Phytopathometry of Fungal Diseases Associated with Necrotic Syndrome in Wild Cactus (Pachycereus pringlei) in B.C.S., Mexico

Columnar cacti do not provide direct economic benefits; they are vital for maintaining the ecological balance of flora and fauna in desert ecosystems. Over the past 20 years, necrotic disease has been observed in the southern part of the peninsula, leading to a decline in populations. The infectious nature of the disease associated with cactus necrosis syndrome (CNS) was determined by estimating the incidence, severity, and dispersion index. The pathogenic fungi were studied based on symptoms, dispersion patterns, morphological features, and molecular analysis. To determine the pathogenicity and severity of the isolated fungi, experimental inoculations were performed on small cacti. Results showed that at least five fungi (Phoma spp., Nigrospora sphaerica, Chaetomium spp., Coniochaeta spp., and Alternaria alternata) may be associated with CNS, with responses varying depending on whether infections are mixed or straightforward. Common symptoms included canker and pustules, with prevalence rates of 78.87% and 85.3%, respectively. An increase in incidence of 9.89% was noted compared to 2019 (74.83%) and 2020 (84.72%). The average severity rate for all observed symptoms was 55.21%. These findings identify the causal agents involved in necrotic diseases, which could influence the severity and progression of CNS in B.C.S.