Articles
Efficiency evaluation of low-dose ulvan spray against Glomerella leaf spot on apple trees
Article number
1427_5
Pages
33 – 40
Language
English
Abstract
Organic apple farming in Santa Catarina state, the largest producer in Brazil, emerged in the late 1990s and has significantly increased over the years.
However, challenges posed by plant diseases like Glomerella leaf spot (GLS), caused by Colletotrichum chrysophilum, continue to be a central constraint for this activity.
In this scenario, the use of ulvans, sulfated heteropolysaccharides naturally obtained from marine green macroalgae (Ulva spp.), has shown potential in previous studies for inducing resistance and reducing GLS severity.
Thus, this investigation aimed to assess the efficacy of consecutive foliar applications of ulvan at a lower concentration to mitigate GLS severity and defoliation in apple trees.
For this study, two outdoor pot experiments were conducted under artificial inoculation of the pathogen, during which three-year-old Gala apple trees were pretreated twice with ulvan solution (1 mg mL‑1) and then weekly treated after inoculation with a conidial suspension of C. chrysophilum. GLS severity was assessed visually every 3 days.
The area under the disease progress curve (AUDPC) was calculated for severity, and defoliation was monitored.
Due to severe defoliation, evaluations were performed until the 29th and 56th day after inoculation (DAI) in the first and second experiments, respectively.
In the first experiment, GLS symptoms appeared 3 DAI, while in the second at 13 DAI due to colder conditions.
Ulvan, applied three times in the first experiment, significantly reduced leaf severity by 30% at 29 DAI compared to untreated plants; however, in the second experiment, it did not affect disease severity.
Defoliation began about 8 DAI in the first experiment, peaking between the 8th and 14th DAI, whereas in the second, defoliation started c. 17 DAI, with the highest intensity between the 17th and 22nd DAI. In both experiments, weekly ulvan spraying failed to prevent defoliation.
However, challenges posed by plant diseases like Glomerella leaf spot (GLS), caused by Colletotrichum chrysophilum, continue to be a central constraint for this activity.
In this scenario, the use of ulvans, sulfated heteropolysaccharides naturally obtained from marine green macroalgae (Ulva spp.), has shown potential in previous studies for inducing resistance and reducing GLS severity.
Thus, this investigation aimed to assess the efficacy of consecutive foliar applications of ulvan at a lower concentration to mitigate GLS severity and defoliation in apple trees.
For this study, two outdoor pot experiments were conducted under artificial inoculation of the pathogen, during which three-year-old Gala apple trees were pretreated twice with ulvan solution (1 mg mL‑1) and then weekly treated after inoculation with a conidial suspension of C. chrysophilum. GLS severity was assessed visually every 3 days.
The area under the disease progress curve (AUDPC) was calculated for severity, and defoliation was monitored.
Due to severe defoliation, evaluations were performed until the 29th and 56th day after inoculation (DAI) in the first and second experiments, respectively.
In the first experiment, GLS symptoms appeared 3 DAI, while in the second at 13 DAI due to colder conditions.
Ulvan, applied three times in the first experiment, significantly reduced leaf severity by 30% at 29 DAI compared to untreated plants; however, in the second experiment, it did not affect disease severity.
Defoliation began about 8 DAI in the first experiment, peaking between the 8th and 14th DAI, whereas in the second, defoliation started c. 17 DAI, with the highest intensity between the 17th and 22nd DAI. In both experiments, weekly ulvan spraying failed to prevent defoliation.
Publication
Authors
G.F. Zappellini, A.C. Velho, R.M. Valdebenito-Sanhueza, M.J. Stadnik
Keywords
Colletotrichum fructicola, apple diseases, organic apple, algal polysaccharide
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