Optimum Harvest Time of Cucumis africanus Fruit Using Concentration of Cucurbitacin B as a Maturity Standard

Fruit of wild watermelon (Cucumis africanus) are used to manufacture nemafric-BL phytonematicide for the management of population densities of the notorious root-knot (Meloidogyne species) nematodes on various crops. However, the concentration of the active ingredient, namely, cucurbitacin B, is dependent on the developmental stage of the fruit. A field study was, therefore, conducted to establish the optimum harvest time where C. africanus fruit would have the highest concentration of cucurbitacin B in order to ensure consistent quality of the phytonematicide. Fruit were harvested weekly from 60 to 110 days after transplating, prepared for extraction and cucurbitacin B quantified using reverse phase HPLC. Concentrations of cucurbitacin B were optimised at 5.0 weeks, which translated to a 95-day harvest time after seeding.