Isaias Olívio Geraldi

New resistance genes in the Zea mays: exserohilum turcicum pathosystem

The use of monogenic race-specific resistance is widespread for the control of maize (Zea mays L.) helminthosporiosis caused by Exserohilum turcicum. Inoculation of 18 Brazilian isolates of E. turcicum onto elite maize lines containing previously identified resistance genes and onto differential near-isogenic lines allowed the identification of new qualitative resistance genes. The inoculation of one selected isolate on differential near-isogenic lines, F1 generations and a BC1F1 population from the referred elite lines enabled the characterization of the resistance spectrum of three new genes, one dominant (HtP), one recessive (rt) and a third with non-identified genetic action. Three physiological races of the pathogen were also identified including two with new virulence factors capable of overcoming the resistance of one of the resistance genes identified here (rt).

Estimates of genetic parameters of wood traits for sawn timber production in Eucalyptus grandis

In this study, the breeding perspectives of 41 open-pollinated progenies of Eucalyptus grandis were evaluated based on their wood traits. The progenies were distributed in two experiments in a randomized complete block design, with three replicates and linear plots containing six plants each. The traits were assessed at eight years of age. Two trees from each plot were selected for this assessment based on better growth, stem form and phytosanity. Significant differences in basic density, sapwood/heartwood ratio, bowing, specific gravity, parallel compression and static bending were detected among the progenies. These traits were potentially promising for breeding programs, with heritability coefficients that varied from 0.34 to 0.61 on a progeny mean basis. There was no genetic variation in the moisture content, board end-splitting, log volume under bark, log eccentricity, bark content, crooking, and shear strength of the progenies. Intermediate to highly significant genetic correlations were detected among the physical and mechanical properties, as well as between pairs of traits such as basic density and log end-splitting, basic density and bowing, specific gravity and bowing, sapwood/heartwood ratio and bowing, log volume and bowing, and log volume and log end-splitting. These results show that the levels of growth stress in trees can be reduced by selection using indirect traits such as the sapwood/heartwood ratio and bowing.

Genetic similarity among soybean (Glycine max (L) Merrill) cultivars released in Brazil using AFLP markers

Genetic similarity among soybean genotypes was studied by applying the amplified fragment length polymorphism (AFLP) technique to 317 soybean cultivars released in Brazil from 1962 to 1998. Genetic similarity (GS) coefficients were estimated using the coefficient of Nei and Li (Nei and Li 1979), and the cultivars were clustered using the unweighted pair-group method with averages (UPGMA). The parentage coefficients of 100 cultivars released between 1984 and 1998 were calculated and correlated with the genetic similarity obtained by the markers. The genetic similarity coefficients varied from 0.17 to 0.97 (x = 0.61), with 56.8% of the coefficients being above 0.60 and only 9.7% equal to or less than 0.50. The similarity coefficients have remained constant during the last three decades. Dendrogram interpretation was hindered by the large number of cultivars used, but it was possible to detect groups of cultivars formed as expected from their genealogy. Another dendrogram, composed of 63 cultivars, allowed a better interpretation of the groups. Parentage coefficients among the 100 cultivars varied from zero to one (x = 0.21). However, no significant correlation (r = 0.12) was detected among the parentage coefficients and the AFLP genetic similarity. The results show the efficiency of AFLP markers in large scale studies of genetic similarity and are discussed in relation to soybean breeding in Brazil.

Response to recurrent selection under small effective population size

A formula was derived for the prediction of the response to recurrent selection when the effective population size (Ne) is small. Usually, responses to selection have been estimated by Rs = ics2A/sPh, where i, c, s2A, and sPh stand for standardized selection differential, parental control, additive variance, and phenotypic standard deviation, respectively. This expression, however, was derived under the assumption of infinite population size. By introducing the effects of finite population size, the expression derived was Rs = [ic(s2A + DFD1)/sPh] - DFID, where DF, ID and D1 are the changes in the inbreeding coefficient, the inbreeding depression, and the covariance of additive and homozygous dominance effects, respectively. Thus, the predicted responses to selection based on these expressions will be smaller than those based on the standard procedures for traits with a high level of dominance such as yield. Responses to five cycles of half-sib selection were predicted for maize by both expressions, considering that 100 progenies were evaluated and 10 S1 progenies were recombined, which corresponds to Ne = 10 for each cycle. The accumulated response to selection estimated with the new expression was about 47 and 28% smaller than that based on the standard expression for yield and plant height, respectively. Thus, the expression usually used overestimates the responses to selection, which is in agreement with reported results, because it does not take into account the effective population size that is generally small in recurrent selection programs

Partial diallel analysis of agronomic characters in rice (Oryza sativa L.)

Rice (Oryza sativa L.) breeding seeking to combine high productivity and cold tolerance for the temperate Latin America region is an important challenge. We estimated some useful parameters which can be used to investigate the genetic control of agronomic characters in crosses combining cold tolerance and productivity. A partial diallel design was used in crosses between six tropical indica rice cold susceptible genotypes (group 1) and seven japonica or indica/japonica cold tolerant rice genotypes (group 2). Parents and crosses were evaluated for agronomic characters under field conditions in two different experiments in 2005. The results showed significant mid-parent heterosis for all characters (plant height, tiller number, days to 50% flowering, panicle length, grains per panicle, sterility, and one-hundred grain weight). The predominant direction of dominance effects was negative for days to 50% flowering, and positive for all the other characters. General combining ability (GCA) and specific combining ability (SCA) were significant for all characters, although the GCA effects of the two groups were more important than the SCA effects.

Experimental alternatives for evaluation of progenies and clones in eucalyptus breeding programs

The feasibility of using augmented block designs and spatial analysis methods for early stage selection in eucalyptus breeding programs was tested. A total of 113 half-sib progenies of Eucalyptus urophylla and eight clones were evaluated in an 11 x 11 triple lattice experiment at two locations: Posto da Mata (Bahia, Brazil) and Sao Mateus (Minas Gerais, Brazil). