Browsing by Author "Majisu, B.N."
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Item Aegilops X Secale Hybrids: the Production and Cytology of Diploid Hybrids(1971) Majisu, B.N.; Jones, J.K.Hybrids between four diploid species of Aegilops and species of Secale were obtained by using embryo culture. There was a marked incompatibility in the crosses between Secale species and each of the four species in Section Sitopsis of Aegilops and Ae. mutica. It is suggested that this genetic incompatibility with Secale species is an additional similarity between these species of Aegilops and the diploid species of Triticum.Item Disruptive Selection in Crop Development(1968) Doggett, H.; Majisu, B.N.; East African Agricutlure and Forestry Research Organization. Serere. Soroti. UgandaCultivated sorghum was developed from a single wild species of the subsection Avundinacea by disruptive selection. It was maintained in the presence of the wild type under disruptive selection in spite of considerable gene flow between the two groups. An intermediate population consisting of early-generation hybrids and homozygous lines was established from the natural wild and cultivated populations. The presence of recently abandoned cultivations and field margins has enabled this intermediate population to become established and persist. The existence of the intermediate population ensures continued intro-gression between the wild and cultivated sorghums and enhances the variability of the cultivated crop whilst the wild type becomes modified in the direction of the cultivated forms. The development of maize can be explained along the same lines except that the crop is of greater antiquity and so divergence has continued further. The pattern Tripsacum-teosinte- maize of maize parallels the wild-intermediate-cultivated pattern of sorghum. The intermediate population could act as a bridge to transfer polyploidy from the wild type to the cultivated crop or polyploidy might arise within the intermediate population. This is shown in Sorghum almum and Zea perennis. [Cf. XXXV, 6435].Item Effects of Autoploidy on Grain Sorghum(1979) Majisu, B.N.; E.A.A.F.R.O.Early generation autotetraploid grain sorghum varieties were studied with special reference to the response of agronomically important characters to artificial autoploidy. Autoploidy substantially reduced fertility, head length, panicle branch number and length, stand and head number. Increased grain size failed to compensate for reductions in other yield components. Protein content increased by 20 per cent on average. but steady decreases occurred with increasing yield~. Differential genotypic responses to autoploidy suggested the need for cautious selection of material for inclusion in tetraploid breeding programmes. Feeding experiments and detailed biochemical studies of the grain are required to determine whether or not tetraploid sorghum is qualitatively superior to normal diploid sorghum.Item Evaluation and Utilization of Sorghum Germ-Plasm(1971) Majisu, B.N. ; E.A.A.F.R.O., Sorghum/Millets Unit, Serere, UgandaThe development of hybrid maize in Kenya (Eberhart et al., 1967) has shown how systematic evaluation and utilization of the genetic diversity of local and exotic material can result in substantial increases of crop yields. A widely represented germ-plasm bank may also be a valuable source of genes for the more simply inherited characters, such as resistance to pathogens and pests, and other environmental constraints which reduce yield. Consequently, the assembly, evaluation and utilization of collections are important aspects of most crop improvement programmes. The routine maintenance of even an average size collection may, however, be unjustifiably costly in the absence of a system for turning it into an exploitable source of breeding material.Item Fertility Improvement in Auto tetraploid Sorghum. 3. Yields of Cultivated Tetraploids(1972) Majisu, B.N.; Doggett, H.; EAAFRO, Serere Research StationThe development of tetraploid grain sorghum as a crop plant continues to show promise. Yields from bulk populations and lines withdrawn from such populations are now approaching levels realized by good diploid varieties. It seems that tetraploid grain sorghum populations in which high levels of recombination are attained by the use of the genetic male-sterile ms3, should respond profitably to the application of recurrent selectionItem Genetic Male-Sterility in Tetraploid Sorghum Improvement(1971) Majisu, B.N.; E.A.A.F.R.O., Sorghum and Millets Unit, Serere, UgandaThe genetic male-sterility ms3 gene of Coes variety was successfully incorporated in tetraploid sorghum. Segregation results showed that the gene is located close to the kinetochore, and that it is not frequently involved in crossovers. Attempts were initiated to introduce genetic male-sterility into tetraploid breeding populations. Breeding methods that might accelerate tetraploid sorghum improvement are suggested.Item Some Cytolocical Aspects of Autotetraploid Sorghum Improvement(1971) Majisu, B.N.; E.A.A.F.R.O., Sorghum and Millet Unit, Serere, UgandaRegular chromosome behaviour is important in natural and artificial polyloids whenever the saleable product of crops depends on the efficiency of sexual reproduction. For example, bread wheat (Triticum aestivum) which is a natural allohexaploid, has a genetic system which favours bivalent formation by restricting pairing to fully homologous chromosomes. In addition to the more commonly used agronomic characters, a cytological basis for selection would be a valuable technique for the improvement of artificially induced polyploids of cereals in which irregular chromosome behaviour frequently occurs. Studies of chromosome pairing therefore form an important part of improvement programmes for artificial polyploids. While a consider3Jble amount of breeding work on autotetraploid sorghum has been carried at Serere, relatively little is known about it from the cytological standpoint. The purpose of this preliminary work was to determine the distribution of quadrivalents in autotetraploid sorghum varieties with a view to initiating a selection programme for regular chromosome behaviour.Item The Yield Stability Of Sorghum Varieties And Hybrids In East African Environments(1972) Majisu, B.N.; Doggettt, H.The ability of varieties and hybrids of crops to perform well over a wide range of environments has particular relevance to regional programmes designed to satisfy the needs of numerous countries that may differ not only climatically and edaphically, but also with respect to crop husbandry standards. In East Africa where resources and priorities justify one sorghum research Programme, varieties and hybrids possessing general adaptability are most desirable. Work previously reported by Doggett and Jowett (1966) gives an impression of the diversity of environments encountered in this region. Although genotype X environment interactions have given some indication of adaptability, the performance of individual entries in a wide range of environments has not been studied critically to facilitate an appraisal of the progress being made to develop superior genotypes.
