重庆万州柑橘轮斑病菌的鉴定及防治药剂筛选

【目的】明确2018年起在重庆万州柑橘种植区新发生病害的病原菌,筛选有效防控药剂,为田间防治该病害和后续深入研究提供理论参考。【方法】通过组织分离法从患病样品中获得菌株,进行病原菌形态学、分子生物学和致病性鉴定,采用生长速率法测定不同药剂对目标菌株的毒力。【结果】此病害的病原菌为柑橘轮斑病菌Pseudofabraea citricarpa。病原菌对万州地区主栽的8个品种柑橘的叶、枝、果和昭通苹果及砀山酥梨果实具有致病性。苯醚甲环唑、咪酰胺、甲基硫菌灵等17种杀菌剂的EC50值小于3 mg/kg,代森锰锌与啶酰菌胺1：64比列复配、克菌丹与苯醚甲环唑1：1比例复配、代森锰锌和矿物油1:50比例复配对菌株生长抑制效果良好。【结论】重庆万州柑橘种植园区发生柑橘轮斑病,病原菌对柑橘枝、叶、果和其它果树果实都具有致病性。17种药剂单用或复配对病原菌生长有抑制作用,可进一步用于田间实验。     

柑橘轮斑病的适生区预测及风险分析

【目的】 柑橘轮斑病（citrus target spot）作为一种新发柑橘病害,造成发病果园严重的经济损失。本研究针对该病害进行适生区预测及风险分析,以便对该病采取及时、有效的管控措施,最终达到降低其流行风险等级,防止病害传播扩展的目的。【方法】 基于环境变量数据和柑橘轮斑病发生分布数据,运用MaxEnt生态位模型模拟预测柑橘轮斑病菌（Pseudofabraea citricarpa）在中国的潜在适生区分布。并通过ROC（receiver operating characteristic）曲线下面积（area under the curve,AUC）评估预测模型的精度,运用正规化训练增益刀切法（regularized training gain）获取气候因子与分布概率间的关系。同时采用有害生物风险分析理论,以有害生物风险分析的规定程序为依据探索柑橘轮斑病病害的风险分析体系和评价值的计算方法,对评价指标进行定性分析,进而量化评价值。在建立综合评价模型的基础上,计算柑橘轮斑病风险性危害值,最后对病害的风险性危害值进行评价。【结果】 柑橘轮斑病菌MaxEnt模型预测结果的平均AUC值为0.998,表明预测结果精度高。柑橘轮斑病菌的潜在适生区面积约占全国面积12.19%,高适生区、中适生区、低适生区各占全国面积约2.85%、3.99%、5.35%。高、中适生区主要集中于长江中上游柑橘优势区及其周边。其中,高适生区主要集中在四川、重庆、陕西南部,以及贵州、湖北等少量地区。中、低适生区是高适生区的外围扩展。通过MaxEnt模型正规化训练增益刀切法获取的环境变量重要性分析结果表明,最冷季度平均温度（Bio11）、最干季度平均温度（Bio9）、最冷月最低温（Bio6）是影响柑橘轮斑病菌分布的3个关键环境因子,这意味着低温、干冷季节柑橘轮斑病发生可能性大。风险分析最终创建出5个准则层、13个指标层的多指标综合评价体系,并对各指标层定量与定性分析,柑橘轮斑病在我国的风险性危害值（R值）为2.08,处于高度风险等级,对长江中上游及湖北西部-湖南西部两大柑橘产区的潜在危害最大。【结论】 柑橘轮斑病风险性较高,需要尽快建立监测体系,针对病害采取有效控制措施,阻止病害在长江中上游柑橘优势区及相邻柑橘产区传播。     

柑桔黑斑病的发病特点及检测方法研究进展

柑桔黑斑病(Citrus Black Spot,CBS)是一种真菌性病害,主要为害果实,并产生褐色斑点,严重时蔓延至全果,造成果实腐烂,显著影响果实的品质和外观,降低经济价值,被欧美等国列为重要的检疫性病害,近年来该病在我国一些柑桔产区已上升为主要病害。本文主要从柑桔黑斑病的病原菌、发病特点及检测方法等几个方面进行简要的概述。     

