Chitosan associated with plant extracts in the post-harvest control of anthracnose in papaya ‘formosa’

ABSTRACT Excessive use of chemicals in papaya (Carica papaya L.) crops puts the efficacy of fungicides at risk because of the resistance problems of pathogens to these products, besides the possibility of toxic residues endangering the human health and the environment. Therefore, the present study aimed to evaluate the efficacy of natural products in controlling Colletotrichum gloeosporioides in vitro and in vivo. In the in vitro assay, the evaluated products were aqueous extracts of clove (Syzygium aromaticum) and cinnamon (Cinnamomum zeylanicum) at 1.5% and chitosan at 4%, separately, and the association of these plant extracts with 4% chitosan, as well as the fungicide prochloraz (100 mg L-1), added to PDA culture medium; they were evaluated for their effect on the mycelial growth of the fungus, maintaining a control without addition of products. The treatment with aqueous extract of clove at 15% and its association with chitosan inhibited mycelial growth. Association of chitosan with aqueous extract of cinnamon was more effective in reducing mycelial growth than the two products used separately. In the in vivo test, papaya ‘Formosa’ fruits were subjected to the following treatments by immersion: 1 - control (distilled water); 2 - control - fungicide prochloraz (Sportak® 450 EC) at a concentration of 0.75 mL L-1; 3 - chitosan (4%); 4 - aqueous extract of clove (10%); 5 - aqueous extract of cinnamon (30%); 6 - aqueous extract of clove (10%) + chitosan (4%); 7 - aqueous extract of cinnamon (30%) + chitosan (4%). After 24h, fruits were inoculated with C. gloeosporiodes and evaluated for the disease severity at every two days. Only in the third evaluation, treatments with fungicide and aqueous extract of cinnamon at 30% associated with chitosan at 4% reduced the disease severity, compared to control. The area under the disease progress curve indicated that the treatment with aqueous extract of clove was also effective in reducing the severity of anthracnose in fruits.

摘要：番木瓜（*Carica papaya* L.）作物过量施用化学药剂，不仅会因病原菌对药剂产生抗药性而降低杀菌剂的防控效能，还可能因有毒残留威胁人体健康与生态环境。为此，本研究旨在评价天然产物对胶孢炭疽菌（*Colletotrichum gloeosporioides*）的体外与体内防控效果。体外抑菌试验中，供试药剂包括1.5%浓度的丁香（*Syzygium aromaticum*）水提物、肉桂（*Cinnamomum zeylanicum*）水提物，4%浓度的壳聚糖（chitosan），上述植物提取物与4%壳聚糖的复配制剂，以及添加至马铃薯葡萄糖琼脂（PDA）培养基的咪鲜胺（prochloraz，100 mg·L⁻¹），以不添加任何药剂的处理为空白对照，评价各处理对病原菌菌丝生长的影响。结果显示，15%丁香水提物及其与壳聚糖的复配处理可抑制病原菌菌丝生长；壳聚糖与肉桂水提物的复配组合，相较于两种药剂单施，对菌丝生长的抑制效果更为显著。体内活体试验以‘佛摩萨’（Formosa）番木瓜果实为材料，采用浸果法设置以下处理：1. 空白对照（无菌蒸馏水）；2. 杀菌剂对照：咪鲜胺（Sportak® 450 EC），使用浓度为0.75 mL·L⁻¹；3. 4%壳聚糖；4. 10%丁香水提物；5. 30%肉桂水提物；6. 10%丁香水提物+4%壳聚糖；7. 30%肉桂水提物+4%壳聚糖。处理24小时后，接种胶孢炭疽菌，每2天调查一次果实病情严重程度。仅在第三次调查时，咪鲜胺处理组以及30%肉桂水提物与4%壳聚糖的复配处理组，相较于空白对照，可降低果实病情严重程度。通过病情进展曲线下面积分析发现，丁香水提物处理组同样可有效降低果实炭疽病的病情严重程度。