Recurrent Selection Research Articles

Combining ability and heterotic grouping of turcicum‐resistant early‐maturing maize inbreds

AbstractMaize (Zea mays L.), an important source of calories and nutrients in sub‐Saharan Africa, is threatened by northern corn leaf blight (NCLB) caused by Exserohilum turcicum. This study examined combining ability and heterotic patterns of early‐maturing maize inbreds, gene action conditioning NCLB resistance, and performance of derived hybrids across environments and identified testers. Fifteen each of white and yellow inbreds were intercrossed using North Carolina Design II to obtain 75 hybrids per endosperm color. Hybrids plus six checks were inoculated with a virulent isolate of E. turcicum 4 wk after planting in six inoculated and three non‐inoculated environments in Nigeria in 2018 and 2019. Inbreds were assigned to heterotic groups using general combining ability (GCA) of multiple traits method. Specific combining ability (SCA), GCA, and genotype × environment (G × E) interactions were significant for grain yield (GYLD), disease severity, and other traits. Northern corn leaf blight caused 46% GYLD reduction. The effects of GCA were preponderant over SCA for GYLD and NCLB severity across environments, indicating that hybridization and recurrent selection would enhance genetic gains and hybrid performance. White and yellow inbreds were placed in two and three heterotic groups, respectively. High‐yielding NCLB‐resistant testers identified could be used to classify other inbreds yet to be field‐tested into heterotic groups. Genotypes TZEI 32 × TZEI 5 and TZEI 124 × TZEI 134 were identified as single‐cross testers. Genotypes TZEI 32 × TZEI 5 and TZEI 5 × TZEI 75 (white) and TZEI 124 × TZEI 134 and TZEI 124 × TZEI 11 (yellow) were identified for on‐farm testing and possible commercialization.

Genomic Prediction of Yield Traits in Single-Cross Hybrid Rice (Oryza sativa L.).

Hybrid rice varieties can outyield the best inbred varieties by 15 – 30% with appropriate management. However, hybrid rice requires more inputs and management than inbred rice to realize a yield advantage in high-yielding environments. The development of stress-tolerant hybrid rice with lowered input requirements could increase hybrid rice yield relative to production costs. We used genomic prediction to evaluate the combining abilities of 564 stress-tolerant lines used to develop Green Super Rice with 13 male sterile lines of the International Rice Research Institute for yield-related traits. We also evaluated the performance of their F1 hybrids. We identified male sterile lines with good combining ability as well as F1 hybrids with potential further use in product development. For yield per plant, accuracies of genomic predictions of hybrid genetic values ranged from 0.490 to 0.822 in cross-validation if neither parent or up to both parents were included in the training set, and both general and specific combining abilities were modeled. The accuracy of phenotypic selection for hybrid yield per plant was 0.682. The accuracy of genomic predictions of male GCA for yield per plant was 0.241, while the accuracy of phenotypic selection was 0.562. At the observed accuracies, genomic prediction of hybrid genetic value could allow improved identification of high-performing single crosses. In a reciprocal recurrent genomic selection program with an accelerated breeding cycle, observed male GCA genomic prediction accuracies would lead to similar rates of genetic gain as phenotypic selection. It is likely that prediction accuracies of male GCA could be improved further by targeted expansion of the training set. Additionally, we tested the correlation of parental genetic distance with mid-parent heterosis in the phenotyped hybrids. We found the average mid-parent heterosis for yield per plant to be consistent with existing literature values at 32.0%. In the overall population of study, parental genetic distance was significantly negatively correlated with mid-parent heterosis for yield per plant (r = −0.131) and potential yield (r = −0.092), but within female families the correlations were non-significant and near zero. As such, positive parental genetic distance was not reliably associated with positive mid-parent heterosis.

Evaluation of Septoria Nodorum Blotch (SNB) Resistance in Glumes of Wheat (Triticum aestivum L.) and the Genetic Relationship With Foliar Disease Response.

