苗期水分胁迫对玉米根系生长杂种优势的影响

Heterosis of Root Growth in Maize(Zea mays L.)Seedling under Water Stress

以玉米杂交种高油115及其亲本(母本220、父本1145)为材料,研究了玉米苗期根系生长的杂种优势及水分胁迫的影响。试验设水分充足、轻度干旱和严重干旱3个处理,田间持水量分别为75%、55%和35%。结果表明,在水分充足条件下,根长(RL)、根表面积(SA)和根干重(RDW)均表现出不同程度的中亲优势和超亲优势,轻度干旱显著降低了各指标的杂种优势,而严重干旱则完全抑制了根系生长的杂种优势。根系各性状中,RL的杂种优势最强。在水分充足条件下,与中等根(根直径0.25～0.45mm)和粗根(根直径>0.45mm)相比,细根(根直径0.05～0.20mm)的RL、SA及其占总根系比例的杂种优势最高。轻度干旱胁迫虽然降低了根系的杂种优势,但RL、SA仍表现出显著的超亲优势和中亲优势(粗根的超亲优势除外)。此外,只有细根RL和SA占总根系的比例在轻度干旱胁迫下具有显著的中亲优势,说明杂交种可以通过生成较亲本更高比例的细根来抵抗轻度干旱胁迫。

Maize （Zea mays L.）, the earliest crop for heterosis application, is highly sensitive to water stress. The root system is one of the important organs contributing to drought tolerance. However, few reports have provided quantitative data on the hybrid vigor in root development of maize, especially on that under water stress. The objective of this study was to investigate the heterosis of maize root growth at seedling stage and the effects of water availability on it. Hybrid maize Gaoyou 115 （220 × 1145） and its parents were subjected to three water treatments： 75%, 55%, and 35% of field water-holding capacity, considered as well watered （WW）, moderate water stress （MWS）, and severe water stress （SWS） respectively. The desired soil water regimes were well prepared at the beginning of the experiment, and kept by weighing. Under WW treatment, substantial midparent heterosis （MPH） and overparent hereosis （OPH） were observed for root dry weight （RDW）, root length （RL）, and root surface area （SA）. MPH for these traits was in the range between 100% and 203%, and OPH between 99% and 189%. MWS clearly reduced the degree of heterosis compared with WW; MPH was in the range between 73% and 108%, and OPH between 55% and 59%. However, SWS arrested hybrid vigor in root growth almost completely. These results indicate that heterosis of root growth in maize seedlings varies with water availability. The maximum heterosis for root growth was obtained in RL with average 155.5% MPH and average 124.2% OPH over WW and MWS. Compared with middle （0.25 mm 〈 root diameter （DA）≤0.45 mm） and coarse （0.45 mm 〈 DA） roots, fine （0.05 mm 〈 DA≤0.20 mm） roots displayed the highest degree of MPH and OPH in absolute RL and SA under WW, MPH for its RL and SA was 265% and 246%, respectively, and OPH 218% and 208%, respectively. For the ratios of RL and SA to the total RL and SA respectively, they only displayed significant and slight MPH, but compared with middle and coarse roots, fine roots （with 21% and 44% of MPH for RL% and SA%, respectively） still had the highest degree of heterosis. Although we still detected significant MPH and OPH for absolute RL and SA regardless of root diameter classes （except for OPH for coarse roots） and significant MPH for the ratios of RL and SA concerning fine roots under MWS, it was obvious that MWS reduced heterosis of RL and SA, especially for fine roots. MPH values for absolute RL and SA showed about one-fold decreases, and OPH showed more than two-fold decreases. Additionally, absolute RL and SA for fine roots do not reveal heterosis under SWS, but the ratios of RL and SA for them significantly displayed 9% and 16% of MPH, respectively. This suggests that the seedlings of hybrid maize develop more and greater proportion of fine roots than its parents （especially under water stress）, which enable them to resist moderate drought better.