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Twenty-two spathiphyllum cultivars were evaluated for resistance to Cylindrocladium root rot (CRR). Four isolates of the fungus Cylindrocladium spathiphylli Shoult., El-Gholl & Alf. were selected from two different locations each in Florida and Hawaii. Spores of isolates were applied as a soil drench in replicated experiments using a randomized complete block design. The most severe symptoms were those produced by C. spathiphylli isolates from Hawaii. None of the spathiphyllum cultivars tested were highly resistant to CRR although resistance among the cultivars was observed. The cultivars Chris and Textura were the most promising cultivars, having fairly uniform resistance to the four isolates of C. spathiphylli. The cultivars Cupido, Daniel, Frederik, Jetty, and Vanessa were moderately resistant when combined data from all tests were analyzed. Results from this research permit the selection of more resistant breeding lines and also creates a baseline against which resistance of newly developed cultivars can be compared. T he potted ornamental tropical foliage industry has a wholesale value of over $514 million (Henley, 1996). Of the plants sold in the United States, spathiphyllum consistently outsells other popular foliage plants (Sheehan, 1994). The most damaging disease during spathiphyllum production is root rot caused by Cylindrocladium spathiphylli, first reported on spathiphyllum in the early 1980s (Schoulties and El-Gholl, 1980, 1983). Losses in production caused by Cylindrocladium root rot (CRR) are most severe during warm summer months and uncommon during cooler periods of the year. The first visible symptoms on infected spathiphyllum plants are chlorotic lower leaves and a wilted appearance, but these symptoms are secondary to the extensive root damage caused by this pathogen. Reddish-brown lesions, found on newly infected roots, expand rapidly causing total root collapse. Profuse numbers of spores are produced within infected root masses, providing inoculum that can be splashed onto leaves causing dimesized circular brown necrotic lesions surrounded by yellow halos. In cool fall weather, fungal growth slows and the fungus over winters in infected roots. Plants that harbor the fungus will not show symptoms until warm weather conditions return. Therefore, when new tissue-cultured spathiphyllum plants are purchased, they should never be placed with established plants that may be infected with CRR. Infected plants should be identified and removed from the production facility and remaining plants should be drenched with an appropriate fungicide. The most effective registered fungicides contain one of the following three compounds: triflumizole, thiophanate methyl, or copper sulfate (Norman, 1996). However, since chemical control of CRR is expensive and not always effective (Norman, 1996), development of resistant cultivars through breeding would be the most desirable solution to manage this disease. In a previous report, CRR resistance was shown in two spathiphyllum species but not in commercial cultivars (Henny and Chase, 1986). Unfortunately, the resistant species have little ornamental potential and do not hybridize with commercial cultivars. As a step toward the development of resistant cultivars, 22 popular commercial spathiphyllum cultivars were evaluated in this study.

Resistance in Twenty-two Cultivars of Spathiphyllum to Cylindrocladium Root Rot