Luciano Lourenço Nass

Pre-breeding: a link between genetic resources and maize breeding

Activities related to genetic resources are characterized by high cost and long term return. Thus the conservation of genetic variability for the future and the efficient utilization of available accessions are two important goals to be attained. However, the low utilization of germplasm banks is not restricted to Brazil but to other developing countries as well. Therefore, pre-breeding is a promising alternative to link genetic resources and breeding programs. Several aspects for maize are discussed such as concept, importance, methods and results. Problems to be investigated and suggestions are also presented.

Characterization and evaluation of maize landraces

The choice of germplasm plays an important role in any plant breeding program. The goals of this paper were to characterize and to evaluate the genetic potential of IAPARs maize (Zea mays L.) landraces for breeding purposes. Characterization of 25 landraces of maize for endosperm type and kernel color is shown. In 1998/99, experiments using randomized complete block designs with two replications were carried out in three locations of Brazil (Londrina-PR, Ponta Grossa-PR, and Anhembi-SP). For grain yield, the most promising landraces were GI156 (Cayano Sobralia) and GI045 (Tupy Pyta Sope). Their performances for grain yield represent 86.9% and 84.6% of the hybrid AG122 yield, respectively, and were of the same magnitude of the adapted varieties (BR-105 and BR-106).

Combining ability of maize inbred lines evaluated in three environments in Brazil

Em regioes tropicais a interacao genotipo x ambiente e uma importante fonte de variacao. Esse estudo teve por objetivos avaliar em cruzamentos dialelicos as capacidades de combinacao e suas interacoes com ambientes e identificar as combinacoes hibridas mais promissoras entre dez linhagens selecionadas de milho (Zea mays L.). Os hibridos e as testemunhas foram avaliados no delineamento latice triplo 7 x 7 em tres ambientes durante o ano agricola de 1984/85. Nesse trabalho sao discutidos apenas os dados de producao de graos, os quais foram corrigidos para a variacao de estande (50 plantas por parcela) e umidade de grao (15,5%). Os dados de peso de espigas foram analisados utilizando-se uma adaptacao do metodo IV de Griffing, no qual os cruzamentos obtidos no dialelico completo sao avaliados em varios ambientes. A media dos hibridos considerando todos os ambientes variou de 6,6 t/ha a 10,3 t/ha. Na analise dialelica conjunta foram detectadas diferencas altamente significativas (P<0,01) para ambientes, capacidade geral de combinacao (CGC), capacidade especifica de combinacao (CEC) e para a interacao CGC x ambientes; a interacao CEC x ambientes nao foi significativa. Os resultados obtidos mostraram que tanto CGC como CEC foram importantes para esse conjunto de hibridos. Para os 13 hibridos mais produtivos as contribuicoes dos efeitos da CGC e CEC foram 56% e 44%, respectivamente. Por outro lado, tomando-se apenas os cinco melhores hibridos, os efeitos da CEC foram sempre mais expressivos em relacao aos efeitos da CGC, para cada hibrido e na media dos ambientes.

Capacidade de combinação e heterose para resistência a Puccinia polysora Underw. em milho

Genetic resistance is the most efficient way of controlling maize leaf diseases. To evaluate the specific and general combining ability (CGE and CGC, respectively) as well as heterosis for resistance to Puccinia polysora, nine inbred lines and a partial diallel set of their 36 F1 hybrids were used in experiments conducted in three environments. Disease severity was evaluated in the whole plant (PI) and in the leaf positioned at the point of insertion of the main ear (AFA). Trials were conducted in a randomized block design 5 m row plots. Analyses of variance for disease severity were performed by Gardner and Eberharts Analysis II, in combination with Griffings Method 4, Model I. The diallel analysis of environments indicated highly significant environment (E), CGC and CGC x E effects for both evaluation methods; CEC effects significant for PI but not for AFA; interactions CEC x E not significant for both disease severity variables. CGC effects were more important than CEC. This suggests that additive genetic effects are more important as sources of variation for disease resistance in this set of inbred lines. Heterotic effects were found in crossings between resistant lines and between susceptible ones, although in the first case the effects were more evident. Specific hybrid combinations of lines with high potential for the genetic control of this pathogen were identified.

