First Report of Fusarium oxysporum f. sp. cubense Tropical Race 4 Causing Fusarium Wilt in Cavendish Bananas in Peru

Abstract

Fusarium oxysporum f. sp. cubense Tropical Race 4 (Foc TR4), the causal agent of Fusarium wilt of banana (FWB), is currently the major threat to the banana industry worldwide (Dita et al. 2018). Restricted to South Asia for more than 20 years, Foc TR4 has spread in the last years to the Middle East, Mozambique, and Colombia (García-Bastidas et al. 2019; https://pestdisplace.org/embed/news/map/disease/11). The incursion of Foc TR4 in Colombia increased awareness and prevention efforts across Latin American and the Caribbean (LAC). However, new Foc TR4 outbreaks in LAC countries were considered a matter of time. In April 2021, banana (Musa spp., Cavendish, AAA) plants (30% of incidence) showing typical symptoms of FWB, such as leave yellowing, wilting and vascular discoloration were observed in one farm (about 1 ha) located in Querecotillo, Peru (4°43’54.84”S 80°33’45.00”W). Mycological analyses of samples (pseudostem strands) collected from 10 symptomatic plants were performed as described by Dita et al. (2010). These analyses revealed a continuous presence of fungal colonies identified as Fusarium oxysporum species complex. Molecular diagnostics targeting two different genome regions (Dita et al 2010; Li et al. 2013) identified nine of these isolates as Foc TR4. These results were further confirmed by qPCR analyses using the commercial Clear Detections TR4 kit. The genome of four single-spore isolates (PerS1, PerS2, PerS3 and PerS4) was sequenced using the Illumina platform (MiSeq Kit, 2x151 bp Paired-End). The strain PerS4 was also sequenced using Oxford Nanopore (FLOW-MIN111; R10.3 chemistry) as described by Lopez-Alvarez et al., (2020). The generated draft assembly yielded 533 contigs for a size of 47 Mbp (BioProject: PRJNA755905), which is comparable with sizes of previously reported Foc TR4 strains (Asai et al. 2019; García-Bastidas et al. 2019; Maymon et al. 2020; Warmington et al. 2019; Zheng et al. 2018). The sequence assembly showed high contiguity (94.9%) and high similarity (95.48%) with the high-quality genome sequence of the Foc TR4 isolate ‘UK0001’ (Warmington et al. 2019). Further analyses to identify the presence/absence of full sequences for the putative effector genes (Secreted In Xylem - SIX) and their allelic copies, also revealed that the SIX genes profile of the strains isolated from Querecotillo matched with previously reported Foc TR4 isolates (Czislowski et al. 2017). Pathogenicity tests with three isolates and water controls were performed as described by Dita et al. (2010), using five Cavendish plantlets per treatment. Four weeks after the inoculation typical external and internal symptoms of FWB were observed only in the inoculated plants. Fungal isolates recovered from inoculated plants tested positive for Foc TR4 when analyzed with PCR diagnostics as mentioned above. No fungal isolates were recovered from water-control plants which did not show any symptoms. Altogether, our results confirm the first incursion of Foc TR4 in Peru. Currently, Foc TR4 has the phytosanitary status of a present pest with restricted distribution in Peru and it is under official control of the National Plant Protection Organization – SENASA. Reinforced prevention and quarantine measures, disease monitoring and capacity building to detect, contain and manage eventual new outbreaks of Foc TR4 are strongly encouraged across LAC banana producing countries, especially for those bordering Peru with larger banana plantations, such as Ecuador and Brazil.

Draft Genome Sequence of Fusarium oxysporum f. sp. cubense Tropical Race 4 from Peru, Obtained by Nanopore and Illumina Hybrid Assembly

“…In April 2021, banana plants ( Musa acuminata group AAA, subgroup Cavendish) showing symptoms of Fusarium wilt were observed on a farm in Querecotillo, Peru (4°43′54.84″S, 80°33′45.00″W). Diagnostic analyses confirmed the identity of the pathogen as Foc TR4 ( 4 ). Pseudostem strands from symptomatic plants were transferred to potato dextrose agar (PDA) medium and incubated at 25°C.…”

Induced resistance to Fusarium wilt of banana caused by Tropical Race 4 in Cavendish cv Grand Naine bananas after challenging with avirulent Fusarium spp.

“…To date, there are no commercial cultivars resistant to Fusarium wilt in banana TR4 with similar levels of resistance as Cavendish to Fusarium Race 1, hence the importance and benefit on studying the presence of fusarium wilt in banana, the favourable environmental conditions and the mechanism of the induced resistance among other factors (109). Our results could serve as the basis for future lines of research by molecular plant scientists in Colombia and Peru where Fusarium TR4 has been recently described [ 107 , 108 ]. Such research would be an essential contribution in adjacent banana areas of Latin America [ 109 ] to avoid the spread and devastation of banana plantations.…”

Uncontained spread of Fusarium wilt of banana threatens African food security

“…Nevertheless, in 2021, TR4 also appeared in the neighboring Magdalena department [ 27 ], demonstrating the spread of TR4 irrespective of the implemented containment strategies. A recent incursion in Peru [ 26 ] illustrates ongoing local and global spread but is considered to be independent of the presence of TR4 in Colombia [ 27 ]. However, this can only be concluded after sufficient sampling in Colombia.…”