Powdery mildew of Allium species caused by Oidiopsis taurica in Brazil

Oidiopsis taurica Salmon (Syn. Oidiopsis sicula Scalia) was identified as the causal agent of a powdery mildew disease occurring on distinct Allium species in Brazil. This disease was initially observed in plastic house and field-grown garlic (Allium sativum) and leek (A. porrum) accessions in Brasília (Federal District) and in field-grown and greenhouse onion (A. cepa) cultivars in Belém do São Francisco (Pernambuco State) and Brasília, respectively. Typical symptoms consisted of chlorotic areas on the leaf surface corresponding to a fungal colony. These lesions turned to a brownish color with the progress of the disease. Fungi morphology was similar to that described for O. taurica. Endophytic mycelium emerging through estomata, light pale conidia were dimorphic (lanceolate primary conidia and somewhat cylindrical secondary conidia), fibrosin bodies were absent, conidia formed predominantly single (not in chains), and appressoria were non-lobed. Its sexual stage, Leveillula taurica (Lev.) Arnaud, was not observed. Inoculations were performed with the O. taurica isolates from distinct Allium hosts. These isolates were also pathogenic to sweet pepper and tomato, indicating an apparent absence of host specialization. One bunching onion (A. fistulosum) accessions was not infected by O. taurica suggesting that this species might carry useful resistance alleles to this pathogen. This is the first formal report of a powdery mildew disease on species of the genus Allium in Brazil. This disease might become important on these vegetable crops especially in hot and dry areas such as those in the Central and Northeast regions of Brazil. O fungo Oidiopsis taurica Salmon (= Oidiopsis sicula Scalia) foi identificado como sendo o agente causal de uma nova doença do tipo oídio em alho (Allium sativum), alho porró (A. porrum) e cebola (A. cepa) no Brasil. Esta doença foi observada tanto em condições de casa de vegetação quanto a campo em Brasília e Pernambuco. O sintoma mais típico é o aparecimento de uma área clorótica na superfície da lâmina foliar que corresponde a uma colônia fúngica. Com o progresso da doença, estas lesões tornaram-se marons. As características morfológicas do fungo, corresponderam àquelas descritas para O. taurica, incluindo micélio endofítico emergindo através das aberturas estomáticas, conídio solitários de coloração hialino-amarelada, ausência de corpos de fibrosina, apressório não-lobado e a presença de dois tipos diferenciados de conídios sendo