Showing papers on "Plant breeding published in 1991"

Changes in physiological attributes of the dry matter economy of bread wheat ( Triticum aestivum ) through genetic improvement of grain yield potential at different regions of the world

Abstract: The understanding of the changes produced by plant breeding on wheat grain yield and on its determinants, through the study of the behaviour of cultivars released at different times during the breeding process, could be a useful tool to define future selection criteria. The aim of this paper was to examine the genetic improvement effects on bread wheat grain yield potential and on its major physiological determinants in different countries. Generally, it seems that the genetic improvement produced important increases in harvest index, but it did not produce important changes in total biomass. The genetic gain in grain yield ranged from 0.58 g m-2 year-1 (India) to 5.84 g m-2 year-1 (Mexico); reflecting important differences among genetic improvement programmes. However, when the comparisons were made in relative values, the difference was much lower, ranging from 0.16% year-1 to 0.90% year-1, for the previously mentioned countries, respectively. Most of the regions showed relative genetic gains of around 0.45% year-1. Similar patterns of relative genetic gains in harvest index were found. Half of the total gain in grain yield in the past was due to genetic gain in grain yield potential. However, it is expected for the future, that further increases in grain yield will rely more on genetic gain than on technologic gain. Thus, a discussion about possible strategies in future breeding programmes of bread wheat is attempted throughout the paper. The changes in grain yield were mostly associated with changes in number of grains per m2 rather than with changes in individual grain weight. It appears that the source: sink ratio during the grain-filling period was very high in old cultivars, whereas the source: sink ratio in modern cultivars is more balanced. Further increases in number of grains m-2 could be compensated by a reduction in individual grain weight, if simultaneous improvement in source strength during grain-filling is not achieved. The crop attributes which have been changed together with the mentioned traits are discussed and alternative selection criteria are suggested.

Organization of Rapid Analysis of Lipids in Many Individual Plants

Abstract: There is considerable interest in changing the composition of oilseed plants through plant breeding and genetic engineering (Greiner 1990). This may involve increasing or decreasing the total lipid in the seed or the composition of the lipid. Modern plant breeding is largely empirical and produces large numbers of plants whose oilseed composition must be evaluated. For example, two plants may be crossed and give rise to many offspring that are a genetic mixture of the two parents (Graef et al. 1988). Each of the offspring may differ genetically, and those with interesting oilseed compositions must be identified. Or, a batch of seed may be treated with a chemical or physical agent to induce mutations (Hammond and Fehr 1985). The surviving seed will give rise to plants that may have random mutations and must be evaluated to identify those with interesting compositions. In these situations plant breeders turn to those skilled in oilseed analysis, and close cooperation between breeder and analyst is needed for success.

Advanced Methods in Plant Breeding and Biotechnology

Abstract: Breeding plants for the 21st century, D. Murray chromosomal organization and gene mapping, N.F. Weeden gene transfer to plants using agrobacterium, J.E. Grant, et al electroporation for direct gene transfer into plant protoplasts, C. Rathus and R.G. Birch microprojectile techniques for direct gene transfer, T. Franks and R.G. Birch localizatio of transferred genes in genetically modified plants, A. Mouras, et al chloroplast and mitochondrial genomes - manipulation through somatic hybridization, G. Pelletier modification of the chloroplast genome with particular reference to herbicide resistance, R.J. Rose somatic embryogenesis - potential for use in propagation and gene transfer systems, W. Parrott, et al breeding for insect resistance, J. Gatehouse breeding for resistance to funal diseases, K.J. Scott and A Chakravoty breeding for resistance to bacterial pathogens, M.C. Whalen genetic engineering for resistance to viruses, G.M. Timmerman breeding for resistance to physiological stresses, C.A. Cullis.

Nuclear and Cytoplasmic Control of Anther Culture Response in Wheat: III. Common Wheat Crosses

Abstract: Another culture represents a potentially important technology for production of wheat doubled haploids for plant breeding and geneticq research; however, the yields of haploids from culture must be increased to achieve competitive efficiencies for the method. Genetic differences for culturability are now well know that the relative roles of nuclear and cytoplasmic genetic factors are still nuclear. The purpose of this study was to determine the significance of cytoplasm genetic variation for anther culture responses among common T. aestivum wheats

Measuring the Potential Contribution of Plant Breeding to Crop Yields: Flue-Cured Tobacco, 1954–87

Abstract: Measurements are made of plant breeders' success in increasing potential flue-cured tobacco yields from 1954 to 1987 in North Carolina. Nongenetic sources of yield increases are measured by the yield levels of a standard variety. New genetic material accounted for between 20% and 35% of yield increases on research station plots in the three tobacco-growing regions. Recent genetic contributions have been small. The slowdown is not attributable to a federal tobacco policy shift in 1965 that slowed the growth in grower yields. There is also no evidence that tobacco breeders increased their output in response to the Plant Variety Protection Act of 1970.

