Glauco Vieira Miranda

Genetic variability and heterotic groups of Brazilian popcorn populations

The development of successful advanced lines and cultivars in maize is dependent on parental selection and assignment to defined heterotic groups. So, the objectives of this study were to evaluate genetic variability and identify heterotic groups among Brazilian popcorn varieties. Thus, diallel crosses of advanced generations of the popcorn hybrids, IAC 112 and Zélia, and of three open-pollinated popcorn varieties, RS 20, Branco, and SAM were performed. Ten hybrid combinations, the five parents, and five check treatments were arranged in a block design with four replicates in two tropical-zone locations (CWb climate). Both additive and non-additive effects were important for grain yield, plant height, ear height, and husk cover. For popping expansion, only the additive effects were important. Hybrid combinations between the local variety (Branco) and F2 populations (IAC 112 and Zelia) resulted in the third and fourth highest values for popping expansion. The best grain yields were obtained with hybrid combinations involving SAM. Cultivars Zélia, IAC 112, and RS 20 increased popping expansion, whereas cultivar Branco increased grain yield of hybrid combinations. The following conclusions may be drawn: Brazilian popcorn populations have reduced heterosis and genetic variability to popping expansion in relation commercial cultivars; there is genetic variability among Brazilian popcorn populations that allows the exploitation of additive and non-additive effects for grain yield; it is possible to increase grain yield by using local varieties; but it would be difficult to obtain commercial hybrids from local varieties because they have poor performance for popping expansion.

Dinâmica populacional de plantas daninhas sob diferentes sistemas de manejo nas culturas de milho e feijão

Com o objetivo de avaliar a dinâmica populacional de plantas daninhas por meio de parâmetros fitossociologicos, realizou-se este trabalho com as culturas de milho e feijao em cultivos sucessivos, no periodo de novembro de 1998 a maio de 2001, em um Argissolo Vermelho-Amarelo Câmbico, fase terraco, em Vicosa-MG. A comunidade de plantas daninhas era composta por Amaranthus deflexus, Brachiaria plantaginea, Cyperus rotundus, Galinsoga parviflora, Mucuna aterrima e Oxalis latifolia. Os tratamentos foram constituidos de dois sistemas de manejo do solo (plantios convencional e direto) e duas finalidades de uso da cultura do milho (grao e silagem), em blocos com quatro repeticoes. No plantio convencional, antes da semeadura das culturas, o solo foi arado e gradeado, e, no plantio direto, foi realizada a dessecacao das plantas daninhas com herbicidas sistemicos. As avaliacoes de plantas daninhas na cultura do milho foram realizadas antes e apos a aplicacao dos herbicidas nicosulfuron e atrazine em pos-emergencia (aos 20 e 55 DAE, respectivamente) no ano agricola 1999/00, e apos a aplicacao de atrazine e metolachlor em pre-emergencia (aos 20 DAE) em 2000/01. Em se tratando do feijoeiro, as avaliacoes tambem foram feitas antes e apos a aplicacao dos herbicidas fluazifop-p-butil e fomesafen, em pos-emergencia aos 20 e 40 DAE, respectivamente. A dinâmica populacional foi avaliada por meio do uso de parâmetros fitossociologicos baseados na densidade, frequencia e biomassa das especies amostradas. Verificou-se aos 20 DAE, antes da aplicacao dos herbicidas em ambas as culturas (milho e feijao), maior densidade e importância relativa das especies dicotiledoneas no plantio direto. No plantio convencional constatou-se maior densidade, dominância e importância relativa de Cyperus rotundus. Apos aplicacao dos herbicidas seletivos, Cyperus rotundus foi a especie de maior importância relativa em todos os sistemas estudados. Em ambas as finalidades de uso do milho, Cyperus rotundus teve sua populacao reduzida no plantio direto, quando comparado com o convencional.

Multivariate analyses of genotype x environment interaction of popcorn

The objectives of this work were to evaluate the genotype x environment (GxE) interaction for popcorn and to compare two multivariate analyses methods. Nine popcorn cultivars were sown on four dates one month apart during each of the agricultural years 1998/1999 and 1999/2000. The experiments were carried out using randomized block designs, with four replicates. The cv. Zelia contributed the least to the GxE interaction. The cv. Vicosa performed similarly to cv. Rosa-claro. Optimization of GxE was obtained for cv. CMS 42 for a favorable mega-environment, and for cv. CMS 43 for an unfavorable environment. Multivariate analysis supported the results from the method of Eberhart & Russell. The graphic analysis of the Additive Main effects and Multiplicative Interaction (AMMI) model was simple, allowing conclusions to be made about stability, genotypic performance, genetic divergence between cultivars, and the environments that optimize cultivar performance. The graphic analysis of the Genotype main effects and Genotype x Environment interaction (GGE) method added to AMMI information on environmental stratification, defining mega-environments and the cultivars that optimized performance in those mega-environments. Both methods are adequate to explain the genotype x environment interactions.