Septoria nodorum blotch (SNB) is a necrotrophic disease of wheat prominent in some parts of the world, including Western Australia (WA) causing significant losses in grain yield. The genetic mechanisms for resistance are complex involving multiple quantitative trait loci. In order to decipher comparable or independent regulation, this study identified the genetic control for glume compared to foliar resistance across four environments in WA against 37 different isolates. High proportion of the phenotypic variation across environments was contributed by genotype (84.0% for glume response and 82.7% for foliar response) with genotype-by-environment interactions accounting for a proportion of the variation for both glume and foliar response (14.7 and 16.2%, respectively). Despite high phenotypic correlation across environments, most of the eight and 14 QTL detected for glume and foliar resistance using genome wide association analysis (GWAS), respectively, were identified as environment-specific. QTL for glume and foliar resistance neither co-located nor were in LD in any particular environment indicating autonomous genetic mechanisms control SNB response in adult plants, regulated by independent biological mechanisms and influenced by significant genotype-by- environment interactions. Known Snn and Tsn loci and QTL were compared with 22 environment-specific QTL. None of the eight QTL for glume or the 14 for foliar response were co-located or in linkage disequilibrium with Snn and only one foliar QTL was in LD with Tsn loci on the physical map. Therefore, glume and foliar response to SNB in wheat is regulated by multiple environment-specific loci which function independently, with limited influence of known NE-Snn interactions for disease progression in Western Australian environments. Breeding for stable resistance would consequently rely on recurrent phenotypic selection to capture and retain favorable alleles for both glume and foliar resistance relevant to a particular environment.

Improving Fusarium Basal Rot Resistance of Onion Cultivars through Artificial Inoculation and Selection of Mature Bulbs

Fusarium basal rot (FBR) of onion, caused by the soil-borne fungus Fusarium oxysporum f.sp. cepae (FOC), results in a substantial storage loss of marketable bulbs. Seedling and field screening methods, which were used to generate FBR resistant long-day and intermediate-day onion cultivars, were found to be ineffective at increasing FBR resistance in short-day onion cultivars. This study attempted to improve the FBR resistance of seven commercial short-day onion cultivars and two check cultivars when evaluated at their mature bulb stage. Mature bulbs were artificially inoculated with 1 cm diameter potato dextrose agar plugs containing conidia of a virulent FOC isolate, CSC-515, at a concentration of 3 × 104 spore mL−1, after transversely cutting the basal plate tissue. Incubated bulbs, which had few or no FBR symptoms, were selected after 20 d using visual scoring, from 1 (no disease) to 9 (>70% basal plate is infected), and combined in seed production cages to produce the selected generation of a cultivar. Multiple cycles of phenotypic recurrent selection were conducted, and the resultant populations were compared with their respective original populations for FBR severity and incidence, from 2016 to 2019, using the same conidial inoculation method. A variable amount of progress was achieved in reducing FBR severity and incidence in the seven cultivars, with maximum improvement in the most advanced selected populations. FBR development in the advanced selected populations differed between mature bulbs of each entry and was influenced by yearly environmental variation. The progress of FOC infections was slower in resistant bulbs when compared to susceptible bulbs. These results indicated a partial or quantitative resistance against FBR. The partial FBR resistant cultivar populations could be used to develop synthetic short-day FBR resistant cultivars after multi-locational and multi-seasonal field trials. These populations could also be used to study the mechanism(s) of FBR resistance in onion, which has yet to be determined.

Recurrent Selection with Sub-Lethal Doses of Mesotrione Reduces Sensitivity in Amaranthus palmeri.

