Evaluation and molecular marker assessment for disease resistance towards Fusarium oxysporum f. sp. cubense (FOC TR4) in Musa acuminata ssp. malaccensis and Musa gracilis

Over the past decades, banana plantations worldwide were severely damaged by Fusarium oxysporum f. sp. cubense Tropical Race 4 (FOC TR4). Breeding of new elite resistant cultivars from wild banana species are expected to provide valuable sources of resistance. Populations of M. acuminata ssp. malaccensis and M. gracilis were developed by using embryo culture technique. Germinated embryos were transferred onto new medium to generate replicates for each individual. Rooted plantlets were then transferred into polybag for acclimatisation. Plants (10 – 15 cm) were uprooted and immersed in microconidial suspension before being replanted into double-tray for screening of differential symptoms expression of FOC TR4. Molecular screening of banana plants with different disease expression (resistant, tolerant and susceptible) using RAPD and IRAP analysis were carried out to determine potential markers associated to resistance and/or susceptible towards FOC TR4. Micropropagation of M. acuminata ssp. malaccensis population was successful but most of the M. gracilis plantlets succumbed to necrosis during acclimatisation. A total number of 65 individuals of M. acuminata ssp. malaccensis and only 38 individuals of M. gracilis were used for disease screening. Out of 65 individuals, 6 individuals of M. acuminata ssp. malaccensis were resistant, 23 were tolerant and 36 were susceptible to Fusarium wilt. However, all 38 plants of M. gracilis were susceptible to FOC TR4. Thus, only M. acuminata ssp. malaccensis population was used for molecular screening. Based on the bulked segregation analysis of M. acuminata ssp. malaccensis, 2 potential markers were obtained when RAPD analysis was used (OPA-03 and OPA-21). IRAP showed 3 potential markers (primer combination of 3‘ LTR/Nikita, 3‘ LTR/LTR 6150 and 3‘ LTR/LTR 6149) that produced polymorphic bands between resistant and susceptible individuals within the M. acuminata ssp. malaccensis population. Future research using a bigger population could be done to fully discover the potential of M. gracilis in creating new elite banana cultivar that is resistant towards FOC TR4 because insufficient number of sample can affect the accuracy result of screening towards FOC TR4.