Genetic diversity studies and analysis of the selection gain of wheat (Triticum aestivum L.) genotypes released over the decades allow the planning of strategies and support decision-making for crossing in wheat breeding. We investigated genetic diversity in tropical wheat germplasm, discussed the main trends in breeding programs and selected potential parents. Therefore, a trial with 90 commercial cultivars released in Brazil between 1800-2000 and 2001-2019 was conducted during the 2020 winter crop in Viçosa, MG, Brazil. The following traits were evaluated: spike height and plant height, heading date, spike weight, grain mass per spike, 100grain mass, number of spikelets per spike, number of grains per spike, hectoliter weight, and grain yield. The data were subjected to restricted maximum likelihood or best linear unbiased prediction analysis and used to calculate the standardized average Euclidean distance and then unweighted pair group method with arithmetic mean clusters were generated from the genotypic distance matrix. The selection of the genotypes with the best performance in each phase was accomplished using the multitrait genotype-ideotype distance index (MGIDI). High genetic diversity was observed between the genotypes evaluated. Multitrait index revealed selection gain in the desired direction in the two phases. The present study will support the efficient use of the genetic variability present in tropical wheat germplasm. Three genotypes were selected by MGIDI in the first phase, while in the second phase 12 were selected.Two groups of dissimilar and potential genotypes were proposed to compose a partial diallel.
Canonical correlation analysis based on genotypic correlations allows determining the associations between groups of traits and carrying out the direct or indirect selection of superior genotypes. This study investigated the existence of linear and multivariate relationships between high and low heritability traits via canonical correlation analysis based on genotypic correlations. The experiment was conducted at the Professor Diogo Alves de Melo Experimental Field at the Universidade Federal de Viçosa, in Viçosa, MG. 90 wheat cultivars were evaluated under a 9 × 10 alpha-lattice design, with three replications and plots consisting of four rows of three meters spaced at 0.20 meters. Canonical groups were established between spike height and plant height, days for heading, number of spikelets per spike, and number of grains per spike (Group I) and, spike weight, spike grain mass, 100-grain mass, hectoliter weight, and grain yield (Group II). There was dependence between the established groups, which allowed the investigation of the relationships between traits based on their genotypic values. The traits cycle and plant height can be used for indirect selection of genotypes superior in hectoliter weight and grain yield, which are important factors for industries and farmers.
High-throughput phenotyping (HTP) approaches are potentially useful for the accurate and efficient evaluation and selection of superior genotypes, leveraging high genetic gains. Vegetation indices are of particular interest because they allow indirect selection. Considering the lack of information regarding high-throughput phenotyping approaches in tropical wheat breeding, this study aimed to (i) determine the best stages to carry out image acquisition for applying multi-spectral vegetation indices; (ii) evaluate the heritability and accuracy of multi-spectral vegetation indices; (iii) understand the relationships between vegetation indices and target agronomic traits; and (iv) evaluate the efficiency of indirect selection via UAV-based high-throughput phenotyping. A diversity panel of 49 tropical wheat cultivars was evaluated during the 2022 winter season. Weekly flight campaigns were performed to further build multi-spectral vegetation indices, which were then analyzed together with four target agronomic traits. Mixed model analyses were performed to estimate genetic parameters and predict genetic values, which were subjected to correlation analysis. Additionally, factor analysis was applied, and the factorial scores were used in an indirect selection strategy (indirect via HTP). This strategy was compared to three alternative strategies: direct via grain yield, direct via days to heading, and the multi-trait genotype-ideotype distance index. The results indicate that vegetation indices are suitable for indirect selection strategies and highly efficient for the indirect selection of grain yield and cycle. The findings of this study will help decision making regarding the use of these approaches in Brazilian public wheat breeding programs.
The selection of segregating populations with the potential for derived lines is essential for breeding programs. The present work analyzes the potential of tropical F2 wheat (Triticum aestivum L.) populations originated from complete diallel cross combinations. For this purpose, eight tropical wheat cultivars were combined in a complete diallel design in 2019 after F1 seeds were multiplied in a greenhouse and the seeds of 56 F2 populations, plus the eight parents, were evaluated in the field in Viçosa, MG, Brazil in the winter harvest of 2020 using a simple lattice design (8×8). The trait scores of (1) severity of tan spot (Pyrenophora tritici-repentis), (2) severity of wheat head blast (WHB) (Magnaporthe oryzae pathotype Triticum), (3) days to heading, (4) spike height, (5) and total grain weight of the plot were evaluated. We performed a diallel analysis using mixed models to obtain the effects of general combining ability (GCA), specific combining ability (SCA), and estimation of population genotypic values. The additive effect predominated for the control of all traits, except for spike height. There were greater GCA effects for the set of parental maternal plants. Heritability, in the narrow sense, ranged from 0.20 (blast) to 0.66 (heading). There was an effect of maternal GCA for all variables, while for paternal GCA the effect was only for days passed for head and total grain weight. Populations derived from the cultivars TBIO Aton, TBIO Ponteiro, and TBIO Sossego had lower disease severity, while the combinations from BRS 254, BRS 264, and BRS 394 had earlier maturation time. The most promising combinations to derive lines for the set of traits were BRS 254 × CD 1303, BRS 394 × TBIO Aton, TBIO Aton × BRS 254, CD 1303 × BRS 254, and CD 1303 × BRS 264.
