Senescence Characteristics of Maize Leaves at Different Maturity Stages and Their Effect on Phyllosphere Bacteria
Leaf,as a photosynthetic organ of crops,its senescence process has an important impact on yield formation,but the relationship between leaf senescence and phyllosphere microorganisms has been less studied.In order to explore the impact of the senescence process of maize leaves on the phyllosphere bacterial community,this study used three maize varieties of different maturity time(early-maturation variety Heike Yu 17(H17),mid-maturation variety Zhongdan 111(Z111),and late-maturation variety Shen Yu 21(S21)in Northeast China as the experimental materials,and the leaves of the ear position of the three maize varieties were sampled five times starting from the blooming stage of early-maturation varieties,and the physiological indexes of senescence were determined.And at the same time,the community composition of endogenous and exogenous bacteria in/on the leaves was determined based on high-throughput sequen-cing technology.The results showed that at the late reproductive stage,leaf water content,POD and SOD activities were significantly higher in the mid-and late-maturation varieties than in the early-maturation varieties.At the phylum level,Cyanobacteria were endemic to mid-and late-maturation cultivars;at the genus level,the relative abundance of the en-dogenous shared bacteria Sphingomonas,Methylobacterium,and Deinococcus in maize leaves decreased significantly at later stages of maturation(Ⅳ and Ⅴ).The relative abundance of endogenous bacteria Streptomyces and exogenous bacteria P3OB-42 were significantly enriched in the late senescence period,with similar trends and significant differences in relative abundance among the three species.The relative abundance of endogenous and exogenous bacteria differed significantly,with the top 5 exogenous bacteria accounting for more than 60％,while for endogenous bacteria,the top 5 accounted for only more than 30％.Soluble sugar content,photosynthetic pigment content and SOD activity were sig-nificantly correlated with bacterial community structure and abundance.In conclusion,mid-and late-maturation varieties were effective in prolonging leaf greening period,maintaining late leaf physiological activity with delaying senescence.The effects of senescence on the composition and diversity of endogenous bacterial communities were significantly greater than those of exogenous bacteria,and there were significantly different genera among three maize varieties studied.Moreover,soluble sugar content,photosynthetic pigment content and SOD activity were the key factors affecting the phyllosphere bacterial communities as well as the dominant species.
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