First Report of Pythium myriotylum Causing Root and Stem Rot on Tobacco in Zimbabwe

Abstract

Pythium species have a wide host range and are important pathogens of many agricultural crops. In Zimbabwe, 15 isolates of Pythium have been obtained from symptomatic tobacco (Nicotiana tabacum) in the new float seedling production system. This production system now accounts for 25 to 30% of the tobacco industry's annual requirement of 975 million seedlings. Disease symptoms are observed usually 5 to 6 weeks after sowing as wilting and yellowing of leaves followed by rotting of the roots, and in severe cases, seedling death. Up to 70% seedling loss has been reported in commercial seedbeds. In a study to fulfill Koch's postulates and to determine the susceptibility of 16 commercially grown tobacco cultivars, seedlings were produced in float trays and inoculated individually with 1 ml of Pythium (Isolate Py 19) spores (1 × 104 CFU/ml) and mycelium pipetted around the base of the stem of each seedling 9 weeks after sowing. First symptoms appeared 7 to 10 days after inoculation as yellowing and wilting of leaves. When seedlings were pulled, the lower portion of the stem and roots were brown and rotted. Seedling mortality averaged 29% and disease incidence was 96 to 100% among cultivars. All 16 tobacco cultivars were susceptible to Pythium root and stem rot and there were no significant (P > 0.05) differences in their susceptibility to the disease. The pathogen was reisolated from the inoculated seedlings. The representative isolate (Py 19) sent to Centraalbureau voor Schimmelcultures, the Netherlands was identified as Pythium myriotylum Drechsler (CBS Accession No. 125021) (2). P. aphanidermatum, causing black stem rot, and P. debaryanum and P. ultimum, responsible for damping-off (3), have been reported in the predominant conventional soil-based tobacco seedling production system, but do not cause economic losses. However, stem and root rot caused by P. myriotylum threaten the float seedling production system in Zimbabwe, although a chemical curative control of the disease has been recommended and is now widely practiced. P. myriotylum has previously been reported in the tobacco float seedling production system in South Carolina (1). To our knowledge, this constitutes the first published report of P. myriotylum on tobacco in Zimbabwe. References: (1) M. G. Anderson et al. Plant Dis. 81:227, 1997. (2) Centraalbureau voor Schimmelcultures. Retrieved from http://www.cbs.knaw.nl , 2010. (3) A. J. Masuka et al. List of Plant Diseases in Zimbabwe. Department of Research and Extension and Tobacco Research Board. Harare, Zimbabwe, 2003.

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

“…In Zimbabwe, Pythium root rot is a problem in tobacco and became particularly serious in the float tray seedling production system. The float tray hydroponic production system provides favourable conditions for the growth of the fungus (Sigobodhla, Dimbi, & Masuka, ). Pythium is known to cause extensive root and stem rot which results in reduced seedling vigour and subsequent poor plant growth and field performance in transplanted plants (Sigobodhla et al., ).…”

“…The float tray hydroponic production system provides favourable conditions for the growth of the fungus (Sigobodhla, Dimbi, & Masuka, ). Pythium is known to cause extensive root and stem rot which results in reduced seedling vigour and subsequent poor plant growth and field performance in transplanted plants (Sigobodhla et al., ). In Zimbabwe, the species P. aphanidermatum , P. debaryanum, P. myriotylum and P. ultimum have been occasionally isolated from tobacco seedlings brought to the Tobacco Research Board's Plant Clinic (Sigobodhla et al., ).…”

“…Pythium is known to cause extensive root and stem rot which results in reduced seedling vigour and subsequent poor plant growth and field performance in transplanted plants (Sigobodhla et al., ). In Zimbabwe, the species P. aphanidermatum , P. debaryanum, P. myriotylum and P. ultimum have been occasionally isolated from tobacco seedlings brought to the Tobacco Research Board's Plant Clinic (Sigobodhla et al., ). However, studies have not been carried out to characterize Pythium spp.…”

First report of Pythium recalcitrans infecting flue-cured tobacco

“…Damping-off of tobacco seedlings is known to be caused by P. aphanidermatum (Fajola and Alasoadura 1974). Additionally there are reports of P. ultimum and P. debaryanum infecting seedlings of flue-cured tobacco (Wang 1997), Pythium myriotylum infecting the seedlings and stems of tobacco (Sigobodhla et al 2010), Pythium dissotocum causing yellow stunt disease of tobacco in Southern Parts of Brazil (Corrêa et al 2011), and Pythium vexan causing the shank rot of flue-tobacco (Miao et al 2014).…”

Characterization of species associated with Pythium soft rot of ginger and evaluation of Pythium Oligandrum as a biocontrol

“…This widespread pathogen causes pre-and post-emergence damping off and mature plants of many agricultural and horticultural crops Pacumbaba et al, 1992;Plaats-Niterink, 1981;Porter, 1970;Sigobodhla et al, 2010;Stirling et al, 2004;2009;Tsror et al, 2004). Depending on the crop and field conditions, yield losses caused by P. myriotylum have been reported to be between as little as 4% on soybean grown in Japan (Tomioka et al, 2013) to as much as 90% on cocoyam grown in Cameroon (Pacumbaba et al, 1992) or even up to 100% on ginger grown in Australia (Stirling et al, 2009).…”