Alternatives in the control of Alternaria brown spot in ‘Dancy’

ABSTRACT The tangerine ‘Dancy’ has desirable characteristics such as color, aroma, flavor and wide acceptance by the market. This variety is highly produced in the state of Paraíba but is susceptible to Alternaria brown spot (MMA), caused by Alternaria alternata, responsible for compromising the fruit quality in tangerine producing regions. To prevent this disease, research using alternative products has been expanded. Therefore, the objective of this study was to determine the potential of the extract of Caesalpinia ferrea and Chitosan® in the management of MMA in fruits of ‘Dancy’ tangerine. The fruits were disinfested and immersed in extract of C. ferrea at concentrations of 0, 10, 100, 500 and 1000 µg/mL, and Chitosan® at 0.5, 1.0, 1.5 and 2.0 g/L. After 24 h of the application of products, the fungus A. alternata was inoculated (105 spores/mL). From the second day after inoculation (DAI), severity (AUDPC) was daily evaluated. For analysis of the activities of phenylalanine ammonia-lyase, peroxidase and polyphenol oxidase, three fruits/replicate were taken on the first and twelfth days of the experiment. The design was completely randomized including 9 treatments (concentrations of products) and 5 replicates with 5 fruits, which constituted an experimental unit with 225 fruits. Regression analysis and Dunnett’s test (P ≤ 0.05) were performed by using SAS® System 9.3 software. The concentrations of 500 µg/mL of C. ferrea extract and 1.5 g/L Chitosan® reduced the severity of Alternaria brown spot and promoted high activities of the enzymes in ‘Dancy’ tangerine fruits.

摘要：‘丹西’橘（Dancy tangerine）具备色泽、香气与风味俱佳的优良性状，且市场接受度广泛。该品种在帕拉伊巴州（Paraíba）种植规模较大，但易受交链孢褐斑病（Alternaria brown spot, MMA）侵染，该病害由链格孢菌（Alternaria alternata）引发，会降低柑橘产区的果实品质。为防控该病害，基于替代药剂的相关研究日益增多。本研究旨在探究云实（Caesalpinia ferrea）提取物与壳聚糖（Chitosan®）对‘丹西’橘果实上MMA的防控潜力。将果实进行表面消毒后，分别置于浓度为0、10、100、500及1000 μg/mL的云实提取物溶液，以及浓度为0.5、1.0、1.5与2.0 g/L的壳聚糖（Chitosan®）溶液中浸泡处理。药剂处理24小时后，接种浓度为10^5孢子/mL的链格孢菌（Alternaria alternata）。自接种后第2天（DAI，接种后天数）起，每日评估病情严重程度（AUDPC，病程曲线下面积）。为检测苯丙氨酸解氨酶（phenylalanine ammonia-lyase, PAL）、过氧化物酶（peroxidase, POD）与多酚氧化酶（polyphenol oxidase, PPO）的活性，分别于试验第1天与第12天，每个重复取样3个果实。本试验采用完全随机设计，设置9个药剂浓度处理，每个处理下设5个生物学重复，每个重复包含5个果实；单个试验单元共25个果实，全试验总计225个果实。采用SAS®系统9.3软件进行回归分析与Dunnett多重比较检验（检验水准P≤0.05）。结果表明，浓度为500 μg/mL的云实提取物与1.5 g/L的壳聚糖（Chitosan®）可有效降低‘丹西’橘果实的交链孢褐斑病病情严重程度，并显著提升上述三种防御酶的活性。