Fusarium oxysporum causal agent of wilt on crop fields of Phoenix canariensis in Buenos Aires Province, Argentina

In the North region of Buenos Aires Province, two-year-old Phoenix canariensis plants showed severe wilt of some lower leaves and tip death, followed by eventual plant death. Cross sections of vascular tissues showed dark discoloration. The disease had low prevalence and high incidence. A pathogen was isolated from stem sections with symptoms, surface disinfested for 2 min in 2% NaOCl, plated on potato dextrose agar (PDA) and incubated at 24±2°C. Pure cultures formed white rose cottony colonies, that developed a purplish tint visible from the underside. Abundant single-celled microconidia and some macroconidia with 2 to 3 partitions (27-50 x 3-5 µm) were observed. Abundant chlamydospores were formed on water agar (WA). Pathogenicity tests were carried out on two-year-old P. canariensis plants. Prior to inoculation, the basal rachis was wounded with a sterile needle. Ten plants were sprayed with a water suspension of 1 x106 conidia per ml. Simultaneously three mycelia plugs per plant from ten-day-old PDA cultures were placed below the collar on another ten plants. Control plants were inoculated with sterile distilled water and agar disks that did not contain the fungus. Plants were covered with plastic bags for 48 h and incubated at 23°C and 100% relative humidity, before being transferred to growth chambers at 25°C with natural light for 15 days. Symptoms first appeared on plants 10 days after inoculation. Initially, rachis lesions developed in proximity to the wounds and chlorotic leaves were observed. In the course of one month the basal leaves died and the apex showed symptoms of infection (Fig. 1). Cross sections through the base revealed darkened vascular tissue (Fig. 2). The non-inoculated control remained healthy.

The pathogen was isolated from the inoculated plants. The morphological and micrometrics studies conclued that Fusarium oxysporum is the causal agent of this disease (Booth, 1977; Nelson et al. 1983). Based on the morphology, natural symptoms, and pathogenicity test results, the pathogen appears to be F. oxysporum f. sp. canariensis which was first observed in 1970 in France (Mercier & Louvet, 1973). This is the first report of this pathogen on P. canariensis in Argentina.