Chitosan as an Adjuvant to Enhance the Control Efficacy of Low-Dosage Pyraclostrobin against Powdery Mildew of Rosa roxburghii and Improve Its Photosynthesis, Yield, and Quality

Abstract

Powdery mildew is the most serious fungal disease of Rosa roxburghii in Guizhou Province, China. In this study, the control role of chitosan-assisted pyraclostrobin against powdery mildew of R. roxburghii and its influences on the resistance, photosynthesis, yield, quality and amino acids of R. roxburghii were evaluated. The results indicate that the foliar application of 30% pyraclostrobin suspension concentrate (SC) 100 mg L−1 + chitosan 500 mg L−1 displayed a superior control potential against powdery mildew, with a control efficacy of 89.30% and 94.58% after 7 d and 14 d of spraying, respectively, which significantly (p < 0.01) exceeded those of 30% pyraclostrobin SC 150 mg L−1, 30% pyraclostrobin SC 100 mg L−1, and chitosan 500 mg L−1. Simultaneously, their co-application could effectively enhance their effect on the resistance and photosynthesis of R. roxburghii leaves compared to their application alone. Meanwhile, their co-application could also more effectively enhance the yield, quality, and amino acids of R. roxburghii fruits compared to their application alone. This work highlights that chitosan can be applied as an effective adjuvant to promote the efficacy of low-dosage pyraclostrobin against powdery mildew in R. roxburghii and improve its resistance, photosynthesis, yield, quality, and amino acids.

Association of Physcion and Chitosan Can Efficiently Control Powdery Mildew in Rosa roxburghii

“…In our recent report, we found that 500 mg L −1 chitosan had a good control effect on R. roxburghii powdery mildew with an efficacy of 77.80% after 14 d of application [ 9 ]. Moreover, Zhang et al [ 34 ] found that 12.5~25.0 mg L −1 0.5% physcion AS had a significant inhibitory effect on R. roxburghii powdery mildew with the control efficacy of 77.01~82.26% after 14 d of application.…”

“…The above-ground part of R. roxburghii plants was sprayed with 1.50 L of fungicide liquid or clear water on April 5 and 12 in 2022, respectively. The disease index and control efficacy of powdery mildew were respectively surveyed on, before, and after spraying according to Zhang et al [ 9 ]. The incidence levels were classified as: no incidence for 0 level, thin hyphae with 1~2 diseased lobules for 1 level, thick hyphae with 3~4 diseased lobules for 2 levels, dense hyphae with 5~6 diseased lobules for 3 levels, dense hyphae with exceeding 7 diseased lobules for 4 levels.…”

“…Subsequently, R. roxburghii leaves from five orientations on each tree were stochastically gathered for determining their chlorophyll content and disease resistance parameters. Chlorophyll content with an ethanol/acetone ( v / v , 1:2) extraction was measured using a UV-5800PC spectrophotometer [ 9 ]. The method of Cao et al [ 36 ] was used for determining the phenolics and flavonoids of leaves, 2.00 g of sample was ground in 20 mL of HCl-methyl alcohol (1%, v / v ) and centrifuged (8000× g , 8 min, 4 °C) for extracting 1 h without light, then the supernatant was checked at OD 280 nm and OD 325 nm, respectively.…”

“…Powdery mildew caused by Sphaerotheca pannosa (Wallr.) Lev is an extremely serious fungal disease of all R. roxburghii production regions in China, which has been responsible for serious growth restrictions and quality declines, as well as 30~40% of yield or economic losses [ 7 , 8 , 9 ]. Although several chemical fungicides (e.g., pyraclostrobin, prothioconazole, myclobutanil, and tebuconazole, etc.)…”

“…Soon afterward, we further found that the mixed-use of chitosan and allicin viably controlled R. roxburghii powdery mildew with an effect of 85.97% [ 19 ]. In our recent report, we also manifested that chitosan could be used as a favorable assist to improve the effect of low-dose pyraclostrobin control R. roxburghii powdery mildew [ 9 ]. Many studies have also evidenced that chitosan is an inductor or biological fungicide for preventing and controlling plant’s diseases, as well as also a growth enhancer for boosting plant’s growth [ 20 , 21 , 22 , 23 , 24 , 25 ].…”