Effects Of Sowing Date And Water Stress On Growth,Development And Grain Quality Of Broomcorn Millet (Panicum Miliaceum L.)

Broomcorn millet（Panicum miliaceum L.）is an important crop for disaster relief,as well as an important food crop in arid and semi-arid areas,which can sowing in a long period,barren resistance,strong adaptability and high water use efficiency.At the same time,with the national advocacy of healthy diet structure for residents and the change of market demand,broomcorn millet has become an important crop for structural adjustment and characteristic advantage in the new century,and the market demand for high-quality broomcorn millet has been increasing.Adjusting sowing date directly affects the growth process and maturity of broomcorn millet.Suitable sowing dates can avoid low temperature during sowing and harvesting and heat stress during key growth stages,thus increasing the yield potential of broomcorn millet.On the other hand,with the global climate change and frequent disastrous weather,drought have become one of the important factors affecting the yield in the northwest arid region.Therefore,it is of great practical significance for crop production and industrial development in dryland farming area to screen and cultivate the varieties suitable for long sowing time and study the response mechanism of broomcorn millet to sowing time and water.However,as a minor crop,the research foundation is weak,especially for sowing date,varieties and water stress on the regulation of growth and grain quality of broomcorn millet.In this study,the effects of sowing date and water on the growth and grain quality of broomcorn millet were systematically studied through multi-year and multi-site experiments of sowing date×variety and sowing date×water stress.The correlation between sowing date and water stress and meteorological factors was analyzed,and the effects of water stress deficit on the growth of broomcorn millet were analyzed from the transcription level.The main conclusions of the study are as follows:（1）The varieties and sowing date had significant effects on the main agronomic traits,leaf photosynthesis and fluorescence characteristics,and yield traits in summer sowing area（Baoji）and spring sowing area（Yulin）（p<0.05）.With the delayed sowing date,the yield of broomcorn millet in summer sowing area（Baoji）decreased by 12.4%-27.2%,while that in spring sowing area（Yulin）decreased by 3.6%-15.5%.In summer sowing area（Baoji）,broomcorn millet had short filling time,long and slender grains and low 1000-grain weight.The optimal yield combinations in Yulin were Shaanmei No.1（YL1,May 10）,Yumei No.2（YL3,June 10）,Black millet（YL4,June 25）and Jinshu No.5（YL4,June 25）.The optimal yield combinations of Baoji were Shaanmei No.1（BJ1,June 4）,Yumei No.2（BJ2,June 14）,Black millet（BJ1,June 4）and Jinshu No.5（BJ2,June 14）,respectively.Sunshine duration(S_VG),total growth days（D_M）and total sunshine duration（S_M）during the reproductive growth period were the key factors affecting the yield of broomcorn millet in summer sowing area（Baoji）,while precipitation（P）during the whole growth period was the most important factor affecting the yield of broomcorn millet in spring sowing area（Yulin）（p<0.05）.（2）The grain size,color and flour physicochemical properties of broomcorn millet in spring sowing area（Yulin）were significantly affected by variety and sowing date（p<0.01）.Yumei No.2 had the largest grain weight,with the 1000-grain weight>9.0 g and the 1000-kernel weight>7.39 g under all sowing dates.The sowing date which contained maximum nutrient content in different varieties was different,and the maximum total starch was as follow:Yumei No.2（B5,June 25）>Shaanmei No.1（B1,April 25）>Black millet（B1,April25）>Jinshu No.5（B4,June 10）;amylose content was as follow:Yumei No.2（B3,May 25）>Black millet（B3,May 25）>Jinshu No.5（B6,July 10）>Shaanmi No.1（B5,June 25）;and the total protein content was as follow:Black millet（B2,May 10）>Yumei No.2（B2,May 10）>Shaamei No.1（B1,April 25）>Jinshu No.5（B6,July 10）.Among them,non-waxy broomcorn millet（Yumei No.2）has the characterwastics of poor water absorption,easy gelatinization,poor stability of hot paste and good stability of cold paste,and is more suitable for processing frozen food.Shaanmei No.1 and Black millet has stronger hot paste stability,are more suitable for hot food processing,and significantly improved the thermal paste stability of flour under late sowing（B5 and B6,June 25 and July 10）.The suitable varieties and sowing dates could be selected according to the purpose in production.