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To measure the contributions of parental inbreds per se and heterosis to the genetic gain of single- cross maize (Zea mays L.) hybrids, yield trials of 29 historically important hybrids used in China during 1964 through 2001 and their parental inbreds were conducted. Mean rate of genetic gain for single-cross hybrids when measured across all locations was 55 kg ha-1 yr-1; heterosis contributed 37 kg ha-1 yr-1 (67%) of yield gain. Inbred yields at stressed locations were exceptionally poor and may have inflated measurements of heterosis. At unstressed locations, heterosis contributed 5 kg ha-1 yr-1 (8%) and 16 kg ha-1 yr-1 (39%) or 10 kg ha-1 yr-1 (19%) when locations were combined. For individual characteristics, the highest percent heterosis was for kernel weight per ear (58.6%), corresponding to and emphasizing the historic goal in China of increasing yield on an individual plant rather than on a unit area basis. There are opportunities to further improve the productivity of Chinese maize by increasing inbred parent yields, increasing tolerances to stresses associated with higher planting densities, and also increasing the contribution of heterosis through optimal assignation of inbreds into complementary heterotic groups. [ABSTRACT FROM AUTHOR]

Increasing seed yield and quality of key cool-season perennial grasses is an important component of meeting China's environmental, food security, and urban beautification goals. Determining a suitable seed producing region and developing best management practices for this region with specific, high priority grasses will contribute to the availability of seed for reducing desertification, increasing livestock production, and improving urban living conditions. Previous research in other areas has addressed various agronomic practices on some grasses, but none has evaluated optimal row spacings for producing high yields of high quality seed in conditions similar to the Hexi Corridor, currently a major seed producing area in China for other seed crops. We compared our field trials in this area with those of other regions in China and the world to determine if this area would be suitable as a grass seed production center. Five important perennial, cool-season grasses {[Elymus kamoji (ohwi) S.L. Chen, slender wheatgrass [Elymus trachycaulus (Link) Gould ex Shinners ssp. Trachycaulus], smooth bromegrass (Bromus inermis Leyss), Siberian wildrye (Elymus sibiricus L.), and Chinese sheepgrass [Leymus chinensis (Trin) Tzvel]} were evaluated from 2010 to 2012 under four row spacing treatments (30, 50, 70, and 90 cm). Results showed all five grasses have potential for high seed production in this region, with yields equivalent to or significantly higher than other areas. Optimal row spacing for Elymus kamoji and smooth bromegrass was 30 cm while a 50 cm row spacing was better for seed production and weed control for slender wheatgrass, Siberian wildrye, and Chinese sheepgrass. This work will allow multinational seed companies, development agencies, and government program directors to better evaluate the potential economic sustainability of grass seed production in this region compared to importing seed from other regions of the world. [ABSTRACT FROM AUTHOR]