Research On Occurrence Mechanism Of Genetic Defect Barren Stalks Of Maize (Zea Mays L.)

The experiment was conducted on the south farm of Shenyang Agricultural University (41°49’N,123°34’E) from2011-2013, which is classified as a north temperate climate. The experiment applied a split-plot experimental design with inbred lines as the main plots and shading intensities as subplots. Low-light sensitivity differences of different types of varities and lines to shade stresses were compared by using paired near-isogenic line of vulnerable and invulnerable barren stalk inbred lines of Shennong98A and Shennong98B, vulnerable barren stalk hybrids of Dongdan90and Dongdan80, and invulnerable barren stalk hybrid Zhengdan958, to make explicit the key stress period inducing barren stalks, to explore dynamic adaptive changes in the photosynthetic rate and also fluorescence characteristics to different shade stresses and after light intensity transfer. The experiment also aimed to explain the photosynthetic characteristics of barren stalk of low-light-sensitive inbred lines when exposed to limited light conditions. The main results are followed:1. Pairs of near-isogenic line Shennong98A and Shennong98B are developed by the Institute of Specialty Corn of Shenyang Agricultural University. Shennong98A is a barren-stalk defective inbred line, and Dongdan80and Dongdan90are barren-stalk defective hybrids with barren stalk under weak light conditions. They are prone to barren stalks under weak light conditions. Compared with nonbarren-stalk varieties (or lines), barren-stalk varieties (or lines) show significant differences in three aspects:the ratio of barren-stalk is much higher than the barren-stalk varieties (or lines) under the same light intensity, light intensities induced barren-stalks are lower than the light of nonbarren-stalks, critical light intensity induced barren-stalks are clear. It further confirme the existence of genetic defect barren stalk of maize.2. The low-light-sensitive stage inducing genetic defect barren stalk of maize is from tasseling to the end of silking stage. At this stage, weak light stress will generate a large number of barren stalks because of non-silking. The shade stress inducing gene expression of the genetic defect barren stalks of Shennong98A is38%. Shade tolerance of Shennong98B and Chang7-2are similar, whose stress intensities should be between38%and60%. That is to say, more than38%shade or close to38%shade is the light intensity limit to distinguish Shennong98B, Changqi-2and Shennong98A. Zhendan958has the better adaptation ability to weak light condition in three hybrids. There are significant differences in three hybrids under the75%shade. Dongdan90and Dongdan80are basically barren stalks under the75%shade, but Zhengdan958is only50%.3. Shade stresses could make young female ear shorter and thinner, decrease grains per ear, and increase the number of abortive grains. The spindle length of tassel, the first branch numbers, the first branch lengh, and total of male floret numbers decreased with the increase of shade intensity and the reactions of easy barren stalk varieties were much more obvious, even caused100%barren stalk led by female ear agenesis. The reaction of plant height to shade was more complexed.38%shade could promote the increase of plant height, but75%shade for a long period would reduce plant height. In addition, shade stresses also can reduce leaf area, specific leaf weight, straw stiffness and the dry matter of stem, leaf, sheath.4. There were large differences in the weak-light adaptation of different inbred lines, and its performance was determined by the weak-light sensitivety of inbred lines. Whether in natural light or under shade stresses, the net photosynthetic rate of low-light sensitive inbred line Shennong98A was lower than Shennong98B.38%shade is the light intensity limit to distinguish the differences of Shennong98A and Shennong98B. In addition, chlorophyll content of weak-light sensitive varieties (or lines) was lower than insensitive varieties (or lines).5. The effects of shading on the fluorescence parameters of maize were obvious. The noncyclic photosynthetic electron transport rate (ETR) and nonphotochemical quenching (NPQ) of maize were significantly reduced while maximum photochemical conversion efficiency (Fv/Fm), actual photochemical efficiency (φpsn) and photochemical quenching (qP) increased after shading, with effective degrees exacerbated with increases in shade intensity. Upon removal of the shading treatment, NPQ increased and Fv/Fm,φpsu, qP and ETR were restored. Photosynthetic characteristics and their differences are important photosynthetic physiological indexes for identifying barren stalk and nonbarren stalk lines. The PN and fluorescence parameters of the barren-stalk line Shennong98A were lower than that of the nonbarren stalk line Shennong98B, both under a shade and nonshade environment, indicating that the light adaptability of Shennong98B is better than Shennong98A.