Plant Phenology and Leaf Maturity Influences on the Nematicidal Activity of Castor Leaf Extracts Against Okra Root-Knot Nematodes
Plant Phenology and Leaf Maturity Influences on the Nematicidal Activity of Castor Leaf Extracts Against Okra Root-Knot Nematodes
Kouakou Yadom Yao François-Regis*, Kra Kouamé Daniel and Atta Diallo Hortense
ABSTRACT
The nematicidal efficacy of castor plants was usually assessed using leaves, regardless of maturity or plant phenology. Under these conditions, the efficacy of each leaf type is unknown. This study aimed to identify the maturity level of castor leaves that exhibit the highest nematicidal activity against okra root-knot nematodes. Aqueous extracts of five types of castor leaves were prepared. These were immature (ILV) and mature (MLV) leaves from vegetative plants and immature (ILF) and mature (MLF) leaves from flowering plants. The fifth type (ATL), a mixture of all leaf types, was used as a control. Second-stage juveniles and eggs of M. incognita were exposed to extracts for 72 hours and 10 days, respectively. Egg-hatching inhibition and juvenile mortality were used to evaluate the in vitro efficacy of extracts. Castor leaf extracts were applied to okra soils infested with M. incognita. The gall index, gall reduction, and nematode reproduction were determined. The unhatched egg rate ranged from 49.50 to 81.60%, and the juvenile mortality varied from 73.10 to 100% depending on extracts. The immature leaf extract from flowering plants was the most effective, with 81.60% unhatched eggs and 100% juvenile mortality. Regardless of plant phenology, immature leaf extracts were the most effective in limiting gall development by approximately 50%. Immature castor leaf extracts have high nematicidal activity. Farmers could prefer immature leaves in order to develop nematicides for okra root-knot nematode management.
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