A leaf bud technique for rapid propagation of cassava (Manihot esculenta Crantz)

The slow rate of multiplication is one of the main constraints on the production of cassava (Manihot esculenta Crantz). This work aimed to evaluate the use of leaf buds for rapid propagation of cassava varieties. Leaf buds were excised from three cassava varieties (BRS Kiriris, 98150-06 and 9624-09) for plantlet generation. The experiment was completely randomized with a 5 (age of mother plant) × 3 (position of the leaf buds on the stems) × 2 (agrochemical treatments) factorial design. Data were collected on leaf sprouting percentage (Spro.Per), plantlet height (Plant.Hei) and total dry mass of plantlets (Dry.Mass.Plant). There was a difference between the three traits for most of the varieties, demonstrating significant effects on the agronomic attributes evaluated. Better agronomic performance (higher sprouting percentage, plantlet height and total dry mass) in plantlets was observed in leaf buds of: i) maturing plants up to six months old; ii) more herbaceous (upper) parts; and iii) plants treated with agrochemicals (fungicides and insecticides). Considering four-month-old plants, three annual cycles, and an 81 % average sprouting, it would be possible to reach an annual multiplication rate of 1:72, which is much higher than that achieved by traditional methods using mature stem cuttings from 12-month-old plants (around 1:5). These results are important because they demonstrate the possibility of using cassava leaf buds to produce high-quality plantlets rapidly for greater multiplication and diffusion of new varieties and cultivation on a larger scale

Avaliação de genótipos de mamoeiro com uso de descritores agronômicos e estimação de parâmetros genéticos

O objetivo deste trabalho foi avaliar descritores quantitativos e estimar parâmetros genéticos em genótipos de mamoeiro (Carica papaya). Foi instalado um experimento em blocos aumentados, para a avaliação de 27 genótipos, entre cultivares, variedades melhoradas e variedades locais, com o uso de 30 descritores relacionados à planta, folhas, flores, frutos e sementes. Após diversos ciclos de melhoramento, os genótipos ainda mostravam ampla variabilidade quanto aos descritores avaliados. A maior parte da variação fenotípica ocorreu em razão da variância genotípica. A herdabilidade variou de 60,48 a 99,05% e, em 80% dos casos, foi superior a 80,46%. A razão entre o coeficiente de variação genético e o ambiental foi maior do que a unidade para 63% das características. Há diferenças agronômicas suficientes para uso dos genótipos “per se” ou como parentais em programas de melhoramento, em razão de agregarem variação genética, qualidade de frutos e tipo agronômico.The objective of this work was to evaluate quantitative descriptors and to estimate genetic parameters in genotypes of papaya (Carica papaya). An experiment was settled using augmented blocks, for the evaluation of 27 genotypes, among cultivars, improved lines and local varieties with 30 descriptors related to the plant, leaves, flowers, fruit and seeds. After several cycles of breeding, the genotypes still showed broad variability for the evaluated descriptors. Most of the phenotypic variation occurred due to genetic variance. The heritability ranged from 60.48 to 99.05%, and in 80% cases it was higher than 80.46%. The ratio between genetic and environmental coefficients of variation, was greater than the unity for 63% traits. There are enough agronomic differences which allow for the use of the genotypes “per se” or as parents in breeding programs because they aggregate genetic variation, fruit quality and agronomic type

Survey of fungi associated with cassava root rot from different producing regions in Brazil

Although root rot is one of the major diseases affecting Brazilian cassava (Manihot esculenta Crantz.), little is known about the diversity of root rot pathogens. In this study, diseased plants exhibiting root rot symptoms were collected from cassava-producing regions in five Brazilian states: Bahia, Sergipe, Paraíba, Maranhão, Tocantins, and Paraná. Seventy isolates were obtained and assigned to species complexes based on rDNA's ITS (internal transcribed spacer of the ribosomal DNA) region (ITS1, ITS2 and 5.8S). A total of seven species complexes was found belonging to the genus Fusarium (56/74), followed by Lasiodiplodia (8/74), Neoscytalidium (6/74), and Diaporthe/Phomopsis complex (2/74), Phytophthora, and Corallomycetella (1/74 each). These species were distributed differently according to sample locations and states, but overall, the F. solani species complex (FSSC) was the most prevalent. A number of phylogenetic lineages had not been previously reported as being associated with cassava-root rot disease, such as: F. graminearum (FGSC), F. incarnatum-equiseti (FIESC) and F. chlamydosporum (FCSC) complexes, and a phylogenetic lineage most closely related to P. phaseolorum. Results suggest the need to improve knowledge of the species associated with cassava, including multilocus phylogeny for a more specific characterization, and differences in the resistance background associated with these species, as a strategy to incorporate resistance to multiple pathogens in cassava breeding programs