Evidence for Differences Between Three Wheat Cultivars in Yield Response to Plant Population

Abstract: Three wheat cultivars were grown at five seed levels in 15 experiments under rain-fed conditions in the central wheatbelt of Western Australia in the 1986, 1987 and 1988 seasons. Guthea (released in 1982, 87 cm tall) required less seed and fewer plants on average to achieve its maximum grain yield than either Gamenya (released in 1960, 82 cm) or Aroona (released in 1981, 73 cm). At sites where Gutha was best adapted its optimum population was 65 plants m-*, about half of the population required by the other two cultivars. At sites where Aroona was best adapted its optimum population was 110 plants m-*. Gutha produced larger ears, especially at small populations, but did not increase kernel numbers per m2 in response to increased populations as much as Aroona. It is suggested that when a new cultivar is released its optimum plant population should be assessed in the area for which it is recommended.

Productive oat ideotype for northern growing conditions

Abstract: Yield formation of four Finnish and three Nordic oat varieties and 12 breeding lines developed at the Hankkija Plant Breeding Institute was studied during four different growing seasons (1986–1989). Seventeen characteristics were measured, including traits representing the date of maturity and architecture of the oat stand. The variation between genotypes in the examined traits was studied by means of two-way analysis of variance. The relationship between grain yield and morpho-physiological traits was studied by means of simple correlation analysis and stepwise regression analysis.

Genetic Yield Improvement of Cereal Varieties in Northern Agriculture since 1920

Abstract: Long-term cultivar trial data were used to estimate the genetic contribution to yield improvement in spring cereals in Finland in 1920–1988. Genetic gains were evaluated by comparing widely grown varieties with long-time check cultivars. Barley yields did not clearly increase, while oat and spring wheat yields improved by 35% and 30%, respectively. The average annual genetic yield increase for oats was 0.49–0.56% and for spring wheat 0.38–0.45%. These results indicate that plant breeding has successfully increased oat and spring wheat yields in Finland, but barley breeding has been less productive.

Recent advances in breeding for improving iron utilization by plants

Abstract: Iron-chlorosis deficiency may occur when an iron-inefficient genotype is grown on calcareous soil. One way to correct the problem is to modify the genotype by plant breeding. Cultivars have been released for oat (Avena byzantina C. Koch), sorghum [Sorghum bicolor (L.) Moench], dry bean (Phaseoulus vulgaris L.), and soybean [Glycine max (L.) Merr.]. Progress is being made in peanut (Arachis hypogea L.), forage species such as clovers (Trifolium sp.) and bluestems (Botriochloa sp.), and pepper (Capsicum annuum L.). Screening of rootstocks is done on citrus (Citrus sp.), mango (Manguifera indica L.), and avocado (Persea americana Mill.).

Effects of plant population density on determinate and indeterminate forms of winter field beans (Vicia faba) 1. Yield and yield components

Abstract: Using an indeterminate cultivar, Bourdon, and a determinate selection, 858 (provided by Plant Breeding International, Cambridge), of winter field bean, the effect of plant population density on yield was investigated in field trials at the University of Nottingham at Sutton Bonington in three consecutive seasons beginning in 1985/86.Plant morphology had no effect on the optimum plant density, which for both entries lay between 10 and 20 plants/m2. Bourdon yielded significantly more (2 t/ha, on average) than 858 and this was attributable to more pods/pod-bearing stem, more seeds/pod and heavier seeds. Selection 858 was also less winter hardy.Yield was most closely correlated with number of seeds/plant, but other components were almost as important, highlighting the plasticity of yield in Vicia faba and the difficulties in attempting to increase yield by selecting for particular components of yield.In contrast to spring beans, the indeterminate cultivar of winter field bean produced as many branches as the determinate entry and both produced fewer branches at higher densities. There was no difference between the two growth habits in the relative contribution of each stem class to the yield of the whole plant. Higher-order branches contributed less than the main stem to final yield.

