Characterization Of Populations Of Monilinia Spp. On Stone And Pome Fruits In China And Genetic Evolution Of The Cyt B Genes

So far, researches about brown rot diseases in China are mainly focused on peach but not on other fruit trees. This study was conducted to identify species of Monilinia and Monilia causing brown rot diseases on plum, apricot, cherry, apple, pear as well as peach in China, and to characterize genetic evolution of the cytochrome b gene(Cyt b). The achieved results include:(1) A total of 909 single-spore isolates were collected from different locations and hosts showing brown rot symptoms in China. Based on biological characteristics, ITS sequence analysis and multiple PCR identification, a new record species of Monilia yunnanensis was found on apple and pear, respectively. Two new record species of M. fructicola and M. mumecola were found on cherry. Three new record species, that is, M. fructicola, M. mumecola and M. yunnanensis were found on plum and apricot, respectively. In general, M. fructicola is the dominant species and widely distributed in China, M. mumecola is mainly distributed in central and west China like Hubei and Chongqing, M. yunnanensis is the dominant species in Yunnan province, it is also found in some areas of Shannxi province and Beijing municipality. Phylogenetic analysis based on G3 PDH and TUB2 nucleotide sequences revealed that isolates within same species clustered together regardless of hosts or geographical origin, suggesting that these factors did not play an important role for the evolutionary separation of the Monilinia spp.(2) The Cyt b gene is the target gene of Quinone outside Inhibitors(Qo Is) fungicide, and mutation on Cyt b gene is the main reason for plant pathogenic fungi to develop Qo I fungicide resistance. The Cyt b genes of Monilinia spp. have a large number of huge introns, especially in M. mumecola, it harbors the largest size of introns so far to be known. In order to understand the reason, a systematical analysis was carried out to study the genetic evolution of Cyt b genes. It revealed that the Cyt b genes originated from an ancient prokaryotic gene in Alphaproteobacter, then co-evolved with the host after entering the eukaryotic cells. During the evolution, Cyt b gene could horizontal transfer to different kingdoms.(3) The genetic analysis of the Cyt b gene introns revealed that introns in mitochondrial Cyt b genes were acquired after the endosymbiosis of alphaproteobacteria in eukaryotic cells. The introns of Cyt b gene showed a skewed distribution in organisms. Cyt b gene introns were frequently present in the fungal kingdom and some lower plants, but generally absent or rare in Chromista, Protozoa, and Animalia. It showed a wide and patchy distribution in fungi, suggesting introns have an obvious prefer to some locations. Cyt b gene introns could occur frequent loss-and-gain events by transposition, although intron loss-and-gain events were not necessarily beneficial to their host organisms. The high number of Cyt b introns in Monilinia spp. appeared to be a result of recent intron gain-and-loss events, including the horizontal gene transfers, and directly caused Monilinia Cyt b genes to be the largest ones in eukaryotes.