Successive Cycles Of Selection Research Articles

YS-18 A SINGLE STAND SORGHUM VARIETY WITH IMPROVED STALK AND YIELD POTENTIAL FOR AUTUMN SOWING

The high pace of increasing population along with the diminishing effects of global warming are putting immense pressure on the agriculture system in terms of food security. Great concerns regarding yield enhancement have emerged for crops feeding livestock and the dairy industry. The development of high-yielding dual-purpose fodder varieties is a concurrent demand in breeding programs designed for grain and fodder yield improvement. Sorghum as being highly nutritious and low-input crop provides good prospects for breeding improvement. Because of this, this work was designed with the breeding strategy for sorghum grain and fodder yield improvement. Successive selection cycles with head-to-row, similar plant type, and bulking were adopted among the filial progeny of a cross between two lines ICS73 and ICSR8003. The uniform line YS-18 was then subjected to evaluation at the station and national yield trials. YS-18 secured 22% and 5% yield increase in station trials during 2018 and 2019 over the previously released check variety YS-16. In National uniform Yield Trials, the yield benefit of new candidate line YS-18 was 17% and 27% during 2020 and 2021. Variability studies indicate more grain (14%) and fodder (13%) yield potential than YS-16. This productivity enhancement with 6000 kg/hac grain yield potential and 40000 kg/hac fodder yield is a succession of targeted breeding strategy. Early maturing YS-18 bears sweet juicy stems with stay green broad leaves and long head size that have the potential to be utilized as green feed at cattle farms and the dairy industry. This work will provide a better understanding to a researcher for designing breeding programs for the development of high-yielding germplasm in crops.

Continuous selection pressure to improve temperature acclimation of Tisochrysis lutea.

Temperature plays a key role in outdoor industrial cultivation of microalgae. Improving the thermal tolerance of microalgae to both daily and seasonal temperature fluctuations can thus contribute to increase their annual productivity. A long term selection experiment was carried out to increase the thermal niche (temperature range for which the growth is possible) of a neutral lipid overproducing strain of Tisochrysis lutea. The experimental protocol consisted to submit cells to daily variations of temperature for 7 months. The stress intensity, defined as the amplitude of daily temperature variations, was progressively increased along successive selection cycles. Only the amplitude of the temperature variations were increased, the daily average temperature was kept constant along the experiment. This protocol resulted in a thermal niche increase by 3°C (+16.5%), with an enhancement by 9% of the maximal growth rate. The selection process also affected T. lutea physiology, with a feature generally observed for ‘cold-temperature’ type of adaptation. The amount of total and neutral lipids was significantly increased, and eventually productivity was increased by 34%. This seven month selection experiment, carried out in a highly dynamic environment, challenges some of the hypotheses classically advanced to explain the temperature response of microalgae.

Genetic Gain in the Resistance of Arabica Coffee Progenies to Root‐Knot Nematode

The nematode Meloidogyne exigua infests Arabica coffee (Coffea arabica L.) plants, leading to severe growth reduction in young trees and decreased bean yield. We investigated the responses of coffee plants to this nematode and estimated the genetic gain in progenies derived from the cross between the cultivar Catuaí and the Timor hybrid. We evaluated 85 F4:5 progenies; the cultivars Mundo Novo IAC 379‐19 and Catuaí Vermelho IAC 99 were used as susceptible controls, and Paraíso MG H 419‐1 and IPR 100 were used as resistant controls. Progeny responses were evaluated using the gall index (GI), reproduction factor (RF), reproduction factor reduction (RFR), and number of eggs and juveniles (J2) per gram of roots (NEJGR). The cultivars IPR 100 and Paraíso MG H 419‐1 and 75 progenies were resistant to M. exigua. Little or no segregation for resistance was observed within the progenies, indicating potential homozygosity at this locus. The GI, RF, RFR, and NEJGR showed high genotypic correlation. The correlated response of decreased NEJGR when selected indirectly by GI was higher than that by direct selection. The GI scale allowed genetic gain to decrease the nematode population and increase resistance; therefore, it can be used as a selection criterion. Linear regression showed that the NEJGR mean was reduced by a value of 450 per selection cycle, which led to a change in the phenotypic mean and explained 95% of the variation. Thus, successive selection cycles could prevent nematode development in coffee tree roots.

