Effects Of Jointing And Booting Low Temperature Stress On The Morphology Of Wheat

Wheat(Triticum aestivum L.)is one of the most important crops in the world,and the safety of wheat production has an important role in ensuring the food security in China.With the global warming,the frequency,intensity and duration of extreme low temperature events are rising sharply.To a large extent,the morphological structure of the plant determines the competitive ability and resource acquisition intensity,which determines the execution of plant function.Therefore,the study of morphological characteristics of wheat under low temperature stress can provide theoretical basis and data support for the improvement of wheat morphological model and the visual expression of wheat growth in the future climate conditions.In this study,the environment-controlled phytotron experiments under different low temperature levels and durations at jointing and booting stages for pot wheat are conducted,aiming at investigating the dynamic responses of different morphological indexes of wheat to low temperature stress,quantifying the effect of low temperature stress on wheat morphological structures.The results are as follows:At jointing and booting stages,the low temperature levels and durations have different effects on wheat leaf length,leaf width and leaf color.The leaf length,leaf width and green leaf area ratio decreased with the decreasing low temperature level(from T1 to T4)and the increasing low temperature duration(from D1 to D3),while the R,G and B values increased.With the effect of low temperature,the time of leaves emerging and reaching the fixed length for part of the treatments was later than the control treatment.Comparing with CK,the times of leaves emerging and reaching the fixed length for the main stem of Yangmai16 were delayed by 0-4 days under the low temperature treatment at jointing while the times of leaves emerging and reaching the fixed length for the main stem of Xumai30 were delayed by 0～6 days and 0～8 days under the low temperature treatments at jointing.The effect of low temperature stress at jointing stage on leaf length and leaf width of the second last leaves was less serious than that on flag leaf.For every 1℃ d increase of accumulated cold degree day(ACDD)at jointing,the length of flag leaf and the second last leaf of Yangmail6 and Xumai30 shortened by 1.04%and 0.92%,and 0.87%and 0.75%,respectively,and the maximum leaf width decreased by 1.04%and 1.12%.Wheat leaves under low temperature stress at booting stage showed marginal curling upwards and leaves width decreasing,which lead to the changing of the leaf shape.The leaf width in upper part was more sensitive to low temperature at booting stage than the basal part.For every 1℃·d increase of ACDD at booting stage,the maximum leaf width of Yangmail6 and Xumai30 decreased by 1.18%and 1.36%,respectively.In addition,leaves are partly or totally died and turned to yellow under sever low temperature stress(T4)at booting stage,with the green leaf ratio of main stem decreased to about 21%.For the effect on leaf color which is caused by low temperature stress,the sequence of leaf position is flag leaf>second last leaf>third last leaf.For every 1℃·d increase of ACDD at booting stage,the R,G,and B values of leaves on the main stem of Yangmail6 and Xumai30 increased with 7.53,3.88 and 3.01,and 7.74,4.29 and 3.10,respectively.At jointing stage,with the effect of low temperature stress,the heights of main stem and tiller Ⅰ,Ⅱ and Ⅲ for both two cultivars decreased.The heights of main stem,tiller Ⅰ,Ⅱ and Ⅲ decreased with the decreasing low temperature level and the increasing low temperature dxration.Comparing with the CK,the time of main stem,tiller Ⅰ,Ⅱ and Ⅲreaching maximum heights were delayed by 1～6days delay and 1～7days delay under low temperature treatment at jointing stage for Yangmail6 and Xumai30.For the effects on different tillers for Yangmai16 which is caused by low temperature stress at jointing stage,the sequence is tillerⅢ>tiller Ⅱ>tiller Ⅰ>main stem,which higher position tillers were badly influenced,for every 1v·d increase of ACDD at jointing stage,the height of main stem,tiller Ⅰ,Ⅱ and Ⅲ decreased by 0.68%,0.73%,0.85%and 1.05%for Yangmai16.But the differences among decreases in heights of different tillers caused by low temperature stress at jointing stage for Xumai30 were not significant,with 1 ℃·d of increase of ACDD at jointing stage,the heights of main stem,tiller Ⅰ,Ⅱ and Ⅲ of Xumai30 decrease by 0.60%,0.62%,0.55%and 0.58%comparing with CK.At jointing and booting stages,the length and width of panicle decreased with the decreasing low temperature level and increasing low temperature duration,causing the shape of panicle changed respectively.The morphological changes in panicle which were caused by low temperature at booting stage was much more higher than that at jointing stage,every 1℃·d increased of ACDD at booting stage,0.68%decreased in length of panicle for both Yangma16 and Xumai30 were observed,and the maximum width of panicle for Yangmai16 and Xumai30 decreased by 1.46%and 1.49%,respectively,while in booting stage,with every 1℃ · d of increase of ACDD the panicle length and width of these Yangmail6 and Xumai30 decrease by 1.86%and 1.58%,and 3.16%and 3.04%,respectively.In addition,the panicle width in top and basal part was more sensitive to low temperature stress at jointing stage,and the panicle shape changed from spindle-like to oval,while the panicle width in lower quarter part changed significantly under low temperature stress at booting stage,and the panicle shape changed from spindle-like to inverted-bottle like.