Management of date palm root rot diseases by using some biological control agents under organic farming system

In the current work an attempt was made to find out the most suitable bioagents that have the ability to protect Date palm cv. Zaghloul (Phoenix dactylfera L.) from some soilborne fungal diseases. Several soilborne fungi were isolated from root rots of date palm trees located in the farms of El-Beheira Governorate, Egypt, including; Fusarium solani, F. oxysporum, Rhizoctonia solani and Macrophomina phaseolina, and their pathogenicity were confirmed on date palm seedlings in the greenhouse. These fungi cause economic losses in date palm yield and a wide range of other cultivated plants. Many different antagonistic isolates (bioagents) i.e. Trichoderma album, T. harzianum, T. viride and T. hamatum were isolated from the rhizosphere soil of healthy date palm trees. For comparison of results, bio-commercial preparations mainly “Bio-zeid (T. album 10×10⁶ cfu/ ml)” and “Plant guard (T. harzianum 30×10⁶ cfu/ ml)” were also used to detect their antagonistic potential against the mycopathogens of date palm. In vitro antifungal efficacy of the bioagents was evaluated against all the pathogens, where T. harzianum was the most effective as it caused 87.10, 81.55, 77.60 and 68.55% reduction in the radial growth of F. solani, F. oxysporum, R. solani and M. phaseolina, respectively. In vivo assays under field conditions, all tested biotic treatments significantly reduced severity of root rot diseases caused by the concerned pathogens. Moreover, they increased the percentages of survived date palm plants in infested soils during both successive growing seasons of 2016 and 2017, where T. harzianum was the most effective bioagent as it showed an increase in date palm survival of about 82.35 and 86.67% at both seasons, respectively. In addition, all  bioagents  enhanced  the  growth parameters of date palm, i.e. plant  height (cm),  number  of  leaves/ plant and number of leaflets/ leaf, compared  with  the control  treatment. Thus, these effective bioagents could be used as biofungicides to control the root rot diseases of date palm in the field; accordingly, we could displace the use of non-ecofriendly and health hazards synthetic fungicides.