Phenotypic recurrent selection in artichoke breeding

The phenotypic recurrent selection aims to increase the favourable allelic frequency during successive selection cycles, which may result in an open-pollinated cultivar. Therefore, the purpose of this work was to obtain an artichoke population improved for traits related with head quality as well as to estimate the genetic gains for quantitative traits after selection. From a base population with 147 plants (C0), 12 were selected for desirable characteristics for in natura consumption and intercrossed to form the C1 population, consisting of 180 plants. Eleven of them were selected and intercrossed to originate the C2 (324 individuals). From C2, 11 individuals were selected and recombined performing the C3 population. Three of these populations (C0, C1 and C2) were evaluated regarding 12 quantitative and three qualitative traits. Quantitative data were subjected to an analysis of variance (ANOVA) and mean values were compared by Tukey's test (p<0.05). Genetic gain was estimated for each cycle. For qualitative data the plants frequency for each trait was evaluated in each cycle. There was a total increase of 25.42% in the frequency of violet head, in the C1, 87% of plants presenting heads with traces of violet colour. The total increase in the frequency of circular heads was 34.7%, whereas the absence of thorns increase was 43.2%. Significant variations among cycles for most of the quantitative traits were observed. Phenotypic recurrent selection results in an improved artichoke population for heads quality and some quantitative traits.

Ozone toxicity to Sitophilus zeamais (Coleoptera: Curculionidae) populations under selection pressure from ozone

Two populations of Sitophilus zeamais (Coleoptera: Curculionidae) were subjected to selection pressure with ozone (O3), and the possibility of acquiring resistance to O3 was investigated. The pattern of locomotion and the rate of respiration were evaluated following each selection cycle. Two source populations were used in the study: one was a mixture composed of 30 populations (MP), and the other was composed of the population that was the least susceptible to O3 among these 30 populations (LSP). The beetles from each source population experienced selection cycles with O3 using the lethal time for 80% (LT80) of the insect population from each generation. The O3 toxicity (50 ppm at a continuous flow rate of 2 L min−1) to each generation was calculated using time-response bioassays. The locomotor pattern (distance traveled, resting period, and walking speed) and the respiratory rate (CO2 production) were also evaluated. The S. zeamais populations that were subjected to successive cycles of selection with O3 did not acquire resistance to O3, and the pattern of locomotion and the rate of respiration did not change following the selection cycles with O3.

Evaluation of Three Breeding Cycles for Seedling Weight of Switchgrass, Big Bluestem, and Indiangrass

ABSTRACTA modified form of restricted, recurrent phenotypic selection was used to select for seedling shoot weight in switchgrass (Panicum virgatum L.), big bluestem (Andropogon gerardii Vitman), and indiangrass [Sorghastrum nutans (L.) Nash] populations for three generations. Seedlings were grown in micropots in trays in a greenhouse and were individually clipped and weighed 4 wk after emergence. The seedlings were allowed to regrow, and the heaviest seedlings were transplanted to field nurseries for polycrossing to produce Syn 1 seed. Three breeding cycles were conducted for each grass. After the third breeding cycle, Syn 2 generation seed was produced for each cycle, including cycle 0 for 2 yr, and was used in subsequent greenhouse and field evaluations to determine if the breeding procedure improved seedling vigor as measured by seedling shoot weight. In two greenhouse evaluation trials, the increase in seedling weight per cycle was 7.8, 5.6, and 10.2% for big bluestem, switchgrass, and indiangrass, respectively. In two field trials, seedling weight also increased with successive cycles of selection except for indiangrass in one trial. Establishment success as measured by stand counts did not differ among the cycles of selection for the three grasses in the field trials. Based on these results and the results of subsequent breeding and field evaluation work on seedling tiller number, it is apparent that seedling traits of these grasses can be modified by breeding. To improve establishment of these grasses, research on developing agronomic seed production practices that result in improved seed quality would also be beneficial.

