Effect of Planting Density on Spike Differentiation and Kernel Development in Maize (Zea mays L.)

The study was expanded for the low light phenomenon during the late development ofmaize, different densities were used to simulate the low light stress of kernel development.The effects of low light on the male and female spike differentiation and kernel developmentwere studied, intending to clarify the internal mechanism bald under mid-high density and toprovide a theoretical basis for corn production.Two cultivars ZD958(bald not seriously) and DH661(bald seriously)were used asmaterials and three different planting densities (45000plant·ha-1,75000plant·ha-1,105000plant·ha-1) were set to analyze spike differentiation and kernel development response todensity with methods of field determination, dissecting microscope and indoor measurement,the main results were as follows:1. Effects of planting density on canopy light transmittance of maize: In the same period,both ear layer and bottom light transmission of two cultivars decreased with the densityincreasing. Under the same density, ear layer transmittance reduced firstly after pollination[at0days after pollination(DAP) got the minimum] and then began to increase gradually.While bottom transmission of two cultivars was not significant.2. Effects of planting density on corn yield: the results showed that two cultivars got themaximum yield at75000plant·ha-1. Grain number per ear and1000-grain weight reducedsignificantly with density increasing, therefore suitable planting density will be conduciveto the improvement of corn yield.3. Effects of spike differentiation on kernel barrenness in maize:(1) High density reducedthe male ear length, branch number and pollen number per plant. But total pollen amountof corn population was not the main factor that affected barrenness, while the shorteningof pollen shedding duration under high density was.(2) The differentiation of ear waspostponed under high density, but its effects on flowers number were not significant. Theear length, ear volume and dry-weight were also reduced under high density, thedifferentiation degree of apical kernels was low and their capacity was reduced. And high density could lead to flower abortion easily.(3) The number of abortive florets andunfertilized florets increased with the increase of plant density, while ratio of canopytransmission before pollination was significantly associated with flower abortion. Itindicated field environment had great impact on the floret development per ear and thenresulted in kernel abortion later.(4) The anthesis-silking interval (ASI) was elongated, thenumber of silked-plants was decreased under high density, it was a main reason thatcaused empty lever and reduced spike.4. Relationship between kernel development and abortion: kernel abortion got the mostobvious in10days after pollination (DAP), but it remained unchanged after30DAP.Spikelet number and flowering period revealed strong positive correlation with canopytransmission after20DAP. Compared physiological characteristics between normal andabortive kernel, the results showed that it had a certain relationship among storagecapacity, assimilation supply, key enzymes activities during grain-filling and hormonecontent in normal and abortive kernel. The grain size, dry-weight, soluble sugar, starchcontent and activity of the key enzyme that catalytic sucrose synthesis (such as SS andSPS) in abortive kernel were significantly lower than normal kernel. Correlation analysisshowed that final kernel weight had significantly correlated with the content of solublesugar, starch, SS and SPS. Kernel development was regulated by hormone content. Finalkernel weight had significantly relationship with ABA content(0-20d) as well as the ABAand GA content(21-30d). When breeding superior cultivars, the measures that makereasonable plant-density and ideal canopy type will play an important role in reducingkernel abortion.