Inhibition of growth of fungi isolated from plants by Acremonium strictum

Abstract: The fungus Acremonium strictum was isolated from rye grass, kikuyu and another species of Pennisetum. Two isolates of A. strictum significantly inhibited, in vitro, the rate of growth of five fungi commonly associated with grasses. Extracts from cultures of the isolates also inhibited the rate of hyphal elongation. From the evidence, these isolates of Acremonium are classified as endophytes and their relationship with the 'Balansioid' endophytes must be reconsidered.

Effects of plant population density on determinate and indeterminate forms of winter field beans (Vicia faba). 2. Growth and development.

Abstract: In studies at the University of Nottingham at Sutton Bonington in two consecutive seasons beginning in 1986/87, Bourdon, an indeterminate cultivar, and 858, a determinate selection (provided by Plant Breeding International, Cambridge), were compared under six target plant population densities ranging from 10 to 80 plants/m2.As the season progressed, total dry matter production increased to a maximum and then declined. However, growth rates slowed at pod set because, it is suggested, of the change in the chemical composition of the newly synthesized biomass, from carbohydrate to protein, at that time. Leaf area duration was greater in Bourdon than in 858, especially during pod set, but it bore no relation to seed yield. Specific leaf area was unaffected by competition for light. It is proposed that changes in plant population density affect the competition for assimilates within a plant rather than the competition for light between different plants. Losses of branches and reproductive nodes, with time, are cited as evidence for this. The apparent causes of the lower yield of determinate forms of winter field bean relative to indeterminate forms are discussed.

Plant genetics in pest management

Abstract: The potential of plant genetics in the overall context of integrated pest control could be viewed simply as the potential of plant resistance in pest management. Genetic resistance in plants is one of the most effective and economic means of controlling plant pests. Resistant plants are the first line defence against pests. Successes in breeding for pest resistance depend upon the sound knowledge of the plant genes controlling resistance to pests. Recent report on the existence of two nonallelic and independent genes, Rac1 and Rac2 in cowpea cultivars ICV 10 and TVu 310, and ICV 11 and ICV 12, respectively, from the ICIPE bas broadened the scope of cowpea breeding against aphid biotypes. Use of biotechnology as a plant breeding tool in transferring resistance genes into agronomically suitable cultivars appears to hold good promise for the future.

Haploid plants from tissue culture: application in crop improvement.

Abstract: Haploid plants are of great interest to geneticists and plant breeders. Haploids offer geneticists the opportunity to examine genes in the hemizygous condition and facilitate identification of new mutations. Plant breeders value haploids as a source of homozygosity following chromosome doubling from which efficient selection of both quantitative and qualitative traits is accomplished (Griffing, 1975). As a tool in crop improvement strategies, it is imperative that haploids are produced from individual heterozygous genotypes in sufficiently large numbers to compensate for undesirable gene combinations that result from linkage and random assortment via meiosis. Just as plant breeders advance large populations through several generations (to maximize variability in later generations), application of haploidy in plant breeding is dependent on the ability to produce a haploid population of sufficient size to accommodate selection of desired gene combinations.

Morphological influences on the seed yield of field peas

Abstract: In a preliminary trial at Perth with spaced plants which were supported to prevent lodging and allow for irrigation, the seed weight on plants was correlated with the ability of pea plants to produce reproductive nodes on the main stem and branches. Tall cultivars such as Dundale, Dun and Wirrega produced more aerial branches than dwarf cultivars like Huka which gave more basal branches. By contrast, in the dry, short-season Mediterranean climate of the Western Australian wheatbelt at Merredin, the seed yield of peas was derived principally from yield components on the main stem. The plant characters; the number of reproductive nodes, plant height and seed number per pod, had a significant (P< 0.01) and positive correlation with seed yield. The early- and mid-flowering cultivars, Collegian and Dundale (67 and 72 days to flower respectively), had more reproductive nodes on the main stem, with more seeds produced on the first six reproductive nodes than later flowering (88-96 days) cultivars such as Dun and Wirrega. At Merredin, basal branch number was negatively correlated with seed yield and tall cultivars like Collegian, Dundale and Dun had significantly (P< 0.05) less basal branches. Plant breeders should select for increased seed number per pod in early flowering, medium to tall pea plants, to improve the total seed weight from the first three reproductive nodes produced on the main stem.