Experimental selection of paromomycin and miltefosine resistance in intracellular amastigotes of Leishmania donovani and L. infantum

Although widespread resistance of Leishmania donovani and L. infantum against miltefosine (MIL) and paromomycin (PMM) has not yet been demonstrated, both run the risk of resistance selection. Unraveling the dynamics and mechanisms of resistance development is key to preserve drug efficacy in the field. In this study, resistance against PMM and MIL was experimentally selected in vitro in intracellular amastigotes of several strains of both species with different antimony susceptibility background. To monitor amastigote susceptibility, microscopic determination of IC50-values and promastigote back-transformation assays were performed. Both techniques were also used to evaluate the susceptibility of field isolates from MIL-relapse patients. PMM-resistance could readily be selected in all species/strains, although promastigotes remained fully PMM-susceptible. Successful MIL-resistance selection was demonstrated only by promastigote back-transformation at increasing MIL-concentrations upon successive selection cycles. Important to note is that amastigotes with the MIL-resistant phenotype could not be visualized after Giemsa staining; hence, MIL-IC50-values showed no shift. The same phenomenon was observed in a set of recent clinical isolates from MIL-relapse patients. This study clearly endorses the need to use intracellular amastigotes for PMM- and MIL-susceptibility testing. When monitoring MIL-resistance, promastigote back-transformation should be used instead of the standard Giemsa staining. In-depth exploration of the mechanistic background of this finding is warranted.

Rapid Cycling Recurrent Selection for Increased Carotenoids Content in Cassava Roots

ABSTRACTImproving total carotenoids content (TCC) in cassava roots is an important strategy to reduce vitamin A deficiency in human populations that rely on cassava as a source of energy in their diets. The high heritability for TCC in the roots allowed the International Center for Tropical Agriculture to implement a rapid cycling recurrent selection approach that reduced the standard length of each cycle from the ordinary 8 yr to 3. Data from successive evaluation nurseries suggested that gains have been made through time. However, no comparison of different cycles of selection has been made when representatives of each cycle were grown together. This study compares 4 to 5 clones representative of cycles of selection from 2004 to 2009. Results demonstrated significant gains for TCC as well as for total β‐carotene (TBC) expressed both in a fresh and dry weight basis. Although dry matter content (DMC) was not a selection criterion during the selection process, it increased with the successive cycles of selection. This suggests that indeed, simultaneous gains for TCC, TBC, and DMC are feasible. This finding is relevant for the important ongoing efforts at the International Institute of Tropical Agriculture and African National Programs to release biofortified cassava clones in Africa with adequate levels of dry matter content.

Molecular characterization of high performance inbred lines of Brazilian common beans

The identification of germplasm genetic variability in breeding programs of the common bean (Phaseolus vulgaris) is essential for determining the potential of each combination of parent plants to obtain superior genotypes. The present study aimed to estimated the extent of genetic diversity in 172 lineages and cultivars of the common bean by integrating five tests of value for cultivation and use (VCU) that were conducted over the last eight years by the breeding program of Embrapa Arroz e Feijão in Brazil. Nine multilocus genotyping systems composed of 36 fluorescent microsatellite markers distributed across 11 different chromosomes of the common bean were used, of which 24 were polymorphic in all trials. One hundred and eighty-seven alleles were identified, with an average of 7.79 alleles per locus and an average gene diversity of 0.65. The combined probability of identity for all loci was 1.32 x 10(-16). Lineages that are more genetically divergent between the selection cycles were identified, allowing the breeding program to develop a crossbreed between elite genotypes with a low degree of genetic relatedness. HE values ranged from 0.31 to 0.63, with a large reduction in the genetic base over successive selection cycles. The test showed a significant degree of differentiation (FST = 0.159). Private alleles (26%) were identified and can be directly incorporated into the gene pool of cultivated germplasm, thereby contributing effectively to the expansion of genetic diversity in this bean-breeding program.

EVALUATION OF TWO ADVANCED TOLERANT GENERATIONS OF FABA BEAN IN BOTH FREE AND HIGHLY INFESTED FIELDS WITH Orobanche crenata

