A. flavus</em> y <em>Fusarium</em> sp. al aplicar los biológicos solos y combinados; mientras que la inoculación conjunta de <em>T. harzianum</em> y <em>Bacillus</em> ocasionó ausencia de S. minor y baja incidencia de <em>T. frezzi.</em> En las evaluaciones en el campo, los tratamientos con biológicos aumentaron el porcentaje de emergencia (37%) y al final del ciclo se registró reducción del 14% de la incidencia de <em>T. frezzi</em>, aumento de biomasa (27%), rendimiento (46%) y tamaño de grano (34%) respecto al testigo, sin afectar el grado de madurez alcanzado.<br /><br /></p>