The Evolving Threat of Fusarium Wilt TR4 to Small-Scale Mixed Cultivar Banana Production in the Red River Basin of Northern Vietnam

Fusarium wilt (Foc) TR4 was first reported in Northern Vietnam in 2018. Since then, it has rapidly spread across most northern provinces along the Red River basin banana production landscapes, impacting Cavendish (<i>Musa</i> AAA genome) production. The other main banana cultivars which are widely grown in this production zone are Pisang Awak (<i>Musa</i> ABB genome) and Pisang Mas (<i>Musa</i> AA genome). Field surveys were conducted in 2022/2023 across this banana production region to assess pathogen spread from Cavendish monocropping systems into adjacent smaller-scale mixed cultivar systems. Across 130 sites, a total of 210 banana pseudostem tissue samples were collected from symptomatic Cavendish, Pisang Awak and Pisang Mas plants. Foc TR4 incursions into mixed small-to-mid-sized Cavendish-Pisang Awak plantations were confirmed, and the pathogen was also recorded in Pisang Awak plantations and backyard gardens that did not contain any Cavendish mats. A screenhouse-based Foc TR4 screening trial including seven commonly cultivated <i>Musa</i> varieties in Northern Vietnam indicated that Pisang Awak and Pisang Mas are susceptible to the pathogen. While Pisang Awak, an important local variety, is known to be susceptible to both Foc Race 1 and TR4, recent field observations suggest a limited susceptibility of Pisang Awak to Foc TR4 in mixed cultivar plantation settings. Local farmers similarly reported observing reduced susceptibility, with several having already replanted TR4-affected Cavendish fields with Pisang Awak as part of their disease management strategy. No infections were observed on field-grown Pisang Mas plants in TR4-affected mixed banana cultivar production landscapes. These results and insights provide solutions for the revival of TR4-affected Cavendish production fields or landscapes, through the cultivation of less susceptible local cultivars. In addition, the introduction, validation and scaling of Formosana (i.e., GCTCV-218, a Cavendish somaclone with moderate resistance to Foc TR4) should be envisaged.