Abstract
Fusarium oxysporum f. sp. cubense (Foc) has severely curtailed banana production in the tropical regions of the world. The tropical race 4 (TR4) of Foc was detected in Australia in the 1990s and it is virulent to all Cavendish type banana cultivars, which represents the majority of banana production in Australia. Genetic resistance to Foc race 4 is urgently needed. To characterize sources of resistance, we have assessed the Foc resistance response of 34 Musa cultivars with plants grown under controlled settings. Amongst diploid banana cultivars carrying the AA genome, resistance is found in Musa acuminata sub-species including malaccensis ‘Pahang’ and burmannica ‘Calcutta4.’ In the polyploid group, the hybrids such as ‘FHIA-18’ and ‘FHIA-25’ are highly resistant against both Foc-TR4 and subtropical race 4 (Foc-STR4). Interestingly, ‘FHIA-2’ and ‘CAM020’ appear to be resistant to Foc-TR4 but susceptible to Foc-STR4, suggesting potential differences in the resistance mechanisms against the different race 4 strains. Using a GFP tagged Foc-STR4 strain challenged onto both resistant and susceptible M. a. malaccensis lines, a high inoculum dosage rapidly induced vascular wilt in the susceptible M. a. malaccensis lines at 2.5 weeks. This was associated with an accumulation of micro-conidia in the rhizome and the movement of the fungus through the xylem vessels. In contrast, the fungal movement was restrained in the rhizome of the resistant M. a. malaccensis lines and no sporulation was observed. Overall, this research suggests that the resistance response is dependent to an extent on inoculum dosage and that the plant host’s response, in the rhizome, plays an important role in inhibiting the fungus from spreading to the rest of the plant. Identifying race 4 resistant accessions can help to understand mechanisms of resistance and provide banana breeders with the genetic resources to integrate resistance genes into commercial varieties.
Highlights
Banana and plantain (Musa spp.) serve as important sources of staple food and fruit around the world and collectively are considered the world’s leading fruit crop, with a production value reaching over 100 million tons per annum (FAO, 2019)
Using a green fluorescent protein (GFP) tagged Fusarium oxysporum f sp. cubense (Foc)-subtropical race 4 (STR4) strain, we show that the rhizome plays an important role as a barrier to the pathogen preventing it from migrating toward the rest of the plant
Thirty-four genotypes were tested for their response to Foc-STR4 under glasshouse conditions (Table 1)
Summary
Banana and plantain (Musa spp.) serve as important sources of staple food and fruit around the world and collectively are considered the world’s leading fruit crop, with a production value reaching over 100 million tons per annum (FAO, 2019). One of the major constraints in the global production of banana is the disease, Fusarium wilt. It is known as Panama disease, which is caused by Fusarium oxysporum f. Foc gains entry into the plant host via roots. Once inside, it colonizes the rhizome and travels up the pseudostem, where it blocks the water-conducting xylem vessels and prevents the transport of water and nutrients to the aerial parts of the plant. The disease incidence varies depending on the cultivar, the environment and the level of inoculum, but can extend to total crop loss in heavily infested fields (Moore et al, 2001)
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