This work was conducted in the experimental farm of Mallawy Agricultural Research Station, Agricultural Research Center, Egypt, during the two successive winter seasons of 2009/2010 and 2010 /2011 to compare the performance of 10 populations of advanced generations of faba bean in two successive cycles of selection under free infested with broomrape (Orobanche crenata) and compare the productivity of free fields to that resulted from highly infested fields. Ten populations already evaluated revealed from crosses between five faba bean parents of Giza-843, Giza-429, (57/721/94) Line-3, Line-4 (664/689/94) and Giza 2 and continued to F5 and F6 selected generations. Two cycles of selection were done on 10 F5 and F6 populations that exceeded Giza-843 in seed yield per plant and the results indicated surpassing 6 out of the 10 populations of the F5 and F6 selected families that permit to high performance populations of faba bean. The most outstanding yielding ability of faba bean populations were Giza-843 × G-429, Giza-843 × Line 3, Giza-843 × Line 4, Giza-843 × Giza-2, G-429 × Line 3 and Line 4 × Giza-2 that gave promise for high yield and make a good chance for high yield faba bean cultivars in the future. The results of F6 families were similar to those of F5 families where the performance of faba bean plants under heavily infested fields revealed selected populations of high seed yield that surpassed that of Giza-843 and that was represented in the first five families already mentioned and these six families gave parallel performance under free infested fields exceeded family Giza-429 × Line 4. The performance under both types of fields was clear from the highly decreased values of yield of faba bean plants grown under heavily infested fields. Then it is rather grow faba bean in free fields than in heavily infested fields in order to attain high productivity of this important crop.

Early characterization of maize plants in selection cycles under soil flooding*

With 2 figures and 3 tablesAbstractTo insert maize crop in the lowlands, the National Maize and Sorghum Research Center has developed, through the recurrent phenotypical selection, a maize variety called Saracura‐BRS‐4154, which has the capability to survive in periods of flooding. This study was carried out with the purpose of characterizing young plants of successive selection cycles of the variety ‘Saracura’, under flooding, concerning the morpho‐physiology. The assay was carried out in greenhouse by sowing 10 alternate selection cycles and a BR 107 variety known for its susceptibility to flooding. It was found that the last selection cycles resulted in a greater development of thin roots, greater volume and root length. The selection cycles decreased the exodermis and increased aerenchyma formation in the roots over time. There was also leaf plasticity throughout the cycles, and it was noted an increase in the gas exchange parameters and also in the stomata number and size. Our results showed that there was a genetic gain in the morpho‐physiological changes related to flooding throughout the selection cycles of ‘Saracura’ maize young plants.

Morpho-physiology and maize grain yield under periodic soil flooding in successive selection cycles

This study was carried out to evaluate maize plants of different recurrent selection cycles of the variety (Zea mays L.—Saracura-BRS-4154) regarded to genetic gains, morphophysiology, and grain yield, achieved over the selection cycles under intermittent flooding of the soil. This variety has the capacity to survive and produce in temporarily flooded soils and was developed by the National Maize and Sorghum Research Center (EMBRAPA). The experiment was conducted in greenhouse by using ten alternating selection cycles (Cycle 1–18) and BR 107 a variety known for its susceptibility to flooding. The flooding initiated at six-leaf stage by applying 50 mm of water three times a week. At flowering, the following parameters were evaluated: rate of leaf photosynthesis, stomatal conductance, intercellular CO2 concentration, transpiration rate, photosynthetically active leaf area, root porosity, relative chlorophyll content, grain yield, harvest index, ear length, and interval between male and female flowering. Yield as a function of root porosity and photosynthesis were also evaluated. An index was created in this study, in order to help the discussion of the characteristics evaluated, it was called “Relative Tolerance Value—RTV”, only gaseous exchange measurements was not included in this index. By the way, it was observed throughout the selection cycles an increase in all gaseous exchange parameters, being the cycle 18, the one which presented the greatest averages. RTV for leaf area showed the greatest values for cycles 7 and 18, whereas root porosity, chlorophyll relative content, and harvest index, the greater RTV values were found in cycles 17 and 18. The largest grain yield RTV was observed in cycle 7, followed by cycles 13, 15, and 18. Flooding resulted in longer Anthesis-Silking Interval, especially for the first cycles. At flooding condition, grain yield was strongly related to root porosity (R2 = 0.66). These results showed that the selection cycles of “Saracura” maize improved some morphophysiologic characters, which favor their survival in flooded environments, also resulting in higher productivity.

