Donald C. Rasmusson

Quantitative trait loci associated with resistance to Fusarium head blight and kernel discoloration in barley.

Abstract Resistance to Fusarium head blight (FHB), deoxynivalenol (DON) accumulation, and kernel discoloration (KD) in barley are difficult traits to introgress into elite varieties because current screening methods are laborious and disease levels are strongly influenced by environment. To improve breeding strategies directed toward enhancing these traits, we identified genomic regions containing quantitative trait loci (QTLs) associated with resistance to FHB, DON accumulation, and KD in a breeding population of F4:7 lines using restriction fragment length polymorphic (RFLP) markers. We evaluated 101 F4:7 lines, derived from a cross between the cultivar Chevron and an elite breeding line, M69, for each of the traits in three or four environments. We used 94 previously mapped RFLP markers to create a linkage map. Using composite interval mapping, we identified 10, 11, and 4 QTLs associated with resistance to FHB, DON accumulation, and KD, respectively. Markers flanking these QTLs should be useful for introgressing resistance to FHB, DON accumulation, and KD into elite barley cultivars.

Validation of quantitative trait loci for Fusarium head blight and kernel discoloration in barley

Validation of quantitative trait loci (QTLs) is a prerequisite to marker assisted selection (MAS), however, only a fraction of QTLs identified for important plant traits have been independently tested for validation. Resistance to the diseases kernel discoloration (KD) and Fusarium head blight (FHB) in barley is complex and technically difficult to assess, and therefore QTLs for these traits are suitable targets for MAS. We selected two lines, from a QTL mapping population created using the resistant variety Chevron, and crossed them to susceptible parents to generate two validation populations. Genetic maps of both populations were developed for five chromosomes covering 15 selected regions containing QTLs for FHB severity, KD score and concentration of deoxynivalenol (DON), a mycotoxin produced by the FHB pathogen. QTL analyses using these validation populations confirmed that five of the possible 15 QTL regions were associated with at least one of the three traits. While some QTL were detected inconsistently across environments, QTL that could be subjected to validation in both populations were confirmed in both populations in seven out of eight instances. A QTL for KD score on chromosome 6(6H) was confirmed in both validation populations in eight of nine environments and was also associated with FHB in three of six environments. A QTL for FHB on chromosome 2(2H) was confirmed and was also associated with KD and heading date. Marker assisted selection at these two QTLs should enhance disease resistance, however, the QTL on chromosome 2(2H) will also delay heading date.

Recurrent selection for mineral content in wheat and barley

SummaryThree cycles of recurrent selection were completed for 89Sr content of grain in wheat and barley. The purposes were to ascertain the gain that could be achieved in three cycles of selection and to learn about correlated changes in content of other mineral elements. In each species selection was bidirectional resulting in two populations, one high and one low in 89Sr content. In wheat each cycle of selection resulted in genetic gain. The average response per cycle was 7.4±2.6% in the high population and -12.4±1.5% in the low population. In barley gain was achieved in cycles 1 and 2. The average response per cycle was 12.2±3.8% in the high population and -11.2±4.9% in the low population. The heritability of 89Sr content in the F2 generation was 24% and 38% in the high and low populations of wheat and 31% and 34% in the high and low populations of barley, respectively.Selection for Sr content in grain caused correlated changes in Sr content in other plant parts. In wheat there was a negative correlated response in Sr content in mature leaves, while seedling plants in in the two populations did not differ. In barley, leaf Sr content was unaffected, but seedling plants in the high and low populations differed significantly. Correlated changes in Ca content tended to parallel changes in Sr content in all plant parts in both species. Selection for grain Sr also affected P, K, Mg and Mn in wheat, and K, Mg and Na in barley. These correlated responses were not always consistent with the direction of Sr selection among plant parts or between species.

Ideotype Research and Plant Breeding

Crop yield is closely related to the genetic yield potential of the cultivar. Evans (1983) defined genetic yield potential as the yield of a cultivar grown in environments to which it is adapted, with nutrients and water non-limiting, and with pests, diseases, weeds and other stresses effectively controlled. In this context the plant breeder may opt to enhance yield potential or breed to reduce the impact of yield-limiting factors. It is not trivial to ask whether breeding to enhance genetic yield potential affords an opportunity equal to breeding to reduce yield-limiting factors. Pertinent to the answer is the fact that yield gains have been made in the major crops where breeding has been done over a period of time using both approaches; and it is encouraging that yield gains have been sizeable and sustained (Duvick, 1977; Austin et al., 1980; Riggs et al., 1981; Wych and Rasmusson, 1983; Wych and Stuthman, 1983). We should take satisfaction in and applaud conventional plant breeding.

Crop Productivity and Quality: Chairman’s Introduction

If you ask a plant breeder about the major objectives of his/her program, the answer will likely include controlling pests, enhancing yield potential, reducing losses due to stress (such as salt and drought), and improving crop quality. This portion of the conference focuses on these four topics which are at the heart of plant breeding. They are pertinent topics from the standpoint of the plant breeder who is at times frustrated with slow progress, and uncertain about how to proceed in the breeding program. They are also pertinent to genetic engineers and others who desire to learn about plant breeding goals and new approaches in dealing with them. The four speakers consider selection strategies and genetic stocks that may have utility in improvement programs as well as important fundamental aspects of the traits. In considering selection strategies the authors do not limit themselves to molecular genetics, but rather emphasize a full range of possibilities which are emerging as an outgrowth of ongoing research in the four areas.