Amaranthus palmeri, ranked as the most prolific and troublesome weed in North America, has evolved resistance to several herbicide sites of action. Repeated use of any one herbicide, especially at lower than recommended doses, can lead to evolution of weed resistance, and, therefore, a better understanding of the process of resistance evolution is essential for the management of A. palmeri and other difficult-to-control weed species. Amaranthus palmeri rapidly developed resistance to 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitors such as mesotrione. The objective of this study was to test the potential for low-dose applications of mesotrione to select for reduced susceptibility over multiple generations in an A. palmeri population collected from an agricultural field in 2001. F0 plants from the population were initially treated with sub-lethal mesotrione rates and evaluated for survival three weeks after treatment. All F0 plants were controlled at the 1× rate (x = 105 g ai ha−1). However, 2.5% of the F0 plants survived the 0.5× treatment. The recurrent selection process using plants surviving various mesotrione rates was continued until the F4 generation was reached. Based on the GR50 values, the sensitivity index was determined to be 1.7 for the F4 generation. Compared to F0, HPPD gene expression level in the F3 population increased. Results indicate that after several rounds of recurrent selection, the successive generations of A. palmeri became less responsive to mesotrione, which may explain the reduced sensitivity of this weed to HPPD-inhibiting herbicides. The results have significance in light of the recently released soybean and soon to be released cotton varieties with resistance to HPPD inhibitors.

Effects of artificial inoculation on trait correlations with resistance to Fusarium ear rot and fumonisin contamination in maize

AbstractBreeding for resistance to Fusarium ear rot (FER; Fusarium verticillioides Nirenberg) and fumonisin (FUM) contamination in maize (Zea mays L.) is labor intensive, time consuming, and expensive. The objective of this study is to explore three possible shortcuts to improve the efficiency of breeding for resistance to FER and FUM: relying on natural instead of artificial inoculation of Fusarium verticillioides, selecting inbred lines per se instead of topcross hybrids, and using grain test weight (TW) as an indirect selection criterion. We selected the 27 most resistant and 26 most susceptible S0:1 lines from the third cycle of a broad‐based recurrent selection population and topcrossed them to a common inbred line. The resulting topcross hybrids were evaluated in three North Carolina environments under artificial and natural inoculation of F. verticillioides. The entry‐mean heritabilities for FER and FUM are considerably reduced under natural conditions compared to artificial inoculation; therefore, artificial inoculation should be practiced for efficient selection for resistance. We found a high correlation between FER and FUM content of S0:1 lines per se and their topcross hybrids, suggesting that selection among early generation inbred lines per se is an efficient method to improve resistance in their topcross hybrids. The TW of inoculated S0:1 lines per se was strongly and negatively correlated with FER and FUM of their topcross hybrids, suggesting that TW can be utilized as an indirect selection criterion to improve resistance to FER and FUM contamination.

Hearing Sensitivity of Primates: Recurrent and Episodic Positive Selection in Hair Cells and Stereocilia Protein-Coding Genes.

The large spectrum of hearing sensitivity observed in primates results from the impact of environmental and behavioral pressures to optimize sound perception and localization. Although evidence of positive selection in auditory genes has been detected in mammals including in Hominoids, selection has never been investigated in other primates. We analyzed 123 genes highly expressed in the inner ear of 27 primate species and tested to what extent positive selection may have shaped these genes in the order Primates tree. We combined both site and branch-site tests to obtain a comprehensive picture of the positively selected genes (PSGs) involved in hearing sensitivity, and drew a detailed description of the most affected branches in the tree. We chose a conservative approach, and thus focused on confounding factors potentially affecting PSG signals (alignment, GC-biased gene conversion, duplications, heterogeneous sequencing qualities). Using site tests, we showed that around 12% of these genes are PSGs, an α selection value consistent with average human genome estimates (10–15%). Using branch-site tests, we showed that the primate tree is heterogeneously affected by positive selection, with the black snub-nosed monkey, the bushbaby, and the orangutan, being the most impacted branches. A large proportion of these genes is inclined to shape hair cells and stereocilia, which are involved in the mechanotransduction process, known to influence frequency perception. Adaptive selection, and more specifically recurrent adaptive evolution, could have acted in parallel on a set of genes (ADGRV1, USH2A, PCDH15, PTPRQ, and ATP8A2) involved in stereocilia growth and the whole complex of bundle links connecting them, in species across different habitats, including high altitude and nocturnal environments.

