A Protocol for Assessing Resistance to Aphelenchoides fragariae in Hosta Cultivars.

The use of resistant and tolerant cultivars is an important component of an integrated management plan for foliar nematodes on hosta. In order to identify tolerance and resistance in commercial hosta cultivars, reliable and efficient screening methods are required. To optimize the screening protocol, a series of greenhouse experiments was conducted using six hosta cultivars and two types of nematode inoculum. The pathogenicity and reproduction of Aphelenchoides fragariae maintained on fungal cultures versus maintenance on hosta were evaluated with two inoculation methods (with injury and without injury). Both sources of inoculum were pathogenic on all six cultivars tested but the plant inoculum caused two to eight times larger lesions than the fungus inoculum. Both inocula caused larger lesions and resulted in higher reproduction rates on injured leaves than on noninjured leaves. Water soaking was more efficient than traditional Baermann funnel extraction methods. Correlations between foliage symptom severity and nematode reproduction were low or nonexistence. A numerical scale for faster assessment of disease severity was developed, and recommendations for a reliable protocol for assessment of resistance and tolerance are discussed.