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Volume 4 Number 1 2010
CONTENTS AND ABSTRACTS
Saeed Rauf (Pakistan), Jaime A. Teixeira da Silva (Japan), Asif Ali Khan, Abdul Naveed (Pakistan) Consequences of Plant Breeding on Genetic Diversity (pp 1-21)
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ABSTRACT
Review: It is generally perceived that activities related to plant breeding have reduced the genetic diversity within crop species. Therefore, the impact of plant breeders’ activities i.e. introduction, selection and hybridization on plant genetic diversity have been reviewed. After examining a large number of scientific reports it may be generalized that losses of genetic diversity occurred but followed spatial and sometimes temporal trends. Furthermore, losses of genetic diversity in plant material occurred in a specific order i.e. the highest in elite open-pollinated cultivars or inbred lines and the lowest in wild germplasm followed by land races. Plant introduction increased genetic diversity when local germplasm was partially substituted or supplemented by introduced germplasm. Selection enhanced genetic differentiation at the expense of genetic diversity. Losses in genetic diversity were observed when plant populations were subjected to domestication during the pre-systematic plant breeding era and pedigree selection during the systematic plant breeding era. However, participatory plant selection effectively generated an allelically rich and broad genetic-based plant material. Intraspecifc hybridization lowered genetic diversity due to utilization of similar types of parents in generating trangressive segregation. Commercial hybrids, when used to substitute land races or diverse indigenous germplasm, also lowered the genetic diversity of the area. In order to broaden the genetic base of plant material, interspecific hybridization was performed in many crop species with some success. Transgenics were released as a product of biotechnology, spontaneous pollination between conventional cultivars and wild germplasm may enhance genetic diversity but may, on the other hand, raise the issue of genetic pollution. These are all pertinent issues as 2010 has been considered by the UN as the International Year of Biodiversity.
Heathcliffe Riday (USA) Progress Made in Improving Red Clover (Trifolium pratense L.) Through Breeding (pp 22-29)
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Invited Review: Red clover (Trifolium pratense L.) is a major forage legume grown on approximately 4 million hectares worldwide. It has a long and varied history in agriculture. Active breeding efforts began at the end of the 19th century. Since this time, significant improvement in red clover cultivars has occurred. The major focus of breeding and accompanying research efforts has involved increasing persistence. Improved persistence has been achieved through general persistence selection, pathogen resistance breeding, and breeding for tolerances to other agronomic stresses. Dry matter yield has received less attention, but has nevertheless been improved. More recently, selection for adaptation and performance of red clover in a grass-legume mixture used especially in grazing has received attention. Genomic resources in red clover have matured with the availability of numerous genetic maps and publicly available molecular markers. Transformation techniques have been developed to allow creation of genetically modified plants. Numerous opportunities still exist to improve agronomic characteristics of red clover, particularly by continuing efforts to increase persistence and dry matter yield. In a world with expensive fossil fuel-based fertilizer, breeding to develop and maintain improved red clover will continue to remain important.
Michael D. Casler (USA) Genetics, Breeding, and Ecology of Reed Canarygrass (pp 30-36)
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Invited Mini-Review: Reed canarygrass is a cool-season perennial with a circumglobal distribution in the northern hemisphere, native to Europe, Asia, and North America. It is tolerant of a wide range of environmental stresses including cold, heat, drought, and flooding, and utilized for many purposes, including pasture, hay production, biomass for bioenergy, and soil conservation. It has become notorious in North America, recently classified as “invasive” because it has opportunistically invaded wetlands across much of temperate North America. Numerous cultivars of reed canarygrass have been developed in Europe and North America. Early 20th-century cultivars represented seed increases from meadows and hay fields that were considered to have desirable agronomic traits. Cultivars developed later in the 20th century were products of selection for productive and persistent plants from long-term meadows and pastures. With the discovery of indole alkaloids and the strong linear relationship of alkaloid profiles, including both type and concentration, to palatability and preference of ruminant livestock, modern cultivars have been bred to contain only the more benign alkaloid gramine, generally in relatively low concentration. Indeed, the popularity of these new cultivars has led to complete replacement of older “wild-type” cultivars in the commercial sector, so that seed of old cultivars can often be obtained only from gene banks.
