Recurrent Selection Research Articles

Gene pyramiding for achieving enhanced disease and insect multiple resistance in Coffea arabica

AbstractDeveloping a new coffee cultivar can take up to 25 years using traditional approaches. The implementation of molecular tools into the coffee breeding pipeline can speed up the development of high‐yielding varieties with multiple resistance to pests and diseases. This study aimed to verify the presence of gene pyramiding for resistance to coffee berry disease (CBD) and coffee leaf rust and access the breeding potential of a breeding population of coffee (Coffea arabica L.) that presents partial phenotypic resistance to coffee leaf miner. A progeny of 128 individuals was evaluated in 2019 during the coffee maturation stage for 11 agronomic traits. The individuals were genotyped for four loci related to rust and CBD resistance. Gene pyramiding was verified based on the presence of markers linked with the resistance alleles. Genetic parameters were estimated, and a selection index was used to rank the individuals based on the phenotypic evaluation. Gene pyramiding for rust and CBD was detected in ∼82% of the individuals. Moreover, the phenotypic evaluation of rust indicated high levels of resistance, confirmed by the presence of the resistance alleles. Ninety‐five percent of the 38 top‐ranked individuals presented resistance alleles and could be used in an interpopulation recurrent selection scheme with marker‐assisted selection. The studied coffee population has the potential to be used in coffee breeding programs since it presents vigorous individuals with low levels of coffee leaf miner incidence (CLMI) and gene pyramiding for CBD and rust resistance, the main pest and diseases of this crop.

Differential gene expression of salt-tolerant alfalfa in response to salinity and inoculation by Ensifer meliloti

BackgroundAlfalfa (Medicago sativa L.) experiences many negative effects under salinity stress, which may be mediated by recurrent selection. Salt-tolerant alfalfa may display unique adaptations in association with rhizobium under salt stress.ResultsTo elucidate inoculation effects on salt-tolerant alfalfa under salt stress, this study leveraged a salt-tolerant alfalfa population selected through two cycles of recurrent selection under high salt stress. After experiencing 120-day salt stress, mRNA was extracted from 8 random genotypes either grown in 0 or 8 dS/m salt stress with or without inoculation by Ensifer meliloti. Results showed 320 and 176 differentially expressed genes (DEGs) modulated in response to salinity stress or inoculation x salinity stress, respectively. Notable results in plants under 8 dS/m stress included upregulation of a key gene involved in the Target of Rapamycin (TOR) signaling pathway with a concomitant decrease in expression of the SNrK pathway. Inoculation of salt-stressed plants stimulated increased transcription of a sulfate-uptake gene as well as upregulation of the Lysine-27-trimethyltransferase (EZH2), Histone 3 (H3), and argonaute (AGO, a component of miRISC silencing complexes) genes related to epigenetic and post-transcriptional gene control.ConclusionsSalt-tolerant alfalfa may benefit from improved activity of TOR and decreased activity of SNrK1 in salt stress, while inoculation by rhizobiumstimulates production of sulfate uptake- and other unique genes.

Unlocking the secrets of intraspecific hybrids (Vitis vinifera L.) cold hardiness: A comprehensive study of genetic factors and trait correlations

Challenges arise in global viticulture due to low temperatures. To ensure the sustainable and high-quality development of the wine industry, it is essential to breed wine grape varieties that are not only of high quality but also possess cold hardiness. Intraspecific recurrent selection in Vitis vinifera can enhance cold hardiness while maintaining fruit quality. In this study, we used ‘Ecolly ’as an intermediary grape variety for crossing with ‘Cabernet Sauvignon’, ‘Marselan’, and ‘Dunkelfelder’, including three reciprocal crosses and a total of 1,657 intraspecific hybrids. We characterized the cold hardiness of these intraspecific hybrids and analyzed the genetic aspects of cold hardiness, ultimately identifying excellent strains with cold hardiness. Parameters like mean high-temperature exotherm (mHTE), mean low-temperature exotherm (mLTE), bound/free water ratio, water loss ratio in vitro, frost damage grades, and overall performance displayed partially normal distributions. In intraspecific hybrids, there was a maternal advantage in traits related to bound/free water ratio and water loss ratio. Some hybrid populations exhibited values for mHTE, mLTE, and water loss ratio that were lower than the low parent's values, while bound/free water ratio showed values higher than the high parent's values. Among the 1,657 intraspecific hybrids, 52 strains could bud under stress at −18 °C, and seven of these strains excelled in three important cold hardiness measures. Our study revealed that cold hardiness in V. vinifera is influenced by multiple genes and is a quantitative trait. Intraspecific hybridization can produce a small number of superior strains with enhanced cold hardiness.