Influência de um polímero hidroabsorvente sobre a retenção de água no solo

Com este trabalho, objetivou-se avaliar a influencia da concentracao de um polimero hidroabsorvente nas caracteristicas de retencao de agua de dois solos classificados como Latossolo Vermelho-Amarelo, de textura franco-argilo-arenosa, e Argissolo Câmbico Vermelho-Amarelo, de textura argilosa. Os estudos consistiram na obtencao das curvas caracteristicas de retencao de agua desses solos misturados com o polimero hidroabsorvente Terracottem®, nas concentracoes 0,01, 0,05, 0,10, 0,15 e 0,20 dag kg-1. A avaliacao de alteracao das caracteristicas de retencao de agua foi feita com base nos valores de disponibilidade total de agua (DTA) no solo e nas umidades correspondentes a capacidade de campo e ao ponto de murchamento permanente. Verificou-se que, para potenciais matriciais superiores a -1,0 MPa, a retencao de agua foi maior a medida que se aumentou a concentracao do polimero na mistura, para os dois solos estudados. No entanto, para potenciais matriciais inferiores, a retencao de agua nao foi influenciada pela concentracao do produto. O polimero, usado na concentracao de 0,2 dag kg-1, aumentou a umidade no potencial matricial de -0,03 MPa em cerca de 41% para o solo franco-argilo-arenoso e em 37% para o solo argiloso, em relacao as respectivas testemunhas, com aumento da DTA correspondente a 123 e 135%, respectivamente.

Efeitos de sistemas de manejo sobre a população de tiririca

Em experimento conduzido em campo, de novembro de 1998 a maio de 2001, sobre Argissolo Vermelho-Amarelo Câmbico de alta fertilidade, em Vicosa-MG, foram avaliados os efeitos de sistemas de manejo do solo na populacao de tiririca (Cyperus rotundus). Na area experimental, antes da instalacao do experimento predominava infestacao alta (720 ± 130 plantas m-2) de tiririca. Os tratamentos foram constituidos de dois sistemas de manejo do solo (plantios convencional e direto) e duas finalidades de uso da cultura do milho (grao e silagem), cultivados com feijao de outono-inverno em sucessao a cultura do milho, em blocos com quatro repeticoes. No plantio convencional, antes da semeadura das culturas, o solo foi arado e gradeado, e, no plantio direto, foi realizada a dessecacao das plantas daninhas com glyphosate + 2,4-D. As avaliacoes das manifestacoes epigeas da tiririca na cultura do milho ocorreram aos 20 e 55 dias apos a emergencia (DAE) no ano agricola 1999/00 e aos 20 DAE em 2000/01 e, para o feijoeiro, aos 20 e 40 DAE. A avaliacao do banco de tuberculos foi realizada apos a colheita do milho, no ultimo ano de conducao, determinando-se a densidade, a biomassa e a porcentagem de brotacao dos tuberculos coletados. Verificou-se reducao das manifestacoes epigeas da tiririca no sistema de plantio direto em ambas as finalidades de uso da cultura do milho durante todo o periodo de conducao do ensaio. Tanto no milho cultivado para grao quanto para silagem, constatou-se elevada reducao do banco de tuberculos no plantio direto, com predominio de tuberculos dormentes, em relacao ao plantio convencional.

Eficiência de glyphosate no controle de Commelina benghalensis e Commelina diffusa

The weed dayflower, Commelina spp., can survive in a great diversity of environments, what makes its control difficult. In coffee plantations of the Zona da Mata, Minas Gerais - Brazil, glyphosate is repeatedly applied to control weeds, but Commelina benghalensis and C. diffusa have not been successfully controlled. To confirm such fact and to verify the effect of increasing doses of glyphosate (720, 1,400, 2,160, 2,880 and 3,600 g a.i. ha-1) on these weed species, an experiment was installed in a randomized block design with six replications. The rates of herbicide were applied in the flowering period of plants grown in polyethylene boxes 10 cm high, 27.5 cm wide and 39.5 cm long, in unprotected environment. The effectiveness of the treatments was evaluated through the percentage of weed control related to the check treatment (no herbicide), and by the shoot dry biomass that survived the treatments. C. benghalensis was efficiently controlled by glyphosate, but C. diffusa presented herbicide tolerance. The control of C. benghalensis was above 94%, starting from the smallest rate, 25 days after treatments (DAT), and it was 100% in all the doses at 63 DAT. For C. diffusa, in general, as the doses of glyphosate increased, the shoot dry biomass became smaller. However, even with the three higher doses, when up to 98.3% of control at 46 DAT was observed, plant recovery occurred at 88 DAT. Under the conditions of this experiment, glyphosate provided an excellent control of C. benghalensis starting from 720 g a.i. ha-1, 25 DAT. However, excellent control of C. diffusa for over 60 DAT was only achieved with glyphosate rate starting from 2.880 g a.i. ha-1.

