In Vitro and In Vivo Pathogenicity of A. alternata to Sugar beet and Assessment of Sensitivity to Fungicides

A. alternata is a weak and opportunistic pathogen, but recently this pathogen has been reported in major sugar beet growing regions in the US. Therefore, we were interested to investigate the in-vitro and in-vivo pathogenesis of A. alternata to sugar beet seed, seedlings, tissue slices, stecklings, and roots. The in-vitro study demonstrated that A. alternata reduces seed germination, causes damping-off of seedlings, and decomposes beet tissue. The in-vivo study showed the same inoculum responsible for Alternaria leaf spots, and black circular spots on beetroot. Furthermore, we did a preliminary study to determine in vitro sensitivities of some fungicides to determine the effective concentration that inhibited 50% of radial mycelial growth (EC50 values) of A. alternata. The results indicated that EC50 values ranged from 0.0023 to 0.0058 for PROLINE, from 0.0004 to 0.0021 for OMEGA, and from 0.0027 to 0.0053 for Super TIN. Among the potential fungicides, the efficiency of quinone outside inhibitors (QoI- PRIAXOR) was relatively higher to inhibit the radial growth of A. alternata, irrespective of concentrations.