Molecular Pathogens 2024, Vol.15, No.3, 119-128 http://microbescipublisher.com/index.php/mp 121 virus (Boukari et al., 2019; Holkar et al., 2020). The virus is not transmitted mechanically, which underscores the importance of aphid vectors in its spread (Paray et al., 2011; Holkar et al., 2020). The initial multiplication of SCYLV in a virus-free plant occurs exclusively in very young sink tissues. When a single leaf is inoculated, only the meristems and subsequently formed new leaves become infected, while older leaves remain virus-free. The spread of SCYLV within plantation fields via aphids is relatively slow, typically in the range of a few meters per year, with no indication of long-distance transfer. This slow spread suggests that it may be possible to produce and use virus-free seed cane for planting high-yielding but YLS-susceptible cultivars (Boukari et al., 2019). In field conditions, the prevalence of SCYLV can vary significantly depending on the cultivar, location, and crop season. For instance, in Florida, virus prevalence ranged from 83% to 100% in plots planted with infected seed cane, while healthy sugarcane became progressively infected over multiple crop seasons (Boukari et al., 2019). The impact of SCYLV on yield can also vary, with some cultivars showing significant yield reductions while others remain unaffected (Rassaby et al., 2003; Boukari et al., 2019). 4 Symptoms and Diagnosis 4.1 Visual symptoms in infected plants Sugarcane yellow leaf virus (SCYLV) infection manifests primarily through yellowing of the leaf midrib, which can progress to leaf necrosis and growth suppression in severe cases (Figure 1) (Holkar et al., 2020). The visual symptoms are not always consistent across all cultivars, as some may show symptoms sporadically or not at all despite being infected (Fitch et al., 2001). In Réunion Island, leaf yellowing was observed at harvest, particularly when sugarcane was no longer irrigated, with 10%-59% of symptomatic stalks attributed to SCYLV presence (Rassaby et al., 2003). Additionally, the severity of yellowing symptoms was directly related to the extent of SCYLV infection (Rassaby et al., 2003). Figure 1 Symptoms of yellow leaf disease in sugarcane and natural occurrence of aphid colonies (Adopted from Holkar et al., 2020) Image caption: (A) aphid (Melanaphis sacchari) infesting sugarcane and reported vector of Sugarcane yellow leaf virus (SCYLV) in India; (B) matured leaves with mild yellowing of midrib; (C) young leaves showing mild midrib yellowing and matured leaves showing initial discoloration of leaf lamina; (D) young leaves showing bright midrib yellowing and matured leaves showing extensive discoloration of lamina with necrosis; (E) severe necrosis of leaf area in matured leaves; (F) plant showed extensive stunting with complete drying (Adopted from Holkar et al., 2020)
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