Orlando Peixoto de Morais

An Unprecedented Outbreak of Rice Blast on a Newly Released Cultivar BRS Colosso in Brazil

Rice blast occurred in epidemic proportions on a newly released upland rice cultivar BRS Colosso, in the rice growing season 2004/2005. Twenty isolates were collected from the affected panicles of the cultivar BRS Colosso from three different States, two pathotypes IB-1 and IB-17 were identified. They were classified into thirteen Brazilian pathotypes based on the reaction pattern on eight upland rice cultivars, utilized as local differentials. Differences in aggressiveness of the isolates on the cultivar BRS Colosso were evident. Ten highly aggressive isolates were used to determine the partial resistance to leaf blast in the BRS Colosso and BRS Bonanca. There was no significant isolate x cultivar interaction for partial resistance. The mean leaf blast severity was significantly higher in BRS Colosso than in BRS Bonanca. Inoculation of culms with the same ten isolates showed cultivar x isolate interaction. Some isolates were more aggressive showing severe culm blast. There was no correlation among the aggressiveness of the isolates on leaf and culm. The disease outbreak in BRS Colosso could be attributed to the absence of adequate degree of partial resistance, the preexistence of compatible pathotypes IB-1 and IB-17 and their dissemination through seed.

Ganho de produtividade pelo melhoramento genético do arroz irrigado no nordeste do Brasil

Os ganhos geneticos para produtividade obtidos pelo programa de melhoramento do arroz irrigado por inundacao na Regiao Nordeste do Brasil no periodo de 1984 a 1993 foram estimados visando avaliar a eficiencia do programa e tracar novas estrategias. Esta estimativa foi feita a partir dos dados de 59 ensaios regionais de rendimento conduzidos pelas empresas de pesquisa agropecuaria do Nordeste, em cooperacao com a Embrapa-Centro Nacional de Pesquisa de Arroz e Feijao (CNPAF), Goiânia, GO. O metodo estatistico utilizado baseia-se em medias ajustadas por modelo linear generalizado. O ganho genetico medio estimado foi de 54,9 ± 14,4 kg/ha/ano (0,8%). Nos ultimos tres anos houve uma tendencia de interrupcao dos ganhos. A pequena magnitude dos ganhos para producao nesta regiao podem ser atribuidos ao direcionamento do programa de geracao de linhagens da Embrapa para qualidade de graos e resistencia a doencas, as diferencas ambientais existentes entre Goiânia e a Regiao Nordeste e ao pequeno numero de ensaios conduzidos. A genealogia das linhagens foi tracada e verificou-se que os principais ancestrais sao os mesmos das cultivares recomendadas. A base genetica das linhagens e estreita, o que tambem pode estar contribuindo para a obtencao de pequenos ganhos geneticos para produtividade.

A new method to estimate genetic gain in annual crops

The genetic gain obtained by breeding programs to improve quantitative traits may be estimated by using data from regional trials. A new statistical method for this estimate is proposed and includes four steps: a) joint analysis of regional trial data using a generalized linear model to obtain adjusted genotype means and covariance matrix of these means for the whole studied period; b) calculation of the arithmetic mean of the adjusted genotype means, exclusively for the group of genotypes evaluated each year; c) direct year comparison of the arithmetic means calculated, and d) estimation of mean genetic gain by regression. Using the generalized least squares method, a weighted estimate of mean genetic gain during the period is calculated. This method permits a better cancellation of genotype x year and genotype x trial/year interactions, thus resulting in more precise estimates. This method can be applied to unbalanced data, allowing the estimation of genetic gain in series of multilocational trials.

Progresso genético obtido pelo melhoramento do arroz de sequeiro em 21 anos de pesquisa em Minas Gerais

This work aimed to estimate the genetic gain obtained by the upland rice (Oryza sativa L.) breeding program developed in Minas Gerais State, Brazil, in cooperation with Empresa de Pesquisa Agropecuaria de Minas Gerais (Epamig), Embrapa-Centro Nacional de Pesquisa de Arroz e Feijao (CNPAF), Universidade Federal de Lavras (UFLA) and Universidade Federal de Vicosa (UFV), from 1974/75 to 1994/95. Results of the comparative trials of upland rice cultivars and lines conducted over the above quoted period were utilized. Because of irregular rainfall distribuition and the distinctive response of different cycles to climatic conditions, the option was to divide them into two groups, one encompassing the early genotypes and the other those of medium cycle. The achieved result showed that an average genetic gain of 1.26% and 3.37% for the early group and medium cycle, respectively, occurred. In addition, it was found that the early group statistically outyielded (P £0.01) as to grains the medium cycle group, denoting that in Minas Gerais the short cycle cultivars should be preferred.

Avaliação do progresso genético obtido em 22 anos no melhoramento do arroz irrigado em Minas Gerais

The goal of this work was to evaluate the performance of the genetical improvement program of irrigated rice in the State of Minas Gerais, Brazil. The grain yield data of the advanced comparative trials of both cultivars and lines of irrigated rice, conducted in several regions of the State of Minas Gerais over the period of 1974/75 to 1995/1996 were utilized. The average genetical gain obtained was of 33 kg/ha/year (0.98%), being highly significant (P< 0.01). The 22 year period was subdivided into two phases: at the first phase (1974/75 to 1979/80), a gain of 203 kg/ha/year (6.06%) was noticed, which was highly significant, and the second phase (1980/81 to 1995/96) presented a gain of 15 kg/ha/year (0.25%) being non significant. The high gain of the first phase is ascribed to the replacement of traditional high size and poor yielding potential for breeding materials such as Inca, BG 90-2 and MG 2. In the second phase of the program, increased attention was given to obtain materials more resistant to diseases and with better grain quality and non-significant gains for yield were obtained.

