Endemic fungal disease is involved in anamorph reproduction in Citrus cultivars in Malabing Valley, Kasibu, Nueva Vizcaya [Philippines]

Citrus production started in 1960s in Malabing Valley, Kasibu, Nueva Vizcaya [Philippines]. Dominant cultivars are Mandarin such as Satsuma and Ponkan which makes Nueva Vizcaya as the Citrus Bowl of the Philippines. However, quality of fruits started to diminish due to pests and diseases. Early this year, new symptoms on the leaves were visible with small lesions. Thus, the study tried to document the casual agent of an endemic foliar disease and investigate the pathogenesis in Mandarin citrus cultivars. Infected young leaves were collected, isolated and purified into pure culture for characterization. Pure culture in plates with potato dextrose agar (PDA) were incubated for 1 week prior to morphological characterization. In-vitro pathogenesis was also conducted to confirm the identity of the disease. Prominent appearance of whitish mycelia on stomatal gradient on the abaxial portion of leaves. Infected leaf samples were turned yellow 2 weeks after colonization following falling of infected leaves with leaf rot disease (LRD). Full mycelial growth was observed in PDA plates 3 days after incubation. The presence of falcate-shaped macroconidia and microconidia with 1 to 8 celled conidia while unipolar and bipolar germination were observed 2 days after dispersal from conidiogenous cell. Formation of appresoria and haustoria were prominent and that the casual agent is in asexual stage, In-vitro colonization was observed on the stomatal portion of the leaves fully colonized by mycelia 14 days after inoculation. Based on morphological characterization and etiology of symptoms, the casual agent was identified as asexual stage infecting leaves. Hence, the casual agent of LRD was identified as Fusarium solani. This information, proved that the disease is an endemic disease at Malabing Valley, Kasibu, Nueva Vizcaya. This is the first documented report showing the detailed morphological characteristics and etiology of signs and symptoms of LRD of Mandarin in the Philippines.