Wang X F, Li Z A, Tang K Z, Zhou C Y, Yi L
National Citrus Engineering and Technology Research Center, Citrus Research Institute, Southwest University, Chongqing 400712, P. R. China.
Jiangxi Navel Orange Engineering and Technology Research Center, Gannan Normal University, Ganzhou 341000, P. R. China.
Plant Dis. 2010 Mar;94(3):375. doi: 10.1094/PDIS-94-3-0375C.
Brown spot of citrus is considered a major problem on the fruit of many citrus cultivars grown for fresh markets including tangerines (Citrus reticulata) and their hybrids. It causes lesions on leaves, stems, and fruit and reduces yield and fruit quality (2). In 2003 in southern Wenshan Municipality, Yunnan Province in China, sporadic occurrence of Alternaria brown spot was observed on Tangfang mandarin, a local citrus cultivar identified preliminarily as a kind of mandarin hybrid. From 2006 to 2008, nearly 80% of local orchards were infected with the disease. Fruit symptoms typical of Alternaria brown spot ranging from light brown, slightly depressed spots to circular and dark brown areas were observed. Leaves showed small, brown, circular spots and irregular blighted areas with characteristic yellow halos. Tissues from the margin of fruit spots or infected leaf parts of eight different trees were surface sterilized in 1.5% sodium hypochlorite for 1 min, plated on potato dextrose agar (PDA), and then incubated at 27°C in the dark for 1 week. Dark brown mycelia and pigmented septate conidia with lengths of 10 to 35 μm and widths of 5 to 13 μm were produced. On the basis of conidial morphological characteristics, the pathogen was identified as Alternaria alternata (Fr.:Fr.) Keissl (1). Detached young healthy leaves of 'Minneola' tangelo (C. reticulata × C. paradisi) were sprayed with a conidial suspension of 10 conidia per ml and incubated in a moist chamber at 27°C. A control treatment with an equal number of leaves was sprayed with distilled water only. After 48 h, seven of these isolates caused necrotic lesions on detached leaves, characteristic of the disease, whereas there were no symptoms on leaves of the water control. Pure cultures were recovered on PDA from symptomatic tissues and the morphological characteristics of the conidia closely fit the description of A. alternata, confirming Koch's postulates. Currently, the distribution of Alternaria brown spot of citrus is confined to southern Wenshan Municipality in Yunnan Province where it is a serious disease problem on the most important commercial cultivar in this region. The identification of the pathogen now allows for appropriate field management and control measures. To our knowledge, this is the first report of Alternaria brown spot of citrus in China. References: (1) Z. Solel. Plant Pathol. 40:145, 1991. (2) J. O. Whiteside. Plant Dis. Rep. 60:326, 1976.
柑橘褐斑病被认为是许多用于鲜销的柑橘品种果实上的一个主要问题，这些品种包括蜜柑（宽皮柑橘）及其杂交种。该病会在叶片、茎和果实上造成病斑，从而降低产量和果实品质（2）。2003年，在中国云南省文山州南部，在当地一种初步鉴定为蜜柑杂交种的唐芳蜜柑上发现了链格孢褐斑病的零星发生情况。从2006年到2008年，当地近80%的果园受到该病感染。观察到了典型的链格孢褐斑病果实症状，从浅褐色、稍有凹陷的斑点到圆形深褐色区域。叶片上出现小的褐色圆形斑点以及带有特征性黄色晕圈的不规则枯萎区域。从八棵不同树木的果实斑点边缘或感染叶片部分采集的组织，在1.5%次氯酸钠中进行表面消毒1分钟，接种到马铃薯葡萄糖琼脂（PDA）平板上，然后在27°C黑暗条件下培养1周。产生了深褐色菌丝体以及长度为10至35μm、宽度为5至13μm的有色素的分隔分生孢子。根据分生孢子的形态特征，该病原菌被鉴定为链格孢（Fr.:Fr.）Keissl（1）。将‘明尼奥拉’坦普尔橘柚（宽皮柑橘×甜橙）的离体幼嫩健康叶片用每毫升含10个分生孢子的分生孢子悬浮液进行喷雾处理，并在27°C的保湿箱中培养。对同等数量的叶片进行对照处理，仅喷洒蒸馏水。48小时后，其中七个分离株在离体叶片上引起了坏死病斑，这是该病的特征，而水对照的叶片上没有症状。从发病组织在PDA上获得了纯培养物，分生孢子的形态特征与链格孢的描述非常吻合，证实了柯赫氏法则。目前，柑橘链格孢褐斑病的分布仅限于云南省文山州南部，在该地区它是最重要商业品种上的一个严重病害问题。病原菌的鉴定使得能够采取适当的田间管理和控制措施。据我们所知，这是中国柑橘链格孢褐斑病的首次报道。参考文献：（1）Z. Solel. Plant Pathol. 40:145, 1991.（2）J. O. Whiteside. Plant Dis. Rep. 60:326, 1976.
