Screening of Resistance Genes and Some Reactive Oxygen Specific Enzymes against Xanthomonas axonopodis Pv. Phaseoli and Pseudomonas savastanoi Pv. Phaseolicola in Bean Varieties

Background: Common bacterial blight (CBB) and halo blight (HB) are among the most destructive bacterial diseases affecting common beans, leading to significant yield and quality losses. The use of resistant cultivars remains the most effective and sustainable management strategy. Identifying the presence of resistance genes and understanding the role of antioxidant enzymes before and after bacterial inoculation are crucial for developing resistant breeding lines. Methods: This study investigated the presence of resistance genes against Xanthomonas axonopodis pv. phaseoli (Xap) and Pseudomonas savastanoi pv. phaseolicola (Psp) in eight bean varieties (Ozmen, Noyanbey, Akman, Alberto, XAN159, Vax1, Aras 98 and 36K). Additionally, the activities of antioxidant enzymes; Peroxidase (POX) and Catalase (CAT) were evaluated in two selected varieties (Aras 98 and 36K) following bacterial inoculation. Resistance genes (SAP6, BAC6, BC420 and R7313 for Xap; SR13, ST8, SH11 and SB10 for Psp) were screened using SCAR markers under greenhouse conditions. Four-week-old bean seedlings were inoculated with Xap and Psp isolates and leaf samples (1 g) were collected at 0, 12, 24, 48 and 72 hours post-inoculation for enzyme assays. Result: Under greenhouse conditions, the lowest disease incidence and severity for CBB and HB were observed in XAN159, Vax1, Ozmen, Noyanbey and 36K (p≤0.01). The SAP6 and BAC6 resistance genes were present in all cultivars except Alberto and Aras 98, respectively, while the SR13 gene was absent in Noyanbey and Aras 98. POX activity increased by 198.40% in the 36K cultivar at 36 hours post-inoculation, whereas CAT activity reached its peak (0.4087 U/g FW) in the same cultivar at 72 hours after Psp inoculation (p≤0.01). The enhanced activities of antioxidant enzymes, along with the presence of specific resistance genes, appear to play a critical role in the defense mechanisms of resistant and susceptible bean genotypes against bacterial infection.