Genomic Selection in an Outcrossing Autotetraploid Fruit Crop: Lessons From Blueberry Breeding.

Blueberry (Vaccinium corymbosum and hybrids) is a specialty crop with expanding production and consumption worldwide. The blueberry breeding program at the University of Florida (UF) has greatly contributed to expanding production areas by developing low-chilling cultivars better adapted to subtropical and Mediterranean climates of the globe. The breeding program has historically focused on recurrent phenotypic selection. As an autopolyploid, outcrossing, perennial, long juvenile phase crop, blueberry breeding cycles are costly and time consuming, which results in low genetic gains per unit of time. Motivated by applying molecular markers for a more accurate selection in the early stages of breeding, we performed pioneering genomic selection studies and optimization for its implementation in the blueberry breeding program. We have also addressed some complexities of sequence-based genotyping and model parametrization for an autopolyploid crop, providing empirical contributions that can be extended to other polyploid species. We herein revisited some of our previous genomic selection studies and showed for the first time its application in an independent validation set. In this paper, our contribution is three-fold: (i) summarize previous results on the relevance of model parametrizations, such as diploid or polyploid methods, and inclusion of dominance effects; (ii) assess the importance of sequence depth of coverage and genotype dosage calling steps; (iii) demonstrate the real impact of genomic selection on leveraging breeding decisions by using an independent validation set. Altogether, we propose a strategy for using genomic selection in blueberry, with the potential to be applied to other polyploid species of a similar background.

Revisiting the notion of deleterious sweeps.

It has previously been shown that, conditional on its fixation, the time to fixation of a semi-dominant deleterious autosomal mutation in a randomly mating population is the same as that of an advantageous mutation. This result implies that deleterious mutations could generate selective sweep-like effects. Although their fixation probabilities greatly differ, the much larger input of deleterious relative to beneficial mutations suggests that this phenomenon could be important. We here examine how the fixation of mildly deleterious mutations affects levels and patterns of polymorphism at linked sites-both in the presence and absence of interference amongst deleterious mutations-and how this class of sites may contribute to divergence between-populations and species. We find that, while deleterious fixations are unlikely to represent a significant proportion of outliers in polymorphism-based genomic scans within populations, minor shifts in the frequencies of deleterious mutations can influence the proportions of private variants and the value of FST after a recent population split. As sites subject to deleterious mutations are necessarily found in functional genomic regions, interpretations in terms of recurrent positive selection may require reconsideration.

Correction to: Index selection can improve the selection efficiency in a rice recurrent selection population

In the above mentioned publication, the affiliations of the last 4 authors were interchanged.

LEAF-SPOTTING DISEASES AS A MATTER OF DAMAGE OF ALFALFA BREEDING POPULATIONS IN AN EVIDENT MULTIFOLIATE PHASE IN DIFFERENT CYCLES OF PHENOTYPIC RECURRENT SELECTION

