相对其它作物，玉米生产虽然需要较高的温度，但35℃以上高温不利于玉米产量的形成。在华北平原地区，≥35℃ 的温度在夏玉米营养生长和生殖生长并进阶段普遍发生，并对玉米产量的形成造成不可逆的伤害。因此，本文研究了9叶期至抽雄期增温对夏玉米产量形成过程的影响。结果表明，持续增温导致了花丝的伸长速率和活力下降、开花吐丝间隔期增加、果穗顶端穗粒数减少，最终影响了产量。尽管抽雄前持续增温破坏了雄花序中花药的结构，花粉活力因此降低，散粉推迟和散粉时间缩短。但是，从表型、生理层面分析，此时期的持续增温可能对雌穗的生长发育影响更加显著。总之，在玉米营养生长和生殖生长并进阶段，持续增温导致雌雄穗生长受阻，最终引起果穗秃尖和产量的大幅度降低。

Soybean mosaic virus (SMV), a member of the genus Potyvirus, is a major pathogen of soybean plants in China, and 16 SMV strains have been identified nationwide based on a former detailed SMV classification system. As the P3 gene is thought to be involved in viral replication, systemic infection, pathogenicity, and overcoming resistance, knowledge of the P3 gene sequences of SMV and other potyviruses would be useful in efforts to know the genetic relationships among them and control the disease. P3 gene sequences were obtained from representative isolates of the above-mentioned 16 SMV strains and were compared with other SMV strains and 16 Potyvirus species from the National Center for Biotechnology GenBank database. The P3 genes from the 16 SMV isolates are composed of 1 041 nucleotides, encoding 347 amino acids, and share 90.7-100% nucleotide (NT) sequence identities and 95.1-100% amino acid (AA) sequence identities. The P3 coding regions of the 16 SMV isolates share high identities (92.4-98.9% NT and 96.0-100% AA) with the reported Korean isolates, followed by the USA isolates (88.5-97.9% NT and 91.4-98.6% AA), and share low identities (80.5-85.2% NT and 82.1-84.7% AA) with the reported HZ1 and P isolates from Pinellia ternata. The sequence identities of the P3 genes between SMV and the 16 potyviruses varied from 44.4 to 81.9% in the NT sequences and from 21.4 to 85.3% in the AA sequences, respectively. Among them, SMV was closely related to Watermelon mosaic virus (WMV), with 76.0-81.9% NT and 77.5-85.3% AA identities. In addition, the SMV isolates and potyvirus species were clustered into six distinct groups. All the SMV strains isolated from soybean were clustered in Group I, and the remaining species were clustered in other groups. A multiple sequence alignment analysis of the C-terminal regions indicated that the P3 genes within a species were highly conserved, whereas those among species were relatively variable.