Isolation of Pythium litorale from irrigation ponds used for vegetable production and its pathogenicity on squash

Abstract

Irrigation water can harbour propagules of pathogenic oomycetes that may be a primary source of disease outbreak in crop plants. Irrigation ponds associated with vegetable production in southern Georgia, USA, were assessed in this study. Camellia and rhododendron leaves were used as baits for recovery of oomycetes that were further identified by morphological characteristics and analysis of the internal transcribed spacer rDNA regions. Pythium litorale was frequently isolated from all irrigation ponds sampled. Assessment of growth rates of P. litorale isolates at 5–45 °C indicated that the optimum and maximum temperatures were 30 and 40 °C, respectively. It appeared that these isolates were more tolerant to higher temperatures than previously described P. litorale isolates from Europe that had a maximum growth temperature of 35 °C. Pathogenicity assay with the P. litorale isolates showed that they caused fruit rot and seedling damping-off of yellow squash. Pythium litorale was first described as a new species in 2006 and the present study is the first report indicating it is pathogenic on plants. This study provides useful information for a more comprehensive understanding of the nature of P. litorale and its potential impact on vegetable production.