Interferência das plantas daninhas na cultura da soja cultivada em dois espaçamentos entre linhas

O presente trabalho teve como objetivo determinar o periodo anterior a interferencia, o periodo total de prevencao da interferencia e o periodo critico de prevencao da interferencia das plantas daninhas na cultura da soja, cultivar UFV-16, nos espacamentos entre linhas de 30 e 60 cm, mantendo-se uma populacao fixa de 400.000 plantas ha-1 nos dois espacamentos. Os tratamentos foram constituidos de dois grupos: em um manteve-se a cultura na ausencia de plantas daninhas em periodos iniciais apos a emergencia da cultura, e, no outro, a cultura foi mantida na presenca de plantas daninhas em periodos iniciais apos a emergencia da cultura. Os periodos foram os seguintes: 0, 10, 20, 30, 40, 50 e 60 dias apos a emergencia, totalizando 14 tratamentos, dispostos em blocos casualizados, com quatro repeticoes. O periodo critico de prevencao da interferencia na soja, considerando a reducao na produtividade de 2%, localizou-se entre o 7o e 53o dia e o 18o e 47o dia para os espacamentos de 30 e 60 cm entre linhas, respectivamente. Assim, para a soja cultivada em menor espacamento entre linhas (30 cm), o controle das plantas daninhas deve ser iniciado mais cedo, quando comparado com espacamento maior nas entrelinhas (60 cm).

The difference between breeding for nutrient use efficiency and for nutrient stress tolerance

This study aimed to verify the relationship between breeding for tolerance to low levels of soil nutrients and for nutrient use efficiency in tropical maize. Fifteen inbred lines were evaluated in two greenhouse experiments under contrasting levels of N and P. The relationship between nutritional efficiency and tolerance to nutritional stress was estimated by the Spearman ranking correlation between the genotypes for the traits related to N and P use efficiency and phenotypic plasticity indices. The lack of relationship between the traits, in magnitude as well as significance, indicates that these characters are controlled by different gene groups. Consequently, simultaneous selection for both nutrient use efficiency and tolerance to nutritional stress is possible, if the mechanisms that confer efficiency and tolerance are not competitive.

Caracteres anatômicos de duas espécies de trapoeraba e a eficiência do glyphosate

The genus Commelina includes weed species of difficult control in several crops, chiefly when the herbicide glyphosate is used repeatedly. This work was conducted to evaluate the differences between the anatomic features of Commelina benghalensis and Commelina diffusa, grown under sun and shade conditions, which could influence herbicide absorption and translocation. The stomatal apparatus of the two species is similar and the leaf is amphistomatic. C. diffusa has a greater number of stomata in relation to C. benghalensis. The number of stomatas in the leaf epiderm is greater in C. diffusa (38/mm2) than in C. benghalensis (33.66/mm2), in the abaxial (54.86/mm2) rather than in the adaxial epiderm (16.80/mm2) and under sun (37.89/mm2) rather than shade conditions (33.77/mm2). The abaxial epiderm has a greater number of stomata under sun conditions. Similar secretory hair is present in both species, but in greater number in C. diffusa. Only C. benghalensis presented tector hair: (i) long with slender extremity and (ii) short with curved extremity. Long hair is concentrated in the abaxial epiderm and short hair in the adaxial epiderm. Although the presence of hair in the leaf epiderm is frequently associated to greater herbicide absorption, it is believed that the determinant factor of greater susceptibility of C. benghalensis to glyphosate in comparison to C. diffusa could be related to the starch stock of the stem. While C. benghalensis presents fewer and smaller starch grains in the pith parenchyma, C. diffusa presents larger and numerous starch grains, which may make herbicide simplastic translocation slower, reducing the herbicide accumulated in the growth points, and allowing it to regrowth even after total leaves loss.

Efeitos gênicos de caracteres associados à eficiência no uso de nitrogênio em milho

The objectives of this work were to determine the genetic control of nitrogen use efficiency (NUE), to identify the importance of N acquisition (NAE) and utilization (NUtE) efficiencies on its composition, and to quantify the relation between production of shoot (SDM) and root dry matter mass with NUE and its components. Forty-one hybrid combinations were evaluated in two N availabilities: low (LN) and high (HN). A randomized complete block design with two replicates, in a simple factorial arrangement (hybrid combination x N availability), was used. Statistical analyses were done using mixed model equations. High magnitude correlations were detected between NAE and NUE, and between these efficiencies and SDM in LN and HN. In both N availabilities, additive genetic effects were more important for the traits associated with NUE. Therefore, selection based on the individual performance of inbred lines as to SDM can allow for the obtainment of genotypes with high NUE. Independently of N availability, NAE is the most important component of NUE.