Studies On Biology Of Leptospharia Biglobosa And Evaluation Of The Impact Of This Pathogen On Seed Yield Of Oilseed Rape

Blackleg(or phoma stem canker) caused by Leptosphaeria maculans/L. biglobosa(anamorph: Phoma lingam) is an economically important disease of oilseed rape(Brassica napus, B. rapa) as well as of many cruciferous vegetables. Worldwide, hundreds of millions of US dollars per cropping season are lost due to blackleg of oilseed rape. As the international trade of rapeseed became more and more frequent, the quarantine problem of L. maculans is more important than before. The research of blackleg(including L. maculans and L. biglobosa) was initiated in China. For now, only L. biglobosa has been reported in China, while L. maculans has yet to be found. However, L. biglobosa is generally less damaging on oilseed rape, whereas L. maculans is considered more damaging. So, there is no data about the yield loss caused by blackleg on oilseed rape. Hubei province is the most important growing area of oilseed rape in Central China. There is no systematic study available on blackleg in this area. So we initiated a study on the biology of L. biglobosa and the impact of this pathogen on seed yield of oilseed rape.1. From 2008 to 2013, surveys of 33 oilseed rape growing sites of Hubei province were conducted to investigate of presence of L. biglobosa/L. maculans. A total of 374 Leptosphaeria isolates were obtained from oilseed crops and cruciferous vegetables. On the basis of morphological and molecular identification, only L. biglobosa was found in Hubei, while L. maculans has yet to be found.2. In the diversity analysis, nighty-four isolates from five different hosts were selected. Morphological observation, pathogenicity test and ISSR analysis were conducted. All these isolates showed high similarity on biology and molecular patterns. The results suggest that the population of L. biglobosa in Hubei appears low diversity.3. A study was conducted to assess the effect of flooding on survival of L. biglobosa ‘brassicae’(Lbb) in the stubble of winter oilseed rape(Brassica napus). Flooding for 1 to 2 weeks substantially reduced recovery of Lbb and flooding for 4 weeks resulted in negligible recovery of Lbb as compared to control. These results suggest that oilseed rape-rice rotation is probably an efficient way to reduce survival of Lbb in stubble of winter oilseed rape in central China.4. Formation of pseudothecia and ascospores by L. biglobosa under controlled and field conditions were observed. Under the climatic condition in central China, it was observed that L. biglobosa can form mature pseudothecia and ascospores in autumn. It was also observed that the blackleg disease may possibly spread by airborne ascospores in central China as in other countries.5. Sever phoma stem canker symptoms were observed on winter oilseed rape in China but the yield losses caused by this disease is unknown. To evaluate the yield losses, yield components(No. of branches/plant, No. of spots/plant, weight of 1000 seeds, No. of seeds/pot) were assessed for plants sampled from fields and plants from pot experiments. The results showed that the yield losses were lower than 15% on fields. However, the yield losses were up to 40% in pot experiments.6. We also reported two new cruciferous hosts of L. biglobosa in China: white radish(Raphanus sativus) and purple cai-tai(Brassica campestris ssp. chinensis var. purpurea).The above-mentioned findings will be useful for understanding of the epidemiology of blackleg on oilseed rape and other cruciferous crops and for management of this disease in central China.