First report of Pythium recalcitrans causing cavity spot of carrot in Michigan.
During a survey of carrot (Daucus carota) cavity spot in Michigan, USA, in September 2010, carrot roots with typical cavity spot symptoms were collected from production fields. Among the 33 isolates obtained, M2-05 was identified as a Pythium sp. that differed from the known cavity spot pathogens of carrot. The isolate had spherical hyphal swellings but no other distinguishing morphological characteristics. M2-05 was further classified by analysing the partial sequences of four genes: the internal transcribed spacer (ITS) region of ribosomal DNA, β-tubulin, cytochrome c oxidase subunit 2, and NADH dehydrogenase subunit 1. A BLAST search of these sequences for M2-05 was conducted using the nucleotide database of GenBank, resulting in 100% similarity to all four sequenced genes of P. recalcitrans. This is thought to be the first published report of P. recalcitrans naturally infecting carrot roots.