Molecular Pathogens 2024, Vol.15, No.3, 155-169 http://microbescipublisher.com/index.php/mp 158 The diagnosis of PM is often based on these visible symptoms and can be confirmed by the identification of the fungal species responsible for the infection. Morphological characteristics such as conidia shape, the presence of fibrosing bodies, and the formation of cleistothecia are used for species identification (Pérez-García et al., 2009; Aguiar et al., 2012; Liang et al., 2020). Molecular tools, such as sequencing of the ITS region of rDNA, have also been employed to accurately identify the causal agents of PM in cucurbits (Liang et al., 2020; Caligiore-Gei et al., 2022). 3 What Problems Does PM Cause 3.1 Economic impact on Cucurbitaceae cultivation and yields PM, primarily caused by the fungus P. fusca (synonymP. xanthii), poses a significant threat to the cultivation of Cucurbitaceae, which includes economically important crops such as cucumbers, melons, and squashes. The disease can lead to substantial yield losses worldwide, as it affects the plants during critical growth stages. In China, for instance, the incidence of PM on hulless Cucurbita pepo reached 100%, indicating the potential for complete crop failure if the disease is left unmanaged (Liang et al., 2020). The economic impact is further exacerbated by the costs associated with disease control measures, including chemical treatments and the development of resistant cultivars (Pérez-García et al., 2009). 3.2 Effects on plant health and productivity PM affects plant health by forming white colonies on leaf surfaces, petioles, and stems, which can coalesce under favorable conditions, leading to chlorosis and early senescence of the host tissue (Pérez-García et al., 2009). This disease reduces plant growth and can cause premature defoliation, which in turn diminishes the photosynthetic capacity of the plant and its overall productivity (Priyanka et al., 2020). The severity of the disease varies with environmental conditions and can range from mild to severe, affecting the plants in different seasons (Wani, 2012). 3.3 Impact on fruit quality and marketability The presence of PM not only reduces the quantity of the harvest but also impacts the quality and marketability of the fruits. Infected plants produce fruits that are often of inferior quality due to the compromised health of the plant. The disease can lead to a reduction in both the aesthetic and nutritional value of the fruits, which affects their marketability and the economic returns for farmers (Priyanka et al., 2020). The control of PM is therefore crucial not only for maintaining the yield but also for ensuring the quality of the produce that reaches the market. 4 Genetic Characteristics of PM The genetic characteristics of PM fungi, particularly P. xanthii, are marked by a large and complex genome with significant genetic diversity and variability. Comparative genomics has provided valuable insights into the mechanisms of adaptation and pathogenesis, which are essential for developing effective disease management strategies for cucurbit crops. 4.1 Overview of the fungal genome The genome of P. xanthii, a pathogen causing PM in Cucurbitaceae, has been characterized and assembled, revealing a size of 209.08 MB and 142 Mb in two separate studies, with the latter resulting in 14 911 complete genes identified (Table 1) (Kim et al., 2020; Polonio et al., 2020). The genome contains a significant proportion of repetitive sequences, which comprise 76.2% of the genome (Polonio et al., 2020). Comparative analysis with other fungal pathogens has been conducted to identify candidate secreted effector proteins, which are crucial for the pathogenesis of P. xanthii (Kim et al., 2020). 4.2 Genetic diversity and variability among different PM species Genetic variation among isolates of P. xanthii from various cucurbit hosts and geographic locations has been investigated, showing a trend of isolates clustering from New York and Italy (Xiang et al., 2019). This diversity is also reflected in the virulence of the isolates, with significant differences observed among them (Xiang et al.,
RkJQdWJsaXNoZXIy MjQ4ODYzNA==