Rhizoctonia solani, Fusarium solani, F. oxysporum F. equiseti and F. semitectum were found to be associated with root rot and wilt symptoms of fodder beet plants collected from different fields in New Valley governorate, Egypt. All the obtained isolates were able to attack fodder beet plants (cv. Starmon) causing damping-off and root rot/wilt diseases. R. solani isolate FB1, F. solani isolate FB7 and F. oxysporum isolate FB11 were the more virulent ones in the pathogenicity tests. The efficacy of 4 different potassium salts for controlling damping-off, root rot and wilt diseases in fodder beet were evaluated in vitro and in vivo.
In vitro studies, all the tested potassium salts were significantly suppressed growth of the pathogenic fungi at different concentrations. KHCO3 showed superior higher inhibitory effect on redial growth of the tested pathogenic fungi especially at higher concentration (20 mM).
Under green house and field conditions, all potassium salts significantly reduced damping-off and root rot/wilt severity and increased survival of plants. The reduction in damping-off and root rot/wilt increased with increasing of potassium salts concentration except potassium sulfate (K2SO4), while concentration 10 mM was more effective for reducing damping-off and root rot/wilt severity than 20 mM. K2SiO3 followed by K2HPO4 recorded highly protection against damping-off and root rot/wilt severity more than the other tested potassium salts. Under field conditions, all these potassium salts at different concentrations significantly submitted to various growth and yield parameters viz. root length, root diameters, fresh and dry weights compared with control during growing seasons 2013-14 and 2014-15. While, % dry maters was no significant in both growing seasons. The applied treatment K2SiO3 achieved the highest increase in all the mentioned parameters over the other entire three potassium salts during both growing seasons.
In physiological studies, activity of defense-related enzymes, including peroxidase (PO), polyphenol oxidase (PPO), phenylalanine ammonia lyase (PAL), and tyrosine ammonia lyase (TAL) and total phenols content were increased in inoculated plants with R. solani, F. solani, and F. oxysporum individually and treated with potassium salts compared with untreated plants. K2SiO3 at 20 mM showed the highest level of all oxidative enzymes activity and total phenols content followed by K2HPO4 and K2SO4 at 20 mM. Whereas, the least enzymes activity was recorded with KHCO3 at 10 mM. These results suggested that these chemicals may be play an important role in controlling the fodder beet damping-off, root rot and wilt diseases; through they have induction of systemic resistance in fodder beet plants.