Fusarium oxysporum-causal agent of wilt on crops of Phoenix canariensis in Argentina

摘要

In the North region of Buenos Aires Province,2-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.A pathogen was isolated from stem sections with symptoms following surface sterilization for 2 mm in 2% NaOCl,transfer to potato dextrose agar (PDA)and incubated at 24 +-2degC.Pure cultures formed white rose cottony colonies that developed a purplish tint visible from the underside.Abundant single-celled microconidia and some macroconidia with two to three partitions (27-50 x 3-5 mum)were observed.Abundant chlamydospores were formed on water agar (WA).Pathogenicity tests were carried out on 2-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 x 10~6 conidia ml~(-1).Simultaneously three mycelial plugs per plant from 10-day-old PDA cultures were placed below the collar on another 10 plants.Control plants were inoculated with sterile distilled water and agar-only discs.Plants were covered with plastic bags for 48 h and incubated at 23degC and 100% relative humidity,before being transferred to growth chambers at 25degC 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 1 month,the basal leaves died and the apex showed symptoms of infection.Cross-sections through the base revealed darkened vascular tissue.Control plants remained healthy.