Identification of environmental and genetic factors causing "delayed stem senescence" in soybean.

该项目的目的是确定环境和遗传因素导致大豆“茎衰老延迟(DSS)”的症状，最近在大豆产区增加。对不同气温和土壤水分条件下生长的大豆植株的角果器官发育、角果灌浆期间氮素的固定和分配以及角果灌浆期的持续时间进行了研究。1.温度对大豆生殖器官发育和生殖器官发生的影响：6个大豆品种在开花后的温度梯度室中生长，在温度梯度室内建立了4个温度小区(T1-T4)，平均温度为23.1(T1)~25.8(T4)℃。T4的每小花完美粒数、单粒完美粒重和籽粒产量显著低于T1。但温度对DSS的发生无影响(…更不明显了。2.土壤水分条件对氮素平衡、细胞分裂素通量和DSS发生的影响：利用Cv.达契那加。中度水分亏缺显着降低了豆荚灌浆期间的固氮量，导致籽粒灌浆所需氮素相对不足，减轻了DSS症状。角果灌浆期间水分过多或R5后20天短暂缺水导致角果数减少，整个角果灌浆期木质部反式玉米素核苷通量增加。结果表明，不利的土壤水分条件，尤其是土壤水分的不稳定性，会通过降低氮库源比和增加根系细胞分裂素的供应来增加DSS的发生。3.DSS的遗传因素：利用来自北京和Tamahomare的重组自交系，对DSS性状进行了为期两年的QTL分析。在连锁群L上两年均检测到1个QTL，该QTL位于Dt1附近，Dt1是不确定/确定性状的主效基因。有几个QTL被检测到，但它们在DSS中的参与程度在不同年份之间不一致。虽然DSS的遗传因素似乎与环境条件有很大的交互作用，但存在一个主要的遗传因素存在于DTL附近或作为该基因座的多效性效应。较少

The aim of this project is to identify environmental and genetic factors causing the symptom of "delayed stem senescence(DSS)" in soybean, which has recently increased in the soybean production area. The development of pod organs, fixation and partitioning of nitrogen during pod-fill and duration of pod filling stage were examined for the soybean crop/plants grown under various air-temperature and soil-water conditions. A QTL analysis also was conducted for the DSS trait.1.The effect of temperature on development of reproductive organs and the occurrence of DSS : Six soybean cultivars were grown in the Temperature Gradient Chambers(TGC) and four temperature plots (T1-T4) with mean temperatures from 23.1 (T1) to 25.8(T4)℃) were established in the TGC during the period after the flowering stage. The number of perfect kernels per floret, single perfect kernel weight and seed yield were significantly lower in T4 than in T1. However, the effect of temperature on the occurrence of DSS was no … More t evident. On the other hand, the effect of cultivar on the DSS occurrence was evident irrespective to temperature conditions.2.The effect of soil water condition on the nitrogen balance, cytokinin flux and occurrence of DSS : Three experiments with soil water treatments were conducted using cv. Tachinagaha. A moderate water deficit significantly reduced nitrogen fixation during pod-filling resulting in a relative shortage of nitrogen for seed filling and decreased the DSS symptom. Excess water during pod filling or temporal water deficit during 20 days after R5 caused reduced pod number and higher flux of trans-zeatin riboside in the xylem throughout pod filling stage. It was concluded that unfavorable soil water condition, especially its unstableness, would increase occurrence of DSS through lowered sink/source ratio for nitrogen and also increased supply of cytokinin from the root.3.The genetic factors causing DSS : A QTL analysis on the DSS trait was conducted for two years using the recombinant inbred lines (RILs) from a cross between Peking and Tamahomare. One QTL was detected on the linkage-group L in both years and it was located close to Dtl, which is known as the major locus for the indeterminate/determinate trait. There were several QTLs detected but their involvement in DSS were inconsistent between years. Although the genetic factors of DSS seem to have great interactions with environmental conditions, there is a possibility that a major genetic factor exists near Dtl or as a pleiotropic effect of that locus. Less