Effects of light stress at different stages on the growth and yield of different maize genotypes (Zea mays L.)
弱光胁迫对不同基因型玉米生长发育和产量的影响

Light is one of the most important factors affecting corn (Zea mays L.) production. The light saturation point of corn is much higher than that of most other crops, allowing corn to take advantage of the higher light intensity. During the growing season, however, corn frequently encounters low light intensities that restrict growth capacity, therefore limiting the grain yield. The level of photosynthetic active radiation (PAR) can markedly change the growth environment, which directly impacts photosynthesis capacity, even the accumulation and reallocation of dry matter, thus affecting yield. Several studies on the effects of light stress on corn had been done, but none have studied differences among various Maize genotypes. The objective of this trial was to assess the growth and yield response to shading at different growth stages for different Maize genotypes. The two-year pot-culture experiments were conducted during 2001 and 2002. Cylindrical plastic pots, 27 cm in height and 30 cm in diameter, were used in this trial. Each pot was filled with 12.5 kg air dried soil. The planting dates were June 13 and June 4 in 2001 and 2002, respectively. The experiment involved two factors: cultivars and shading. The first factor included four cultivars: Yedan22, Yedan3638, Yuyu2, and Danyu13, and the second factor consisted of four levels of shading: control (no shading), seedling shading (shaded from germination to 6th full-expanded leaf), ear shading (shaded from 6th fully-expanded leaf to silking), and grain shading (shaded from silking to maturity). The shade environment was created by using black polypropylene fabric with 50% light penetration. The shading fabric was 6 metres long and 6 metres wide, and was hung horizontally 3 meters above the bottom of the pots. To insure shading treatment was effective in the early morning and late afternoon, the eastern and western sides of the corn canopy were also covered by the same fabric. The results indicated that corn growth rate expressed by leaf appearance was slower and the leaf blade was thinner under shade conditions. The shading treatment delayed the senescence of leaves directly, but shortened the leaf functional period as the shaded leaves ageing process was accelerated once they regained the normal light. Under shade conditions, the plants were taller, but shorter than that of the control once regaining normal light. Dry matter accumulation was reduced and growth stage was delayed for all the shading treatments, particularly at the silking stage. Compared with the control, the yield was also reduced by shading. The magnitude of the yield reduction was related to the shading stages, the yield was decreased significantly by the ear shading treatment compared to other treatments. There were differences among the genotypes in the responses to light stress: Yedan3638 and Danyu13 were more sensitive to light stress than Yedan22 and Yuyu2.