Defense-related enzymes associated with resistance to onion Fusarium basal rot

This study was carried out to quantify changes in the activities of antioxidative enzymes such as catalase (CAT), peroxidase (POX) and superoxide dismutase (SOD) in two resistant onion cultivars 'Saba - HS' and 'Saba' and two susceptible cultivars 'Golden Eye' and 'Savannah Sweet' following an inoculation with Fusarium oxysporum f. sp. cepae (FOC) at seedling stage. Further, we assessed the expression of transcription factors (TFs), R1, PR5 and RGA29-genes that are involved in conferring resistance post-inoculation using qRT-PCR. The results revealed that the least disease severity occurred with the resistant 'Saba - HS' (4.7%) and 'Saba' (6.7%) cultivars, whereas the highest disease severity occurred with the susceptible 'Golden Eye' (89.6%) and 'Savannah Sweet' (88.9%) cultivars, respectively. Both resistant genotypes 'Saba' and 'Saba-HS' showed a significant increase in CAT, POX, and SOD activities at a transcriptional level. CAT activity was upregulated 4.81-fold in 'Saba' and 4.22-fold in 'Saba-HS' followed by POX where 'Saba' showed an increase by 3.53-fold and 'Saba-HS' by 2.35-fold, and SOD 'Saba' 17.46-fold and 'Saba-HS' 22.95-fold, relatively. Marker genes, RGA29, R1 and PR5, were also upregulated in the resistant-genotypes by 3.83, 4.78 and 5.01-fold, in comparison to their-controls, respectively. Similar trends were recorded for the biomass growth parameters (BGPs).