Chitosan has recently shown potential for the control of plant diseases and can act as an elicitor in the induction of defence mechanisms. This study was made to assess the effect of chitosan on bacterial spot control caused by Xanthomonas gardneri in tomato plants. The chitosans used were commercial (Ccom), low molecular weight (Clmw) and medium molecular weight (Cmmw). Chitosans provided disease protection of up to 56%, with best results from Clmw at 3 mg/ml, applied 3 days prior to bacterial inoculation. The spectrophotometric profile of tomato plants that were treated with Clmw showed an increase of absorbance between wavelengths 280 and 300 mm, indicating that the polysaccharide may have induced the plants into synthesizing different compounds as a response to X. gardneri. The analysis of total phenolic compounds and flavonoids supported the results obtained in spectrophotometric scanning, showing a significant increase of those metabolites 3 days after inoculation. Therefore, chitosan has the capability of controlling bacterial spot in tomato plants, which is thought to be attributable to the induction of defence mechanisms in the plant.
[Show abstract][Hide abstract] ABSTRACT: Claims have been made recently that glyphosate-resistant (GR) crops sometimes have mineral deficiencies and increased plant disease. This review evaluates the literature that is germane to these claims. Our conclusions are: (1) although there is conflicting literature on the effects of glyphosate on mineral nutrition on GR crops, most of the literature indicates that mineral nutrition in GR crops is not affected by either the GR trait or by application of glyphosate; (2) most of the available data support the view that neither the GR transgenes nor glyphosate use in GR crops increases crop disease; and (3) yield data on GR crops do not support the hypotheses that there are substantive mineral nutrition or disease problems that are specific to GR crops.
Journal of Agricultural and Food Chemistry 09/2012; 60(42). DOI:10.1021/jf302436u · 2.91 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The effectiveness of composted sewage sludge incorporated into Pinus bark-based substrate with or without biofertilizer, fish hydrolyzate, chitosan and Trichoderma asperellum was evaluated for the control of Fusarium wilt in chrysanthemum. The substrate was obtained from pots containing chrysanthemum plants killed by the pathogen. Half of the substrate was sterilized prior to the incorporation of sewage sludge (0, 10%, 20% and 30% v/v). These substrates were or were not supplemented with the following: biofertilizer, fish hydrolyzate and Trichoderma. The mixtures were transferred to pots, and the chrysanthemum was transplanted. For all treatments, half of the plants were sprayed weekly with chitosan. Assessment of severity was performed on the 8th, 12th, 15th and 20th week after transplanting. In the 12th week, microbiological and chemical analysis of the substrate was performed. The incorporation of composted sewage sludge into the Pinus bark-based substrate significantly reduced Fusarium wilt, which was progressively decreased as the concentration of sewage sludge increased. The addition of biofertilizer, fish hydrolyzate, chitosan and Trichoderma had no effect on the disease. The microbial community was greater in non-disinfested substrates. The results indicate that suppressiveness is related to the interaction of chemical and microbiological factors.
[Show abstract][Hide abstract] ABSTRACT: This chapter deals with both naturally derived inducers (biotic inducers) of resistance and agents which mimic the action of these inducers (abiotic inducers). It concentrates on the effects of topical treatment with inducers on disease control under controlled conditions and in the field. Chitin is the main cell wall component of many filamentous fungi and, along with its deacetylated derivative chitosan, has been shown to elicit defence responses in plants, including lignification and phytoalexin production. Marine algae provide a source of numerous elicitors, including ulvans from green seaweeds, agarans and carrageenans from red seaweeds, and alginates, fucans and laminarin from brown seaweeds. The chapter provides an overview of the effects of Benzo(1,2,3)thiadiazole-7-carbothioic acid S-methyl ester (BTH) on a range of different host-pathogen interactions. The use of abiotic elicitors has become a major promising approach for the agricultural application of induced resistance.
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