Genetic progress after cycles of upland rice recurrent selection

Periodic assessment of the genetic progress made in recurrent selection programs is essential for assessing the evolution of the programs and identifying the main factors that have contributed to this progress. This study aimed to estimate genetic progress in grain yield, plant height and days-to-flowering achieved in the CNA6 population of upland rice (Oryza sativa L.), after four cycles of recurrent selection; and evaluate the genetic potential of this population to generate superior inbred lines after each selection cycle. The experimental data were obtained from progeny yield trials of each recurrent selection cycle. These trials were carried out in two or three locations per cycle, and consisted of S0:2 progenies and at least three checks. Federer’s augmented block design, with one replication on location (the environment), was adopted. Results revealed genetic progress for grain yield and plant height, with total genetic gains of 375.87 kg ha−1 and -3.90 cm, respectively, during the four selection cycles. The annual relative gain observed for grain yield was 1.54 %. The genetic potential of the population was analysed by the expected proportion of superior inbred lines. The standard adopted as the limit for obtaining superior inbred lines was the average of the checks for each trait. The genetic potential for grain yield and plant height increased during the study period. For days-to-flowering, no genetic gain occurred; however, the genetic potential of the population to generate superior inbred lines for this trait was maintained after the selection cycles.

Upland Rice Genotype Evaluations for Acidity Tolerance

Upland rice is an important crop in South American cropping systems. In Brazil it is mainly grown in the central area, locally known as the Cerrado region. Soils of the Cerrado region are acidic and have poor fertility. A greenhouse experiment was conducted with the objective to evaluate thirty upland rice genotypes for acidity tolerance. Two acidity levels were created: high (without lime addition) and low (addition of 2.5 g dolomitic lime per kg soil). Plant height, straw yield, grain yield, panicle number, thousand-grain weight, spikelet sterility, grain harvest index (GHI), maximum root length, and root dry weight were significantly influenced by lime and genotype treatments. Lime × genotype interactions were also significant for most of these traits, indicating variation in these treats with the variation in acidity levels. Based on grain yield acidity tolerance index (GYATI), genotypes were classified as tolerant, moderately tolerant, and susceptible to soil acidity. Among thirty genotypes, 30 percent were classified as tolerant, 53 percent were classified as moderately tolerant, and 17 percent were classified as susceptible to soil acidity. Most of the growth, yield, and yield components had significant quadratic positive association with grain yield across two acidity levels. Soil acidity indices such as pH, base saturation, calcium (Ca) saturation, magnesium (Mg) saturation, and potassium (K) saturation increased with the addition of lime. Phosphorus content also increased with the addition of lime. However, hydrogen and aluminum (H + Al) and iron (Fe) content decreased with the addition of lime. Adequate soil acidity indices for grain yield were established.

Progressos do melhoramento genético do arroz de sequeiro no Estado do Amapá

The upland rice (Oryza sativa L.) program progress in Amapa State, Brazil, is evaluated for grain yield, flowering period, plant height, lodging, disease resistance and grain type in lines from seven advanced and five preliminary tests conducted at Embrapa-Centro de Pesquisa Agroflorestal do Amapa (CPAF-AP) Experimental Station, during 1990/91 to 1995/96 crop seasons. Grain yield average annual gain of 83.0 kg/ha during the period is significant using t test at 1% level of probability, corresponding to 3.5% of annual increase in yield. Among the evaluated lines the CNA 6843-1, CNA 8386, CNA 8394, CNA 8170 and CNA 8441 were superior for the characters considered. CNA 6843-1 and CNA 7706, especially, showed remarkable improvement for lodging resistance and grain quality, two of the majors rice problems in Amapa. Theses results reinforce the collaborative rice breeding program strategy developed by the research institutions from the North and others regions of Brazil, based on a collaborative program by breeders that share their results from areas with similar conditions.

Variabilidade genética durante quatro ciclos de seleção recorrente em arroz

The objective of this work was to estimate genetic and phenotypic parameters among progenies of the CNA6 population of upland rice (Oryza sativa) for grain yield and plant height in four cycles of recurrent selection, in order to evaluate the genetic variability and the genotype × location interaction. The experimental data were obtained from yield trials of S0:2 progenies, which were carried out in the experimental design of Federer’s augmented blocks, without replications for progenies within each location. The effect of S0:2 progenies was significant in all cycles for grain yield and in the first three cycles for plant height, indicating the maintenance of the population’s genetic potential to generate transgressive progenies. The participation of the component of the progeny × location interaction in phenotypic variance was of high magnitude. The genetic variability of the CNA6 population of upland rice is maintained for grain yield and plant height during the four cycles of recurrent selection.

Brasilian Upland Rice Cultivars Selected for Complete Resistance Maintain Higher Level of Field Resistance than Those Selected for Partial Resistance

The upland rice breeding program of CNPAF/EMBRAPA has been developing partial resistance to rice blast since 1977. Crosses were evaluated under heavy disease pressure in a blast nursery and highly resistant plants, score 0-2; (scale 0-9, where 0 = resistant and 9 = dead), were selected from F2 to F4. Under field conditions, in a blast prone area, plants from several crosses were selected with moderate leaf and panicle blast (0-4). Araguaia is a cultivar resulting from the first strategy and Guarany is from the field selection. These cultivars have been planted under farmer’s condition in Brazil since 1987. Cultivar performance indicates that the blast resistance of Guarani is less stable than that incoporated into Araguaia. Therefore, partial resistance selected for in this manner, may not confer durable resistance to blast more than selecting for complete resistance.