Showing papers in "Journal of crop production in 1997"
TL;DR: Allelopathy includes both positive and negative effects of one plant on the other through environment, though most of the studies seem to focus on its deleterious impacts.
Abstract: Summary Allelopathy includes both positive and negative effects of one plant on the other through environment, though most of the studies seem to focus on its deleterious impacts. It plays a key role in both natural and managed ecosystems. In agroecosystems, several weeds, crops, agroforestry trees and fruit trees have been shown to exert allelopathic influence on the crops, thus, affecting their germination and growth adversely. Some of the agricultural and horticultural crops affect their own seedlings grown in succession which is commonly known as replant problem/syndrome. Available studies indicate that allelochemicals act via bringing certain changes in physiological functions like respiration, photosynthesis and ion uptake. These, in turn, result in visible changes in seed germination, further growth reduction and overall performance of the target plants. The studies on interplant interactions assume significance in agroforestry programmes for selecting the types of crops complementary to the select...
133 citations
TL;DR: The evolutionary bottlenecks through which today's wheat germplasm has descended are discussed, and the ways in which the wheat gene pool is being enriched with genes from other species are discussed.
Abstract: Summary For many crop species, genetic uniformity is a result of modern breeding and farming practices. Common wheat (Triticum aestivum L.) is an exception, having been a genetically narrow species throughout its entire existence. This paper discusses the evolutionary bottlenecks through which today's wheat germplasm has descended, and the ways in which the wheat gene pool is being enriched with genes from other species. The worldwide gene pool of common wheat is descended from a very small number of spontaneous interspecific hybrids, which originated as a result of two natural amphiploidization events. In the more recent event, plant(s) of emmer wheat, which were being cultivated at the time by early Neolithic fanners, were fertilized by a weedy diploid goatgrass, Aegilops tauschii, producing primitive common wheat. Because of the rarity of this event, today's common wheat has extremely low levels of polymorphism at enzyme, storage protein, and DNA marker loci, compared with its parent species, especiall...
116 citations
TL;DR: Microsatellites are tandem repeats of short sequence motifs that occur ubiquitously in eukaryotic genomes and are an extraordinarily high level of variation among taxa, mainly expressed as a variable copy number of tandem repeats.
Abstract: Summary Microsatellites are tandem repeats of short sequence motifs that occur ubiquitously in eukaryotic genomes. A key feature of this class of repetitive DNA is an extraordinarily high level of variation among taxa, mainly expressed as a variable copy number of tandem repeats. A multitude of techniques were described that exploit microsatellite variability as molecular markers. Basically, these approaches can be classified into four different experimental strategies. (1) Oligonucleotides complementary to microsatellites are used as hybridization probes for multilocus RFLP fingerprinting. (2) Microsatellite-complementary oligonucleotides serve as PCR primers, either alone or in combination with arbitrary primers, to amplify certain regions of genomic DNA. (3) (Non)radioactively labelled microsatellite motifs are hybridized to electrophoretically resolved RAPD fragments, resulting in new and unexpected banding patterns on the autoradiograms. (4) Length variation of individual microsatellite loci is analy...
103 citations
TL;DR: In this paper, two peaks of high sensitivity are encountered during the reproductive development of plants, from meiosis to seed set, and are common to all species studied, including rice, maize and some dicots.
Abstract: Summary Reproductive development of plants, from meiosis to seed set, is highly vulnerable to water deficit. Two peaks of high sensitivity are encountered during this period. The first one occurs during meiosis in reproductive cells, and is common to all species studied. Water deficit at this stage causes pollen sterility, but usually affects female fertility only when the stress is severe. Pollen sterility does not result from a desiccation of the reproductive organs, but is an indirect consequence of water deficit in the vegetative parts, and may be mediated by a transportable sporocidal signal. The second peak of sensitivity occurs during flowering, and is conspicuous in rice, maize and some dicots. Depending on species, stress during this period can cause loss of pollen fertility, spikelet death or abortion of newly formed seed. These injuries, unlike those caused by the meiotic-stage stress, are associated with a decline in the water status of the reproductive structures. Changes in carbohydrate avai...
