Field evaluation of non-pathogenic fusarium oxysporum isolates UPM31P1 and UPM39B3 for the control of fusarium wilt in 'pisang berangan' (Musa, AAA)

Fusarium wilt of banana is a devastating disease affecting many banana plantations worldwide. This study aims to establish the potential of using endophytes as part of a biological control approach. The efficacy of Fusarium oxysporum (fungal) isolate UPM31P1 and Serratia marcescens (bacterial) isolate UPM39B3 in suppressing Fusarium wilt incidence in 'Pisang Berangan' (AAA genome) was evaluated. These isolates were selected after a series of in vitro assessments, which showed their inhibitory effects on the growth of cultures of F. oxysporum f. sp. cubense 'tropical race 4' (Foc-TR4). Glasshouse trials have also indicated that treatments with UPM31P1 singly and in combination with UPM39B3 were effective in delaying the onset of Fusarium wilt symptoms and in reducing disease severity and incidence. In field assessments in a Foc-TR4 'hot spot', UPM31P1 was also applied to plants of 'Pisang Berangan' singly and in combination with UPM39B3. Inoculation with the biocontrol isolates was undertaken twice during the nursery stage and once when transplanted to the field. Field observations showed that treatment with UPM31P1, either singly or in combination with UPM39B3, was able to suppress wilt incidence in plants up until week 13 after planting. This amounted to a 6-week delay in the appearance of symptoms compared to untreated control plants. By week 15, percentages of surviving treated plants were 95-96% compared to 89% of the untreated controls. However, treated plants gradually succumbed to wilt disease. By the end of week 28, only 3-11% of treated plants still survived compared to 25% of untreated controls. Vegetative growth parameters were higher in treated plants than in untreated plants after 12 weeks growth in the field. Treatment with UPM31P1 and UPM39B3 thus seems to initially suppress wilt incidence and encourage vegetative growth. However, the study indicated that despite the endophytic nature of the isolates, their growth and proliferation in the host plant did not ultimately offer any defence against Foc-TR4. It may be possible to optimise the control strategy by more frequent applications and new formulations of isolates.