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Considering the high incidence of white mold caused by Sclerotinia sclerotiorum in a variety of field crops and vegetables, different control strategies are needed to keep the disease under economical threshold. This study assessed the effect of foliar application of a calcium formulation on disease symptoms, oxalic acid production, and on the oxidative stress metabolism in soybean plants inoculated with each of two isolates of the pathogen that have contrasting aggressiveness (HA, highly-aggressive versus WA, weakly-aggressive). Changes in reactive oxygen species (ROS) levels in soybean plants inoculated with S. sclerotiorum isolates were assessed at 6, 24, 48 and 72 h post inoculation (hpi). Generation of ROS including hydrogen peroxide (H2O2), anion superoxide (O2-) and hydroxyl radical (OH) was evaluated. Inoculation with the WA isolate resulted in more ROS accumulation compared to the HA isolate. Pre-treatment with the calcium formulation restored ROS production in plants inoculated with the HA isolate. We also noted a marked decrease in oxalic acid content in the leaves inoculated with the HA isolate in presence of calcium, which coincided with an increase in plant ROS production. The expression patterns of genes involved in ROS detoxification in response to the calcium treatments and/or inoculation with S. Sclerotiorum isolates were monitored by RT-qPCR. All of the tested genes showed a higher expression in response to inoculation with the WA isolate. The expression of most genes tested peaked at 6 hpi, which preceded ROS accumulation in the soybean leaves. Overall, these data suggest that foliar application of calcium contributes to a decrease in oxalic acid production and disease, arguably via modulation of the ROS metabolism.

Sclerotinia sclerotiorum (Lib.) de Bary is a fungal plant that causes serious losses in important crops. This study examined the expression of selected defense-related genes in the isoflavonoids pathway after soybean inoculation with two Sclerotinia isolates possessing different levels of aggressiveness (SSPetri, highly aggressive and SS18, weakly aggressive) and the effects of pre-treatment with calcium on disease symptoms. PAL1 displayed an early expression after inoculation regardless of the isolate used. Expression of IFS2 and IFR2 were more pronounced in leaves inoculated with the weakly aggressive isolate SS18 than with its highly aggressive counterpart. Oppositely, CHS3, CHS5 and CHI1B1–CHI1B2 had higher transcript abundance in presence of the highly aggressive isolate SSPetri. Pre-treatment with calcium enhanced the expression of CHS3, CHS5, CHI1B1–CHI1B2 IFS2 and IFR2 in the leaves inoculated with SSPetri. An increase in isoflavone aglycones and their malonyl and acetyl conjugates was recorded in the inoculated leaves, with higher contents in response to SSPetri. Pre-treatment with calcium improved the accumulation of daidzein, genistein and acetyl glycitin, especially in the leaves inoculated with SSPetri. De novo synthesis of glyceollins occurred in response to inoculation, especially in response to the highly aggressive isolate SSPetri.

Entomosporium leaf and berry spot represent the most important disease of saskatoons (Amelanchier alnifolia Nutt.). This disease, caused by the ascomycete Entomosporium mespili (D.C.) Sacc., is difficult to control via conventional methods and no known saskatoon cultivar carries resistance to this pathogen. The aim of the present study was to enhance existing and induced defense responses of saskatoons using two host defense inducers, namely jasmonic acid and an extract from Canada milkvetch on two saskatoon cultivars, Smoky and Martin. Both inducers exhibited an ability to differentially induce the synthesis/accumulation of defense-related genes including those encoding for PR-1, PR-2, PR-5, LOX and PAL. Pre-treatment of saskatoon leaves with these inducers reduced the disease levels especially when applied to the moderately susceptible cultivar Martin. An accumulation of various hydroxycinnamic acid and proanthocyanidin derivatives also correlated with the disease levels recorded on both cultivars. Results are discussed on the basis of the induced pathways in an attempt to lay the ground for a better understanding of this hostpathogen interaction. In the meantime,wehave shown that the use of defense enhancers may be useful in integrated management strategies to control entomosporium leaf and berry spot in saskatoons spot in saskatoons. Fil: Wolski, Erika Alejandra. Universidad Nacional de Mar del Plata. Facultad de Ciencias Agrarias; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata; Argentina Fil: Henriquez, Maria A.. University Of Manitoba; Canadá Fil: Adam, Lorne R.. University Of Manitoba; Canadá Fil: Badawi, Mohamed. University Of Manitoba; Canadá Fil: Andreu, Adriana Balbina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigaciones Biológicas; Argentina. Universidad Nacional de Mar del Plata; Argentina Fil: Hadrami, Abdelbasset El . University Of Manitoba; Canadá Fil: Daayf, Fouad. University Of Manitoba; Canadá

Chitin and chitosan are naturally-occurring compounds that have potential in agriculture with regard to controlling plant diseases. These molecules were shown to display toxicity and inhibit fungal growth and development. They were reported to be active against viruses, bacteria and other pests. Fragments from chitin and chitosan are known to have eliciting activities leading to a variety of defense responses in host plants in response to microbial infections, including the accumulation of phytoalexins, pathogen-related (PR) proteins and proteinase inhibitors, lignin synthesis, and callose formation. Based on these and other proprieties that help strengthen host plant defenses, interest has been growing in using them in agricultural systems to reduce the negative impact of diseases on yield and quality of crops. This review recapitulates the properties and uses of chitin, chitosan, and their derivatives, and will focus on their applications and mechanisms of action during plant-pathogen interactions.

Plants have evolved sophisticated mechanisms to sense and respond to pathogen attacks. Resistance against necrotrophic pathogens generally requires the activation of the jasmonic acid (JA) signaling pathway, whereas the salicylic acid (SA) signaling pathway is mainly activated against biotrophic pathogens. SA can antagonize JA signaling and vice versa. Here, we report that the necrotrophic pathogen Botrytis cinerea exploits this antagonism as a strategy to cause disease development. We show that B. cinerea produces an exopolysaccharide, which acts as an elicitor of the SA pathway. In turn, the SA pathway antagonizes the JA signaling pathway, thereby allowing the fungus to develop its disease in tomato (Solanum lycopersicum). SA-promoted disease development occurs through Nonexpressed Pathogen Related1. We also show that the JA signaling pathway required for tomato resistance against B. cinerea is mediated by the systemin elicitor. These data highlight a new strategy used by B. cinerea to overcome the plant's defense system and to spread within the host. © 2011 American Society of Plant Biologists. All rights reserved. Fil:Rigano, L. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina. Fil:Rodriguez, M.C. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina. Fil:Vojnov, A. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.