Seleção dos descritores morfoagronômicos mais informativos para germoplasma de mandioca

O objetivo deste trabalho foi selecionar os descritores morfoagronômicos mais informativos para o germoplasma de mandioca (Manihot esculenta), e avaliar a capacidade de diferentes métodos em selecionar os descritores. Foram caracterizados 95 acessos com uso de 51 descritores morfoagronômicos. Os dados foram submetidos à análise de correspondência múltipla (ACM), cujas informações foram utilizadas nos seguintes quatro métodos de seleção de descritores: ordem inversa do descritor para o eixo fatorial pth da ACM (Jolliffe); análise de correspondência múltipla sequencial (ACMS); média das ordens de contribuição do descritor nos três primeiros eixos fatoriais (C3PE); e método C3PE ponderado pelos pesos dos respectivos autovalores da análise completa (C3PEPond). As correlações entre a matriz de dissimilaridade com todos os descritores e os descritores mais informativos foram altas e significativas (0,75, 0,77, 0,83 e 0,84 para C3PEPond, C3PE, ACMS e Jolliffe, respectivamente). Os descritores menos informativos foram descartados, tendo-se considerado apenas aqueles comuns entre os métodos de seleção e relevantes para os interesses do melhoramento. Assim, foram selecionados 32 descritores morfoagronômicos com correlação entre as matrizes de dissimilaridade (r=0,81), em razão de sua alta capacidade para discriminar o germoplasma de mandioca e de sua habilidade de manter alguns caracteres agronômicos preliminares, úteis para a caracterização inicial do germoplasma.The objective of this work was to select the most informative morphoagronomic descriptors for cassava (Manihot esculenta) germplasm and to evaluate the ability of different methods to select the descriptors. Ninety‑five accessions were characterized using 51 morphoagronomic descriptors. Data were subjected to a multiple correspondence analysis (MCA), whose information was used in the following four methods of descriptor selection: reverse order of the descriptor for the pth factorial axis of the MCA (Jolliffe); sequential, multiple correspondence analysis (SMCA); mean of the contribution orders of the descriptor in the first three factorial axes (C3PA); and C3PA method weighted by the respective eigenvalues of the full analysis (C3PAWeig). The correlations between the dissimilarity matrix with all descriptors and the most informative descriptors were high and significant (0.75, 0.77, 0.83, and 0.84 for C3PAWeig, C3PA, SMCA, and Jolliffe, respectively). The less informative descriptors were discarded, considering those common among the selection methods and relevant for the breeding interests. Therefore, 32 morphoagronomic descriptors with correlation between the dissimilarity matrices (r=0.81) were selected, due to their high capacity to discriminate cassava germplasm and to their ability to maintain some preliminary agronomic traits, useful for the initial characterization of the germplasm

Plant selection in F2 segregating populations of papaya from commercial hybrids

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Desenvolvimento de escala diagramática para avaliação da deterioração fisiológica pós‑colheita em mandioca

The objective of this work was to develop a scale to assess the severity of postharvest physiological deterioration (PPD) of cassava roots, and to validate this scale for accuracy and reproducibility estimates. A diagrammatic scale (0 to 100%) for the damaged roots was analyzed according to precision, accuracy, and reproducibility. Seven evaluators (four with experience and three without it) quantified the PPD severity, with or without the scale, considering 150 roots with different levels of PPD. Without and with the use of the scale, respectively, the inexperienced evaluators obtained coefficients of determination (R2) from 0.76 to 0.86 and 0.87 to 0.92, and the experienced evaluators obtained R2 from 0.90 to 0.96 and 0.96 to 0.97. The values of the intercept (a) obtained by both the experienced and inexperienced evaluators who did not use the scale were all significant, while after using the scale, only two evaluators got values that were not significantly different from one. Evaluation reproducibility between the evaluators ranged from 0.61 to 0.91 for the inexperienced ones and from 0.83 to 0.95 for the experienced ones. The proposed diagrammatic scale was considered appropriate to estimate the severity of PPD in cassava roots, and can be used to identify sources of tolerance to postharvest deterioration.O objetivo deste trabalho foi desenvolver uma escala para avaliar a severidade da deterioração fisiológica pós‑colheita (DFPC) da mandioca, e validar esta escala quanto a estimativas de acurácia e reprodutibilidade. Uma escala diagramática (0 a 100%) referente à área lesionada das raízes foi avaliada de acordo com sua precisão, acurácia e reprodutibilidade. Sete avaliadores (quatro experientes e três inexperientes) quantificaram a severidade da DFPC, com ou sem o uso da escala, tendo-se considerado 150 raízes com diferentes níveis de DFPC. Sem e com o uso da escala, respectivamente, os avaliadores inexperientes obtiveram coeficiente de determinação (R2) de 0,76 a 0,86 e de 0,87 a 0,92, e os avaliadores experientes obtiveram R2 de 0,90 a 0,96 e de 0,96 a 0,97. Os valores do intercepto (a), obtidos tanto pelos avaliadores experientes como pelos inexperientes, sem uso da escala, foram significativos, enquanto, após o uso da escala, apenas dois avaliadores obtiveram valores que não foram significativamente diferentes de um. A reprodutibilidade das avaliações entre os avaliadores variou de 0,61 a 0,91, para os inexperientes, e de 0,83 a 0,95, para os experientes. A escala diagramática proposta foi considerada adequada para estimar a severidade da DFPC em raízes de mandioca e poderá ser utilizada para identificar fontes de tolerância à deterioração pós‑colheita

