Effects Of Water Deficit On Growth And Grain Filling Characteristics In Broomcorn Millet

As an important food crop and cash crop in arid and semi-arid regions, water is a majorlimiting factor for broomcorn millet’s production improving and growth. Enhancing thelimited water use efficiency has great significant in improving the growth and production ofbroomcorn millet. Water deficit in different growth periods with different levels havedifferent effects on crop’s growth and yield. Grain filling process and the top three leaves’photosynthetic efficiency are having close relationship with crop’s yield formation. Leaves’antioxidase activities reflect its strength of scavenging reactive oxygen species and the abilityto maintain their metabolic balance. To study the effects of water deficit which are imposed indifferent growth stages with different degrees on photosynthetic characteristics andantioxidase activities of the top three leaves of broomcorn millet after flowering and its grainfilling characteristics have important significant in revealing the response of broomcorn milletto water deficit and improving water conservation and drought cultivation techniques andwater use efficiency. Using Yumi2as the material, a pot experiment was conducted: takewhole growth period adequate water supply (70%~75%of field capacity, CK) as CK.6treatments are moderate water deficit (40%~45%of field capacity) and severe water deficit(20%~25%of field capacity) in jointing, booting and blossom mature stage respectively. Bymeasuring grain filling characteristics, yield and the top three leaves’ photosyntheticcharacteristics, antioxidase activities and malondialdehyde content after flowering, the studyreached the following main results.(1) The effects of water deficit on green leaf area and chlorophyll content of the top threeleaves are as follow. Compared with CK, except moderate water deficit in booting stageincreased the top third leaf’s green leaf area after flowering, other treatments all decreased thetop three leaves’ green leaf area. Water deficit in jointing and booting stage had a largerdecline in flag leaf while water deficit in blossom mature stage had a larger decline in topsecond and third leaf. For the deficit in same stages, severe water deficit had greater reductionon green leaf area than moderate water deficit. After flowering, the chlorophyll content of topthree leaves of all treatments performed as flag leaf> the top second leaf> the top third leaf. Water deficit in jointing stage and booting stage decreased the chlorophyll content of topthree leaves in early and middle stages of blossom mature period, and increased its content inthe later stage of blossom mature period, of which severe water deficit had greater ascendingextent than moderate. Water deficit in blossom mature stage decreased the top three leaves’chlorophyll content since flowering and severe water deficit had greater reduction extent thanmoderate.(2) After flowering, moderate water deficit in jointing stage and booting stage increasedthe top three leaves’ net photosynthetic rate in a certain degree, while moderate and severewater deficit in blossom mature stage decreased the top three leaves’ net photosynthetic ratein a certain extent. Compared with CK, all treatments decreased the top three leaves’ netphotosynthetic rate at6th d after flowering, severe water deficit in blossom mature stage hadthe largest decline range which was lower than CK89.51%(P<0.05). Water deficit injointing and booting stage improved the top three leaves’ net photosynthetic rate at middleand later stage of flowering and mature period, moderate water deficit had greater increasingextent than severe water deficit, and water deficit in jointing stage had larger increasing extentfor flag leaf while in booting stage had larger increasing extent for the top second and thirdleaf. Water deficit in blossom mature stage decreased the top three leaves’ net photosyntheticrate since flowering and speeded its senescence, sever water deficit had larger reduction thanmoderate water deficit.(3) Water deficits at different times with different levels had different effects on the topthree leaves’ MDA content and SOD and POD activities after flowering. In terms of differentdeficit period, water deficit in jointing and booting stage had larger effects on SOD activitywhile the respond of POD activity had no obvious difference for the different deficit times.Compared with CK, water deficit in blossom mature stage increased flag leaf’s SOD activityduring0-18d after flowering, other treatments all decreased the top three leaves’ SODactivity, basically performed as sever water deficit had larger decrease extent than moderate.When under same water deficit condition, POD activity had less affected than SOD. Alltreatments’ POD activity was lower than CK in a certain degree and no significant differencebetween treatments. Water deficit in jointing stage and booting stage increased the MDAcontent of middle stage of blossom mature period, water deficit in blossom mature stageincreased the top three leaves’ MDA content at the whole blossom mature period, sever waterdeficit had larger increasing range than moderate. Among all the treatments, AAS had thehighest MDA content.(4) The effects of water deficit on grain filling characteristics and yield are shown asfollow. Under sever water deficit, R0decreased, Tmax prolonged, the filling later stage shortened, contribution rate of middle and later stage of filling process declined, the materialtransport from stem and shealth to spike reduced, thus setting rate and yield decreased, ofwhich sever water deficit in booting stage had the serious effects. Under moderate waterdeficit, the filling process was fasted, the material transport from stem and shealth and leavesto spike improved, and setting rate and yield were improved, of which moderate water deficitat jointing stage had the highest ascending range.Overall, sever water deficit at jointing stage and sever water deficit at booting stagesignificantly reduced the top three leaves’ area, net photosynthetic rate, chlorophyll content,antioxidase activities, delayed the grain filling process, reduced the grain filling rate, stem andsheath output and transfer rate, ear length and ear number, and their grain quality were lowerthan that of the CK21.40%(P>0.05) and41.51%(P<0.05). Therefore, sever water deficit,15%~20%of field capacity, should be avoided happening to broomcorn millet at jointingstage and booting stage. However, moderate water deficit at jointing stage, booting stage andblossom mature stage respectively all increased the top three leaves’ net photosynthetic rate,grain filling rate and setting percentage in a certain degree, and their grain quality were higherthan that of the CK41.14%(P<0.05),11.44%(P>0.05) and7.75%(P>0.05). This illustratesthat water deficit of40%~45%field capacity at jointing stage has positively effects on growthand yield improving of broomcorn millet.