First Report of Banana End Rot Caused by Corynespora torulosa in Pakistan

Abstract

Banana (Musa acuminata Colla) is an important crop in Sindh, Pakistan, where Basrai (Dwarf Cavendish) is the dominant cultivar (Muhammad et al. 2020). In November 2023, banana end rot (BER) was observed on Basrai fruits in Naushehro Feroze District (26.7878°N, 68.2680°E). Only 3 of 204 randomly surveyed plants showed symptoms, indicating low, localized incidence (1.47%). This may reflect early-stage emergence of the disease. Symptoms began as black necrotic lesions at the distal end or side of the tip, later exposing the pulp, encircling the fruit and extending 2–10 cm proximally within 10–20 days and affected tissue rarely detaches spontaneously. Three symptomatic fruits per plant were collected and processed aseptically. Five 1-cm² segments from each fruit were surface-sterilized and plated on PDA. Pure cultures were obtained by hyphal-tip isolation. Colonies were effuse, brown to black and fast-growing. Conidiophores were erect, 100–220 ×1–14 µm, with terminal, monoblastic and doliiform conidiogenous cells. Conidia were cylindrical, slightly curved to falcate, 60–90×10–15 µm and bearing 1–8 transverse pseudosepta, rarely aseptate. The micromorphology agrees with the description of C. torulosa by Crous et al. (2013). Ten isolates were obtained from infected tissues, all morphologically consistent with C. torulosa; PPL-93 was selected for molecular analysis. For molecular identification, genomic DNA was extracted. The ITS and 28S regions of nuclear rDNA were amplified using primers ITS1/ITS4 (White et al. 1990) and LR0R/LR5 (Vilgalys & Hester 1990), respectively. TEF1-α was amplified using EF1-983F/EF1-2218R (Rehner and Buckley 2005). The sequences were deposted in GenBank under accession numbers PQ198513 (ITS), PZ389741 (28S), and PZ429897 (TEF1-α). BLASTn analysis revealed a close resemblance between isolate PPL-93 and GenBank entries of C. torulosa. In the phylogenetic analysis, the ITS sequence of our isolate showed 100% identity with C. torulosa strain CBS 136419 (NR145181), while the 28S and TEF1-α sequences showed 99.7% (MH877634) and 99.8% (OM893035) identity, respectively. A maximum-likelihood phylogenetic tree based on concatenated ITS and 28S sequences placed PPL-93 within the C. torulosa clade with strong support; TEF1-α gene was excluded due to the absence of TEF1-α sequences for some reference species. Pathogenicity was tested in field on 30–45-day-old Basrai fruits. Conidia were suspended in sterile water, counted with a hemocytometer (1.3 × 10⁵ conidia mL⁻¹) following Almenares and Pérez-Vicente (2019). Surface-sterilized distal ends were injected with 0.5 mL suspension or sterile water as control treatments. Both treatments were replicated nine times (n=18) and bagged for 15 days. Symptoms appeared on inoculated fruits within 5–10 days and extended to 5–8 cm by 25 days. Control fruits remained asymptomatic. The pathogen was re-isolated from symptomatic tissues on PDA and morphometrically identified as C. torulosa, fulfilling Koch’s postulates. C. torulosa (as Deightoniella torulosa) was reported for BER in Jamaica (Meredith 1965). In Pakistan, C. torulosa (as Cercospora musarum) was previously listed on banana as a leaf spot pathogen (Government of Pakistan 1973). To our knowledge, this is the first confirmed report of C. torulosa causing BER in Pakistan. Since Basrai dominates commercial banana production in Sindh, BER may reduce fruit quality and marketability, this study highlights the need for improved surveillance and management.