A estimação da capacidade de combinação de genitores é uma importante ferramenta para a seleção de populações segregantes promissoras com potencial de originar genótipos que possam ser recomendados para regiões com distintas condições edafoclimáticas e que expressem o máximo potencial genético. Este trabalho objetivou avaliar o potencial genético de genitores e populações segregantes de trigo (Triticum aestivum L.) tropical. Os cruzamentos, o avanço de geração e a avaliação das populações segregantes foram realizados no Campo Experimental Professor Diogo Alves de Melo, da Universidade Federal de Viçosa, Viçosa, MG. Para os cruzamentos, o esquema dialélico parcial (4 x 5) foi realizado em 2020 em casa de vegetação, considerando os seguintes cultivares: TBIO Aton, TBIO Duque, TBIO Astro e TBIO Toruk (genitores do grupo 1) e; RBO 2B5, ORS Citrino, ORS Madrepérola, ORS Destak e RBO 3B6 (genitores do grupo 2). No verão de 2021 foi realizado o avanço de geração e durante a safra de inverno de 2021, os nove genitores e as 20 populações F 2 foram conduzidos sob o delineamento de blocos casualizados com duas repetições. Os caracteres avaliados foram espigamento (ESPIG, dias), altura de planta (AP, cm), mancha amarela (MA, 1 a 5), ferrugem (FER, 0 a 4), número de espiguetas por espiga (NEspE, unidade), massa de cem grãos (M100, g) e rendimento de grãos (RG, kg.ha -1 ). Os dados foram submetidos à análise de variância, dialélica e comparação de médias pelo teste de Dunnett a 5% de probabilidade. O efeito da capacidade geral de combinação (CGC) foi significativo para ESPIG, FER e M100 e, FER, NEspE e RG nos grupos 1 e 2, respectivamente. Os genitores que apresentaram maiores contribuições com as estimativas da CGC em magnitude e direção desejada foram: TBIO Astro (ESPIG), ORS Citrino (AP), TBIO Astro, TBIO Toruk e ORS Destak (MA), TBIO Toruk (FER), RBO 3B6 (NEspE), TBIO Astro (M100) e ORS Destak (RG). Houve efeito significativo da capacidade específica de combinação para M100, com maiores estimativas apresentadas pelos cruzamentos TBIO Aton x ORS Madrepérola, TBIO Duque x RBO 3B6, TBIO Astro x ORS Madrepérola e TBIO Toruk x RBO 3B6, com destaque para TBIO Aton x ORS Madrepérola e TBIO Astro x ORS Madrepérola em que pelo menos um dos genitores apresenta alta CGC para o referido caráter. Foram obtidas diferenças significativas (p<0,05) entre as médias das combinações híbridaspara a maioria dos caracteres, com exceção de FER, porém estas não superaram a testemunha em sentido desejável. Houve predominância do efeito aditivo dos genes envolvidos na determinação dos caracteres para o conjunto de genitores analisados. É possível selecionar genitores para uso em cruzamentos com grupos complementares visando o desenvolvimento de populações segregantes de trigo tropical com elevado potencial genético a partir de estimativas da CGC em magnitude e sentido favoráveis para incrementos nos caracteres desejados. Os genitores TBIO Astro e ORS Destak são promissores para derivação de linhagens de trigo tropical com elevado potencial genético. Palavras-chave: Capacidade de combinação. Dialelo em trigo. Triticum aestivum L.
Although Brazil is one of the main agricultural countries in the world, it is historically an importer of wheat. For this reason, strategies aimed at the expansion of wheat in the country, to areas that are not traditionally producing (warmer), are of paramount importance. In wheat breeding, phenotypic values are usually used in simultaneous selection, however, they do not always correspond with genetic superiority. Therefore, the objective of this work was to evaluate the efficiency of five selection indexes applied to the genotypic values of wheat, the coincidence between the indexes and to select the most promising lines. For this, we evaluated a panel with 41 genotypes of tropical wheat, for the traits: days for flowering, disease note, plant height, hectoliter weight and grain yield. Data were submitted to REML/BLUP analysis to estimate genetic parameters and genotypic values. We applied on the BLUPs the rank summation index, multiplicative index, genotype- ideotype distance index, additive index and FAI-BLUP index. There is a genotypic variation shown by analysis of deviance for all evaluated traits. We presented different estimates of gains from selection according to the selection index applied. We observed higher estimates of gains from selection for additive and genotype-ideotype distance indexes. High similarity was observed in the selection of genotypes through the coefficient of coincidence between the indexes. Eight lines were selected simultaneously by three or more indexes. Lines VI 14047, VI 14774 and VI 14980 showed the best performance among the eight lines evaluated by the Z index.
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