Use of image analysis to assess radial growth of Passalora arachidicola and Nothopassalora personata on solid media

Despite significant research on early and late leaf spot diseases of peanut, in vitro study of the respective causal agents, Passalora arachidicola and Nothopassalora personata, has been limited due to cultural challenges that make growth of these fungi difficult to quantify with traditional methods. Studies were conducted to evaluate the practicality of image analysis to assess radial growth and tissue volume by correlating these assessments to dry mass. Image analysis was also used to estimate radial growth rates for these fungi over time. Tissue area and volume were significantly correlated to dry mass for P. arachidicola in two separate experiments, and for N. personata when medium had been removed from tissues prior to dry mass assessments. Tissue area densities were the same for P. arachidicola and Pseudocercospora smilacicola, evaluated as a nonstromatal cercosporoid comparison, whereas tissue volume densities were greater for P. archidicola and N. personata than P. smilacicola. A quadratic relationship was observed between radial growth and incubation time for all isolates evaluated. Growth rates of P. arachidicola isolates were 2 to 4 times faster than N. personata during the first week of incubation and slowed over time. Growth rates of NP18R, a phenotype variant of N. personata, increased after neighboring colonies met and was nearly 2.5 times faster than the fastest rates observed for P. arachidicola. These experiments demonstrate that when fungal tissues are observable, image analysis is a useful assessment tool for P. arachidicola and N. personata. Care should be taken to monitor fungal phenotypic changes in these species because phenotype degeneration can affect growth rates.尽管针对花生早斑病与晚斑病的相关研究已较为充分，但由于传统培养方法难以定量表征这两种致病菌的生长情况，针对其各自致病菌——花生柱隔孢（Passalora arachidicola）与诺氏柱隔孢（Nothopassalora personata）的体外研究仍相对有限。本研究通过将图像分析所得的评估结果与真菌干重进行关联，旨在验证图像分析技术用于评估两种真菌径向生长与菌丝组织体积的可行性。同时，本研究还利用图像分析技术对两种真菌随时间变化的径向生长速率进行了估算。在两组独立实验中，花生柱隔孢的菌丝组织面积与体积均与其干重呈显著相关；对于诺氏柱隔孢，仅在干重测定前去除培养基的情况下，其组织面积与体积才与干重呈显著相关。以非子座型尾孢类真菌菝葜假尾孢（Pseudocercospora smilacicola）作为对照时，花生柱隔孢与菝葜假尾孢的组织面积密度并无显著差异；而P. archidicola与诺氏柱隔孢的组织体积密度均显著高于菝葜假尾孢。所有受试菌株的径向生长与培养时间均呈现二次函数关系。在培养的第一周，花生柱隔孢菌株的生长速率是诺氏柱隔孢的2至4倍，且其生长速率随培养时长增加逐渐放缓。诺氏柱隔孢的表型变异株NP18R的生长速率在菌落毗邻生长后出现提升，其最高生长速率几乎达到花生柱隔孢最快生长速率的2.5倍。本实验结果表明，当真菌菌丝组织可被观测时，图像分析技术可作为评估花生柱隔孢与诺氏柱隔孢生长情况的有效工具。需注意监测这两种真菌的表型变化，因为表型退化会对其生长速率产生影响。