Improved <i>in vitro</i> bioassay for <i>Musa acuminata</i> cv. Pisang ambon kuning (AAA group) based on quantitative analysis of necrosis area and biomass changes during Foc4 infection

Efforts in improving banana plants that are resistant to the Fusarium wilt-causing Fusarium oxysporum f.sp. cubense tropical race 4 (Foc4) are indispensable. In this study, we developed rapid, space-efficient in vitro bioassay for assessing banana plant resistance to Foc4 using 35 × 150 mm glass test tubes, followed by quantitative and objective analysis of necrosis area and biomass changes as represented by fresh weight changes. Disease resistance screening was conducted based on the necrosis area as quantified using ImageJ software and on biomass gain during in vitro bioassay. In vitro banana plantlets showed age-related resistance during the development of necrosis (p = .034, Kruskal–Wallis test in root and shoot system and p = .027, one-way ANOVA in shoot system only), in which plantlets that were infected at the youngest age (24 weeks’ post-initiation) showed the largest necrosis area (up to 46.6%). In addition, plant fresh weight gain in this group (0.233 ± 0.041 g) was higher compared to the gains in older plantlets (0.079 ± 0.117 and 0.009 ± 0.069 g, infected at 28 and 38 weeks’ post-initiation, respectively). Overall, for consistent and reliable result, the age of banana plantlet should be taken into consideration in interpreting the result of this in vitro bioassay.