Potential of twenty exotic germplasms to improve Brazilian maize architecture

Temperate and temperate x tropical germplasms were introduced into the maize breeding of the Department of Genetics (ESALQ-USP). Twenty populations designated as P-1 to P-20 and a check population were evaluated in a randomized complete block design with two replications at Piracicaba, SP, Brazil. Plots were 2.0 m long, spaced 1.0 m apart, with 10 plants per plot after thinning. The following traits were evaluated: PH, plant height; EH, ear height; TB, tassel branch number; KW, 100 kernels weight; EL, ear length; ED, ear diameter; KR, kernels per row, and RN, number of rows of kernels. The means of the exotic populations showed a variation in performance for all traits. The population means were greater than check means for KW, EL, and KR. Populations P-9, P-10, P-12, and P-13 showed low relative ear placement values (EH/PH index), indicating that these materials could contribute to lower ear placement in local populations. P-1 and P-9 showed a high potential to reduce TB. The phenotypic correlation coefficients among populations were positive for most combinations, except for RN with PH, EH, TB, and KW. Predictions of 19 composite means were obtained for all traits.

Genetic resources: the basis for sustainable and competitive plant breeding

Plant genetic resources are the fuel for breeding, which in the search for higher yield and adapted genotypes, manipulates genes in order to meet the needs of farmers, and especially, of the current market. However, the use of accessions available in germplasm banks is low. Topics discussed in this paper emphasize the importance of plant genetic resources, and warn about problems related to genetic vulnerability; also, they discuss about aspects of costs involved in conservation and suggest recommendations for strengthening the area in Brazil.

Quantitative variation for grain quality in Brazilian maize populations

Development of maize (Zea mays L.) cultivars with high grain protein and oil concentrations and an appropriate amino acid composition, without losses in grain yield, represents a challenge in breeding programs. The objective of this work was to study the nutritional quality of ten Brazilian maize populations evaluated in three environments. A randomized block design with six replications was used. Ear yield and the concentrations of protein, oil, serine, glutamic acid, alanine, leucine, tyrosine and phenylalanine were evaluated. Individual and combined analyses of variance were performed. Populations diverged for most of the traits. Environmental effects influenced variation for most of the traits, unlike genotype-environment interaction, allowing the selection on the average of environments. Positive association exists among protein and most of the amino acids, when considered on a dry matter basis and there is no association between nutritional quality and yield; therefore, the development of cultivars that are superior for both traits is expected to be feasible.

Rooting performance from leaf petioles of accessions and hybrids of wild Arachis species

The genus Arachis has 69 species, the majority native to Brazil. Arachis spp. seedling root tips have been used to obtain dividing cells for cytological preparations. Several wild species produce small amounts of seeds and consequently few root meristems, making the cytogenetic characterization very difficult. The purpose of this study was to evaluate the rooting capacity of several wild species of Arachis using the detached leaves technique for obtaining roots from petioles. One hundred and thirty accessions and 27 interspecific hybrids were studied. Three evaluations were performed at 15, 31, and 49 days after planting. Leaf rooting observed in the wild species confirmed the great genetic variability typical of the Arachis genus, indicating that the number of days interferes with the rooting percentage. The Arachis Section presented the highest rate of rooting leaves. The Caulorrhizae Section showed the same pattern observed in the Erectoides Section. Accessions from Heteranthae, Trierectoides, Extranervosae, and Rhizomatosae Sections did not differ among each other. Differences were not observed in Erectoides Section when compared to Rhizomatosae and Extranervosae Sections. The number and morphology of roots obtained through this technique were promising to be used on cytological preparations.

Chemical control of coccid (Orthezia praelonga Douglas, 1891) for orange-trees, with insecticide granulated

The experiment was carried out on adult orange-trees in the county of Limeira, SP, Brazil. The objective was to evaluate the efficiency of insecticide granules with 15% aldicarb and 5% imidadoprid, applied to the soil, to control the citrus coccid Orthezia praelonga Douglas, 1891. Treatments were six: A) check; B) aldicarb, 100g/pl; C) aldicarb, 65g/pl; D) imidacloprid 100g/pl; E) aldicarb, 130g/pl; F) imidacloprid, 75g/pl of commercial insecticide granules. Six evaluations were made, one previous and other five 07, 20, 34, 49 and 70 days after application. The most efficient treatments were E and B at 49 and 70 days, respectively.