Identification and characterization of Phytopythium helicoides causing stem rot of Shatangju mandarin seedlings in China

Abstract

Citrus mandarin (Citrus reticulata) cultivar Shatangju has great economic importance in southern China because of its delicious fruit and medicinal peel. During surveys conducted in 2012 and 2013, stem rot and plant death were observed on 2-to 3-year-old Shatangju grafted seedlings in 21 nurseries located in three regions (Yangjiang City, Sihui City and Deqing County) of Guangdong Province, China. The aims of this study were to characterize the symptoms of seedling stem rot and death; evaluate the incidence and loss; identify the causal agent and evaluate its pathogenicity. The disease was present in all surveyed nurseries but incidence varied with location. A Pythium-like oomycete was consistently obtained from symptomatic plants collected in the nurseries surveyed. On the basis of morphological and cultural characteristics and combined phylogenetic analysis of three DNA sequences including the internal transcribed spacer region (ITS), mitochondrial CoxI and CoxII genes, 21 of the isolates obtained were identified as belonging to the species Phytopythium helicoides. The isolates were pathogenic to the scions but not rootstocks of Shatangju mandarin seedlings cultivated in a controlled greenhouse and symptoms identical to that observed in the field were reproduced. The pathogen was re-isolated consistently from the inoculated plants, confirming Koch's postulates. Seedling stem rot and eventual death caused by P. helicoides represents a serious threat to Shatangju mandarin nursery productivity and longevity in southern China.

Investigation of the genetic diversity of Phytophthora capsici in China using a universal fluorescent labelling method

“…Approximately 1‐cm 2 segments including partial lesion and adjacent asymptomatic tissues were cut and surface‐sterilized with 0.5% sodium hypochlorite for 1–3 min. Samples were then rinsed twice by sterilized water, plated onto selective 10% V8 agar containing 10 μg/ml carbendazim, 50 μg/ml pentachloronitrobenzene, 50 μg/ml ampicillin and 50 μg/ml rifampicin (Chen et al, ) and incubated in the dark at 25°C. Hyphae growing from the plated tissues after 1–3 days were subcultured onto 10% V8 agar.…”

Development of a Loop-Mediated Isothermal Amplification Method for the Rapid Detection of Phytopythium vexans

“…At present, there are over 20 species in this genus, with most of them showing strong association with the freshwater environment ( Tkaczyk, 2020 ) and being saprophytes. However, a few Phytopythium species have been observed to cause diseases in plants, such as Phytopythium litorale infecting the Old-World sycamore Platanus orientalis ( Derviş et al, 2020 ); Phytopythium helicoides causing citrus fruit and root rot ( Chen X. R. et al, 2016 ); and Phytopythium vexans (de Bary) ( Lévesque et al, 2008 ; Bala et al, 2010 ) causing root rot in many economically important plants ( Adhikari et al, 2013 ; de Cock et al, 2015 ).…”

Sensitivity of Pythium spp. and Phytopythium spp. and tolerance mechanism of Pythium spp. to oxathiapiprolin

“…This pathogen also causes stem rot of Shatangju mandarin seedlings. 15,16 To the best of our knowledge, there is no registered fungicide to control Phytopythium diseases in China.…”

“…helicoides had been reported to cause rhizome rot of Asian lotus, which is an economically important aquatic plant in China. This pathogen also causes stem rot of Shatangju mandarin seedlings 15, 16 . To the best of our knowledge, there is no registered fungicide to control Phytopythium diseases in China.…”