芒果球座菌在茶园的分布、传播和自然循环

分离健康茶树叶片、落叶、种子、实生苗和扦插苗等的内生真菌,研究影响芒果球座菌分布的因素、季节变化规律、传播方式和生活史.结果表明:芒果球座菌的分离率在不同的山茶属植物叶片中存在明显差异,茶树中最高,油茶次之,山茶最低;新抽出的叶芽中没有内生真菌分布,但随着叶片龄期的增长,芒果球座菌的分离率逐步提高,至老叶中高达73.5%.在茶树中,品种是影响芒果球座菌分布的重要因素,不同品种间芒果球座菌的分离率有明显差异;1年之中,芒果球座菌的消长明显受新梢抽出期、叶龄、茶叶采摘、温度和降水等多因素的综合影响;2-4月和6月芒果球座菌的分离率低,而5月、7-8月和12月是芒果球座菌分布的高峰期.种子、新长出的实生苗中没有分离到芒果球座菌;随实生苗的生长,芒果球座菌感染逐步增多.结合枯叶和空气中真菌孢子检测结果可知:茶树中的芒果球座菌通过水平传播方式在茶园扩散.而在扦插苗中芒果球座菌的分离结果说明茶树中的芒果球座菌也可以通过存在于插穗中的菌丝体扩散到下一代,在茶园进行垂直传播.因此,茶树中的芒果球座菌同时存在水平传播和垂直传播2种扩散方式.     

Spray volume and fungicide rates for citrus black spot control based on tree canopy volume

The control of citrus black spot (CBS) caused by Phyllosticta citricarpa relies mainly on fungicide sprays. Generally, high and non-standardized spray volumes are adopted and the sprays are based on litre per tree or per hectare. However, the tree canopy volume may vary with age, density and variety, and this is expected to impact on the spray volume and fungicide rates needed for disease control. This study evaluated the efficacy of different fungicide spray volumes and rates for CBS control based on the tree-row-volume (TRV) concept. Two field trials were carried out during three seasons in São Paulo state, Brazil. Trials were set up in commercial orchards of late-maturing ‘Valencia’ sweet orange grown for juice production. In field trial 1, the volumes tested were 125 (standard), 100 (internal runoff point), 75 (intermediate) and 50 (half the internal runoff point) mL of spray mixture/m³ of the tree canopy. In field trial 2, 100 and 50 mL/m³ were evaluated. The fungicide rates ranged from 40 to 110 mg of metallic copper/m³ and from 1.9 to 4.7 mg of pyraclostrobin/m³. Untreated control trees (UTC) were kept unsprayed. CBS incidence and severity, premature fruit drop, yield, fungicide deposition and spray coverage were evaluated. All spray volumes tested reduced CBS incidence and severity on fruit at 75–95% and resulted in 1.6–3.0-fold higher yields than the UTC. However, a slight trend of more CBS symptoms and fruit drop, and lower yield was observed for trees treated with 50 mL/m³ compared to those treated with higher volumes. Spray volume change, from 125 to 75 mL/m³, irrespective of fungicide rate correction, led to a 40% reduction of CBS spray costs and water usage and increased the financial return of the control by up to 35%. TRV-based sprays may contribute to sustainable citrus production by reducing costs and environment impacts while maintaining efficient CBS control.     

Contribution of active defense responses in the limitation of fungal spread in the sapwood of living sugi (Cryptomeria japonica) tree

The participation of active defense responses in the limitation of fungal spread in the sapwood of living sugi tree was determined. Isolates ofGuignardia cryptomeriae were inoculated to living trees, fresh logs, frozen and thawed logs and autoclaved logs, and the spread of wood discoloration and fungal hyphae was assessed. In autoclaved logs and freeze-treated logs, wood discoloration and reaction zone formation were not observed, and fungal hyphae of both of virulent and avirulent isolates grew rapidly in the wood. In fresh logs, wood discoloration and the formation of a pale reaction zone and transition zone were observed. Virulent isolates spread rapidly, but the spread of avirulent isolates was inhibited. In living trees, wood discoloration was observed and reaction zones were formed at lesion margins. These results indicated that constitutive defense mechanisms had no effect on the spread of both of virulent and avirulent isolates, and that active defense responses were important in the limitation of spread of fungal hyphae, hence in the limitation of wood discoloration. Further, it appeared that avirulent, but not virulent, races ofG. cryptomeriae were easily inhibited even by weak host responses. This study was presented at 105th and 106th Annual Meeting of the Japanese Forestry Society.     

