Peduncle Rot of Banana Caused by Fusarium petroliphilum and F. pernambucanum in Guangxi, China.

ABSTRACT

Banana is one of the main fruit crops worldwide. In October 2020, peduncles with rot were observed on bananas (Musa sp. ABB, Pisang Awak subgroup) at a about 1600 square meter commercial banana plantation in Dayu Town (23.17° N, 109.80° E), Guigang, Guangxi, China. The incidence of the disease was about 40%. The interior of the peduncle initially appeared reddish-brown and gradually turned black, and the peduncle eventually rotted. Two whole diseased bunches diseased samples were collected from banana plantations. Small pieces of tissues from the peduncle at the junction of disease and health were surface-disinfected in 75% ethanol for 10 s, 2% NaClO for 1 min, and rinsed three times in sterile water, then placed on potato dextrose agar (PDA) for incubation at 25°C. Forty-nine fungal isolates with similar morphology were recovered from diseased tissues, with 82% isolation frequency. Six isolates (GG3-1, GG3-2, GG3-3, GG4-1, GG4-2 and GG4-3) were selected for further study. Genomic DNAs of these isolates were extracted from 7-day-old mycelia. The internal transcribed spacer (ITS), translation elongation factor (TEF1), calmodulin (CAM), and partial RNA polymerase second largest subunit (RPB2) of six representative isolates were amplified and sequenced (O'Donnell et al. 2000, 2010; White et al. 1990). Sequences were deposited in GenBank. (accessions PP087392-PP087397 for ITS; PP102792-PP102797 for TEF1; PP102798-PP102803 for CAM; PP102804-P102809 for RPB2). A phylogenetic tree based on concatenated sequences of all markers using the Maximum Likelihood algorithm (Xia et al. 2019; Schroers et al. 2016). Based on phylogenetic analyses, GG3-1, -2 and -3 were identified as F. petroliphilum with 100% bootstrap support, and GG4-1, -2 and -3 were tightly clustered with F. pernambucanum with 95% bootstrap support. The two representative isolates GG3-2 and GG4-2 were selected for morphology and pathogenicity observation. Colonies of GG3-2 were light yellow and flat mycelium. They produced falciform macroconidia of 46.1 ± 5.3 × 2.6 ± 0.4 µm with 3 to 5 septates, and hyaline, ovoid microconidia of 7.6 ± 0.9 × 4.0 ± 0.6 µm with 0 septate (Brown et al. 2022). Mycelia were whitish to yellowish aerial mycelium for GG4-2. Their macroconidia were falcate of 31.6 ± 3.0 × 4.3 ± 0.3 µm with curved apical cells, foot-shaped basal cells, and 3 to 5 septates. The microconidia were fusoid of 8.9 ± 1.0 × 2.7 ± 0.3 µm with 0 to 1 septate (Santos et al. 2019). For pathogenicity tests, the ends of the banana peduncles were cut off. Needle punctures were made on the ethanol-treated peduncle pieces, followed by inoculation with 20 µL of conidial suspension (106 spores/ml) of each of the two isolates with three replications each. Sterilized water was used as a control. Peduncle pieces were placed in a humid box and incubated at 28ºC. After 7 days, reddish-brown to black lesions were observed on all inoculated peduncle pieces, while no symptoms were observed on the control pieces. The fungus was isolated from the inoculated peduncle pieces and found to match the morphological characteristics and marker sequences of the original isolates, confirming Koch's postulates. To our knowledge, this is the first report of peduncle rot on banana caused by F. petroliphilum and F. pernambucanum in China. This study will provide valuable information on causal pathogens of this disease which can contribute to improving prevention and disease management strategies for growers.