The role of Bacillus megaterium and other bio-agents in controlling root-knot nematodes infecting sugar beet under field conditions

摘要

A micro-plot field experiment was conducted in loamy soil naturally infested with Meloidogyne spp. to assess the potential of bio-agents namely bio-arc (Bacillus megaterium), nemastrol (a mixture of active ingredients), humisun (humic acid), and dried sweet basil callus to suppress nematodes’ population and induce resistance in sugar beet. Results indicated that integration of two or more components of such bio-agents gave better results in sugar beet growth parameters than did single ones. Hence, nemastrol and humisun in concomitant with bio-arc, sweet basil callus, and oxamyl (half recommended dose) induced significant (P ≤ 0.05) and maximum improvement in total plant fresh weight and shoot dry weight. Similar trend was also noticed in root diameter and number of leaves of sugar beet infected with Meloidogyne spp. Additionally, the greatest suppression in nematodes’ population (95.7%), root galling (83.0%), and number of egg masses (100%) was also sustained at the soil amended with nemastrol + humisun + bio-arc + sweet basil callus + oxamyl since incorporation of such organic materials into soil might enhance B. megaterium activity that initiates antibiotics towards nematode population. However, single application of dried sweet basil callus showed better performance than did the dried leaves in terms of female fecundity and total nematodes’ population. Thin-layer chromatography (TLC) and nuclear magnetic resonance (NMR) indicated the presence of higher content of triterpenoides that belong to three groups, i.e., lupane, ursane, and oleanane, in dried sweet basil callus compared to native dried leaves powder. Concomitant treatment with nemastrol + humisun + bio-arc + sweet basil callus + oxamyl exhihited significantly increased in sucrose (17.1%), total sugar solids (21.8%), and purity (79.0%). The activities of both peroxidase (PO) and polyphenol oxidase (PPO) showed detectable fluctuations at the end of the experiment compared to untreated plants.