The rust and brown eye spot, caused by Hemileia vastatrix and Cercospora coffeicola, respectively, are the most important fungal diseases on coffee in South America. Their management is mainly by chemical treatment, and there is no genetic resistance to brown eye spot known so far. Considering the need for developing alternative products for their control, the goal of this work was to evaluate the effects of phosphites and by‐products of coffee and citrus industries on rust and brown eye spot. Formulations of coffee and citrus industry by‐products, phosphites and their combination with fungicide were evaluated in field experiments, and their effect on fungal urediniospores and conidia was evaluated in vitro. In the field, treatments were applied individually or in combination and the in vitro assays were performed with manganese phosphite (Reforce Mn), potassium phosphite and citrus industry by‐product (Fortaleza), copper phosphite and coffee industry by‐product (Fitoforce Full), and fungicide. The severity and incidence of rust and brown eye spot on coffee leaves, yield, and leaf retention were evaluated in the field. Percentage of spore germination was evaluated in vitro for both fungi, whereas mycelial growth was evaluated for C. coffeicola only. The treatments Fortaleza, Reforce Mn and Fitoforce Full suppressed both diseases with a reduction in defoliation. In the year 2012, the plants treated with Reforce Mn and Reforce Mn + Fortaleza showed a yield increase of 72 and 88%, respectively, which was similar to the results shown by the fungicide treatment. In vitro inhibition of germination of H. vastatrix urediniospores and of C. coffeicola conidia was observed and suggests that the products exert some toxic effects to both fungi. Finally, the results observed indicate that the combined use of by‐products of plant‐processing industries and phosphites is an alternative and can be added efficiently to the management of coffee diseases.
The aim of this study was to investigate the effectiveness of potassium phosphites for the control of anthracnose and the mode of action of these products on common bean plants against Colletotrichum lindemuthianum, comparing it with the standard resistance inducer acibenzolar‐S‐methyl. The protection of plants against anthracnose was evaluated in greenhouse after treatment with potassium phosphites (Phosphite A and B, 5.0 ml/L), acibenzolar‐S‐methyl (0.25 g/L), or no treatment (control). Two sprayings of the treatments were performed, respectively, at V4 stage (three trifoliate leaves) and at the R5 stage (flower buds present). The inoculation with C. lindemuthianum was performed 5 days after the first spraying. Phosphite formulations A and B reduced the severity of anthracnose by 68.7% and 55.6%, respectively, and the presence of phosphites in the leaf tissues were detected at concentrations between 1 and 3 mm by 7 days after spraying. These same concentrations of phosphites reduced the mycelial growth of C. lindemuthianum in vitro by 15.0% to 25.7%. In addition, the activities of defence enzymes and the levels of phenolic compounds and lignin were assessed. Phosphite treatments enhanced the activity of various enzymes, including superoxide dismutase, peroxidase, chitinase, and β‐1,3‐glucanase, and increased the lignin and a small increase in the levels of soluble phenolics. This study provides evidence that phosphite treatments control anthracnose by acting directly on C. lindemuthianum and by inducing the production of defence responses.
This study considers the influence of temperature, incubation time and virulence in the production of the toxin cercosporin by Cercospora coffeicola, the causal agent of brown eye spot in coffee. The area under the progress curve of cercosporin production (AUPCCP) was also evaluated. A pathogenicity test was performed in a group with 58 isolates of C. coffeicola, which allowed the selection of four isolates, two representing the highest (LFP 12 and LFP 59) and two the lowest (LFP 24 and LFP 43) severity groups. The four isolates were cultivated in potato dextrose agar (PDA) and incubated in growth chambers at different temperatures (15, 20, 25 and 30°C) for 20 days. The experiments were conducted in a randomized complete block design with four replications. The cercosporin production decreased in all tested isolates at 30°C, resulting in a lower AUPCCP. The higher values of cercosporin were obtained at 20 and 25°C between 8 and 12 days of incubation. The isolates that produced the highest and lowest cercosporin concentrations were LFP 12 and LFP 43, respectively. After 15 days of incubation, toxin production is practically null in all isolates independently of the incubation temperature. Thus, the hypothesis for quantification of cercosporin production as a variability parameter within the species is suggested.
Determining the intra-specific variability of response to a given herbicide is important for monitoring the possible shifts in the sensitivity of weed populations. This study describes the responses of populations of Alisma plantago-aquatica, Cyperus difformis, and Schoenoplectus mucronatus from Italy, Greece, Portugal, and Spain to penoxsulam, an acetolactate synthase (ALS) inhibitor widely used in rice. To evaluate previously evolved resistance to ALS inhibitors, sensitivity to azimsulfuron and bensulfuron-methyl was assessed. Dose-response experiments with penoxsulam were performed in a greenhouse simulating paddy rice field conditions. Log-logistic dose-response curves were used to estimate the ED50, ED80, ED90 and GR50, GR80, and GR90. To calculate the average ED and GR and assess the intra-specific variability, an artificial resampling method was performed. Populations ALSPA 0364, 0365, 0469, 0470, 0471; SCPMU 0371, 0475, 0267; CYPDI 0013, 0431, 0432, 0433 appeared to be resistant to sulfonylureas, while a higher sensitivity to penoxsulam was observed, while populations ALSPA 0363, CYPDI 0223 and SCPMU 9719 proved to be cross-resistant. Regardless of species, ED90 of susceptible populations were below penoxsulam label dose (40 g ai ha−1) while they reached values higher than 320 g ai ha−1 for resistant populations. Average GR50 were generally lower than ED50. Sensitivity variability among susceptible populations is relatively low, allowing for discrimination between susceptible and resistant populations, and previously evolved resistance to sulfonylureas can influence sensitivity to penoxsulam.
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