Cleso Antônio Patto Pacheco

Predição de ganho genético com diferentes índices de seleção no milho pipoca CMS-43

Simultaneous breeding for expansion volume and grain yield in popcorn (Zea mays L.) is difficult because of negative correlation between these traits. The use of selection indexes allows to overcome this difficulty. In 1997/1998, at Embrapa-Centro Nacional de Pesquisa de Milho e Sorgo, in Sete Lagoas, MG, Brazil,166 half-sib families from CMS-43 popcorn were evaluated, using random blocks design. The selection indexes used were Smith and Hazel, Pesek & Baker, Elston and Williams. The selection index of Smith and Hazel allowed larger predicted gains in more traits, and on the contrary, the prediction using the selection index of Williams was insignificant. The use of selection indexes allows simultaneous prediction of gains in the two main traits.

Heterotic groups based on yield-specific combining ability data and phylogenetic relationship determined by RAPD markers for 28 tropical maize open pollinated varieties

Twenty eight maize open pollinated varieties (OPVs) were crossed in a diallel scheme and the 378 F1s were evaluated in 10 environments in Brazil. Based on yield-specific combining ability data (SCA), these varieties were classified in four heterotic groups. The consistence of the proposed heterotic groups was confirmed comparing intra- and inter-group F1 values and midparent heterosis. Superior OPVs combinations for use as a source of inbreds in hybrid breeding programs were determined. RAPD markers were used to genotype these varieties. A UPGMA dendogram, based on marker data from 50 primers and 178 polymorphic bands, was obtained. Phylogeny obtained with RAPD markers agreed with known pedigree data. Dent germplasm tended to group separately from flint germplasm. Multidimensional Scaling Analysis on marker data and morphological data showed a higher degree of genetic divergence among the dent germplasm than among the flint germplasm used in this study. Correlation between RAPD marker estimated genetic distance and SCA for yield was low and positive (r = 0.16**).

Análise dialélica e heterose de populações de milho-pipoca

A diallel set of crosses among nine varieties of popcorn (Zea mays L.) - UNB-2, RS-20, UEM-J1, UEM-M2, CMS 42, CMS 43, Vicosa, Beija-flor and advanced generation of hybrid three-way Zelia) and their hybrid combinations was carried out to obtain capacity hability and heterosis estimates. These varieties and F1s were evaluated in two crop years (98/99 and 99/00) with three replications each year in Iguatemi, State of Parana, Brazil. The results allowed the synthesis of composts based in varieties of high combining ability for yield, like UNB-2 and CMS-42 and the varieties Zelia, RS-20 e UEM-M2 to popping expansion. The varieties Beija-flor and RS-20 were recommend to be used in a reciprocal recurrent selection program. For popping expansion there are positive and negative heterosis, indicating non unidericional dominance.

Adaptabilidade e estabilidade de cultivares de milho-pipoca na região centro-sul do Brasil

Este trabalho teve como objetivo estudar a adaptabilidade e estabilidade de cultivares de milho-pipoca avaliadas pela Embrapa-Centro Nacional de Pesquisa de Milho e Sorgo, no ano agricola 1991/92. Foram avaliadas 15 cultivares em 19 locais quanto a produtividade, e em 15 locais quanto ao indice de capacidade de expansao (ICE) na regiao centro-sul do Brasil. As cultivares GO 100P, MF 1001, Pirapoca-Amarela, Pirapoca-Branca e Colorado Pop 1, foram mais promissoras, pois apresentaram boas medias de produtividade (1.700 a 2.100 kg/ha de graos) e razoaveis ICE (17 a 21 mL/mL). Quanto a variavel produtividade, as cultivares Pirapoca-Amarela e Colorado Pop 1 apresentaram-se adaptadas a ambientes favoraveis, e foram estaveis. As cultivares MF 1001, Pirapoca-Branca e GO 100P, demonstraram capacidade satisfatoria no aproveitamento dos estimulos ambientais, e foram estaveis. Todas foram estaveis em relacao ao ICE, e as cultivares MF 1001, Colorado Pop 1, Pirapoca-Amarela e Pirapoca-Branca demonstraram capacidade satisfatoria no aproveitamento dos estimulos ambientais. A cultivar GO 100P foi melhor adaptada para ambientes favoraveis.

Depressão por endogamia em populações de milho-pipoca

Eight popcorn populations (CMS-42, CMS-43, Zelia, RS-20, Catedral, Zaeli, UEM-J1 and UEM-M2) were evaluated aiming at obtaintion of estimates of inbreeding depression and average genetic components and to compare these estimates to each genetic group. Each trial was carried out with plots in randomized complete block design with three replications in split-plot experiment, in which the plots were the inbreeding levels (S1 and S0) and in the sub-plots the populations in two years (1998/99 and 1999/00). The characteristics grain yield and popping expansion were evaluated. The GARDNER methodology (1965) was used for obtaining the estimates of average genetic components. It was observed lower values of inbreeding depression and predominance of additive effects for popping expansion in relation to yield. The values of inbreeding depression for grain yield were higher in the composite than in bath, improved and not improved varieties. Using these populations the probability of success in the obtaining vigorous and high popping expansion inbred lines is low.