Implementation of rapid cycle recurrent genomic selection for forage yield in perennial ryegrass

Implementation of rapid cycle recurrent genomic selection for forage yield in perennial ryegrass

Recurrent selection in Passiflora: a new approach for the development of cowpea aphid-borne mosaic virus resistant cultivars with desired agronomic traits

Recurrent selection in Passiflora: a new approach for the development of cowpea aphid-borne mosaic virus resistant cultivars with desired agronomic traits

Genetic Gain and Inbreeding in Different Simulated Genomic Selection Schemes for Grain Yield and Oil Content in Safflower.

Safflower (Carthamus tinctorius L.) is a multipurpose minor crop consumed by developed and developing nations around the world with limited research funding and genetic resources. Genomic selection (GS) is an effective modern breeding tool that can help to fast-track the genetic diversity preserved in genebank collections to facilitate rapid and efficient germplasm improvement and variety development. In the present study, we simulated four GS strategies to compare genetic gains and inbreeding during breeding cycles in a safflower recurrent selection breeding program targeting grain yield (GY) and seed oil content (OL). We observed positive genetic gains over cycles in all four GS strategies, where the first cycle delivered the largest genetic gain. Single-trait GS strategies had the greatest gain for the target trait but had very limited genetic improvement for the other trait. Simultaneous selection for GY and OL via indices indicated higher gains for both traits than crossing between the two single-trait independent culling strategies. The multi-trait GS strategy with mating relationship control (GS_GY + OL + Rel) resulted in a lower inbreeding coefficeint but a similar gain compared to that of the GS_GY + OL (without inbreeding control) strategy after a few cycles. Our findings lay the foundation for future safflower GS breeding.

Comparing two recurrent selection methods for developing superior apomictic hybrids in Paspalum notatum

AbstractRecurrent selection methods have been successful in generating superior Paspalum notatum families through the accumulation of favorable alleles. However, the effectiveness of these methods in producing apomictic hybrids with superior agronomic traits has not been thoroughly evaluated. The aim of this study was to characterize the reproductive behavior of P. notatum progenies obtained through recurrent selection based on combining ability (RSCA) and recurrent phenotypic selection (RPS) and assess the performance of the apomictic hybrids concerning various agronomic traits. The reproductive mode of 144 RSCA and 144 RPS hybrids was determined using a molecular marker tightly linked to the apospory trait (BCU243‐377). The expressivity of apospory was estimated observing mature embryo sacs. The apomictic hybrids were then evaluated for six agronomic traits. A segregation ratio of 5:1 between sexual and apomictic hybrids was observed for the RSCA progeny, while 4.3:1 was registered for the RPS progeny. Although apospory expressivity was variable among hybrids, 75% and 86% of the RSCA and RPS hybrids, respectively, exhibited a high expression (>81%). Non‐significant differences between breeding methods in the number of apomictic hybrids and the level of apospory expressivity were observed. Variations for all agronomic traits were observed among apomictic hybrids within each breeding method. However, no differences between methods in the performance of the highly apomictic hybrids were observed. This demonstrates that the reproductive behavior of P. notatum is not affected by the recurrent selection method. Therefore, the RPS method would be the most suitable since it was equally effective than RSCA but it is cheaper, faster, and easier to apply.

Inheritance and Response to Selection for Seed Weight Using the Large Seeded Landrace Oman 2 of Lucerne

Seed weight in lucerne (Medicago sativa) may affect subsequent seedling vigour and stand establishment. A landrace of lucerne (Oman 2) from Oman has a 100-seed weight over 60% larger than the largest seeded parent used in previous studies. Crosses were made between Oman 2 and the smaller-seeded cultivar Titan 9, and segregating families were produced for genetic analysis and measurement of response to selection for seed size. There were significant differences in 100-seed weights between the parents (Oman 2 and Titan 9) and subsequent families. Regression of 100-seed weights of F2 families versus F1 parents was highly significant (p < 0.001), as well as 100-seed weights of the F3 families versus F1 parents. Analysis of diallel crossing among large and small-seeded F1 plants revealed highly significant general (GCAs) and specific (SCAs) combining abilities, as well as highly significant reciprocals. The GCA effect was much greater than the SCA effect with a GCA/SCA ratio of 15.9. This large ratio agrees with the significant regression coefficients and indicates that 100-seed weight in lucerne has high heritability. The significance of reciprocals was due to a large maternal effect in which large-seeded maternal parents produced progenies with significantly larger seeds relative to small-seeded parents. These results indicate that large-seeded plants should be used as the maternal parents in crosses and for recurrent selection to increase the seed size of progenies.

