| Japanese brome?Bromus japonicus?is a winter annual weed commonly found in wheat?Triticum aestivum L.?fields in China.It is not strict to the requirement of ecological niche and can grow in the region with 150-560 mm annual rainfall.This weed has the same growth period with wheat and is difficult to distinguish which can compete with wheat in light,moisture,nutrients and space.At last,Japanese brome seriously affects the wheat yield and quality and has become one of the malignant weeds which are difficult to eradicate in wheat fields of our country.Now,it is widely distributed in Anhui,Hebei,Henan,Hunan,Hubei,Jiangsu,Shandong,Shanxi,Shaanxi and Gansu provinces with more and more serious damage degree and the trend of rapid spread.Weeds biological ecology research is the basis of weed management system.The aim of this study was to study the effect of the outside environment factors on the germination and emergence;determine the field of dynamics,the competition relationship with wheat and its economic threshold;screen the wheat varieties with strengthen inhibition;clarify the populations genetic diversity from Shandong,Beijing,Jiangsu,Hebei,Henan,Shanxi,Shaanxi,Gansu provinces;predict the potential distribution area.The main results are as follows:1.Japanese brome is a kind of typical winter weeds.Germination was greater than 98%under a wide temperature range of 5 to 30 C and onset of germination was shorten as temperature increased.The optimum germination temperature was 25 to 30 C.Light was not required for germination to occur and pH from 5 to 10 had insignificant effect on germination.Japanese brome seed was quite tolerant to osmotic potential and salinity.Even at low osmotic potential or high salinity environment,some seeds still could germinate.Seedling emergence was greatest?98%?when seeds were placed on the soil surface but decreased with increasing of burial depth.No seedlings emerged at a depth of 6 cm.2.Japanese brome had two main peaks of seedling emergence during the whole growing stage.One period was middle October to early November account for 85.3%of the total with the weeks average temperature of 11.9-14.4C,and the other one was from middle March to early April account for 14.7%of the total with the weeks average temperature of 10C.Before winter,wheat started tillering in the early November and Japanese brome was middle November until early December.In the early March of next year,wheat and Japanese brome both began tillering in spring until the end of March.Tillering ability of Japanese brome was stronger than wheat.Japanese brome and wheat had the same change trend in aspects such as plant height,fresh weight.They both grew slowly before the winter and began to rapid growth in late march of next year with the increase of ambient temperature.3.In the density experiment,the density of Japanese brome was negative correlation with the density of the wheat panicles.With the increasing of density of Japanese brome,per square meter effective panicles of wheat gradually reduced.When the Japanese brome density increased from 0 to 640 plants m-2,the wheat panicles density reduced from 557.8 to 358.7.Besides,Japanese brome had slight influence on grain number and thousand seed weight of wheat.The results indicated that Japanese brome effected wheat yield mainly through affecting the spike density.When the Japanese brome density was 640 plants m-2,the wheat yield loss was 36.72%.The ET of Japanese brome on wheat was between 4 to 5 plants m-2.4.In forty-two main wheat varieties from Huang-huai-hai winter wheat growing areas,we screened four varieties which not only had stronger allelopathic inhibition on Japanese brome but also could bear Japanese brome's allelopathic inhibition well.They were Zhengmai379,Zhengmai9023,Zhoumai22,Tanmai98.5.ISSR molecular marker method was used to study the genetic diversity of 24 Japanese brome populations with 12 primers.The results showed that Japanese brome had the high degree of genetic diversity because of the percentage of polymorphic loci ranging from 2.83to 47.17%and a total percentage of 95.28%.Total genetic diversity for Japanese brome was0.2125,the mean heterozygosity within populations was 0.0730 and the coefficient of gene differentiation was 0.06562.These parameters showed that there was high levels of genetic differentiation among Japanese brome populations.The results of the AMOVA analysis further revealed that genetic variation occurs mainly among the population?63.72%?rather than within the population?36.28%?.Genetic distance among Japanese brome populations was ranging from 0.0401 to 0.3524 with an average of 0.1717 and it is bigger than the average genetic distance between populations of same species?0.05?.It also could indicate than there were large differences in genetic diversity among Japanese brome populations.The gene flow between Japanese brome populations was comparatively small?0.2619?and the limited gene flow may be one of the causes leading to the genetic differentiation among populations.UPGMA analysis showed that 24 populations were grouped into four major clusters and the geographical position consistent approximately clustered together indicating that geographical position has certain correlation relationship with genetic clustering.6.Measuring the sequence of trnT-trnLand atpI-atpH of cpDNA,the results showed that merging sequence is 1226 bp,has nine mutation sites accounting for 0.73%of the total.There were identified 15 kinds of haploid?H1-H15?.The haploid diversity was 0.717 and nucleotide diversity was 0.00137 showing that Japanese brome had abundant genetic diversity.The mean heterozygosity within populations was low?0.486?and total genetic diversity for species was high indicating that Japanese brome had a high level of genetic differentiation.There also existed a limited gene flow between populations.The results of the AMOVA analysis revealed that genetic variation occurs mainly among the population?52.7%?.The coefficient of gene differentiation between populations Nst?0.517?was significantly bigger than Gst?0.332?showing that haploid types with similar genetic distance were obvious relative to geographic structure.Through the analysis of the haploid type network diagram,15haploids could be divided into two distinct groups and haploid H2 and H5 were centered respectively.By the above results,we preliminary cleared the origins center of Japanese brome-Gansu region and determine the main spread path in China-from west to east.7.The main suitable areas of Japanese Brome in world were the areas of mid of Europe,the Middle-east,west of Asia,northwest of Africa,most areas of America,huang-huai-hai basin and southwest scattered parts of China,south of Korea and Japan.In China,Huang-huai-hai plain?Beijing,Tianjin,Shandong,Henan,Anhui,Jiangsu,southern Hebei?,Guan-zhong plain?Central and southern Shaanxi,southern Shanxi,Ningxia,southern Gansu?,Middle-lower Yangtze plain?Zhejiang,parts of Jiangxi?,Chengdu plain?Central and western Sichuan?,Hunan,Mid-north of Guizhou were the high risk areas.The secondary risk areas were the scope on the basis of the high-risk area to expand further.This study firstly explored the effect of the outside environment factors on the Japanese brome germination and emergence,cleared the field of dynamics,determined its economic threshold-4 to 5 plants m-2,screened four varieties which had stronger allelopathic inhibition on Japanese brome-Zhengmai379,Zhengmai9023,Zhoumai22,Tanmai98.ISSR molecular marker results showed that Japanese brome had high genetic diversity and there was a high level of genetic differentiation between different geographic populations.Genetic variation mainly occurred among populations and gene flow was smaller.Phylogeography research preliminary cleared origin center of Japanese brome and its main spread path in China.In addition,MaxEnt model forecasts the potential distribution area of of Japanese brome in China and the world. |
PDF Full Text Request