Centre for Horticultural Science (CHS), Queensland Alliance for Agriculture and Food Innovation (QAAFI), The University of Queensland, Ecosciences Precinct, Dutton Park, QLD 4102, Australia; and School of Agriculture and Forestry, Hue University, Vietnam.
CHS, QAAFI, The University of Queensland, Ecosciences Precinct.
Plant Dis. 2018 Jul;102(7):1386-1393. doi: 10.1094/PDIS-08-17-1331-RE. Epub 2018 May 11.
Citrus black spot, caused by Phyllosticta citricarpa, is one of the most important fungal diseases in many citrus-growing regions with hot and humid summers. Ascospores and conidia are known to contribute to epidemic development of the disease. However, pathogenicity testing has never been done for pure ascospores produced from fully characterized P. citricarpa isolates, due to the inability to induce the sexual state in vitro. Recently, an in vitro mating technique was developed to readily produce pure P. citricarpa ascospores for use in host inoculation studies. To test the pathogenicity of P. citricarpa ascospores, we inoculated Troyer citrange leaves and Murcott tangor fruit with ascospores produced in vitro from characterized P. citricarpa isolates. Typical symptoms of citrus black spot occurred. Recovery of P. citricarpa isolates from symptomatic lesions and their characterization using genetic markers enabled us to identify recombinant genotypes among the isolates recovered from ascospore inoculations and, as such, fulfill Koch's postulates for ascospores. We have also identified Troyer citrange seedlings as a potential model system for citrus black spot inoculation studies, because it allows typical symptoms of citrus black spot to be expressed with a much shorter latent period than on fruit. This will facilitate future studies of epidemiological aspects of P. citricarpa ascospores relative to conidia and improve our understanding of the citrus black spot pathosystem. The susceptibility of Troyer citrange seedlings will also facilitate experimenting with disease management methods, aimed at reducing the impact of citrus black spot.
柑橘黑斑病由柑橘球腔菌引起，是许多夏季炎热潮湿的柑橘种植区最重要的真菌病害之一。已知分生孢子和子囊孢子有助于该病的流行发展。然而，由于无法在体外诱导性状态，从未对完全特征化的柑橘球腔菌分离物产生的纯子囊孢子进行致病性测试。最近，开发了一种体外交配技术，可轻松产生纯柑橘球腔菌子囊孢子，用于宿主接种研究。为了测试柑橘球腔菌子囊孢子的致病性，我们用体外产生的来自特征化柑橘球腔菌分离物的子囊孢子接种 Troyer 甜橙叶和 Murcott 脐橙果实。出现了典型的柑橘黑斑病症状。从接种子囊孢子后的症状性病变中回收柑橘球腔菌分离物，并使用遗传标记对其进行表征，使我们能够识别从子囊孢子接种中回收的分离物中的重组基因型，从而满足子囊孢子的柯赫氏假设。我们还确定 Troyer 甜橙幼苗是柑橘黑斑病接种研究的潜在模型系统，因为它允许在比果实上更短的潜伏期内表达典型的柑橘黑斑病症状。这将有助于未来研究柑橘球腔菌子囊孢子相对于分生孢子的流行病学方面，并提高我们对柑橘黑斑病病理系统的理解。Troyer 甜橙幼苗的易感性也将有助于进行疾病管理方法的实验，旨在降低柑橘黑斑病的影响。