58 citations
TL;DR: Improving and applying the understanding of weed seed and seed bank dynamics is essential to developing improved weed management and to recommend weed control tactics.
Abstract: Summary Weeds continue to have major impacts on crop production in spite of efforts to eliminate them. Most weed species rely on seed for regeneration and persistence. The species composition and density of weed seed in the soil vary greatly and are closely linked to the cropping history of the land. Altering tillage practices changes patterns of soil disturbance and weed seed depth in the soil, which plays a role in weed species shifts. Crop rotation and weed control practices also impact the weed seed bank in the soil. Information on the weed seed bank should be a useful tool for integrated weed management. Decision aid models are being developed that use information on the composition of the weed seed bank to estimate weed populations, crop yield loss, and to recommend weed control tactics. Understanding weed seed bank dynamics can also be used to guide management practices. Improving and applying our understanding of weed seed and seed bank dynamics is essential to developing improved weed management ...
47 citations
TL;DR: In this article, the molecular mechanisms of heterosis have been studied at the molecular level and the results suggest the significance of both the regulatory proteins (and their encoding genes) and the mechanisms of regulation of gene activity in manifestation of complicated phenomena such as heterosis.
Abstract: Summary Although the biological basis of heterosis remains unknown, plant breeders have made wide use of this phenomenon and it is generally believed that the understanding of the mechanisms underlying heterosis will enhance our ability to form new genotypes which may be used directly as F1 hybrids or form the basis for future selection programmes. The original data concerning the phenomenon came out of studies at the phenotypic level. They were followed by physiological and later by biochemical data with the advent of electrophoresis and the easy accumulation of data related to isozyme variability. More recently, efforts have been made at the molecular level and the results suggest the significance of both the regulatory proteins (and their encoding genes) and the mechanisms of regulation of gene activity in manifestation of complicated phenomena such as heterosis. In this article emphasis is given to the molecular mechanisms of heterosis. Recent data on quantifying gene expression at the protein or mRNA...
43 citations
TL;DR: The physiological consequences of incorporating reduced height genes into wheat are reviewed and it is suggested that semidwarf wheat has greater harvest index than tall wheat at maturity, possibly due to less competition for carbohydrate during stem elongation.
Abstract: Summary Yield of wheat has risen dramatically and world-wide in the last two decades, in part because of the widespread introduction of Rht genes that reduce the length of tillers of wheat. We review the physiological consequences of incorporating reduced height genes into wheat. The Rht1 or Rht2 genes modulate the morphology and physiology of wheat in a manner that involves compensation among several physiological processes. For instance, Rht genes decrease leaf area, but photosynthesis per unit area increases, so biomass accumulation is rarely altered. Although Rht genes increase leaf permeability to water vapor, plant water status changes in compensation to minimize differences in water use efficiency. Perhaps due to less competition for carbohydrate during stem elongation, semidwarf wheat has greater harvest index than tall wheat at maturity. Although tall wheat has a greater weight per kernel at maturity, this does not completely compensate for greater grain number per spike in semidwarf wheat. The c...
37 citations
TL;DR: In this paper, the authors reviewed the literature on the relation between vertical leaf nitrogen distribution and canopy photosynthesis, as a possible route to maximize radiation use efficiency, biomass production and yield potential in winter cereals.
Abstract: Summary This article reviews the literature on the relation between vertical leaf nitrogen distribution and canopy photosynthesis, as a possible route to maximize radiation use efficiency, biomass production and yield potential in winter cereals. Main assumptions underlying the prediction of the optimum vertical leaf nitrogen allocation, i.e., the role of light climate within the canopy and total leaf nitrogen content, are revised. Dynamic aspects and possible impact of manipulation of vertical leaf N distribution on yield and quality of winter cereals are discussed and areas for future research highlighted.
30 citations
TL;DR: In Canada, seeding of agronomically important crops takes place during the early months of spring when temperatures are well below the optimum, resulting in slow asynchronous emergence from the soil and poor stand establishment.
