Basal rot of Alstroemeria spp. caused by Fusarium oxysporum in Argentina

Commercial varieties of Alstroemeria spp. (Alstroemeria, Peruvian Lily) were introduced to Argentina in the late 1990s with cropping concentrated in La Plata (Buenos Aires Province). Since 2002, diseased plants have been found in several greenhouses (Fig. 1) and in an experimental soilless culture system. Symptoms included yellowing progressing from the lower to upper leaves, hollow stems constricted at the base, and roots and rhizomes with brown rot (Figs 2 and 3). Some affected floral stems remained shorter than healthy ones.

Isolates of Fusarium sp. were consistently isolated on potato dextrose agar (PDA) from pieces of symptomatic stems, stored or uprooted rhizomes, and roots of different cultivars (following surface disinfection for 2 min in 2% NaOCl). Isolates were identified as F. oxysporum on the basis of cultural and morphological characteristics (Booth, 1971; Nelson et al, 1983). White to cream colonies developed on PDA, with purple pigmentation on the reverse side. Macroconidia (3-5 septate), abundant single-celled microconidia borne in false heads on short monophialides; chlamydospores were observed. Rhizoctonia solani was also isolated.

Pathogenicity tests were done with two isolates each of F. oxysporum and R. solani from alstroemeria, by addition of rice kernels colonised with each isolate to potted soil, and by placing agar plugs of each isolate on stem-base wounds. Six plants of cv. Alpine with 4 to 6 shoots were used per isolate and technique. Plants in uninfested soil, with wounded but uninoculated stems, were used as controls. Plants were incubated in a moist chamber for 48 h and then maintained at 22-28ºC. Typical symptoms were observed on wounded stems inoculated with F. oxysporum after 15-18 days (Fig. 4) and after 20-25 days in stems from soil infested with F. oxysporum. Uninoculated controls and plants inoculated with R. solani remained symptomless (Fig. 5).Alstroemeria basal rot could be a serious problem in the future because it will be difficult to eliminate F. oxysporum from rhizomes, soil- and soil-less systems. Chang & Mirza (1993) and Chang et al. (1994) cited F. oxysporum, R. solani and Pythium ultimum causing rhizome and root rots of Alstroemeria spp. in Canada. More recently, fusarium wilt of alstroemeria has been reported from India (Shanmugam et al., 2006). This is the first report of F. oxysporum causing basal rot of Alstroemeria spp. in Argentina.