Characterization of Pythium spp. associated with root rot of tobacco seedlings produced using the float tray system in Zimbabwe

Abstract

The study was undertaken to identify and characterize Pythium isolates associated with root rot disease of tobacco seedlings as a first step towards developing management strategies for the pathogen. A total of 85 Pythium isolates were collected from diseased tobacco seedlings during 2015-2016 tobacco growing season. The isolates were identified to species level using sequencing of the internal transcribed spacer region. Thereafter, a subset of the isolates was tested for sensitivity to the commonly used fungicides, metalaxyl, azoxystrobin and a combination of fenamidone/propamocarbby growing isolates on Potato Dextrose Agar plates amended with the fungicides. The sequence analysis of the ITS-rDNA identified Pythium myriotylum as the dominant Pythium species associated with the root rot of tobacco seedlings in Zimbabwe. Pythium aphanidermatum and P. insidiosum were also identified albeit at lower frequencies. Phylogenetic analyses of the ITS region of the P. myriotylum isolates showed little sequence diversity giving rise to one distinct clade. The fungicide sensitivity tests showed that metalaxyl provided the best control of P. myriotylum in vitro, as compared to other fungicides. To the best of our knowledge, this is the first comprehensive study to determine and characterize Pythium species associated with root rot of tobacco in the float seedling production system in Zimbabwe. K E Y W O R D Sfloat tray seedling production, fungicide sensitivity, ITSrDNA, Pythium spp., root rot, sequencing, tobacco

Differentiation of Pythium spp. from vegetable crops with molecular markers and sensitivity to azoxystrobin and mefenoxam

“…Less sensitive isolates to azoxystrobin were observed in this study in P. ultimum, P. irregulare complex and P. aphanidermatum . P. ultimum originating from lattughino and basil was the least sensitive species to azoxystrobin with EC 50 values three to six times higher with respect to the average EC 50 of the other five Pythium spp.. One isolate of P. aphanidermatum from pepper (Py 11‐15) was somewhat less sensitive to azoxystrobin compared to the other tested isolates within the same species, but isolated from different hosts in previous studies . Less sensitive Pythium isolates were observed also in P. ultimum and P. irregulare complex by Wheeler et al .…”

Genome of Pythium myriotylum Uncovers an Extensive Arsenal of Virulence-Related Genes among the Broad-Host-Range Necrotrophic Pythium Plant Pathogens

“…7 ), but that this molecule was generally different in monocots and prevented the cytotoxicity ( 27 ). The induction of the NLPs during infection of ginger may be part of a more generic plant infection-related gene upregulation (i.e., not specific to ginger), as P. myriotylum is a broad-host-range pathogen, including of dicots such as tobacco ( Nicotiana tabacum ) ( 11 ), which is closely related to N. benthamiana , in which the tested NLPs induced necrosis ( Fig. 7 ).…”

“… Pythium myriotylum Drechsler is a broad-host-range pathogen that has been shown to infect a range of plant species ( 10 ), including dicots such as Nicotiana tabacum, for example ( 11 ), and monocots such as ginger ( Zingiber officinale ). We have shown recently that P. myriotylum is a major cause of Pythium soft rot (PSR) of ginger in China ( 12 ).…”