Abstract: Summary In Canada, seeding of agronomically important crops takes place during the early months of spring when temperatures are well below the optimum Low temperature reduces the rate and success of germination This in turn can result in slow asynchronous emergence from the soil and poor stand establishment As emergence is a function of both germination and early seedling growth, the effect of low temperature on these developmental processes is of great interest This review examines how low temperature affects germination and early seedling growth in relation to biochemical and molecular processes As Brassica napus L cv Westar, canola, does not exhibit primary or secondary dormancy, it serves as an ideal species in which to study low temperature emergence First, emergence is reviewed by independent sections covering germination and early seedling growth Germination is dissected into the three phases of germination Early seedling growth is broken into sections covering storage reserve mobilizatio
12 citations
TL;DR: Phylogenetic relationships among 16 diploid species, including at least one species for each of the A, C, D, E and G genomic groups, and for the natural AD tetraploid Species were investigated using starch gel electrophoretic techniques for isozyme detection in conjunction with multivariate analysis.
Abstract: Summary Phylogenetic relationships among 16 diploid species, including at least one species for each of the A, C, D, E and G genomic groups, and for the natural AD tetraploid species and one synthetic AD tetraploid species were investigated using starch gel electrophoretic techniques for isozyme detection in conjunction with multivariate analysis. The species were polymorphic for phosphoglucomutase (PGM), malate dehydrogenase (MDH), shikimate dehydrogenase (SKDH), aconitase (ACO) and isozymes, but monomorphic for phosphoglucoisomerase (PGI). Similar isozyme arrays indicated close or perhaps conspecific relationships between natural tetraploids G. hirsutum and G. lanceolatum and between G. barbadense and G. darwinii. Natural tetraploid G. mustelinum was found to be relatively distinct from the other tetraploid species. The synthetic AD tetraploid was intermediate between the natural AD tetraploid and the A and D diploid clusters. The two A genome species, G. aboreum and G. herbaceum were closely related to...
8 citations
TL;DR: This review aims to correlate the preliminary results obtained by molecular biology with the recent advances in understanding the hormonal control of dormancy induction in developing seeds.
Abstract: Summary Primary dormancy develops in seeds during their maturation on the mother plant. In recent years, the use of hormone mutants and the manipulation of endogenous hormone levels by their biosynthetic inhibitors have led to a new approach of the hormonal regulation of the onset of dormancy. There is good evidence to show that ABA synthesis at axis level is an absolute requirement for the induction and maintenance of dormancy. This continued de novo synthesized ABA could positively control the expression of specific ABA-responsive genes. Among the set of late embryo abundant proteins, some appear to be good candidates as “dormancy proteins.” This review aims to correlate the preliminary results obtained by molecular biology with the recent advances in understanding the hormonal control of dormancy induction in developing seeds.
TL;DR: In this paper, the authors highlighted the importance of climate and weather, and the rising level of atmospheric carbon dioxide are highlighted as important changes in the global environment, highlighting the dual and simultaneous effect of global warming and carbon dioxide on the enhancement of crop productivity as reflected by increased photosynthetic capacity, greater water use efficiency and alleviation of other crop stresses.
Abstract: Summary During a period of a presumed world food crisis, the importance of climate and weather, and the rising level of atmospheric carbon dioxide are highlighted as important changes in the global environment. There is a dual and simultaneous effect of the rising level of atmospheric carbon dioxide on first, global warming and second, on the enhancement of crop productivity as reflected by an increased photosynthetic capacity, greater water use efficiency and alleviation of other crop stresses. Climate variability has a greater impact on agricultural productivity than does climate change. The rising level of atmospheric carbon dioxide is a universally free subsidy, gaining in magnitude with time, on which all can reckon when it comes to crop productivity.
TL;DR: In this article, the current situation of crop production in China is reviewed, along with strategies to meet future food needs of its population, and the strategies for meeting future food requirements are discussed.
Abstract: Summary The current situation of crop production in China is reviewed, along with strategies to meet future food needs of its population.