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.）作物过量使用化学药剂，不仅会因病原菌产生抗药性而降低杀菌剂的防效，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）的离体与活体防治效果。离体试验中，供试药剂包括1.5%丁香（Syzygium aromaticum）水提物、1.5%肉桂（Cinnamomum zeylanicum）水提物、4%壳聚糖，上述植物提取物与4%壳聚糖的复配制剂，以及添加至PDA培养基中的咪鲜胺杀菌剂（100 mg·L⁻¹），以不加药剂的处理作为空白对照，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处理相较于单剂使用，对菌丝生长的抑制效果更显著。活体试验选取番木瓜‘福莫萨’（Formosa）品种，通过浸果方式设置以下7组处理：1. 空白对照（无菌蒸馏水）；2. 杀菌剂对照：咪鲜胺（Sportak® 450 EC，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 h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的病情严重程度显著低于空白对照。通过病情进展曲线下面积分析可知，10%丁香水提物处理组同样可有效降低番木瓜果实炭疽病的病情严重程度。