Abstract: 【Objective】 Investigations on the effects of seed maturity on maize (Zea mays L.) hybrid seed vigor and F₁ production in corn seed production base along Hexi corridor in China are the bases of determining optimum harvest time of maize seed, protecting seed from the early frost and ensuring seed quality safety. 【Method】A field experiment combined with biochemical test were carried out with two maize hybrids, i.e. Yudan603 (partial dent maize variety, YD603) and Yudan606 (rigid grain maize variety, YD606). Ear samples were taken at an interval of 5 days after 40 days after pollination to test milk line development, grain water content, hundred-grain weight, standard germination, electrical conductivity, F₁ field performance and production, and study the effects of maize seed maturity on seed vigor and F₁ production.【Result】 There was a significant difference in the occurrence time and development process of milk line between the two hybrids YD603 and YD606. Compared with YD606, milk line of YD603 appeared earlier while disappeared later. On 40 days after pollination (DAP), the milk line position of YD606 was at 0.16, while that of YD603 had not yet appeared. On 65 DAP, both hybrids had a similar milk line position about 0.50, and the grain water content of YD603 was 31.66% and that of YD606 was 35.09%. On 40 DAP, grain water content of YD603 was higher than that of YD606. After 45 DAP, opposite changes in grain water content were found between YD603 and YD606. At physiological maturity, grain water contents of YD603 (75 DAP) and YD606 (80 DAP) were 26.71% and 27%, respectively. The germinating ability of F₁ increased with the seed maturity and reached the maximum at physiological maturity. On 40 DAP, the seeds of two hybrids had partly germinating ability. YD603 reached physiological maturity on 75 DAP with a standard germination rate of 96.67%, while YD606 reached physiological maturity on 80 DAP with a standard germination rate of 98%. Seed simple vigor index of YD603 and YD606 also increased with the seed maturity, and reached the maximum values 5.89 and 8.70, respectively, on 65 DAP. Afterwards, seed simple vigor index of both hybrids decreased slightly. In accordance with standard germination rate, artificial accelerated aging germination rate of the two hybrids increased with the seed maturity. On 40 DAP, aging germination rates of YD603 and YD606 were only 58.33% and 58.33%, respectively, for the low seed maturity, while that were 90.00% (75 DAP), and 92.33% (80 DAP), respectively at physiological maturity. The field germination percentage, uniformity, dry matter accumulation and yield of F₁ generation of two hybrids increased with the seed maturity improvement, and reached maximum value at physiological maturity without significant difference compared with those of 65 DAP, which suggested that good seedling quality and yield of F₁ could be obtained when F₁ seed was harvested on 65 DAP . 【Conclusion】The results suggested that the optimum harvest time of hybrid seed is on 65 DAP, when the seed milk line position was at 0.5 and seed moisture is between 30% and 35%. The harvest time is 15 days earlier than the conventional harvest time (milk line almost disappeared) in corn seed production base along Hexi corridor of Zhangye, which not only can provide more time for seeds air-drying to avoid frost damage, but also can ensure high-quality hybrid seeds.

Key words: maize, seed maturity, seed vigor, harvest time