Evolutionary computing to assemble standing genetic diversity and achieve long-term genetic gain.

Loss of genetic diversity in elite crop breeding pools can severely limit long-term genetic gains and limit ability to make gains in new traits, like heat tolerance, that are becoming important as the climate changes. Here, we investigate and propose potential breeding program applications of optimal haplotype stacking (OHS), a selection method that retains useful diversity in the population. OHS selects sets of candidates containing, between them, haplotype segments with very high segment breeding values for the target trait. We compared the performance of OHS, a similar method called optimal population value (OPV), truncation selection on genomic estimated breeding values (GEBVs), and optimal contribution selection (OCS) in stochastic simulations of recurrent selection on founder wheat genotypes. After 100 generations of intercrossing and selection, OCS and truncation selection had exhausted the genetic diversity, while considerable diversity remained in the OHS population. Gain under OHS in these simulations ultimately exceeded that from truncation selection or OCS. OHS achieved faster gains when the population size was small, with many progeny per cross. A promising hybrid strategy, involving a single cycle of OHS in the first generation followed by recurrent truncation selection, substantially improved long-term gain compared with truncation selection and performed similarly to OCS. The results of this study provide initial insights into where OHS could be incorporated into breeding programs.

Pigmented radish (Raphanus sativus): Genetic variability, heritability and interrelationships of total phenolics, anthocyanins and antioxidant activity

Radish (Raphanus sativus L.) is an important salad vegetable grown and consumed throughout the world for fleshy roots which has numerous categories– varying in root colour, size, shape and flavour. The uses of coloured radishes in the salads and their anthocyanins as colourants are gaining popularity because of the colour characteristics, health benefits as well as antioxidant activities. However, information on the genetic variability, heritability and inter-relationship of total phenolics, anthocyanins and antioxidant activities in pigmented radish is very limited, but pre-requisite to initiate breeding programme; and therefore investigated in the present study. Radish genotypes were significantly diverse for all the antioxidants; differed by 4.98-fold for total phenolics, 36.16-fold for anthocyanins content, 4.96-fold for FRAP activity and 4.03-fold for CUPRAC activity; and the genotypes accounted for >97% of total variations. The meager differences between phenotypic and genotypic coefficient of variation reveals the greater role of genotypes and lesser influence of the environment on the biosynthesis and accumulation of antioxidants. Significantly positive correlations along with higher magnitude for anthocyanins content, total phenolics, FRAP activity and CUPRAC activity (r= 0.823 to 0.964) could be used as indirect selection criteria for improving levels of antioxidant compounds. The estimates of heritability and genetic advance indicate the role of additive and non-additive genes for biosynthesis of antioxidants and root development, respectively; therefore, recurrent selection would be the best breeding approach to improve both the traits simultaneously in coloured radish.

Drivers of genomic differentiation landscapes in populations of disparate ecological and geographical settings within mainland Apis cerana.

Elucidating the evolutionary processes that drive population divergence can enhance our understanding of the early stages of speciation and inform conservation management decisions. The honeybee Apis cerana displays extensive population divergence, providing an informative natural system for exploring these processes. The mainland lineage A. cerana includes several peripheral subspecies with disparate ecological and geographical settings radiated from a central ancestor. Under this evolutionary framework, we can explore the patterns of genome differentiation and the evolutionary models that explain them. We can also elucidate the contribution of non-genomic spatiotemporal mechanisms (extrinsic features) and genomic mechanisms (intrinsic features) that influence these genomic differentiation landscapes. Based on 293 whole genomes, a small part of the genome is highly differentiated between central-peripheral subspecies pairs, while low and partial parallelism partly reflects idiosyncratic responses to environmental differences. Combined elements of recurrent selection and speciation-with-gene-flow models generate the heterogeneous genome landscapes. These elements weight differently between central-island and other central-peripheral subspecies pairs, influenced by glacial cycles superimposed on different geomorphologies. Although local recombination rates exert a significant influence on patterns of genomic differentiation, it is unlikely that low-recombination rates regions were generated by structural variation. In conclusion, complex factors including geographical isolation, divergent ecological selection and non-uniform genome features have acted concertedly in the evolution of reproductive barriers that could reduce gene flow in part of the genome and facilitate the persistence of distinct populations within mainland lineage of A. cerana.

Harnessing monocrop breeding strategies for intercrops.