Abdullah A. Jaradat, Walter Goldstein (USA), Kenton Dashiell (Kenya) Phenotypic Structures and Breeding Value of Open-Pollinated Corn Varietal Hybrids (pp 37-46)
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Original Research Paper: The growing interest in using open-pollinated varieties (OPVs) and varietal hybrids (OPVhs) of corn (Zea mays L.) reflects the value of large plasticity levels available in their plant, ear, and kernel traits. We estimated variation, broad sense heritability, general and specific combining ability, and pairwise phenotypic distances based on 35 traits measured on 46 OPVhs grown under four environments. Average grain yield across environments was inversely related to its variance; we identified OPVhs with large grain yield and small variance along with the traits contributing to this large and stable grain yield. Estimates of heritability ranged from 0.35 to 0.85, with decreasing average values for kernel, ear, and plant traits. Effects of general combining ability and its interaction with the environment for most traits were more important than specific combining ability effects. Largest grain yield and specific combining ability effects resulted from crosses among OPVs of different source germplasm origin. Pairwise phenotypic distances among OPVhs indicate the presence of “functional” OPVh groups based on multiple traits and their interaction with the environment.
Subas Malla, Amir M.H. Ibrahim, Yang Yen, William Berzonsky, Karl D. Glover, Jeffrey Stein (USA) QTL Analysis of a Putative Novel Source of Resistance to Fusarium Head Blight in Hard Winter Wheat (pp 47-54)
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ABSTRACT
Original Research Paper: Host plant resistance is a highly effective approach for managing Fusarium head blight (FHB), an important disease of wheat (Triticum aestivum L.) in many regions of the U.S. and worldwide. This study was conducted to identify QTL linked to an indigenous source of FHB resistance in a South Dakota – adapted winter wheat genotype, SD97060. A population was produced by hybridizing SD97060 with ‘Jagalene’ winter wheat and advancing generations using single seed descent. The F2:4, F2:5 and F2:6 generations were evaluated after artificially inoculating plants in mist-irrigated field nurseries in 2006 and 2007 and in a greenhouse in 2008, respectively. Disease incidence, severity, Fusarium damaged kernels (FDK) and deoxynivalenol (DON) content were evaluated in the 114 recombinant inbred lines (RILs). Four QTL were detected using phenotypic data obtained from field and greenhouse trials. Two QTL, located at chromosomes 2BL and 4BL, exhibited stable expression across the two environments. The 2BL QTL conferred resistance to FHB; whereas, the 4BL QTL was associated with susceptibility to FHB. Two QTLs, which did not exhibit stable expression across environments were detected at the 3BS and 3BSc using field and greenhouse data. The 2BL QTL of SD97060 could serve as a valuable source to enhance FHB resistance in wheat without limiting yield potential.
Mejda Daami-Remadi, Hayfa Jabnoun-Khiareddine, Fakher Ayed, Mohamed El Mahjoub (Tunisia) Comparative Susceptibility of Potato Cultivars to Verticillium Wilt Assessed via Wilt Severity and Subsequent Yield Reduction (pp 55-62)
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Original Research Paper: Experiments were conducted to investigate the relative susceptibility to Verticilliumwilt (VW) of 10 local potato cultivars grown under greenhouse conditions and artificially inoculated with a mixture of Verticillium dahliae isolates in comparison with non-inoculated controls. VW effects were evaluated, 60 days post inoculation, via foliar symptoms intensity, plant growth and production parameters. In fact, for all cultivars pooled, the mean plant height was reduced by 20% whereas the weight of the aerial part and tuber were reduced by about 21 and 32%, respectively on inoculated compared with non-inoculated control plants. However, the response to Verticillium infection i.e. foliar symptoms, stunting effect and the resulting stem weight and yield reduction varied among cultivars. Foliar symptoms and reduction in yield were considered to be criteria in determining the degree of susceptibility to the pathogen. When comparisons are made based on foliar symptoms, all the tested cultivars exhibited varying degrees of susceptibility ranging from moderate to high. However, when based on yield reductions, ‘Tango’ and ‘Elodie’ were the only cultivars which had the lowest yield reductions and were classified as tolerant cultivars. The importance of the results, in relation to the scoring systems used for the assessment of cultivar’s behavior against V. dahliae, is discussed.
