To investigate the genetic mechanisms that underlie morphological evolution in natural populations, we employed QTL mapping to dissect the inheritance of leaf sheath characters that distinguish Chalco from Balsas teosinte. Abundant macrohairs (trichomes) and intense anthocyanin accumulation are found in Chalco teosinte sheaths whereas Balsas teosinte leaf sheaths are green and glabrous. These character states may represent adaptations to the cooler highland (Chalco) vs. warmer middle-elevation (Balsas) climates. QTL mapping in multiple populations revealed a mix of major-and minor-effect QTL affecting both sheath color (anthocyanin) and macrohair abundance. The major QTL for macrohairs accounts for 52% of the parental difference. Epistatic interactions were detected between the major-effect QTL and multiple other QTL for both traits, accounting for substantial portions of phenotypic variance. Developmental analyses suggest that regulatory program changes underlie the phenotypic differences. Sheath anthocyanin QTL are clearly associated with b1 and a3, both of which are regulators of anthocyanin biosynthesis. Our findings suggest that changes in a small number of QTL can lead to morphological evolution by modulating existing developmental programs.

Two quantitative trait loci (QTL) controlling differences in plant and inflorescence architecture between maize and its progenitor (teosinte) were analyzed. Complementation tests indicate that one of these, which is on chromosome arm 1L, is the locus for the maize mutant teosinte branched1 (tb1). This QTL has effects on inflorescence sex and the number and length of internodes in the lateral branches and inflorescences. This QTL has strong phenotypic effects in teosinte background but reduced effects in maize background. The second QTL, which is on chromosome arm 3L, affects the same traits as the QTL on 1L. We identify two candidate loci for this QTL. The effects of this QTL on several traits are reduced in both maize and teosinte background as compared to a maize-teosinte F2 population. Genetic background appears to affect gene action for both QTL. Analysis of a population in which both QTL were segregating revealed that they interact epistatically. Together, these two QTL substantially transform both plant and inflorescence architecture. We propose that tb1 is involved in the plant's response to local environment to produce either long or short branches and that maize evolution involved a change at this locus to produce short branches under all environments.

tance has been difficult for two reasons. First, genetic resistance is complex. There seem to be many QTL that Fusarium head blight (FHB) is a disease problem (primarily caused have relatively small effects and are subject to genoby Fusarium graminearum Schwabe) that affects the quality and yield type ϫ environment interactions. Most QTL are also of barley (Hordeum vulgare L.) grain. The objectives of this study associated with morphological and agronomic traits, were to identify the location of quantitative trait loci (QTL) for resiswhich confound measurement of disease resistance. Sectance to FHB in a two-rowed by six-rowed population, to examine the association of FHB resistance with heading date and the Vrs1 head blight ; QTL, quantitative trait locus; RFLP, restriction fragment length polymorphism, SSR, simple sequence repeat.

Fusarium head blight (FHB) is a disease problem (primarily caused by Fusarium graminearum Schwabe) that affects the quality and yield of barley (Hordeum vulgare L.) grain. The objectives of this study were to identify the location of quantitative trait loci (QTL) for resistance to FHB in a two‐rowed by six‐rowed population, to examine the association of FHB resistance with heading date and the Vrs1 (two‐rowed spike morphology) locus, to validate the location of the major FHB resistance QTL primarily detected in the field, and to identify simple sequence repeat (SSR) markers linked to the QTL for FHB resistance. We created a genetic map of 143 molcular markers from a population derived from the parents Fredrickson (two‐rowed, moderately resistant) and Stander (six‐rowed, susceptible). The Fredrickson/Stander population was evaluated in two field environments by a grain spawn inoculation method, two field environments by a spray inoculation, and two greenhouse environments. QTL analysis detected three distinct regions on chromosome 2(2H) associated with FHB resistance; two of these regions were also associated with resistance to deoxynivalenol (DON) accumulation. One FHB resistance QTL was also associated with heading date, while another FHB resistance QTL was found associated with the Vrs1 locus. The third FHB resistance QTL was detected only in the greenhouse, but was coincident with a QTL for resistance to DON accumulation in the field. All three QTL were detected in the greenhouse, indicating that this environment may be useful for selecting FHB resistant barley genotypes. SSR markers were identified that are linked with each QTL and could prove useful for marker‐assisted trait manipulation. Finally, the two major QTL detected in the field were validated using an independent population with Fredrickson and Stander parents.

Plant breeding that emphasizes crosses among elite parents in a closed population (advanced cycle breeding) is presumed to decrease genetic diversity. To assess the effect of plant breeding on allelic diversity, we evaluated regional ancestors, parental lines, and cultivar candidates from the University of Minnesota six‐rowed barley (Hordeum vulgare L.) breeding program between 1958 and 1998 using pedigree information, 70 simple sequence repeat (SSR) markers, and a gene specific marker. Pedigree and SSR allelic diversity indices revealed a decrease in genetic diversity, from an average of 5.89 alleles per locus in the ancestors group to 2.34 alleles per locus in the fourth decade of breeding. A correspondence analysis showed differentiation in the germplasm with time. At specific loci, we detected both reductions and no change in the number of alleles over time. Several marker loci that demonstrated a reduction in number of alleles were associated with major loci for disease resistance or malting quality and were presumably under selection during breeding. Assessment of locus‐specific allelic variation across the genome in breeding germplasm should identify both the regions of the genome that should be conserved and the regions of the genome where there are opportunities to introgress new allelic diversity without disrupting desirable gene complexes.