Alfalfa (Medicago varia Mart.) is the most important forage crop for considerable amount of regions of the Russian Federation and throughout the entire world. Assessment of the stability and resistance of alfalfa varieties to a complex of leaf-spotting diseases under various environmental conditions is important for breeding programs as a tool for selecting the best varieties and breeding samples. In the course of a three-year experiment (2016-2018) there were tested the productivity and resistance to a complex of leaf spotting diseases of a commercial variety Krasnoyaruzhskaya 1 and breeding populations with high multifoliate expression (evident multi-leaf phase – mf-multi-leaf mutations) obtained on its basis in several cycles (I-III) of periodic (recurrent) selection. Six alfalfa-breeding populations were tested in two ecotopes on two soil differences: plot 1-ecotope of field crop rotation; plot 2-ecotope of a plowed meadow in the floodplain of the river Oskol in Chernyansky district, Belgorod region (meadow ecotope). The data obtained were analyzed by the method of two-way analysis of variance (ANOVA) according to a 2x4 scheme with the calculation of LSD 0.05. There were evaluated organized factors: factor A — selection feature: A1 (G) – high multifoliate expression (mf-mutation) without the manifestation of anthocyanin color of the stem (green color of the stem); A2 (AN) – high multifoliate expression (mf-mutation) with an evident anthocyanin color of the stem (purple color of the stem); factor B – a recurrence selection cycle: C-0, C-1, C-2, C-3. Pearson’s correlation coefficient was used to identify the close relationships between the studied indicators. It has been established that three cycles of recurrent selection are effective for increasing multifoliate expression in alfalfa breeding populations without increasing inbreeding depression based on seed productivity. Multifoliate forms are resistant to the development of leaf-spotting diseases and their prevalence. The most stable are the forms in which selection for the expression of the mf-mutation was carried out simultaneously with the increase in the index of the anthocyanin color of the stem. For a more effective assessment of the resistance of alfalfa breeding populations to leaf-spotting in Central Russia, comparative testing must be carried out simultaneously under conditions of favorable ecotopes of field crop rotation with fertile black soil rich in humus (chernozem) and in adverse conditions of meadow ecotopes.

Breeding and Evaluation of Fine Fescues for Increased Tolerance to Mesotrione Herbicide

Fine fescues (Festuca sp.) are a group of species that require fewer inputs, such as fertilizer, than other cool-season species managed for turf. They are adapted to infertile, acidic soils; shade; and drought. One area that poses additional challenges is the lack of weed control options for fine fescues during establishment from seed. Mesotrione is a herbicide that provides preemergence control of many broadleaf and grassy weeds, such as annual bluegrass (Poa annua), but is currently not labeled for use in fine fescues at seeding. The objectives of this research were 1) to use a recurrent selection technique to develop mesotrione-tolerant chewings fescue (Festuca rubra ssp. commutata), hard fescue (Festuca brevipila), and strong creeping red fescue (F. rubra spp. rubra); and 2) to conduct field trials to compare the new selections to commercially available cultivars and experimental lines not selected for tolerance to mesotrione. Progress was made after each of the three generations of recurrent selection. The top statistical grouping of entries for injury following application of mesotrione at the 8-oz/acre rate included all the third-generation (G3) hard fescues, all the G3 chewings fescues, and the G3 strong creeping red fescue STB1 Composite. After three generations, selections of hard, chewings, and strong creeping red fescues had equivalent or better tolerance to mesotrione than tall fescue (Festuca arundinacea) and kentucky bluegrass (Poa pratensis) cultivars, which are on the label for safe use at seeding. These new selections would provide turf managers an option to control weeds using mesotrione during seedling establishment of fine fescues.

GmMs1 encodes a kinesin-like protein essential for male fertility in soybean (Glycine max L.).

The application of heterosis is a promising approach for greatly increasing yield in soybean (Glycine max L.). Nuclear male sterility is essential for hybrid seed production and the utilization of heterosis. Here we report the cloning of the gene underlying the soybean male-sterile mutant ms-1, which has been widely used for recurrent selection in soybean breeding programs. We initially delimited the ms1 locus to a 16.15 kb region on chromosome 13, based on SLAF_BSA sequencing followed by genotyping of an F2 population segregating for the locus. Compared with the same region in fertile plants, the mutant region lacks a sequence of approximately 38.7 kb containing five protein-coding genes, including an ortholog of the kinesin-like protein gene NACK2, named GmMs1. The GmMs1 knockout plants generated via CRISPR/Cas-mediated gene editing displayed a complete male-sterile phenotype. Metabolic profiling showed that fertile anthers accumulated starch and sucrose normally, whereas sterile anthers had higher anthocyanin levels and lower flavonoid levels and lower antioxidant enzyme activities. These results provide insights into the molecular mechanisms governing male sterility and demonstrate that GmMs1 could be used to create male-sterile lines through targeted mutagenesis. These findings pave the way for designing seed production technology and an intelligent male-sterile line system to utilize heterosis in soybean.

