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COMPARISON OF DIFFERENT METHODS FOR ASSESSING VARIETY RESISTANCE

COMPARISON OF DIFFERENT METHODS FOR ASSESSING VARIETY RESISTANCE OF OILSEED RAPE TO SCLEROTINIA STEM ROT Li Qiang Sheng A H A McCartney B Hu Bao Cheng A A Heran B Chen Feng Xiang A Hou Shu Min A Wu Xin Jie A Fei Wei Xin A

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COMPARISON OF DIFFERENT METHODS FOR ASSESSING VARIETY RESISTANCE

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  1. COMPARISON OF DIFFERENT METHODS FOR ASSESSING VARIETY RESISTANCE OF OILSEED RAPE TO SCLEROTINIA STEM ROT Li Qiang Sheng A H A McCartneyB Hu Bao Cheng A A HeranB Chen Feng XiangA Hou Shu MinA Wu XinJieA Fei Wei XinA ACrop Research Institute, Anhui Academy of Agricultural Sciences, Hefei, 2300031 China BIACR-Rothamsted, Harpenden, Hertfordshire AL5 2JQ, UK

  2. INTRODUCTION Sclerotinia stem rot, caused by Sclerotinia sclerotiorum (Lib.) de Bary, is one of the most important diseases on oilseed rape in the world No commercial varieties possess good resistance There are promising sources of resistance in varieties

  3. OBJECTIVES To comparing assessment methods for screening for resistant sources which method could distinguish differences in resistance among varieties be more practical and reliable

  4. MATERIALS AND METHODS lSource of Isolate, Sclerotia Production and Inducing Apothcia lCollection of Ascospores and Preparation of Ascospore Suspension lPlant preperation

  5. Experiment Design Inoculation Methods • Method A mycelium plug as an inoculum • Method B ascospores in PDA plug as an inoculum • Method C petals infected by ascospore suspension as an inoculum • Method D infected leaf tissue as an inoculum • Method E petals infected by "puffing" ascospores as an inoculum • Conditions 100%RH 18oC 16h photoperiod

  6. RESULTS The development of lesion length plus width on all varieties tested over time using different inoculation methods was shown in the Figure . Method A: Disease lesions of all five varieties have appeared on the first day after inoculation, and afterward increased quickly. There were significant differences between varieties (p<0.001) during day 3-6. The rank of resistance of five varieties from susceptible to resistant, according to lesion length plus width, were RPG681, APEX, PAUC 61, Y 16 and Zhongyou 821.

  7. Method B: On the first and second day, tiny mycelium germinated from ascospores could be seen clearly in PDA, but no lesions occurred until the third day. Lesions developed more slowly than that in method A. The rank of resistance of five varieties was APEX, RPC 681, PAUC 61, Zhongyou 821 and Y 16.

  8. Both methods C and E were ascospore infected petals as inoculum, and mycelium growing on the petals could be seen, but no lesions have found on the leaves on the first and second day. Lesions appeared on four varieties except varieties RPC681 on the third day in method E, one day ahead method C. Method C: the rank of resistance of five varieties was APEX, RPC 681, PAUC 61, Y 16 and Zhongyou 821, and method E was RPC 681, APEX, PAUC 61, Zhongyou 821 and Y 16.

  9. Method D:Lesions of all five varieties occurred on the first day and also developed rapidly. The resistant ranks of the five varieties were changeable on the different assessment date.

  10. In general, lesion initially appeared within 4 days. Method A and D were on day 1, method B and C on day 3, method E on day 2-3. These indicated that mycelia invade host leaf tissue earlier than ascospores because ascospores need germinate and produce mycelia to infect host tissue. The resistance of varieties Zhongyou 821 and Y 16 was stronger than that of PAUC 61,APEX and RPC 681, however, the rank of resistance of five varieties was some differences between methods.

  11. ANOVAvariance analysis for the effects of three factor methods, variety, assessment date on lesions in controlled conditions was shown in Table 1. The results indicated that there were highly significant differences on disease lesions between the different inoculation methods, varieties or assessment dates, and also highly significant effects of interaction to disease lesions between method and variety, method and assessment date, or variety and assessment date. These suggested that disease lesion was obviously related to methods of inoculation, varieties and assessments.

  12. Table 2. Analysis of variance for differences on disease lesion length plus width (mean) of sclerotiniastem rot between variety by using different methods of inoculation at different assessment dates at IACR- Rothamsted in 1998

  13. Table 1. Analysis of variance for the effects of method, variety, assessment date on lesion length plus width (mean) of sclerotinia stem rot in controlled conditions at IACR-Rothamsted in 1998

  14. Therefore, further variety analysis was done for investigating the differences on disease lesion between varieties by using different methods of inoculation at different assessment dates (Table 2). The results demonstrated that there were more differences on disease lesions between varieties using Method A, Method C and Method D than using Method B and Method E. The optimal assessment date were 3-7 days (p<0.001) after inoculation for Method A, 4-5 days (p<0.001) for Method C, 4-6 days (p<0.001) for Method D and the fifth day for Method E

  15. Discussion • Method A, mycelium as an inoculum, it is easy to obtain same age and virulence inoculum.The results showed significant (p<0.01) differences on disease lesions between varieties at all assessment date.The optimal assessment date were 3-7 days after inoculation, and its initial assessment date was earlier (the third day), and period of assessment was longer than (3-7 days) those of other methods. Therefore this method is simplest and fastest for assessing variety resistance.

  16. Method B: ascospores in PDA plug as an inoculum inoculation method, it was difficult to make ascospores uniform in PDA. Thus method B was not suggested as a screening method. • Method D: the rank of the five varieties in relative susceptibility was changeable on the different assessment dates. So this method unlikely to be a reliable method for identifying variety resistance to Sclerotinia sclerotiorum.

  17. Method C and E: there were significant differences (p<0.002) on disease lesions between varieties at day 3-9 for method C and day 4-6 for method E. This indicated that both methods could better identify the differences of resistance between varieties. Method E was closest to natural infection to host plants in the fields, but it was difficult to get petals with uniform ascospores landed and to control ascospore density on the petals. It was not only easy for method C to get petals with uniform ascospores landed and ascospore density could be controlled, but also closer to natural infection in the field. So ascospore infected petals as an inoculum method was suggested as a reliable method for identifying resistance in oilseed rape to Sclerotinia sclerotiorum.

  18. Acknowledgements This research was funded by European Union, was part of the work of an INCO-DC project “Exploitation of biotechnology in developing strategies for integrated control of sclerotinia stem rot in rapeseed” (Contract No. ERBIC18CT970173)

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