Identification and Pathogenicity of Fungal Pathogens Causing Black Point in Wheat on the North China Plain

Abstract

Fungi associated with black point were isolated from three highly susceptible wheat genotypes in the North China Plain. The 21 isolates represented 11 fungal genera. The most prevalent genera were (isolation frequency of 56.7%), (16.1%), and (6.0%). The other eight genera were, ,, ,, ,, and ; their isolation frequencies ranged from 0.8 to 4.8%. The pathogenicity of the isolates was individually assessed in the greenhouse by inoculating wheat plants with spore suspensions. Ten of the 21 isolates caused significantly higher incidences of black point than that the controls. These isolates belonged to eight fungal species (, ,, ,, ,, and ) based on morphological traits and phylogenetic analysis. The average incidences of black point in the eight fungal species were 32.4, 54.3, 43.0, 41.9, 37.2, 38.8, 50.1, and 34.1%, respectively. and were determined to be the most important pathogens in the North China Plain based on fungal prevalence and symptom severity. This study is the first to identify as a major pathogen causing black point in wheat.

Enzymatic Browning in Wheat Kernels Produces Symptom of Black Point Caused by Bipolaris sorokiniana

“…It remains to be determined whether black point is primarily pathogen-induced ( Southwell et al, 1980 ; Rees et al, 1984 ; Conner et al, 1996 ; Kumar et al, 2002 ) or induced by environmental conditions ( Conner and Davidson, 1988 ; Conner, 1989 ; Conner et al, 1992 ; Fernandez et al, 1994 ; Kumar et al, 2002 ; Moschini et al, 2006 ; Walker, 2011 ). Our previous study indicated that pathogens could significantly increase the incidence of black point ( Xu et al, 2018 ), and the incidence was also affected by environmental variations between different years ( Li et al, 2019a,b ). It seems that the pathogen causes black point, and the appropriate environmental conditions will enhance the severity of this disease.…”

“…The fungal isolate Ta-BP33, representing B. sorokiniana ( Xu et al, 2018 ), was cultured on Potato Dextrose Agar (PDA) medium in 9-cm Petri dish and incubated for 10–12 days in a dark growth chamber at 25 ± 1°C. Conidial suspensions were prepared according to the procedure described by Mahto et al (2011) , and the inoculation was as previously reported ( Li et al, 2019b ).…”

“…The fungal isolate Ta-BP33, representing B. sorokiniana (Xu et al, 2018), was cultured on Potato Dextrose Agar (PDA) medium in 9-cm Petri dish and incubated for 10-12 days in a dark growth chamber at 25 ± 1 • C. Conidial suspensions were prepared according to the procedure described by Mahto et al (2011), and the inoculation was as previously reported (Li et al, 2019b). Briefly, at Zadoks growth stage GS 55 (Zadoks et al, 1974), 200 spikes of genotype "PZSCL6" were covered with sulfuric acid paper bags to prevent contamination, and then at GS 65 the spikes were inoculated with conidial suspensions using a hand sprayer until dripping off and covered with transparent plastic bags for 5 days to maintain humidity, after which the spikes were again covered with sulfuric acid paper bags until harvest.…”

“…Black point, characterized by a dark discoloration of the embryo of kernels, is a serious disease in wheat growing regions throughout the world ( Conner, 1989 ; Conner et al, 1992 , 1996 ; Fernandez et al, 1994 ; Williamson, 1997 ; Mak et al, 2006 ; Moschini et al, 2006 ; Toklu et al, 2008 ; Xu et al, 2018 ; Li et al, 2020 ). It causes economic losses for farmers due to the reduction in the commercial grade of the wheat ( Rees et al, 1984 ; Conner and Davidson, 1988 ) and decreases seed germination, inhibits seedling growth, and reduces grain yield ( Conner et al, 1996 ; Li et al, 2014 ; El-Gremi et al, 2017 ).…”

“…In our previous study, we screened seven wheat genotypes that are highly susceptible to black point ( Li et al, 2014 ) and identified eight fungal species, including B. sorokiniana , A. alternata , and Fusarium equiseti , that cause black point in the North China Plain ( Xu et al, 2018 ), of which B. sorokiniana was the most virulent. Here we applied a metabolomics analysis to both the germ fraction (the main discolored part of the kernel) and the endosperm-bran fraction of BP and BPF kernels inoculated with B. sorokiniana using a method that combines gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-high resolution mass spectrometry (LC-MS).…”