Hearing sensitivity of primates: recurrent and episodic positive selection in hair cells and stereocilia protein-coding genes

Hearing sensitivity of primates: recurrent and episodic positive selection in hair cells and stereocilia protein-coding genes

Intraspecific recurrent selection in V. vinifera: an effective method for breeding of high quality, disease-, cold-, and drought -resistant grapes

Intraspecific recurrent selection in V. vinifera: an effective method for breeding of high quality, disease-, cold-, and drought -resistant grapes

Molecular Evolution of Ecological Specialisation: Genomic Insights from the Diversification of Murine Rodents.

Adaptive radiations are characterized by the diversification and ecological differentiation of species, and replicated cases of this process provide natural experiments for understanding the repeatability and pace of molecular evolution. During adaptive radiation, genes related to ecological specialization may be subject to recurrent positive directional selection. However, it is not clear to what extent patterns of lineage-specific ecological specialization (including phenotypic convergence) are correlated with shared signatures of molecular evolution. To test this, we sequenced whole exomes from a phylogenetically dispersed sample of 38 murine rodent species, a group characterized by multiple, nested adaptive radiations comprising extensive ecological and phenotypic diversity. We found that genes associated with immunity, reproduction, diet, digestion, and taste have been subject to pervasive positive selection during the diversification of murine rodents. We also found a significant correlation between genome-wide positive selection and dietary specialization, with a higher proportion of positively selected codon sites in derived dietary forms (i.e., carnivores and herbivores) than in ancestral forms (i.e., omnivores). Despite striking convergent evolution of skull morphology and dentition in two distantly related worm-eating specialists, we did not detect more genes with shared signatures of positive or relaxed selection than in a nonconvergent species comparison. Although a small number of the genes we detected can be incidentally linked to craniofacial morphology or diet, protein-coding regions are unlikely to be the primary genetic basis of this complex convergent phenotype. Our results suggest a link between positive selection and derived ecological phenotypes, and highlight specific genes and general functional categories that may have played an integral role in the extensive and rapid diversification of murine rodents.

Breeding Amaranth for Biomass: Evaluating Dry Matter Content and Biomass Potential in Early and Late Maturing Genotypes

Amaranth (Amaranthus spp.) is a promising biomass crop for silage and biogas production. Under long-day conditions, it exhibits prolonged vegetative growth. To evaluate the breeding potential of amaranth for biomass production, we characterized phenotypic variation in biomass yield components, quantitative genetic parameters, and the relationships between traits. We conducted field trials of 10 biomass-type genotypes exhibiting a ‘giant’ growth habit derived from spontaneous hybridization between genetically diverse parents, and used the variety “Bärnkrafft” as check. We observed two contrasting growth patterns: Bärnkrafft is a variety for grain production and was characterized by a short vegetative growth followed by a long seed ripening. In contrast, the biomass genotypes displayed a long vegetative growth followed by a short seed ripening. We observed strong correlations between dry matter content and stem diameter (r =−0.78, p < 0.01) and between plant height and biomass score (r = 0.95, p < 0.001). High values for broad-sense heritability of stem diameter (H2 = 0.88) and plant height (H2 = 0.92) suggest that the dry matter content and yield can be improved by indirect phenotypic selection. We hypothesize that selection for dry matter content and yield implies a trade-off between earliness and photoperiod sensitivity. Hence, dry matter content should be improved first by recurrent selection, which can be then combined with short-day genes to improve dry matter yield. Overall, this work provides an avenue to the breeding of biomass amaranth.