茶树种质资源抗茶云纹叶枯病鉴定

茶树种质资源抗茶云纹叶枯病鉴定,进行了田间自然发病调查、苗圃茶苗和室内离体茶枝人为接种试验.室内离体接种诱发的病叶还进行了病原菌的再分离.室内离体接种的病情指数与苗圃中接种的病情指数及自然发病调查的病情指数的相关系数分别为r= 0.6993、r= 0.4036,可见离体接种试验结果与苗圃试验和自然发病调查结果具较好吻合性.离体茶枝接种诱发的病叶经分离培养均为该病的分生孢子.确定离体茶枝接种为该病抗性的鉴定方法,拟定抗性等级划分标准,筛选出高抗茶资源1份、抗的12份、中抗的13份.大叶种的抗病性差于中叶种的茶资源.     

培养条件对柑橘黑斑病菌丝生长的影响

以南丰蜜桔黑斑病菌为实验材料,研究了不同生长环境下病原菌生物学特性。结果表明,病菌在5~35℃的范围内均能生长,25℃为菌丝生长的最适温度。适宜pH值范围为5~7,最适pH值为6;在不同培养基中,菌丝在PDA培养基上生长最快,在OA培养基上菌落周围产生一定量的黄色素;光照时间长短对菌丝生长几乎无影响。     

Antifungal activity of chili pepper extract with potential for the control of some major pathogens in grapevine

BACKGROUND

In recent years, biofungicides have drawn increasing interest in vineyards for a more sustainable integrated and copper-limited pest management. Among alternatives, botanicals could represent valuable tools, being rich sources of biologically active compounds. Conversely to the well-known antioxidant and biological properties in relation to health benefits, investigation on bioactivity of hot pungent Capsicum sp. products against fungal phytopathogens in vineyards is still scarce. Therefore, the present study aimed at exploring the biologically active compounds profile of a chili pepper (Capsicum chinense Jacq.) pod extract and its antimicrobial properties against some of the major fungal and Oomycetes pathogens of grapevine, including Botrytis cinerea Pers., Guignardia bidwellii (Ellis) Viala & Ravaz and Plasmopara viticola (Berk. & M.A. Curtis) Berl. & De Toni.

RESULTS

The ethyl acetate-extracted oleoresin from the most pungent varieties was rich in capsaicinoids and polyphenols (371.09 and 268.5 μg mg⁻¹ dry weight, respectively). Capsaicin and dihydrocapsaicin, hydroxycinnamic and hydroxybenzoic acids and quercetin derivatives were the most abundant, while carotenoids represented only a minor fraction. The oleoresin was efficient to inhibit all three pathogenic fungi and ED₅₀ values were determined, evidencing that G. bidwellii was the more sensitive (0.233 ± 0.034 mg mL⁻¹).

CONCLUSION

The results suggested a potentiality of chili pepper extract for the control of some important grapevine pathogens, their possible application being helpful for the recommended limitation in extensive use of copper in vineyard. The complex mixture of high amounts of capsaicinoids, associated to specific phenolic acids and other minor bioactive components might contribute to the observed antimicrobial action of chili pepper extract. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.     

Citrus black spot severity related to premature fruit drop in sweet orange orchards

Citrus black spot (CBS) may cause substantial yield loss in sweet orange orchards. Severity and distribution of CBS symptoms on fruit may be variable and not all affected fruit may fall. However, the relationship between CBS symptoms and yield loss has not yet been investigated. This study aimed to determine CBS characteristics associated with premature fruit drop. A set of fruit was removed from the tree to measure the detachment force and another set of dropped fruit was collected from Pera and Valencia sweet orange orchards in three municipalities in Sao Paulo state, Brazil. CBS severity, distance of the nearest lesion from the peduncle, and fruit peel colour were assessed in both fruit sets. CBS severity was consistently related with the force to remove fruit and hence associated to the premature fruit drop, irrespective of the cultivar and location. The segmented linear regression showed that the fruit detachment force was reduced abruptly, at a rate of 7% for every 1% increase in disease severity up to 4.2 ± 1.0% CBS severity and, above this breakpoint, the force decreased slightly at a rate of 1.5%. Taking into account all orchards, the proportion of dropped fruit with CBS severity higher than the breakpoint was approximately 90%. This study provides a better understanding of the relationship between CBS severity and premature fruit drop of sweet orange. CBS severity breakpoint may be used as a reference to anticipate harvest and reduce CBS-related yield loss in orchards intended for juice processing.