No abstract

Switchgrass (Panicum virgatum L.) is a warm‐season native grass, used for livestock feed, bioenergy, soil and wildlife conservation, and prairie restoration in a large portion of the USA. The objective of this research was to quantify the relative importance of latitude and longitude for adaptation and agronomic performance of a diverse group of switchgrass populations. Six populations, chosen to represent remnant prairie populations on two north–south transects, were evaluated for agronomic traits at 12 locations ranging from 36 to 47°N latitude and 88 to 101°W longitude. Although the population × location interactions accounted for only 10 to 31% of the variance among population means, many significant changes in ranking and adaptive responses were observed. Ground cover was greater for northern‐origin populations evaluated in hardiness zones 3 and 4 and for southern‐origin populations evaluated in hardiness zones 5 and 6. There were no adaptive responses related to longitude (ecoregion). Switchgrass populations for use in biomass production, conservation, or restoration should not be moved more than one hardiness zone north or south from their origin, but some can be moved east or west of their original ecoregion, if results from field tests support broad longitudinal adaptation.

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Soybean [Glycine max (L.) Merr.] seeds contain high levels of protein and oil useful for human consumption. Increasing emphasis in breeding programs to produce soybeans with specific protein or oil content for specialty markets demands that more efficient manipulation of these traits be achieved. The objective of this study was to evaluate eight different soybean populations from the midwestern USA for genetic markers linked to seed protein and oil content. The populations were derived from the breeding programs at the Univ. of Minnesota, the Univ. of Nebraska, and Purdue Univ.‐USDA‐ARS. Each population consisted of between 69 and 100 individuals and was mapped with 21 to 85 restriction fragment length polymorphism markers. The F2‐derived populations were grown in field tests in 1992, 1993, and 1994 in the state in which they originated. Single factor analysis of variance was used to detect significant associations between markers and traits. Environmentally stable and environmentally sensitive quantitative trait loci (QTL) were identified for both protein and oil contents in all eight populations. The identified QTL were sensitive to both environment and genetic background although some common QTL were identified in multiple populations across several years. The results show that a number of QTL affect these traits and that markers could potentially be used in breeding programs designed to alter the seed protein and oil content.

Despite the widespread use of hybrid cultivars in many crop species, most forage crop cultivars are synthetic populations that do not express maximum heterosis for important agronomic traits such as yield. Several aspects of these crops, including severe inbreeding depression, perfect flowers, and polyploidy, limit the ability to produce conventional single-or doublecross hybrids, but the viable alternative of developing semihybrid populations has been relatively unexplored. Both theoretical and empirical evidence support the notion that hybrids, developed by crossing divergent populations, can outyield the better performing parental population. A method to produce semihybrids is discussed, necessitating the development and maintenance of heterotic groups within a species. Progeny formed by crossing populations are semihybrids because in a cross of two populations, 1/2 of the progeny result from interpopulation crosses and 1/2 from intrapopulation crosses. Expected genotype proportions are presented for several scenarios to show the feasibility of using semihybrids to capture partial heterotic gains. Development of pure hybrids is more problematic but could be realized by using transgenic selectable markers, such as herbicide resistances, to rogue nonhybrid plants in production fields. Molecular markers may aid in the development of the heterotic groups and in choosing parents to be crossed. Potential heterotic groups in several forage species are suggested. By requiring attention to germplasm resources, this method will also be useful for broadening and improving the genetic bases of most cultivated forage crops. "The gain in constitutional vigour, derived from an occasional cross between individuals of the same variety, but belonging to distinct families, or between distinct varieties, has not been so largely or so frequently discussed, as have the evil effects of too close interbreeding." (Darwin, 1868). F EW AGRONOMIC IMPROVEMENTS during the 20th century rival the development of hybrid maize (Zea mays L.