Intercropping is considered advantageous for many reasons, including increased yield stability, nutritional value and the provision of various regulating ecosystem services. However, intercropping also introduces diverse competition effects between the mixing partners, which can negatively impact their agronomic performance. Therefore, selecting complementary intercropping partners is the key to realizing a well-mixed crop production. Several specialized intercrop breeding concepts have been proposed to support the development of complementary varieties, but their practical implementation still needs to be improved. To lower this adoption threshold, we explore the potential of introducing minor adaptations to commonly used monocrop breeding strategies as an initial stepping stone towards implementing dedicated intercrop breeding schemes. While we acknowledge that recurrent selection for reciprocal mixing abilities is likely a more effective breeding paradigm to obtain genetic progress for intercrops, a well-considered adaptation of monoculture breeding strategies is far less intrusive concerning the design of the breeding programme and allows for balancing genetic gain for both monocrop and intercrop performance. The main idea is to develop compatible variety combinations by improving the monocrop performance in the two breeding pools in parallel and testing for intercrop performance in the later stages of selection. We show that the optimal stage for switching from monocrop to intercrop testing should be adapted to the specificity of the crop and the heritability of the traits involved. However, the genetic correlation between the monocrop and intercrop trait performance is the primary driver of the intercrop breeding scheme optimization process.

Introgression of early shoot vigour in wheat modifies root systems, increases competitiveness and provides options for integrated weed management

Abstract Background and aims Weeds are a major biotic stressor impacting crop production. Improving the competitiveness of wheat (Triticum aestivum L.) could provide a useful tool in integrated weed management. While wheat typically exhibits conservative early growth, early vigour has been increased through long-term recurrent selection for greater early biomass and leaf area. However, the influence of integrating such vigour into breeding lines for improving competitive ability remains to be explored. Methods In replicated controlled environment experiments, the effect of breeding early shoot vigour on root development and below-ground competitiveness was carefully examined. Physical and chemical characteristics of wheat vigour lines were assessed and compared with commercial cultivars in hydroponics and field soil experiments. Measurements included early root growth, rhizosheath size and growth responses in the presence of annual ryegrass, a major weed in wheat production. Results The vigorous lines exhibited larger leaf widths, increased cell file number, increased total root length and larger rhizosheaths compared with commercial parents. Numerous secondary metabolites with known allelopathic effects on weeds were detected in the roots and the rhizosphere, and significant allelochemical level differences observed between distilled water and soil water extract-treated plants. Although the vigour lines were significantly more competitive than the commercial cultivars against ryegrass, they produced similar levels of phytotoxic secondary metabolites. Conclusion Competition below-ground was strongly suppressive of ryegrass for the more vigorous genotypes suggesting that breeding with shoot vigour had pleiotropic effects on key root traits for below-ground wheat competitiveness.

Breeding Strategies for Simultaneous Improvement in Anthracnose Disease Resistance and Economically Important Traits in French Bean

Background: French bean (Phaseolus vulgaris L.) production in the tropics is threatened by heavy incidence of anthracnose disease causing substantial crop loss when infection is at the early growth stages. Breeding strategies for tolerance against anthracnose disease along with enhanced productivity, and high pod protein content are to be formulated. Methods: Genotypes having broad genetic base and phenotypic diversity in 5 bush and 1 pole types were crossed in a 6 × 6 half diallel mating design to estimate combining ability, mode of gene action, and extent of heterosis for 11 quantitative traits. Result: The additive genetic effect was evident for percent disease index (PDI) of anthracnose and 10 pod weight. Rapid genetic gain can be achieved due to predominance of additive gene action in their control and can therefore be selected in early generation through simple breeding methods. Rest of the economic traits controlled by additive and non-additive gene effects could be improved through biparental mating, reciprocal recurrent selection, or diallel selective mating. Anthracnose disease tolerant and high yielding cultivars of might be developed utilizing parents, ‘Laxmi’, ‘Arka Sharath’ and ‘Vaishnavi-264’ with high gca effects. Although two cross combinations ‘Arka Sharath × Lakshmi’ and ‘Arjun × Arka Sharath’ showed significant heterobeltiosis in desired direction for PDI of anthracnose and other desirable horticultural traits but could not be exploited at commercial level due to complexity in hybridization. Identifying pure lines with tolerance against anthracnose disease and favorable horticultural attributes could be accomplished in segregating generations of the prospective hybrids.

Genetic dissection of green pod yield in dolichos bean, an orphan vegetable legume, using new molecular markers.