Procedimentos para avaliar a tolerância de genótipos de mandioca à deterioração fisiológica pós‑colheita

The objective of this work was to define procedures to assess the tolerance of cassava genotypes to postharvest physiological deterioration (PPD) and to microbial deterioration (MD). Roots of six cassava genotypes were evaluated in two experiments, during storage under different environmental conditions: high temperature and low soil moisture; or low temperature and high soil moisture. Roots were treated or not with fungicide (carbendazim) before storage. Genotype reactions to MD and PPD were evaluated at 0, 2, 5, 10, 15, 20, and 30 days after harvest (DAH), in the proximal, medial, and distal parts of the roots. A diagrammatic scale was proposed to evaluate nonperipheral symptoms of PPD. Fungicide treatment and root position did not influence PPD expression; however, all factors had significant effect on MD severity. Genotypes differed as to their tolerance to PPD and MD. Both deterioration types were more pronounced during periods of higher humidity and lower temperatures. The fungicide treatment increased root shelf life by reducing MD severity up to 10 DAH. Whole roots showed low MD severity and high PPD expression up to 10 DAH, which enabled the assessment of PPD without significant interference of MD symptoms during this period.O objetivo deste trabalho foi definir procedimentos para a avaliação da tolerância de genótipos de mandioca à deterioração fisiológica pós‑colheita (DFPC) e à deterioração microbiana (DM). Raízes de seis genótipos de mandioca foram avaliadas em dois experimentos, durante armazenamento em diferentes condições ambientais: alta temperatura e baixa umidade do solo; ou baixa temperatura e alta umidade do solo. As raízes foram tratadas ou não com fungicida (carbendazim) antes do armazenamento. As reações dos genótipos à DM e à DFPC foram avaliadas aos 0, 2, 5, 10, 15, 20 e 30 dias após a colheita (DAC), nas partes proximal, medial e distal das raízes. Uma escala diagramática foi proposta para avaliar sintomas não periféricos da DFPC. O tratamento com fungicida e a posição das raízes não influenciaram a expressão da DFPC; no entanto, todos os fatores apresentaram efeito significativo sobre a severidade da DM. Os genótipos diferiram quanto à tolerância à DFPC e à DM. Ambos os tipos de deterioração foram mais pronunciados durante os períodos de maior umidade e de temperaturas mais baixas. O tratamento com fungicida proporcionou maior vida de prateleira às raízes, por reduzir a severidade da DM até 10 DAC. As raízes inteiras apresentaram baixa severidade da DM e alta expressão da DFPC até 10 DAC, o que possibilitou a avaliação da DFPC sem interferência significativa dos sintomas da DM nesse período

Genetic correlation and path analysis for the number of commercial fruit per plant in papaya

