Browsing by Subject "Zuchtstrategie"

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Breeding strategies for Sahiwal cattle genetic resources in Kenya
(2011) Ilatsia, Evans D.; Valle Zárate, Anne
The Sahiwal breed is an important cattle genetic resource in the tropics where it is vital for subsistence and economic development among various communities. In Kenya a breeding and conservation programme has been in existence for over 45 years with the ascertains of its relevance in light of the producers? production aims and breeding goals still left pending. Moreover, there have been no systematic efforts undertaken to evaluate the suitability of the existing breeding programme or to examine how competitive it is compared to other alternative programmes in terms of genetic and economic merit. This thesis focused on understanding the breeding strategies for improvement of Sahiwal cattle genetic resources in Kenya. Specific objectives were; 1) to critically examine the existing breeding and conservation programmes for Sahiwal cattle genetic resources in the tropics focussing mainly on the strengths and weaknesses in Pakistan, India and Kenya as the core regions of development, 2) to understand the production conditions under which Sahiwal cattle genetic resources are raised, determine producers production aims and assess the relative importance of breeding goals and production challenges, 3) to identify and define the roles of various stakeholder institutions that are crucial in the realisation of a promising and sustainable Sahiwal cattle breeding programme, 4) to identify based on genetic and economic merits the optimal breeding programme for Sahiwal cattle genetic resources by evaluating the current and alternative breeding programmes, and 5) to analyse and discuss organisational options for implementation of promising breeding and conversion programmes. The results from the literature review study show that most studies on Sahiwal cattle genetic resources in the tropics have mainly concentrated on evaluating their performance levels with only a few published reports describing other breed characteristics. The Sahiwal breed is utilised for dairy and beef production under smallholder dairy pastoral extensive and ranching production systems both as purebreds or crossbreds. The necessary components to strengthen the breeding programme such as performance recording genetic evaluation and AI facilities exist albeit at different degree. Breeding and conservation efforts benefit from the technical and financial support from government research institutions, which also provide incentives to enhance participation in the programmes. However, breeding goals are rather informal and only defined in terms of high production levels with functional traits largely ignored. Field data analysis revealed that Sahiwal genetic resources were mainly kept for domestic milk production and for revenue generation through sales of milk and live animals. To a limited extent they were kept for breeding and also for multiple objectives that included insurance against risks and social functions. Production aims were influenced to varying extents by various household and farmer characteristics. Sahiwal cattle and their crosses were generally perceived to be better with respect to productive traits and fertility traits when compared to the EAZ. However, the EAZ was rated higher with respect to adaptation traits. The breeding objective traits of primary importance were high milk yield and big body size, good reproductive efficiency and relatively good adaptation to local production conditions. Performance and functional traits are important breeding goals that play a major role in fulfilling the multiple production objectives. This forms the basis for the optimisation of a breeding programme for sustainable utilisation to meet the needs of Sahiwal cattle producers. All the breeding programmes evaluated in this study showed positive genetic and economic gains, however, the difference was only in the margins of these benefits. Given the small population of the Sahiwal breed, an open-nucleus breeding programme is economically and genetically optimal because it will allow for efficient utilisation of the existing genetic base by allowing participation of more diverse pastoral born sires in the nucleus. The CNCROSS will continue to play an important role of facilitating the exploitation of trade-offs that exist between the Sahiwal and the EAZ with regard to production and adaption, as well as an intermediate phase in the up-grading programme. However, the full benefits of the open-nucleus breeding programme can only be realised in the presence of proper logistical organisation to facilitate exchange of breeding bulls between the pastoral herds and the nucleus farms and ensure equitable distribution. Co-operation between producers and relevant stakeholder institutions is necessary to ensure the requisite structures for implementation and sustainable execution of the breeding programme.
Wirkung rassenspezifischer Braunrostresistenzen in genetisch diversifizierten Roggenpopulationen
(2004) Wilde, Katinka; Miedaner, Thomas
Leaf rust (Puccinia recondita f.sp. secalis) is the most frequently occuring leaf disease in German winter rye (Secale cereale L.). To test the usefulness and potentially prolong the durability of race-specific resistance genes, we increased host complexity and diversity by producing synthetic (Syn) populations segregating for one to four resistance sources as a model system for hybrid varieties. Thirty synthetics were grown together with three highly susceptible synthetics as checks, two Russian full-sib families (FSF), a leaf-rust-resistant-hybrid variety, a set of 17 differential genotypes and ten parental lines at six locations in three years (17 environments) in Germany under natural infection. The parental lines were only sown in 11 environments. Disease severity of about 120 plants for each synthetic, FSF, hybrid and about 25 plants for each differential genotype and parental line was estimated as percentage of infected leaf area on the leaf below the flag leaf at the mid and the end of the natural epidemic. Susceptible synthetics showed that disease severity was similarly high in all environments. Only two out of 30 synthetics and both FSF were resistant across 17 environments. Low resistance of the synthetic was caused by the low resistance of the parental lines. Nonetheless, some of the synthetics were more resistant than the tested commercial hybrid variety. Even though the resistance was not used in practical breeding programs to date we detected virulence for each resistance gene tested. In conclusion, the German leaf rust population seems to be highly diverse and none of the self-fertile resistance sources used provided full protection. New race-specific resistances or highly effective quantitative resistances are therefore needed and should be combined.