| Maize is an important grain crop in China and plays a pivotal role in national food security.With the increasing demand for domestic industry and feed year by year,domestic maize yield cannot meet its own needs and maize imports increase rapidly.Increasing maize yield is imminent,but maize is vulnerable to suffer from non-biological disasters in the growing season,such as frequent rain and sparse sunshine,high temperature,drought,high wind and other natural disasters which cause great losses to the maize yield.With deteriorating global climate,the frequency of natural disasters shows a trend of increasing.The probability for occurrence of frequent rain and sparse sunshine is relatively large among the natural disasters,especially in the Huang-Huai-Hai district and southwest mountain hill maize areas in China's top 3 corn producing areas.The maize yield in both areas accounts for about half of China's corn yield,thus ensuring the yield of maize in these areas has a strategic importance for the national food security.In areas with frequent rain and sparse sunshine,the most fundamental way to ensure the yield is to breed varieties that are resistant to the frequent rain and sparse sunshine.The prerequisite for breeding maize varieties that are resistant to frequent rain and sparse sunshine is to screen out maize germplasm resources with strong shade tolerance,clarify the optimal period and the evaluation index for shade tolerance identification of maize inbred lines,and establish a set of scientific shade tolerance identification system for maize inbred lines;clarify the shade tolerance genetic laws for maize inbred lines;and illustrate the mechanism of shade tolerance at molecular level.In this study,the evaluation system of maize inbred lines tolerance of shade was established,artificial simulation shading at flowering stage,male and female interval and days of silk were identified,the tolerance of shade evaluation of maize inbred lines was based on the average membership function.Using the evaluation system,the tolerance of shade identification of 40 China's elite maize and 158 American maize inbred lines in China,a batch of shade-tolerant ability germplasm resources were screened out.It clarify shade tolerance genetic laws of corn inbred lines;analyze the differential expressions of mi RNAs in female ear for the Zhong 72 and 502's inbred lines with different shade tolerances under shading condition and natural light,it clarify the key mi RNAs and their target gene functions and effects under the shading condition,and provide the theoretical guidance for the shade tolerant breeding of corn.The results of this paper are as follows:1.The tolerance of shade evaluation system of maize inbred lines was established,artificial simulation of shading at flowering stage.The shading period from maize at bell stage,end of the 10 day of maize powder,the male and female interval and silk days as the identification index.The tolerance of shade evaluation was based on the average membership function.The evaluation system is accurate,stable,reliable,simple operation and practical,and can be used for large-scale tolerance of shade identification.2.Preliminary shade tolerance division was conducted to the domestic elite maize inbred lines,Tangsi Pingtou(SPT)and PB groups had a good shade tolerance,PA and BSSS groups had a medium shade tolerance,and Lanka Site(Lanc)and Lvda Honggu(LRC)groups had a poor shade tolerance;158 samples of the US inbred lines were divided into three groups: strong,medium and poor shade tolerances,there were 24 samples with strong shade tolerance,37 samples with medium shade tolerance,and 97 samples with poor shade tolerance,which provide shade tolerance germplasm resources for shade tolerant breeding of corn.3.Nine inbred lines with different shade tolerances were selected for complete double-row hybridization,artificial light was used to simulate weak light stress at the flowering stage.The shading duration ranges from the bell stage to 10 days after silking,so Griffing I method was used for general combining ability(GCA)and special combining ability(SCA)genetic analysis to the traits such as numbers of tasseling days and silking days,male and female interval period,tassel length,tassel branch and yield.The results showed that the general combining ability effective values of Chang 7-2,Qi 319 and Zhong 72 are high,which improved the shade tolerance ability for future generations.Except for tassel branch,the general combining ability of remaining traits was extremely significant,the special combining ability of yield was not significant but it was significant in all other traits.Tassel branches were controlled by non-additive effect,yield was controlled by additive effect,and all other traits were co-controlled by additive and non-additive effects.The male and female interval and tassel branch traits should be selected at high generation for breeding inbred lines.The 4 traits,including numbers of tasseling days and silking days,tassel length and yield,should be selected at low generation.According to special combining effect values,we can conclude that the maize single cross hybrid upon grouping should follow the following rules: 1.If both parents have strong shade tolerance,the shade tolerance of their combination has a high special combining ability,and the combination has a strong shade tolerance;2.If one of the parents has a strong shade tolerance,but the other has a medium shade tolerance,the shade tolerance of their combination has a relatively high special combining ability,and the combination has a medium shade tolerance,so the inbred lines with strong shade tolerance should be selected as a male parent;3.In case of combination between a parent with strong shade tolerance and a parent with poor shade tolerance,the parent with strong shade tolerance should be used as the male parent,which can improve the special combining ability of shade tolerance for the combination,namely,enhance the shade tolerance for the combination.4.With the high-throughput sequencing technique,the shade-sensitive inbred line 502 and the non-shade-sensitive inbred line 72 were used as the test materials to conduct sequencing with the samples as female ears after 10 days of shading.A total of 130 conserved mi RNAs that belong to 21 families were found in the inbred line 502;and128 conserved mi RNAs that belong to 21 families were found in the inbred line 72.The most of the mi RNAs had a higher expression shading conditions than the natural light in 72 and 502 female ears,of which,12 mi RNAs were expressed only in 72 female ears,and 13 mi RNAs were expressed only in 502 female ears,and the expressions of mature mi RNAs showed a reserved trend in the shade-sensitive inbred line 502 and the non-shade-sensitive inbred line 72.94 mi RNAs of the inbred line 502 were up-regulated under the shade,and 48 mi RNAs were down-regulated;33mi RNAs of the inbred line 72 were up-regulated,and 95 mi RNAs were down-regulated.These differently expressed mi RNAs may be involved in regulation of hormone balance,metabolic process,growth and development and flowering time.17 new mi RNAs are found in 4 databases under natural lighting and shading conditions in 72 and 502;and with q RT-PCR verification for the different mi RNAs and new mi RNAs and their target genes. |
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