关键词: 小麦纹枯病, 禾谷丝核菌, 群体组成, 实时荧光定量PCR, 分布特征

Abstract:

【Objective】Wheat sharp eyespot (WSE) occurs seriously in wheat and maize double cropping system with straw returning to field in Hebei, Shandong and Henan provinces. The objective of this study is to determine the disease occurrence, pathogen population structure and the farmland distribution characteristics of dominant pathogen by extensive investigation, and to provide a basis for the WSE control.【Method】The random five-point sampling method was used to investigate the occurrence degree of WSE in wheat and maize double cropping system with straw returning to field in Hebei, Shandong and Henan provinces. The population characteristics of Rhizoctonia isolates were identified by nuclear staining, hyphal fusion reaction and rDNA sequence analysis. The pathogenicity of 120 R. cerealis strains was determined by pot experiment, and the distribution characteristics of R. cerealis in the field of wheat and maize double cropping system were analyzed by real-time fluorescent quantitative PCR.【Result】The occurrence degree of WSE from serious to light was in the order of Henan, Shandong and Hebei. There were 421 binucleate R. cerealis strains and 24 multinucleate R. sonalis strains collected from 72 collection sites of 11 different ecological regions in Hebei, Shandong and Henan provinces, which could be divided into four types: AG-D, AG-B (0), AG-2 and AG-5 fusion groups, accounting for 91.91%, 2.70%, 3.82% and 1.57% of the total number of tested strains, respectively. According to the disease index of Shixin 828, Jimai 22 and Zhoumai 22, the 120 tested strains could be divided into five pathogenic types: VT1, VT2, VT3, VT4 and VT5. The disease indexes of each type were 44.0, 39.4, 34.2, 29.6 and 27.2 in turn, respectively. Among them, most of the strains from the wheat region in Henan Province had the strongest pathogenicity, and those collected from the wheat region in Hebei Province was the weakest. During the whole growth stage of wheat, the content of R. cerealis increased first and then decreased in overground and root systems. The amount of R. cerealis in the shoot was the lowest at the three-leaf stage, and the highest at the rising stage, with the value of 3 774.60 ng DNA/g fresh tissue. The amount of R. cerealis in the roots reached the peak at the jointing stage. The growth rate of R. cerealis amount was the fastest from the three-leaf stage to the tillering stage. The increase of R. cerealis content in the aboveground parts and roots of wheat was up to 28.17 and 17.26 times, respectively. The amount of R. cerealis increased gradually in rhizosphere soil of wheat and in the shoots of maize. In the rhizosphere soil of maize, the content decreased first and then increased, and the lowest at the tasseling stage was 170.6 ng DNA/g dry soil.【Conclusion】The most serious degree of WSE occurs in wheat area in Henan Province, followed by Shandong and Hebei. The strong pathogenicity of dinucleus R. cerealis is the dominant pathogen in the three wheat areas, the amount of which increases the fastest from the three-leaf stage to the tillering stage, and the relative content in wheat straw is the highest and that in maize straw is the lowest. In the process of crushing returning-straw and at wheat seedling stage before the winter, the monitoring and control of WSE should be strengthened.

Key words: wheat sharp eyespot, Rhizoctonia cerealis, population composition, real-time fluorescent quantitative PCR, distribution characteristics