Crown and Root Infection of Lisianthus Caused by Fusarium solani in South Africa.

Abstract

Cultivation of lisianthus (Eustoma grandiflorum (Raf.) Shinn.) is a minor industry in South Africa, with only a few growers producing the crop commercially. Commercial production at a location in Gauteng Province is hampered by rotting of the crowns and roots of plants that result in mortality of as much as 22% of the plants. At advanced stages of infection, the crowns of affected plants characteristically are covered with masses of fusoid, curved hyalophragmospores. Crowns and roots of symptomatic plants that were submitted by the grower in January 2003 were surface disinfested by immersing for 2 min in a 3% solution of sodium hypochlorite, and segments excised from the plant tissue were plated on potato dextrose agar supplemented with 50 mg l-1 of rifampicin. Fusarium solani (Mart.) Appel & Wollenw. (1), was consistently and exclusively isolated from the segments. Teleomorph Nectria haematococca Berk. & Broome, commonly developed in culture after incubation for 4 to 6 weeks, although no sexual structures were observed on infected plants. A spore suspension containing 104 micro- and macroconidia ml-1 was prepared for each of two single-conidial isolates of F. solani. Using a 0.8-mm-diameter hypodermic needle, 100 μl of each suspension was injected subepi-dermally into the crown of each of three 1-month-old disease-free lisian-thus plantlets (cv. Texas Blue Bell) growing in 500-ml plastic pots filled with sterilized vermiculite. In addition, each suspension was incorporated at 2% (vol/vol) into three pots with sterile vermiculite, and a plantlet was planted in each pot. Control plantlets were treated similarly, but with sterile distilled water. All inoculated plantlets developed crown rot and wilted within 2 weeks while maintained at 28°C in a greenhouse, regardless of mode of inoculation, and F. solani was readily reisolated from their crowns and roots. Control plantlets remained symptomless and did not yield F. solani. Crown and root infection of lisianthus by F. solani has been described (2,3), but to our knowledge, this is the first report of the disease in South Africa.