Natural out-crossing in dwarf pigeonpea

Abstract: Natural out-crossing rate in pigeonpea was studied at ICRISAT Center using plant stature (tall plants in dwarf progenies) as the genetic marker. The data indicated natural out-crossing rates of 9.7% to 24.1% with a pooled value of 13.1% in the six populations studied. These data were comparable to earlier studies at the same site using stem colour and growth habit as genetic markers in tall pigeonpea cultivars thus suggesting that foraging of insect pollination vectors is not influenced by plant type. The implications of natural out-crossing on breeding and maintenance of genetic purity of cultivars is discussed.

Restriction fragment analysis of somaclones

Abstract: Somaclonal variation is a feature common to all plant regeneration via a tissue culture or ‘callus’ phase [7, 10] Whether the intention is to maximise variation (for production of variability in plant breeding) or minimise it (to reduce variability in mass propagation systems or transformation studies) it is very important to be able to identify variants as quickly as possible and to assess the amount of variation a particular treatment produces Most identification of somaclones has been done on the basis of gross plant morphology, especially as the main interest in somaclonal variation was as a novel source of variability in plant breeding Where this was not possible, then biochemical characterisation was performed — usually involving protein electrophoresis Both of these techniques assess the phenotype of the plants and, as such, are affected by the environment in which the plants are grown, thus making it important to prepare the plants and grow them carefully before analysis

Genetically Engineered Resistance in Plants Against Viral Infection

Abstract: Plant viruses cause serious economic losses in crop plants throughout the world. Crop losses due to plant viruses have been estimated at $2 billion annually in the United States alone including $50 million worth of tomato, $95 million worth of wheat and $30 million worth of potato (Ralf, 1988). In general plant viruses have been difficult to control. Traditional approaches include insecticidal sprays to kill vectors or cultural practices. Examples of the latter are late or early planting of crops to avoid seasonal migration of vectors, crop rotation or cross-protection. Breeding resistant cultivars would be the favoured option since conventional plant breeding methods have played an important role in crop improvement for many decades. Genes for a variety of useful traits including resistance to diseases have been successfully transferred from noncultivated plant species and genera to cultivated crops using this approach (Goodman et al., 1987). However, classical plant breeding methods have several limitations. For instance, they are laborious and time-consuming; tightly-linked genes with undesirable traits may not be separated even after several back crossings; the desired resistance is not always available or may be available only in plants that are genetically incompatible; or the resistance may be multigenic and difficult to transfer (Goodman et al., 1987). The advent of recombinant DNA techniques and the dramatic progress made in the development of gene transfer and plant regeneration technologies have now made it possible to transfer desired genes not only between plant families but also from bacteria and other organisms into plants. These findings have provided an unparalleled opportunity to improve crop plants since they have overcome most of the drawbacks associated with the use of conventional breeding methods (Grumet, 1990).

5. The use of genetic resources in breeding and breeding research

Abstract: The dramatic increase in yields of agricultural crops over the last 40 years in developed countries has been attributed equally to improved genetic components and improved agronomic practices. The success of plant breeding is based partly on an increased understanding of the parameters involved, to a great extent on improved and more efficient methods of selection, to greater use of available genetic diversity and also to advances in a number of related disciplines including plant pathology, biochemistry, agronomy and genetics. Successes and problems associated with using various genetic resources in plant breeding are illustrated with examples from some of the world's major crops, including potatoes, barley and cotton.

Molecular Analysis of Rice Genes and Methods for Gene Transfer

Abstract: Plant breeding methods are commonly used to increase rice production. Genetic diversity has been introduced into cultivars through crosses with rice varieties containing novel genotypes and possessing valuable phenotypic traits. In conjunction with selection for desirable traits, superior rice plants can be produced. Characteristics which would benefit rice cultivars include tolerance to environmental stresses and resistance to disease and insects. It is hoped that in the future, molecular biology and genetic engineering techniques will also contribute to improving cultivated rice. For these reasons our research has centered on (1) analyzing the expression and organization of rice nuclear and organellar genes and (2) developing methods for transformation and regeneration of rice plants. Discussed below are a number of recent advances in rice molecular biology, some of which may be applicable to crop improvement.