In the era of genomic-assisted breeding for crop improvement, developing new molecular markers and validating them for use in breeding programs are the prelude. Dolichos bean is one of the most important vegetable legume crops owing to its nutrient-rich green pods used as vegetables. Limitations in genomic resources, including molecular markers, restrict the accelerated improvement of the crop. In the present investigation, a set of 430 new simple sequence repeat markers was developed from sequence information of a reference variety. These markers included di- and tri-nucleotide repeats. The markers were assayed on an association panel, which was evaluated for green pod yield over 5years. A multi-locus model, FarmCPU, was used to assess the marker-trait association analysis. A total of 106 marker-trait associations were identified using an efficient mixed-model approach. Tri-nucleotide repeats were more informative and predominantly associated with trait. Among these markers, 17 were associated with a high level of significance. Markers LP-D-68 and LP-D-14 were identified with a high level of significance in 5-year pooled data and explained 12.70% and 12% of the phenotypic variance, respectively. These markers associated with a high level of confidence have significant scope for use in marker-assisted selection programmes. Other associated markers may be utilized for improving parents through marker-assisted recurrent selection or genomic selection programs.

Genetic Improvement of Some Quality Characteristics of Cabbage (Brassica Oleracea var. Capitata) through Simple Recurrent Selection.

Genetic Improvement of Some Quality Characteristics of Cabbage (Brassica Oleracea var. Capitata) through Simple Recurrent Selection.

Origin of current intermediate wheatgrass germplasm being developed for Kernza grain production

AbstractIntermediate wheatgrass (IWG, Thinopyrum intermedium [Host] Barkworth & D. R. Dewey) has been developed as a perennial grain crop for human consumption along with providing environmental benefits and ecosystem services. Grain and products derived from IWG cultivars improved for food production have been marketed under the registered trademark, Kernza. Development of IWG as a perennial grain crop began in 1980s with a phenotypic recurrent selection program as the Rodale Institute (RI) and the Big Flats Plant Material Center (BFPMC) used IWG plant introductions (PI) from the National Plant Germplasm System (NPGS) to improve populations of IWG. Initial selections were provided to The Land Institute (TLI) where they were subsequently improved for grain production, yet the identity of the founder material of improved, food-grade IWG has not been publicly documented. Recently recovered original documents have been used to reconstruct the early breeding program to identify the most likely 20 PIs that form the founders of modern food-grade IWG. Molecular data using genotyping-by-sequencing in current elite breeding material, and remnant seed and plant material from the initial RI selections have provided supporting evidence for the historical records. The genetic origin for food-grade IWG is focused between the Black Sea and Caspian Sea in the Stavropol region of Russia, with smaller contributions likely from collections as distant as Kazakhstan in the east to Turkey in the west. This work connects the flow of germplasm and utility of NPGS PIs to present day IWG grain cultivars being developed in multiple breeding programs around the world.

Combining Ability of Female Channel Catfish, Ictalurus punctatus, and Male Blue Catfish, I. furcatus, for Early Growth Performance of Their Progeny

The hybrid between the female channel catfish (Ictalurus punctatus) and the male blue catfish (I. furcatus) is the best genetic type currently available for commercial catfish farming due to their superior traits. However, further genetic improvements can be achieved by selecting parents with increased combining abilities. Twenty female channel catfish and twelve male blue catfish were crossed in a partial factorial mating design, resulting in forty hybrid families. These families were evaluated for early growth in three different rearing systems, including ponds and aquaria. The early growth performance of hybrid catfish was significantly (p < 0.05) affected by the additive gene action of the female parent and the male parent. There were genotype–environment or genotype–age interactions affecting the combining abilities, both the amount and the type of genetic variation. Dam GCA was significant in all environments/ages; however, sire GCA was variable, and SCA was not significant. These findings suggest that reciprocal recurrent selection for growth could potentially improve the performance of F1 hybrid catfish.

Biometrics and screening of kale (Brassica oleracea var. acephala) half-sib progenies obtained by recurrent selection in Brazil

Biometrics and screening of kale (Brassica oleracea var. acephala) half-sib progenies obtained by recurrent selection in Brazil

The Role of Pelvic Exenteration in Cervical Cancer: A Review of the Literature.

Pelvic exenteration represents a radical procedure aimed at achieving complete tumor resection with negative margins. Although it is the only therapeutic option for some cases of advanced tumors, it is associated with several perioperative complications. We believe that careful patient selection is related to better oncologic outcomes and lower complication rates. The objectives of this review are to identify the most current indications for this intervention, suggest criteria for case selection, evaluate recommendations for perioperative care, and review oncologic outcomes and potential associated complications. To this end, an analysis of English language articles in PubMed was performed, searching for topics such as the indication for pelvic exenteration for recurrent gynecologic neoplasms selection of oncologic cases, the impact of tumor size and extent on oncologic outcomes, preoperative and postoperative surgical management, surgical complications, and outcomes of overall survival and recurrence-free survival.