Abstract：
Phoenix dactylifera L. is an economically and aesthetically important tree in the southwestern US. Approximately 4900 ha of dates are commercially grown for its edible fruit in the US, including about 1600 ha in the Yuma area and the Hyder Valley of Arizona (USDA, 2023). In October 2022, a severe rot was observed on three date palms in the Phoenix Metropolitan area. Early symptoms were brown spots that turned to a black scorch appearance extending along the leaf base and rachis, leading to the lower fronds\' wilting, drying, and folding. As the disease progressed upwards, the terminal bud became necrotic and eventually collapsed. Isolation from the necrotic leaf lesions on a potato dextrose agar (PDA) consistently yielded a fast-growing fungus that was initially white with abundant fluffy aerial mycelium, which gradually turned dark olivaceous after growing at 22-25oC under 12 h light for a week. Pycnidial conidiomata formed on pine needles in a water agar were black and globose. Conidiogenous cells were hyaline and cylindrical. The conidia exhibited a thick-walled, ovoid to ellipsoid morphology, initially appearing hyaline and aseptate and transitioned to 1-septate with a dark brown, striated appearance, measuring 19.6 to 23.0 μm x 10.3 to 12.2 µm (n = 20). For molecular identification, genomic DNA was extracted from the mycelia of two isolates. Partial DNA sequences of the internal transcribed spacer (ITS) region of rDNA and β-tubulin (TUB) gene were amplified and sequenced using primers ITS5/ITS4 (White et al. 1990) and Bt2a/Bt2b (Glass and Donaldson 1995). The resulting sequences of ITS (PP346666) and TUB (PP372690) were deposited in the GenBank. A BLASTn search of ITS and TUB sequences revealed a 99 to 100% similarity with the sequences (JX456475, KF766198, and OK338070) of Neodeightonia phoenicum strains causing palm rot in Greece (Ligoxigakis et al. 2013), leaf spot on pygmy date palm in China (Zhang and Song 2022), and an ex-type CBS 122528 culture. Based on these morphological and molecular data, the fungus was identified as N. phoenicum. A pathogenicity test was conducted twice in a greenhouse (daily temperatures:18 ~ 30 oC, relative humidity: 45% ~ 95%) on 4 healthy 1-year-old date palm plants. The petioles of 3 older leaves per plant were wounded by pricking the epidermis of the leaf with a needle (ca 20 pricks per petiole) and inoculated with agar discs from a 4-day-old PDA culture of the fungus. The control consisted of 4 mock-inoculated plants by placing plain PDA on the wounds of leaf petioles. Five weeks after inoculation, all the inoculated leaves showed symptoms of black scorch, petiole rot, and leaf necrosis, which were the same as those symptoms observed on the original diseased trees, while the controls did not show any symptoms. The fungus was re-isolated and confirmed as N. phoenicum by morphology. N. phoenicum has been reported to cause leaf spot, shoots blights, stalk and root rots as well as black scorch on different palm species all over the world. However, to our knowledge, this is the first report of N. phoenicum causing black scorch and rot disease in Arizona. The possible spread of N. phoenicum could have a significant economic impact and requires immediate attention through suitable disease management initiatives.
摘要：
PhoenixdactyliferaL.是美国西南部经济和美学上重要的树木。在美国，大约有4900公顷的红枣被商业种植用于其可食用水果，包括约1600公顷的尤马地区和亚利桑那州的海德河谷(美国农业部，2023年）。2022年10月，在凤凰城都会区的三棵枣树上观察到了严重的腐烂。早期症状是棕色斑点，变成黑色的烧焦外观，沿着叶根和轴延伸，导致下部叶状体枯萎，干燥,和折叠。随着疾病的发展，末端芽坏死并最终塌陷。从马铃薯葡萄糖琼脂（PDA）上的坏死叶病变中分离出一种快速生长的真菌，该真菌最初是白色的，具有丰富的蓬松的气生菌丝体，在12小时光照下在22-25℃生长一周后逐渐变成深色橄榄质。在水琼脂中的松针上形成的分生孢子为黑色和球形。分生孢子细胞呈透明和圆柱形。分生孢子显示出厚壁，卵形至椭球形态，最初出现透明和无盐，过渡到1-纵隔，呈深棕色，条纹外观，测量19.6至23.0μmx10.3至12.2μm（n=20）。对于分子鉴定，从两个分离株的菌丝体中提取基因组DNA。使用引物ITS5/ITS4对rDNA和β-微管蛋白（TUB）基因的内部转录间隔区（ITS）区域的部分DNA序列进行扩增和测序（White等人。1990)和Bt2a/Bt2b(Glass和Donaldson1995)。将所得的ITS(PP346666)和TUB(PP372690)序列存入GenBank。对ITS和TUB序列的BLASTn搜索显示，与希腊引起棕榈腐烂的Neodeightoniaphoenicum菌株的序列（JX456475，KF766198和OK338070）具有99％至100％的相似性（Ligoxigakis等人。2013),中国侏儒枣树叶斑病(张和宋2022)，和前CBS122528型文化。基于这些形态和分子数据,该真菌被鉴定为N.phoenicum。在温室中进行了两次致病性测试（每日温度：18〜30oC，相对湿度：45％〜95％）在4种健康的1岁枣树植物上。通过用针刺破叶片的表皮（每个叶柄约20个刺），并从4天大的PDA真菌培养物中接种琼脂圆盘，从而使每株植物的3个较老叶片的叶柄受伤。通过将普通PDA放置在叶柄的伤口上，对照由4株模拟接种的植物组成。接种五周后，所有接种的叶子都显示出黑色烧焦的症状，叶柄腐烂,和叶子坏死，与在原始患病树上观察到的症状相同，而对照组没有任何症状。将真菌重新分离并通过形态学确认为N.phoenicum。据报道，N.phoenicum会导致叶斑病，拍摄枯萎病，在世界各地的不同棕榈品种上，茎和根腐烂以及黑色烧焦。然而,根据我们的知识，这是在亚利桑那州首次报道的由N.phoenicum引起的黑色烧焦和腐烂病。黄牛的可能传播可能具有重大的经济影响，需要通过适当的疾病管理措施立即予以关注。
