Pythium species associated with root rot complex in winter-grown parsnip and parsley crops in south eastern Australia

Abstract

Root rot of parsnip (Pastinaca sativa) and parsley (Petroselinum crispum) crops in south-eastern Australia is a disease complex, causing up to 80 % and 100 % yield losses, respectively. It is attributed to a range of fungi and oomycetes. We report on isolation and identification of eleven Pythium spp. from naturally infected roots of parsnip and parsley collected during systematic monthly surveys of commercial, winter-grown crops with prevailing root rots at Devon Meadows and Clyde, Victoria, Australia in 2009 to 2011. Pythium intermedium, P. ultimum var. ultimum, P. rostratifingens and species from the P. dissotocum complex were common to both hosts. Pythium irregulare, P. sylvaticum, P. camurandrum, P. vanterpoolii and P. tracheiphilum were isolated only from parsnip; and P. mastophorum and P. sulcatum only from parsley. This is the first report of P. camurandrum and P. rostratifingens in Australia and the first report of P. tracheiphilum and P. vanterpoolii from parsnip in Australia. Selected Pythium spp. tested for their pathogenicity in glasshouse conditions were pathogenic to both hosts. Pythium sulcatum, P. mastophorum and P. tracheiphilum caused severe root in 35 %, 53 % and 25 % of parsley seedlings, respectively. Pythium sulcatum and P. intermedium caused severe root in 50 % and 15 % of parsnip seedlings, respectively. In growth chamber studies, P. sulcatum was pathogenic to parsley seedlings at 10 °C, 18 °C and 24 °C.