First Report of Fruit Rot of Bell Pepper Caused by Fusarium incarnatum in Pakistan

Abstract

Evidence of fruit rot disease was observed in 12 bell pepper (Capsicum annuum L.) fields located in the Chakwal district (32°56′00″N, 72°51′30″E) of Pakistan during the period June 2016 to 2017. Disease incidence was estimated to be between 15 and 24%. Yield loss in affected fields was estimated as 11%. Symptoms of disease were seen as water-soaked, discolored necrotic lesions predominantly around the calyx. There were also symptoms of internal rot as seeds and the inner fruit surface were covered with white to light gray fungal growth. In the case of severe disease symptoms, fungal growth was also observed externally at the calyx end. The disease progressed as a soft decay with leakage. Diseased fruits were cut into 5-mm² pieces, surface disinfested with 1% NaOCl for 2 min, rinsed thrice with sterile distilled water, and incubated on potato dextrose agar (PDA) at 25 ± 2°C for 3 to 4 days under continuous fluorescent light. Eighteen isolates of similar morphology were purified using the hyphal tip technique. Colonies were fast growing, fluffy, white with pale cream to beige coloration on the reverse side of the Petri dish. Microconidia were hyaline, single celled to one septate, and 3.5 to 5.0 × 2.7 to 4.0 μm (mean = 4.0 × 3.8 μm). Mesoconidia were fusoid, usually three septate, and 9.8 to 17.5 × 3.0 to 4.5 μm (mean = 13.4 × 4.0 μm). Macroconidia were three to five septate, cylindrical, slightly curved, tapered at the apex, and 26.2 to 37.4 × 3.5 to 4.8 μm (mean = 32.5 × 4.2 μm). Based on morphological characteristics, the fungus was tentatively identified as Fusarium incarnatum (Leslie and Summerell 2006). DNA from two representative isolates, FICW7 and FICW16, was amplified with translation elongation factor (EF1-α) and β-tubulin genes using primers EF1/EF2 (O’Donnell et al. 1998) and Bt1a/Bt1b (Glass and Donaldson 1995), respectively. The obtained sequences for EF1-α (accession nos. MF977815 and MG770586) and β-tubulin (MF977818 and MG770587) were deposited in GenBank. The MegaBLAST and Fusarium ID database analysis revealed 99 to 100% homology to the Fusarium incarnatum-equiseti species complex, GenBank accession no. JF270273 (EF1-α), and AB587036 (β-tubulin) respectively. Pathogenicity tests of six isolates were conducted on three healthy bell pepper fruits per isolate, wound inoculated with a 20-μl drop of 10⁶ spores/ml. Three control fruits per isolate were inoculated with 20-μl droplets of sterile distilled water. Inoculated and control fruits were incubated in moist chambers at 25°C. After 3 to 5 days, white fluffy mycelial growth surrounded by water-soaked necrotic lesions appeared identical to the symptomatic fruits observed in the field/tunnel. No symptoms were observed on control fruits. The fungi isolated from the diseased fruits were morphologically similar to the original isolates on PDA. The pathogen was previously reported to cause the internal fruit rot disease of bell pepper in Trinidad (Ramdial et al. 2016). This is the first report of F. incarnatum (Desm.) Sacc. causing fruit rot on bell pepper in Pakistan. New strategies need to be developed for effective management of disease.