O objetivo deste trabalho foi verificar como o número de frutos comerciais por planta (NFr) se relaciona com 16 características morfológicas e agronômicas do mamoeiro (Carica papaya L.). O experimento foi realizado no ano agrícola de 2008/2009, utilizando o delineamento experimental de blocos aumentados. Foram avaliados 19 genótipos não comuns (acessos de germoplasma) e 3 comuns (variedades e híbridos), em 10 repetições. As correlações entre NFr e as características morfoagronômicas do mamoeiro foram desdobradas em efeitos diretos e indiretos. Observou-se alta variabilidade nas características avaliadas. As estimativas das correlações genotípicas foram maiores do que as fenotípicas, para todas as características. O NFr foi positivo e significativamente correlacionado com número de frutos por axila (NFrAx); e negativamente com diâmetro da cavidade do fruto, espessura da polpa, peso, comprimento (CFr) e diâmetro do fruto. Entretanto, a análise de trilha demonstrou que, entre essas características, NFrAx e CFr possuem maior efeito direto sobre NFr. Além disso, as características altura da planta, número de flores por pedúnculo e largura da folha são de mais fácil mensuração e manifestam-se antes da produção de frutos, o que as torna mais indicadas para a seleção indireta em programas de melhoramento genético dessa cultura.The objective of this work was to determine how the number of commercial fruit per plant (CFrP) is related to 16 morphological and agronomical traits in papaya (Carica papaya L.). The experiment was carried out in the 2008/2009-crop season, using an augmented randomized block design. Nineteen non-common (germplasm accessions) and three common genotypes (varieties and hybrids) were evaluated with ten repetitions. Correlations between CFrP and morpho-agronomic traits were outspread in direct and indirect effects. High variability was found for the evaluated traits. The estimates of genetic correlations were higher than phenotypic correlations for all characters. CFrP was positively and significantly correlated with number of fruits per axil (NFAx) and negatively with the internal diameter of the cavity of the fruit, pulp thickness, fruit weight, fruit length (FrL) and fruit diameter. However, path analysis showed that, among this traits, NFAx and FrL have more direct effect on CFrP. Furthermore, plant height, number of flowers per peduncle and leaf width are more easily measured and are expressed before fruit production, making them more suitable for indirect selection in breeding programs of this crop

Resistência à podridão seca das raízes ocasionada por Fusarium em acessos de mandioca

The objective of this work was to identify sources of resistance to dry root rot induced by Fusarium sp. in cassava accessions. A macroconidial suspension (20 µL) of 11 Fusarium sp. isolates was inoculated in cassava roots, from 353 acessions plus seven commercial varieties. Ten days after inoculation, the total area colonized by the pathogen on the root pulp was evaluated by digital image analysis. Cluster analysis revealed the presence of five groups regarding resistance. The root lesion areas ranged from 18.28 to 1,096.07 mm2 for the accessions BGM 1518 and BGM 556, respectively. The genotypes BGM 1042, BGM 1552, BGM 1586, BGM 1598, and BGM 1692 present the best agronomical traits.O objetivo deste trabalho foi identificar fontes de resistência à podridão seca das raízes ocasionada por Fusarium sp. em acessos de mandioca. Inoculou-se uma suspensão (20 µL) de macroconídios de 11 isolados de Fusarium sp. em raízes de 353 acessos e sete variedades comerciais de mandioca. Dez dias após a inoculação, avaliou-se a área total colonizada pelo patógeno na polpa das raízes, por meio de análise de imagens digitais. A análise de agrupamento revelou a presença de cinco grupos quanto à resistência. As áreas lesionadas das raízes variaram de 18,28 a 1.096,07 mm2 nos acessos BGM 1518 e BGM 556, respectivamente. Os genótipos BGM 1042, BGM 1552, BGM 1586, BGM 1598 e BGM 1692 apresentam as melhores características agronômicas

Triple categorical regression for genomic selection: application to cassava breeding

Genome-wide selection (GWS) is currently a technique of great importance in plant breeding, since it improves efficiency of genetic evaluations by increasing genetic gains. The process is based on genomic estimated breeding values (GEBVs) obtained through phenotypic and dense marker genomic information. In this context, GEBVs of N individuals are calculated through appropriate models, which estimate the effect of each marker on phenotypes, allowing the early identification of genetically superior individuals. However, GWS leads to statistical challenges, due to high dimensionality and multicollinearity problems. These challenges require the use of statistical methods to approach the regularization of the estimation process. Therefore, we aimed to propose a method denominated as triple categorical regression (TCR) and compare it with the genomic best linear unbiased predictor (G-BLUP) and Bayesian least absolute shrinkage and selection operator (BLASSO) methods that have been widely applied to GWS. The methods were evaluated in simulated populations considering four different scenarios. Additionally, a modification of the G-BLUP method was proposed based on the TCR-estimated (TCR/G-BLUP) results. All methods were applied to real data of cassava (Manihot esculenta) with to increase efficiency of a current breeding program. The methods were compared through independent validation and efficiency measures, such as prediction accuracy, bias, and recovered genomic heritability. The TCR method was suitable to estimate variance components and heritability, and the TCR/G-BLUP method provided efficient GEBV predictions. Thus, the proposed methods provide new insights for GWS