<i>In Vitro </i>and<i> in Vivo </i>Management of <i>Sclerotium rolfsii</i> the Cause of Sugar Beet Root Rot Disease

Abstract

Management of sugar beet damping off and root rot diseases caused by <i>Sclerotium rolfsii</i> is urgently needed. Therefore, antifungal activities of 13 materials including 2 bio agents, 2 seaweeds, 3 chemical inducers and 6 fungicides were evaluated. Required inoculum potential of either fungal mass or sclerotia to reach more than 50% of disease incidence was firstly investigated. Fungal mass inoculation (40-500g/10kg of soil) provided 70-100% damping off and 100% root rot. Meanwhile, 6.7-36.7% of damping off and no or negligible root rot were obtained using 300-500 sclerotia /10kg of soil. On the other hand, <i>S. rolfsii</i> mycelial growth was completely suppressed <i>in vitro</i> by all tested materials. However, various antifungal activities of these materials were shown <i>in vivo</i> after seed soaking in the 1^st (2020/2021) trail or seed soaking followed by soil drenching in the 2^nd (2021/2022) trail. Tipo top (Tebuoconazole 25.9%: 1cm/L) fungicide was the most effective material in the 1^st trail since the seedling survival was up to 80%, followed by potassium silicate (1cm/L) and Score (Difenoconazole 25%: 1cm/L) fungicide. Seed soaking followed by soil drenching with Tipo top in the 2^nd trail were protected sugar beet from sowing to harvest and enhanced the root weight. Additionally, this study illustrated that both of sugar beet root weight and sucrose content were decreased as root rot severity increased. In conclusion, chemical fungicides are unfortunately still the fast and potent way for <i>S. rolfsii</i> management, especially with the limitation of resistant sugar beet cultivars.