Positive selection plays a major role in shaping signatures of differentiation across the genomic landscape of two independent Ficedula flycatcher species pairs.

A current debate within population genomics surrounds the relevance of patterns of genomic differentiation between closely related species for our understanding of adaptation and speciation. Mounting evidence across many taxa suggests that the same genomic regions repeatedly develop elevated differentiation in independent species pairs. These regions often coincide with high gene density and/or low recombination, leading to the hypothesis that the genomic differentiation landscape mostly reflects a history of background selection, and reveals little about adaptation or speciation. A comparative genomics approach with multiple independent species pairs at a timescale where gene flow and ILS are negligible permits investigating whether different evolutionary processes are responsible for generating lineage-specific versus shared patterns of species differentiation. We use whole-genome resequencing data of 195 individuals from four Ficedula flycatcher species comprising two independent species pairs: collared and pied flycatchers, and red-breasted and taiga flycatchers. We found that both shared and lineage-specific FST peaks could partially be explained by selective sweeps, with recurrent selection likely to underlie shared signatures of selection, whereas indirect evidence supports a role of recombination landscape evolution in driving lineage-specific signatures of selection. This work therefore provides evidence for an interplay of positive selection and recombination to genomic landscape evolution.

Estimativas de parâmetros genéticos e ganhos de seleção em progênies de maracujazeiro via metodologia REML/BLUP

O objetivo deste trabalho foi estimar os parâmetros genéticos e predizer o progresso genético via índices de seleção utilizando a metodologia REML/BLUP em uma população de maracujazeiro azedo sob seleção recorrente intrapopulacional. Foram avaliadas 118 famílias de irmãos completos (FIC) e três testemunhas adicionais distribuídas em delineamento de blocos casualizado (DBC) com 3 repetições e 3 plantas por parcela, sendo avaliadas 13 características relacionadas a planta e fruto. Foi realizado a estimação dos parâmetros genéticos pela metodologia REML/BLUP e empregados os índices de seleção aditivo (AD), multiplicativo (IM) e Mulamba e Mock (MM) para ranquear todos os indivíduos. Na avaliação dos parâmetros genéticos foram observadas magnitudes de herdabilidade média de progênies para as características: Ratio, comprimento do fruto, formato do fruto, dias para o florescimento e acidez total titulável, sendo observados altos valores de acurácias. Na estimativa de ganhos preditos, os maiores ganhos percentuais preditos para as características, número de frutos e produtividade, foram estimados quando utilizou o índice aditivo com os pesos aleatórios. Os índices de seleção do referente estudo, indicam possibilidade de sucesso no programa de melhoramento visando à seleção de características superiores para o Estado de Mato Grosso.

Index selection can improve the selection efficiency in a rice recurrent selection population

To attain success with selection process, the breeders need to understand the genetic variability into each population developed by breeding program. In this purpose, breeders need to estimate the variance components and genetic and phenotypic parameters. Besides, they need to have the ability to select simultaneously genetically top progenies for multiple traits. This study used a field trial, with a panel of 198 S0:2 lowland rice progenies, evaluated in three environments during two years in order to: (i) estimate genetic parameters for different traits in a rice breeding population, (ii) evaluate the impact of direct selection and selection performed through three selection indices in a rice population developed by recurrent selection, and (iii) compare three selection indices using different economic weights with direct and indirect selection. Significant genetic variation was found among progenies for: grain yield, plant height, days to flowering, panicle blast, leaf scald and grain discoloration. The direct selection provided high gains for single trait selection, but this method may results in undesirable changes in related traits. Thus, between the evaluated indices and in comparison, to indirect selection the Mulamba and Mock index provided simultaneously greater gains for all the evaluated traits. Furthermore, we found that when the random weights and $$b$$ -variation index were used as economic weight, it was found lower gains or no gains, showing that the gains attained with Smith and Hazel and Tai indices were linked to economic weights used.