First Report of Fusarium oxysporum f. sp. apii Race 2 Causing Fusarium Yellows on Celery in Argentina

More than 75% of the area dedicated to celery (Apium graveolens var. dulce) production in Argentina (over 120 ha) is annually cultivated in greenhouses in the green belt area surrounding the city of La Plata. Celery showing symptoms of rapid decline, delayed growth, chlorotic leaves, discolored vascular tissue, and stunted root systems have been observed in this area since the late 1990s. Recently, Fusarium oxysporum f. sp. apii(Foa) was identified as the causal agent (Lori et al. 2008). As three races of the pathogen are known to induce Fusarium yellows of celery worldwide (Puhalla 1984), pathogenicity tests were conducted on two differential cultivars to identify the pathogenic race present in Argentinian crops. Isolates were obtained from diseased celery plants, identified as F. oxysporum morphologically, and the forma specialis apii was assigned by pathogenicity tests on celery 'Golden Boy' as previously described (Lori et al. 2008). Seven strains of Foa were tested on 'Tall Utah 52-70' (resistant to Foa race 1 and susceptible to Foa race 2) and Golden Boy (susceptible to Foa races 1 and 2). Isolates were grown on autoclaved, moistened, polished rice for 10 days, dried, and ground. For each strain, 10 healthy, 4-week-old seedlings of each of the cultivars were transplanted into 1-liter pots containing autoclaved soil inoculated with the colonized rice up to a concentration of 10 super(3) CFU/g. Pots were placed in a greenhouse at 25 + or - 5[degrees]C under natural daylight. Controls consisted of 10 pots of celery seedlings filled with autoclaved soil mixed with sterile ground rice. Plants were evaluated weekly for 7 weeks for Fusarium yellows symptoms using the leaf color (LC) and wilt severity (SI) indexes previously developed (Lori et al. 2008). Plant height, whole plant dry weight, and root volume were also taken into consideration for the assessment of disease severity. All isolates induced typical Fusarium yellows symptoms 50 days after inoculation on both differential cultivars but not on control treatments. On Golden Boy symptoms appeared earlier and were more severe (average SI and LC were 3.7 and 3.5, respectively) than on Tall Utah 52-70 (average SI and LC were 2.3 and 1.8, respectively). Inoculated plants also showed lower height (58.3% and 49.8% reductions were observed for Golden Boy and Tall Utah 52-70, respectively), dry weight (58% and 39.6% reductions were observed for Golden Boy and Tall Utah 52-70, respectively) and root volume. F.