Scientia Agricultura Sinica ›› 2022, Vol. 55 ›› Issue (10): 1938-1948.doi: 10.3864/j.issn.0578-1752.2022.10.005

• PLANT PROTECTION • Previous Articles     Next Articles

Establishment and Application of Rapid Quantitative Detection of Viable Plasmodiophora brassicae by PMAxx-qPCR Method

LI XiaoJing1(),ZHANG SiYu1,LIU Di1,YUAN XiaoWei2,LI XingSheng2,SHI YanXia1,XIE XueWen1,LI Lei1,FAN TengFei1,LI BaoJu1(),CHAI ALi1()   

  1. 1Institute of Vegetables and Flowers, Chinese Academy of Agricultural Sciences, Beijing 100081
    2Shandong Huasheng Agriculture Limited Company, Qingzhou 262500, Shandong
  • Received:2021-11-18 Accepted:2021-12-20 Online:2022-05-16 Published:2022-06-02
  • Contact: BaoJu LI,ALi CHAI E-mail:1041255425@qq.com;libaojuivf@163.com;chaiali@caas.cn

Abstract:

【Objective】Plasmodiophora brassicae is an obligate endoparasite that causes clubroot disease, which is the most devastating soil-borne disease in brassica crops. The propidium monoazide xx (PMAxx) could selectively bind to the chromosomal DNA of dead spores and therefore block DNA amplification by real-time fluorescent quantitative PCR (qPCR). In the present study, a strategy involving a PMAxx pre-treatment followed by the qPCR (PMAxx-qPCR) assay was developed for quantifying viable spores of P. brassicae, so as to provide a basis for early detection and prevention measurement of cloobroot disease. 【Method】 PMA and PMAxx with concentrations of 0, 5, 10, 20, 40 and 60 µmol·L-1 were prepared, respectively, and were used to pre-treat P. brassicae prior to DNA extraction, followed by qPCR. The inhibitory effects of PMA and PMAxx on DNA amplification of P. brassicae dead spores were compared, and the optimal nucleic acid dye and concentration to distinguish between live and dead spores were determined. The illumination time was set as 0, 2, 5, 10, 15 and 20 min, respectively, and the optimal exposure time was optimized to establish a PMAxx-qPCR assay for selectively detection of viable spores of P. brassicae. The mixed suspensions with different ratios of dead and viable spores (0, 0.01%, 0.1%, 1%, 10%, 25%, 50%, 75% and 100% viable spores) were prepared to determine the suitability of PMAxx-qPCR assay for distinguishing viable and dead spores. The assay was also applied to quantitative detection of viable spores of P. brassicae in 25 field soil samples. 【Result】 PMAxx showed a better discrimination effect than PMA on the viable and dead spores of P. brassicae. When the concentration of P. brassicae was 1×108 spores/mL, the optimal PMAxx concentration and light exposure time were 4 μmol·L-1 and 10 min, respectively. The amplification of dead spores could be inhibited effectively, and only the DNA of living spores was targeted for selective amplification. For pre-defined ratio of viable spores, there was a good linear relationship between the lg of the P. brassicae DNA concentration assessed by PMAxx-qPCR and the theoretical viability (R2=0.992). For soil samples, viable P. brassicae was quantified in 11 of 25 samples, with infestation levels of approximately 32.35-6.97×103 fg·g-1. 【Conclusion】 The established method could quantitatively detect the viable spores of P. brassicae, with advantages of rapid, efficiency and sensitivity, which could be useful for avoiding the inability of qPCR method to distinguish between viable and nonviable spores. Application of the assay may potentially improve P. brassicae control and disease management.

Key words: Plasmodiophora brassicae, clubroot disease, propidium monoazide xx (PMAxx), real-time fluorescent quantitative PCR (qPCR), viable spore

Table 1

Strains used for primer specific test"

序号No. 病原菌Pathogen 菌株编号Strain code 寄主Host 采集地Geographic origin
1 芸薹根肿菌Plasmodiophora brassicae BC18052103 大白菜Chinese cabbage 云南省昆明市Kunming, Yunnan
2 尖镰孢Fusarium oxysporum GL17061203 甘蓝 Cabbage 陕西省太白县Taibai, Shaanxi
3 茄镰孢Fusarium solani BC10120305 大白菜Chinese cabbage 辽宁省丹东市Dandong, Liaoning
4 半裸镰孢Fusarium incarnatum HYC15171302 花椰菜Broccoli 河北省承德市Chengde, Hebei
5 立枯丝核菌Rhizoctonia solani BC16072809 普通白菜Pakchoi 河北省张家口市Zhangjiakou, Hebei
6 核盘菌Sclerotinia sclerotiorum YC19081601 油菜Rape 山东省临沂市Linyi, Shandong
7 芸薹链格孢Alternaria brassicae BC15110628 大白菜Chinese cabbage 河北省廊坊市Langfang, Hebei
8 长孢轮枝菌Verticillium longisporum BC13091524 大白菜Chinese cabbage 河北省张家口市Zhangjiakou, Hebei
9 瓜果腐霉Pythium aphanidermatum BC12073101 大白菜Chinese cabbage 江苏常州市Changzhou, Jiangsu
10 灰葡萄孢Botrytis cinerea HYC20051608 花椰菜Broccoli 北京市顺义区Shunyi, Beijing
11 胡萝卜软腐果胶杆菌胡萝卜亚种
Pectobacterium carotovorun subsp. carotovorum
BC14120625 大白菜Chinese cabbage 内蒙古自治区乌兰察布市
Ulanqab, Inner Mongolia
12 野油菜黄单胞菌野油菜致病变种
Xanthomonas campestris pv. campestris
GL18080621 甘蓝 Cabbage 湖南省长沙市Changsha, Hunan