（3）The particle size and distribution,short-range ordering of crystals and thermal characteristics of broomcorn millet starch in spring sowing area（Yulin）were significantly affected by the varietiey and sowing date（p<0.05）.With the delay of sowing date,the short-range order of broomcorn millet starch crystals increased,and the onset temperature（To）and peak temperature（Tp）of decreased,which made the starch easier to gelatinize（p<0.05）.Among them,Shaanmei No.1,Yumei No.2 and Black millet had the lowest onset and peak temperature of gelatinization at B6（July 10）,respectively,while Jinshu No.5 had the lowest onset temperature of gelatinization at B5（June 25）.（4）Sowing date and water stress had significant effects on growth days,plant height,stem diameter,spike length and yield of broomcorn millet in summer sowing area（Baoji）（p<0.05）.With the delay of sowing date,the plant height,stem diameter,spike length,spike stalk length and the number of secondary spike branches of broomcorn millet in summer sowing area were significantly increased,but the yield and 1000-grain weight were higher on April 20 and May 30(6.8 g and 6.8 g;318.0 and 330.9 kg hm^-2,respectively).With the deepening of water stress,the plant height,stem diameter,spike length and spike stalk length of broomcorn millet were significantly decreased,and the yield,1000-grain weight,grain width and diameter were significantly decreased by 76.25%and 28.91%,while the content of small grain starch（<5μm）and gelatinization enthalpy（ΔH）were significantly increased（p<0.05）.The synergistic effect between sowing and water on June 20 was the worst,and the yield was significantly reduced by 82.3%-88.4%under water stress.On the contrary,the synergistic effect between sowing and water stress on May 30 was the best,and the yield reduction was the lowest by 18.8%under water stress,which indicated May 30 was the appropriate sowing date for summer sowing area.（5）Based on transcriptome sequencing technology,the main response mechanism and key metabolic pathways of mining millet in response to water stress were studied.Different levels of water stress can affect the transcription level of genes in the leaves of broomcorn millet,and severe water stress will cause serious damage to the growth and development of broomcorn millet,resulting in the loss of some functions.When broomcorn millet is under water stress,its cells sense water stress signals,regulate the expression of related genes and physiological responses through plant hormone signal transduction,and respond at different levels such as transcription and translation.In addition,at the molecular level,millet leaves enhance water stress tolerance by regulating the expression of plant MAPK signaling pathway related genes.In summary,Shaanmei No.1 and Yumei No.2,which with longer growth period,are more suitable for early sown,benefits to access more precipitation during the growth period,and achieves higher yield.Black millet,which with shorter growth period,is suitable for early sown in summer sowing area,and late sown in spring sowing area,in order to perlong（summer sowing area）and adjust（spring sowing area）growth period and gain more sunshine,accmulated temperature and precipitation.With the delay of sowing date,the total starch content and total protein content of broomcorn millet in the spring sowing area decreased by7.37%and 6.10%,and the color of kernel became lighter and not conducive to commoditization.Moreover,the cold paste stability of non-waxy broomcorn millet flour decreased significantly,while the hot paste stability of waxy broomcorn millet flour increased significantly.The short-range ordering of starch increased,and it was easier to gelatinize due to the To and Tp of starch gelatinization was significantly decreased.However,with the delay of sowing date,the millet biomass and the number of secondary spike branches increased significantly in the summer sowing area,and the yield and 10000-grain weight were significantly reduced by late sowing.With the increase of water stress,the plant biomass,yield and 1000-grain weight of broomcorn millet decreased significantly,grain filling was insufficient,and the gelatinization enthalpy significantly increased resulted in that the starch was more difficult to gelatinize.At the same time,the transcriptional metabolism of broomcorn millet flag leaves changed significantly under water stress,and 48 significantly different metabolic pathways including plant MAPK signaling pathway were regulated to respond to water stress.In conclusion,broomcorn millet had a long suitable seeding period,and both sowing date and water stress have significant effects on its growth,development and grain quality.Suitable sowing time is conducive to the high-efficient use of light,temperature and water resources during the growing period,which is conducive to the development of broomcorn millet with high yield,high efficiency and high quality.