Atividade do sistema antioxidante e desenvolvimento de aerênquima em raízes de milho 'Saracura'

Este trabalho teve como objetivo avaliar a influência de sucessivos ciclos de seleção do milho 'Saracura' na atividade das enzimas do sistema antioxidante, e a relação dessas enzimas com a capacidade dessa variedade em desenvolver aerênquima. Sementes de 18 ciclos de seleção intercalados do milho 'Saracura' e da cultivar BR 107, sensível à hipoxia, foram semeadas em vasos e em casa de vegetação. As plantas foram submetidas ao alagamento intermitente de dois em dois dias. As amostras de raízes foram coletadas após 60 dias e analisaram-se as atividades das enzimas peroxidase do guaiacol, peroxidase do ascorbato e catalase, além da capacidade das plantas de cada ciclo desenvolverem aerênquima. Ao longo dos ciclos, as plantas apresentaram modificações na atividade das enzimas, com aumento na de peroxidase do ascorbato e diminuição na de catalase e de peroxidase do guaiacol. Observou-se, ainda, maior capacidade de desenvolver aerênquima nos últimos ciclos de seleção. A redução na atividade das enzimas do sistema antioxidante parece estar relacionada a um desbalanço na decomposição de H2O2.

Leaf plasticity in successive selection cycles of 'Saracura' maize in response to periodic soil flooding

The objective of this work was to assess the effect of successive selection cycles on leaf plasticity of 'Saracura' maize BRS-4154 under periodical flooding in field conditions. Soil flooding started at the six-leaf stage with the application of a 20-cm depth water layer three times a week. At flowering, samples of leaves were collected and fixed. Paradermic and transverse sections were observed under photonic microscope. Several changes were observed throughout the selection cycles, such as modifications in the number and size of the stomata, higher amount of vascular bundles and the resulting decrease of the distance between them, smaller diameter of the metaxylem, decrease of cuticle and epidermis thickness, decrease of number and size of bulliform cells, increase of phloem thickness, smaller sclerenchyma area. Therefore, the successive selection cycles of 'Saracura' maize resulted in changes in the leaf anatomy, which might be favorable to the plant's tolerance to the intermittent flooding of the soil.

Morpho-anatomical characterization of root in recurrent selection cycles for flood tolerance of maize (Zea mays L.)

Changes in root anatomical structures at successive cycles of selection (cycle 1 to cycle 18, alternating) were observed in the study of maize (&lt;i&gt;Zea mays&lt;/i&gt; L. cv. Saracura-BRS 4154) capable to survive and produce in temporarily flooded soils; this cultivars was developed by the Maize and Sorghum National Research Center through stratified phenotypic recurrent selection for cultivation wetland soils. Field trial was carried out and flooding of the soil was initiated at the six-leaf stage; the soil was flooded with water (20-cm deep) three times per week. Root sample was collected, fixed, and selected for observation in photon microscope. A gradual increase in the number of aerenchyma, the proportion of vascular cylinder, smaller metaxylem, and phloem and epidermis width, and a decrease in exodermis and cortex were observed in successive selection cycles. Such phenotypic changes impart the flood tolerance ability to this maize cultivar.

Selection and elution of aptamers using nanoporous sol-gel arrays with integrated microheaters

RNA and DNA aptamers that bind to target molecules with high specificity and affinity have been a focus of diagnostics and therapeutic research. These aptamers are obtained by SELEX (Systematic Evolution of Ligands by EXponential enrichment) often requiring more than 10 successive cycles of selection and amplification, where each cycle normally takes 2 days per cycle of SELEX. Here, we have demonstrated the use of sol-gel arrays of proteins in a microfluidic system for efficient selection of RNA aptamers against multiple target molecules. The microfluidic chip incorporates five sol-gel binding droplets, within which specific target proteins are imbedded. The droplets are patterned on top of individually addressable electrical microheaters used for selective elution of aptamers bound to target proteins in the sol-gel droplets. We demonstrate that specific aptamers bind their respective protein targets and can be selectively eluted by micro-heating. Finally, our microfluidic SELEX system greatly improved selection efficiency, reducing the number of selection cycles needed to produce high affinity aptamers. The process is readily scalable to larger arrays of sol-gel-embedded proteins. To our knowledge, this is the first demonstration of a chip-based selection of aptamers using microfluidics, thereby allowing development of a high throughput and efficient SELEX procedures.