Fig. 1

Amplification curve of qPCR for primer specificity verification"

Fig. 2

Melting curve of qPCR The melting curve of P. brassicae had single peak with Tm 84.75℃. The melting curve of non-target strains, root tissue of healthy Chinese cabbage and ddH2O had no peak or slightly peaks with different Tm values"

Fig. 3

Standard curve of qPCR system for P. brassicae"

Table 2

Cycle threshold (Ct) of qPCR for the detection of P. brassicae treated with PMA and PMAxx"

光敏染料
Photoactivatable dye
浓度
Concentration
(µmol∙L-1)
Ct
(活孢子Viable spores)
Ct
(死孢子Dead spores)
dCt
(活孢子Viable spores)
dCt
(死孢子Dead spores)
ddCt
PMA/PMAxx 0 14.53a 14.86a / / /
PMA 5 15.53b 25.82b 1.00 10.96 9.96
10 15.90b 27.43c 1.37 12.57 11.20
20 16.84c 28.92d 2.31 14.06 11.75
40 17.90d 29.71e 3.37 14.85 11.48
60 18.52e 29.84e 3.99 14.98 10.99
PMAxx 5 15.56b 27.91c 1.03 13.05 12.02
10 16.21bc 29.57d 1.68 14.71 13.03
20 17.18c 30.59e 2.65 15.73 13.08
40 18.21d 32.10f 3.68 17.24 13.56
60 18.58e 32.61f 4.05 17.75 13.70

Fig. 4

Effect of PMAxx concentration (A) and light exposure time (B) on qPCR amplification of DNA from viable and dead P. brassicae spores"

Table 3

Detection result of different ratios of viable P. brassicae spores by qPCR and PMAxx-qPCR"

活孢子百分比
Ratio of viable spores (%)
活孢子浓度
Concentration of viable spores (spores/mL)
qPCR PMAxx-qPCR
Ct值
Ct value
DNA浓度对数值
Lg DNA concentration
Ct值
Ct value
DNA浓度对数值
Lg DNA concentration
100 1.00×108 10.04±0.28 6.74±0.08a 10.34±0.21 6.66±0.06a
75 7.50×107 10.76±0.56 6.58±0a 11.10±0.24 6.45±0.07b
50 5.00×107 10.26±0.23 6.72±0.12a 12.13±0.47 6.16±0.13c
25 2.50×107 10.48±0.65 6.66±0.10a 13.31±0.37 5.83±0.10d
10 1.00×107 10.19±0.53 6.74±0.10a 14.66±0.25 5.46±0.07e
1 1.00×106 10.40±0.39 6.68±0.14a 18.01±0.39 4.53±0.11f
0.1 1.00×105 10.81±0.62 6.57±0.13a 20.63±0.49 3.80±0.13g
0.01 1.00×104 10.57±0.52 6.63±0.10a 23.59±0.34 2.98±0.09h

Fig. 5

Effectiveness of PMAxx-qPCR for detection of different ratios of viable P. brassicae spores"

Table 4

Quantitative detection of P. brassicae in soil of brassica crops by qPCR and PMAxx-qPCR"

样本
Sample
No.
采集地
Geographic origin
种植作物
Crop
采样时间Sampling time qPCR PMAxx-qPCR 病情指数Disease index
Ct值
Ct value
浓度<BOLD>C</BOLD>oncentration
(fg DNA·g-1 soil)
Ct值
Ct value
浓度<BOLD>C</BOLD>oncentration
(fg DNA·g-1 soil)
1 四川省绵阳市
Mianyang, Sichuan
甘蓝Cabbage 2020-07 18.59±0.16 2.32×104 20.86±0.29 5.43×103 47.61±0.58
2 四川省绵阳市
Mianyang, Sichuan
甘蓝Cabbage 2020-07 20.65±0.26 6.23×103 22.62±0.34 1.76×103 38.20±0.30
3 四川省广元市
Guangyuan, Sichuan
甘蓝Cabbage 2020-08 21.12±1.36 4.61×103 23.50±0.25 1.01×103 32.10±0.44
4 四川省广元市
Guangyuan, Sichuan
甘蓝Cabbage 2020-08 23.59±0.31 9.52×102 25.48±0.28 2.84×102 26.11±0.52
5 湖北省恩施州
Enshi, Hubei
大白菜Chinese cabbage 2020-07 17.00±0.50 6.44×104 20.47±0.70 6.97×103 50.48±0.63
6 湖北省恩施州
Enshi, Hubei
大白菜Chinese cabbage 2020-07 19.95±0.89 9.74×103 20.95±0.53 5.14×103 44.85±0.63
7 山东省青岛市
Qingdao, Shandong
大白菜Chinese cabbage 2020-07 23.08±0.42 1.31×103 25.03±0.33 3.78×102 26.36±0.72
8 山东省青岛市
Qingdao, Shandong
小白菜Pakchoi 2020-07 25.21±0.89 3.37×102 28.88±0.30 32.35 0
9 河南省南阳市
Nanyang, Henan
甘蓝Cabbage 2020-08 20.68±0.77 6.12×103 24.55±0.41 7.86×102 27.94±0.58
10 江苏省无锡市
Wuxi, Jiangsu
甘蓝Cabbage 2020-09 24.80±0.67 4.39×102 26.71±0.23 1.29×102 20.07±0.32
11 辽宁省沈阳市
Shenyang, Liaoning
大白菜Chinese cabbage 2020-10 24.14±0.79 6.70×102 25.95±0.55 2.10×102 21.62±0.60
其余14份土壤样本 The other 14 samples >35.00 0 >35.00 0 0
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