Hayfa Jabnoun-Khiareddine, Mejda Daami-Remadi (Tunisia), Harold W. Platt (Canada), Fakher Ayed, Mohamed El Mahjoub (Tunisia) Variation in Aggressiveness of Tunisian Verticillium dahliae Races 1 and 2 Isolates and Response of Differential Tomato Cultivars to Verticillium Wilt (pp 63-70)
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Original Research Paper: In Tunisia, Verticillium dahliae race 1 and race 2 isolates have been obtained from many tomato-growing regions. To assess the aggressiveness of both races, 29 race 1 and 44 race 2 Tunisian isolates were used for root dip inoculation of tomato seedling belonging to differential cultivars i.e. ‘Ventura’ (ve) and ‘Riogrande’ (Ve). Variation in aggressiveness towards both tomato cultivars was apparent among isolates of both V. dahliae races, via the index of leaf damage and plant stunting. All race 1 and race 2 isolates caused moderate to severe symptoms on cv. ‘Ventura’ and on both cultivars, respectively. All race 1 and race 2 isolates were able to cause variable degrees of stunting on the inoculated tomato plants of both cultivars, compared to the non-inoculated controls. On average, race 2 isolates were more aggressive than race 1 isolates on cv. ‘Ventura’. The response of four resistant and two susceptible tomato cultivars to selected race 1 and 2 isolates was studied under controlled conditions. These cultivars exhibited varying degrees of susceptibility to Verticillium wilt (VW) ranging from moderate to high as measured by leaf damage index and plant height. When grown in a naturally Verticillium infested soil (49 microsclerotia/g of soil), VW incidence was 100% for all the resistant cultivars, four months post-planting. The extent of vascular discoloration occasioned by VW reached and even exceeded the half of stem height for some cultivars.
Nalini Eswaran, Suresh Gopal Bhagwat, Narendra Jawali (India) Allelic Status of puroindolineA and puroindolineB in Indian Bread Wheat Varieties (pp 71-75)
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Original Research Paper: ‘Soft’ and ‘hard’ are classes of wheat (Triticum aestivum) and are distinguished by the texture of grain which in turn is due to expression of puroindoline genes Pina and Pinb, which are the main components of the 15 kDa friabilin protein that is associated with grain texture. Here we report the status of alleles of Pina and Pinb in 54 Indian and six Australian bread wheat varieties. The alleles were identified by PCR amplification of the Pina alleles and using PCR-CAPS markers for alleles Pina-D1b and Pina-D1c using restriction enzymes PvuII and BsrBI respectively. Pina-D1b was found to be more frequent, Pinb-D1b was less frequent and Pinb-D1c was absent among the Indian varieties analyzed. None had mutations in both the puroindoline genes simultaneously. Analysis of a F2 population segregating for the Pina (Pina-D1a and Pina-D1b) and Pinb (Pinb-D1a and Pinb-D1b) alleles showed the absence of recombination between the two loci, which is possibly due to tight linkage.
Simcha Lev-Yadun (Israel), Sarah E. Wyatt (USA), Moshe A. Flaishman (Israel) Unconscious Selection and Domestication in "Wild-type" Arabidopsis thaliana (Brassicaceae) (pp 76-77)
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Research Note: We propose that the two commonly used "wild type" Arabidopsis thaliana cultivars, Landsberg and Columbia became unconsciously domesticated. The conditions used for growing A. thaliana for research are very different from the natural conditions near Landsberg, Germany from where they originated. Laboratory practices for dozens of generations must have selected for characters that give Arabidopsis advantages under laboratory growth conditions and against ones beneficial in the wild but with reduced fitness in laboratory "ecosystems". From what we already know about unconscious selection in agriculture, we can infer that these so-called "wild types" have been changed into laboratory organisms that are inherently different from the native wild type. Because of the detailed genetic knowledge of A. thaliana, these genotypes can be used to study processes of unconscious selection more precisely than any other plant. |