Evolução da anatomia radicular do milho 'Saracura' em ciclos de seleção sucessivos

Este trabalho teve como objetivo verificar as modificações nas características anatômicas radiculares relacionadas à hipoxia, durante 18 ciclos de seleção da variedade de milho (Zea mays) BRS 4154 Saracura, adaptada a áreas sujeitas a alagamento. A variedade BR 107 e o híbrido simples BRS 1010, suscetíveis ao alagamento, foram utilizados como controle. As diferentes cultivares foram submetidas a alagamentos intermitentes, a cada dois dias, durante dois meses. As amostras radiculares foram preparadas e analisadas em microscopiaóptica. Em relação ao grupo controle e aos ciclos anteriores de seleção, a BRS 4154 teve aumento na formação de aerênquima, diminuição do córtex, diminuição do diâmetro dos vasos, diminuição da camada subepidérmica, aumento na espessura do floema e epiderme. Os sucessivos ciclos de seleção melhoraram as características do milho 'Saracura' e sua tolerância a ambientes alagados.

Ciclos de seleção de progênies de meios-irmãos do milho BR 5011 Sertanejo

O objetivo deste trabalho foi obter estimativas de parâmetros genéticos da variedade BR 5011 Sertanejo, a fim de se avaliar o comportamento da variabilidade genética, no decorrer de sucessivos ciclos de seleção. Dezessete ciclos de seleção, entre e dentro de progênies de meios-irmãos, e três ciclos de seleção massal estratificada foram praticados nessa variedade de milho, no período de 1985 a 2005. Nos três primeiros ciclos de seleção, entre e dentro de progênies de meios-irmãos, as progênies foram avaliadas em látice 10x10, e entre os ciclos 4 e 17, as avaliações foram realizadas em látice 14x14. Os ensaios foram realizados nos municípios de Gararu, Propriá, Poço Verde, Neópolis, Lagarto e Nossa Senhora das Dores, no Estado de Sergipe, e em Cruz das Almas na Bahia. As parcelas constaram de fileiras de 5 m, espaçadas de 0,8 m, com 0,4 m entre covas dentro das fileiras. As recombinações das progênies superiores foram realizadas dentro do mesmo ano agrícola, de modo a se obter um ciclo por ano. A variedade BR 5011 Sertanejo apresentou alto potencial produtivo, associado a uma ampla base genética. A magnitude da interação progênies x locais evidenciou a importância de se avaliar a produtividade em mais de um local para melhorar a eficiência do processo seletivo e para se obterem estimativas mais consistentes dos componentes da variância.

Selection of v-Abl Tyrosine Kinase Substrate Sequences from Randomized Peptide and Cellular Proteomic Libraries Using mRNA Display

Methodologies for rapidly identifying cellular protein interactions resulting in posttranslational modification of one of the partners are lacking. Here, we select for substrates of the v-abl tyrosine kinase from two protein display libraries in which the protein is covalently linked to its encoding mRNA. Successive selection cycles from a randomized peptide library identified a consensus sequence closely matching that previously reported for the v-abl tyrosine kinase. Selections from a proteomic library derived from cellular mRNA identified several novel targets of v-abl, including a new member of a class of SH2 domain-containing adaptor proteins. Upon modification, several of the substrates obtained in these selections were found to be effective inhibitors of v-abl kinase activity in vitro. These experiments establish a novel method for identifying the substrates of tyrosine kinases from synthetic and cellular protein libraries.

Protein Selection Using mRNA Display

mRNA display is an in vitro technique that may be used to search natural or synthetic DNA libraries for the functional proteins and peptides they encode. mRNA-displayed proteins are constructs in which a protein is covalently attached to the RNA that encodes it. This direct covalent association of phenotype (protein) and genotype (RNA) renders the protein directly amplifiable. This in turn allows successive cycles of selection, enrichment, and, optionally, mutagenesis, to be performed upon libraries of displayed proteins. At the end of this process, functional sequences will dominate the library; cloning and sequencing will reveal the identity of the selected functional proteins. mRNA display allows new functional proteins to be discovered without resorting to protein design. This unit describes generation of mRNA-displayed proteins by the in vitro translation of mRNA display templates which are mRNA molecules 3'-terminated in puromycin. Puromycin is a translation inhibitor that is able to enter the ribosome during translation and form a stable covalent bond with the nascent protein. This allows a stable covalent linkage to be formed between the mRNA display template and the protein it encodes, resulting in an mRNA-displayed protein.