Adaptability and stability of maize varieties using mixed model methodology

The objective of this study was to evaluate the performance, adaptability and stability of corn cultivars simultaneously in unbalanced experiments, using the method of harmonic means of the relative performance of genetic values. The grain yield of 45 cultivars, including hybrids and varieties, was evaluated in 49 environments in two growing seasons. In the 2007/2008 growing season, 36 cultivars were evaluated and in 2008/2009 25 cultivars, of which 16 were used in both seasons. Statistical analyses were performed based on mixed models, considering genotypes as random and replications within environments as fixed factors. The experimental precision in the combined analyses was high (accuracy estimates > 92 %). Despite the existence of genotype x environment interac- tion, hybrids and varieties with high adaptability and stability were identified. Results showed that the method of harmonic means of the relative performance of genetic values is a suitable method for maize breeding programs.

Inbreeding depression of 28 maize elite open pollinated varieties

The study of inbreeding depression is important for breeding strategies such as use of inbred progenies or extraction of inbreed lines. A diallel of 28 maize open-pollinated varieties was evaluated in 10 environments in the early 1990s. At the same time, S1 populations for each of the 28 varieties were evaluated in the same 10 experiments (environments). Yield reductions of the populations from S0 to S1 (mean of the 10 environments), varied from 34.6% (CMS-01) to 59.2% (CMS-30), with an average of 49.1%. Inbreeding depression was greater in populations with a wider genetic base, which had never been exposed to inbreeding (CMS-30, BR-107, PH4, Cunha, Saracura, Nitrodent, and Nitroflint). Inbred lines with greater yield means should be obtained from the BR-105, BR-111, CMS-01, CMS-03, BR-106, CMS-14c, and CMS-28 populations. The use of parameter estimates generated by analysis of inbreeding depression, allow to make inferences about frequencies of deleterious alleles in the population. The frequencies of favorable alleles in the parents can be obtained by diallel analysis. The association of these two types of information, can provide a better interpretation of the genetic parameters and also can improve the process of selection of parents for either an intra- or an inter-populational breeding program.

Heterotic responses of tropical elite maize accessions from Latin America with Brazilian testers

Little emphasis has been placed on identifying new sources of tropical maize germplasm that can be used in breeding programs. Additional information on the performance and heterotic classification of tropical germplasm is needed. This study was conducted to identify elite maize accessions from Latin America that could contribute to increase the level of heterosis with the best heterotic patterns of Brazil. Seventy-two elite accessions from the Latin American Maize Project (LAMP) were crossed with the testers BR 105 (flint kernel Suwan background) and BR 106 (dent kernel Tuxpeno background). The 72 crosses plus 9 checks were evaluated using a simple 9 ´ 9 lattice in four locations that represent one tropical region. The combined analysis showed highly significant differences among treatments for ear weight and the interaction treatment ´ location was also significant. With both testers better crosses for ear weight were identified in relation to the double cross BR 201 (commercial check). With the tester BR 105, the high parent heterosis ranged from ¾28% to 26%, the accessions SE 032 and PE 001 were selected for further work. With the tester BR 106, the high parent heterosis ranged from ¾35% to 17% and the accessions PE 011 and Pasco 14 were selected for further work. The selected accessions will be improved through recurrent selection schemes to increase yield and improve agronomic traits. Afterwards they can be exploited, within and between heterotic groups, to produce highly productive hybrid combinations, or used per se as improved maize varieties.

Heterozygosity following half-sib recurrent selection in popcorn using isoenzyme markers

Isozyme biochemical marker may be useful tool for genomic analysis of maize populations undergoing recurrent selection. Thus, isozymes markers was utilized for assess the changes in the genetic variability and distance in a Brazilian composite population of popcorn following four cycles of recurrent selection for yield. One hundred and ninety-six half-sib families were evaluated from each cycle and the ten highest-yielding families (5.2%) were recombined to produce the next cycle. Isozyme analysis considered 80 seedlings per cycle. Simple linear regression equations were estimated among the allele frequencies in each locus in function of the selection cycles, the genetic distances among the cycles and the average heterozygosity per locus for each cycle. Regression analysis did not reveal any common trend for changes in allele frequencies presumably due to selection. The estimates of the number of polymorphic locus, of the mean of allele per locus and the mean heterozygosity did not reveal any reduction in variability. It was concluded that four selection cycles did not cause relevant changes in the variability or genetic distance among the selection cycles of CMS-43 popcorn population. Isozymes markers analysis showed that the number of recombined half-sib families in recurrent selection was suitable.

ASSOCIATION BETWEEN GRIFFING'S DIALLEL AND THE ADAPTABILITY AND STABILITY ANALYSES OF EBERHART AND RUSSELL*

The objective of the present work was to provide a methodology to study the inheritance of adaptability and stability through the breakdown of Eberhart and Russell regression coefficients and regression deviations in effects due to the mean and additive genetic effects (gis and gjs) as well as dominance effects (sijs) of Griffing´s methodology, when the diallel is conducted in several environments. It was concluded that the adaptability and stability parameters are determined in the same manner as are genetic effects. So an F1 cross inherits half the general combining ability (GCA) mean effect from each parent, while the effects due to specific combining ability (SCA) are subjected to the same considerations relative to sijs, i.e., they are dependent on specific combinations.