Study On The Coevolution Between Chrysomyxa And Its Host Plants

Chrysomyxa Unger is an important plant pathogen,most Chrysomyxa species are heterecious and complete their life cycle on two different plant hosts belonging to two unrelated genera,i.e.Picea and Rhododendron.However,the coevolution between Chrysomyxa and its host plants were still undetermined.In this study,by clarifying the coevolution between Chrysomyxa and its host plants,it provides scientific basis for further defining the species of in China,establishing the coevolution model between Chrysomyxa and its hosts,and revealing its pathogenic mechanism.In this study,63 Chrysomyxa specimens and 150 infected host specimens from Sichuan,Yunnan,Gansu,Shaanxi,Xinjiang,Tibet,Northeast China and Qinghai were used for molecular analysis.We recognized species based on ITS and 28S rDNA sequence data by using Generalized Mixed Yule Coalescent(GYMC)Approach and Poisson Tree Processes(PTP)models.At the same time,Coleosporium was selected as a fossil calibration point to estimate the origin and divergence time of Chrysomyxa in China.In addition,the phylogenetic trees of Chrysomyxa and Rhododendron,Chrysomyxa and Picea were constructed by combining with chloroplast DNA fragments of the hosts.Based on the analysis of coevolution between Chrysomyxa and its hosts Rhododendron and Picea,the coevolution model of Chrysomyxa and its hosts at each spore stage was revealed.The main research results are as follows:(1)The results of GMYC and PTP analysis showed that Chrysomyxa in China could be divided into 11 different species.The Single threshold,Multi threshold model of GMYC and PTP analysis model also consistently confirmed 11 different species.At the same time,the morphological characteristics of each spore stage also support this conclusion.(2)Molecular clock analysis of Chrysomyxa showed that it originated from Miocene period in the Cenozoic era,approximately 12.99 million years ago(Mya).The results also showed that the origin time of Chrysomyxa was obviously later than that of its aeciaospore and teliospore hosts.In addition,the alternation host plant(Picea)range of recently differentiated Chrysomyxa was basically the same as that of early differentiated Chrysomyxa,while the recently differentiated Chrysomyxa species had a wider range of host plants(Rhododendron),than the early differentiated species.(3)Coevolutionary analysis of Chrysomyxa with its host plants Picea and Rhododendron in aeciaospore and teliospore stages,the results showed that high discordance between topologies of the parasites and hosts.Therefore,it is believed that cospeciation is not the main evolutionary model of Chrysomyxa and in the whole evolutionary stage,host jump event,replication event and loss event,namely host jump,repeated speciation and failure of speciation were the main evolutionary models of Chrysomyxa.