Molecular markers at 103 loci were used to identify the location of quantitative sources of resistance to Exserohilum turcicum in 150 F2∶3 lines of a B52/Mo17 maize population. Host-plant response was measured in terms of the average number of lesions per leaf, the average percent leaf tissue diseased (severity), and the average size of lesions. The location of quantitative trait loci were compared with three loci having known qualitative effects, namely Ht1, Ht2 and bx1. Chromosomal regions containing the Ht1 and Ht2 loci showed a small contribution in determining lesion size, even though alleles with dominant, qualitative effects at these loci have never been reported in either inbred parent. Similar effects were not observed for the number of lesions or for disease severity. Likewise, some contribution was observed for chromosomal regions encompassing the bx1 locus in determining lesion size but not the number of lesions or disease severity. Overall the contribution of loci in the vicinity of Ht1, Ht2 and bx1 was small relative to variation attributable to loci with quantitative effects identified in this study. Molecular-marker-facilitated mapping concurred with previous reciprocal translocation mapping studies on the importance of chromosomes 3, 5 and 7, despite the fact that these studies utilized diverse sources of resistant germplasm.
RFLPs were used to investigate components of host-plant response to Exserohilum turcicum in 150 unselected F2∶3 lines of a B52/Mo17 maize population. Following inoculation with spore suspensions of the pathogen (race 0), components of disease development were measured and then quantitative trait mapping was performed to identify the location and effects of quantitative trait loci (QTLs) determining host-plant response. Components of interest were the average number of lesions per leaf, the average percent leaf tissue diseased (severity) and the average size of lesions (cm(2)). Based on a LOD threshold of 2.31 (P<0.05), the number of lesions appears to be associated with QTLs on chromosomes 1S, 3L, 5S. Severity was associated with analogous regions and, in addition, QTLs on chromosomes 7L and 8L. Most QTLs, for either of these two components, involve additive gene action and partial dominance or overdominance. In contrast, lesion size was associated with QTLs on chromosomes 7L and 5L; recessive gene action may be involved at 7L.
APPENDIX 103 4^ w ''Of the 169 Fj.j lines used create the map, only 150 were used for replicated field tests. See Table A6. ''Trait means for second assessment used only (day 117).
Modern plant breeding has progressed by incorporating knowledge from many disciplines. It has become clear that developments in plant biotechnology have potentially significant application to plant breeding, but it has been and shall remain a challenge to determine how to best integrate advances in this field into graduate curricula. To gain a broader perspective on this topic, we surveyed public and private sector plant breeders and research administrators regarding their graduate and professional training experience and opinions on the utility of plant biotechnology in plant breeding programs. We report and discuss survey results and identify possible avenues for integrating plant biotechnology into graduate plant breeding training programs. The 508 responses were equally divided among the private and public sectors. Plant breeders were optimistic about the potential importance of their knowledge of plant biotechnology. Examination of course programs suggest plant breeders feel well prepared for their profession; however, there seems to be some need to increase exposure to plant pathology, molecular genetics, molecular biology, and cell biology. More recent graduates have incorporated some of these areas through graduate research activities. Opportunities for integration were apparent through seminar topic selection, modest course addition, and postgraduate training programs for graduate students and faculty. The goal of graduate plant breeding programs should remain constant: educating scientists, producing materials, and identifying knowledge leading to production of plant germplasm having the desired characteristics. This goal will be achieved by scientists trained to critically assess developments in plant biology and integrate them into plant breeding research programs.
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