Laboratory and Field Techniques

A method to inoculate detached bean leaves with S. sclerotiorum without using a carbon-nitrogen source has been described by Leone and Tonneijck (1990). Leaves are incubated in plastic trays to maintain air humidity above 95 per cent. Spores of the pathogen inoculated in water alone are generally unable to cause infection. Additions of KH₂PO₄ (62.5 mM) or of mixtures of inorganic phosphate and glucose (1.1 or 5.5mM) to the inoculum stimulate fungal infection. Also spore concentration (2 × 10⁵ or 2 × 10⁶ spore’s ml⁻¹) influences the ability to produce lesions. The fungus concentration (2 × 10⁶ spores ml⁻¹) is able to infect primary bean leaves when inoculated in an inorganic phosphate solution. Since the procedure is simple and does not require blooming plants, it can be rapidly adopted in germplasm screening and breeding programs.

Wu and Liu (1991) indicated the possibility of in-vitro selection of rape (B. napus L.) callus cultures resistant to oxalic acid. However, Callahan and Rowe (1991) suggested that oxalic acid is not the sole inhibitory factor, yet other unidentified macromolecular components share a code terminate role in the inhibitory effect of lucerne S. trifoliorum system.