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The main objective in this research was the genetic analysis of heterosis in rapeseed at the QTL level. A linkage map comprising 235 SSR and 144 AFLP markers covering 2045 cM was constructed in a doubledhaploid population from a cross between the cultivar ''Express'' and the resynthesized line ''R53.'' In field experiments at four locations in Germany 250 doubled-haploid (DH) lines and their corresponding testcrosses with Express were evaluated for grain yield and three yield components. The heterosis ranged from 30% for grain yield to 0.7% for kernel weight. QTL were mapped using three different data sets, allowing the estimation of additive and dominance effects as well as digenic epistatic interactions. In total, 33 QTL were detected, of which 10 showed significant dominance effects. For grain yield, mainly complete dominance or overdominance was observed, whereas the other traits showed mainly partial dominance. A large number of epistatic interactions were detected. It was concluded that epistasis together with all levels of dominance from partial to overdominance is responsible for the expression of heterosis in rapeseed.

Little is known about the genetic control of heterosis in the complex polyploid crop species oilseed rape (Brassica napus L.). In this study, two large doubled-haploid (DH) mapping populations and two corresponding sets of backcrossed test hybrids (THs) were analysed in controlled greenhouse experiments and extensive field trials for seedling biomass and yield performance traits, respectively. Genetic maps from the two populations, aligned with the help of common simple sequence repeat markers, were used to localise and compare quantitative trait loci (QTL) related to the expression of heterosis for seedling developmental traits, plant height at flowering, thousand seed mass, seeds per silique, siliques per unit area and seed yield. QTL were mapped using data from the respective DH populations, their corresponding TH populations and from mid-parent heterosis (MPH) data, allowing additive and dominance effects along with digenic epistatic interactions to be estimated. A number of genome regions containing numerous heterosis-related QTL involved in different traits and at different developmental stages were identified at corresponding map positions in the two populations. The co-localisation of per se QTL from the DH population datasets with heterosis-related QTL from the MPH data could indicate regulatory loci that may also contribute to fixed heterosis in the highly duplicated B. napus genome. Given the key role of epistatic interactions in the expression of heterosis in oilseed rape, these QTL hotspots might harbour genes involved in regulation of heterosis (including fixed heterosis) for different traits throughout the plant life cycle, including a significant overall influence on heterosis for seed yield.

Genetic variation in nutrient efficiency may be attributed to two multifactorial components: (i) genotypes may differ in the efficiency with which the nutrients in the plant are utilized to produce yield (utilization efficiency) and/or (ii) they may differ in their effectiveness in absorbing nutrients from the soil (uptake efficiency). This contribution surveys major aspects of physiological and morphological factors affecting N‐and P‐efficiency. The potential importance of the various factors is discussed and exemplified mainly by own experimental work.

The present book is the fourth in the Plant Breeding Series published by Chapman & Hall, and extends the aspects covered in the three earlier volumes, particularly with its focus on ecological aspects related to breeding. The first book, Plant Breeding: Principles and prospects, edited by Hayward, Bosemark and Romagosa, set a wide ranging, authoritative and broad view of techniques and approaches being adopted in modem plant breeding. The second, Selection Methods in Plant Breeding, by Bos and Caligari, was written to help further secure the scientific basis underlying selection methods as applied in practical plant breeding. The third, Statistical Methods for Plant Variety Evaluation, edited by Kempton and Fox, ensured a strong foundation in the design of trials and the subsequent handling of data, upon which successful breeding is based. It followed the successful formula of the first book in being based on a course taught in Zaragoza.This fourth book starts by giving the underlying philosophy and modelling needed to tackle the ubiquitous genetical variation with which all breeders are confronted, namely quantitative variation. The nomenclature used is new and follows that agreed by a group of us, to be mainly based on that used more commonly by animal breeders than by plant breeders. It was agreed in discussion that this nomenclature has a more direct logic (e.g. additive variation is designated as a, dominance is d, and so on). This led to Kearsey and Pooni's book being the first published using this notation (The Genetical Analysis of Quantitative Variation, by M.J. Kearsey and H.S. Pooni, Chapman & Hall, 1996, ISBN 0412609800) which needed extension from that in common use because of the sophisticated extensions to the theory and analysis already devised by those working with such variation in plants. This approach is continued here and used to give this present book its useful place in providing a valuable interface between the theory and practice of plant breeding (although translation between this and the earlier notation is not too difficult).As noted in all the earlier books, the need for plant breeders to be successful has never been greater. The potential future population growth must fill all of us with concern and is a clear indication of the absolute need for success in plant breeding. This point is picked up again by the present authors in various places within the text and the authors further emphasize this by their appreciation of those concerns in the concluding chapter on 'Genetic resources, genetic diversity and ecogeographic breeding'. The use of a range of traditional and modem techniques must ultimately be united in the genotypes we grow, to ensure their adaptation to their place in the environment in which they are required to grow and in which we share their existence.The present book is aimed, as the other three were, not only at the student who is learning the subject of plant breeding but also at the breeder who is trying to improve our crop species. It has been written to make clear...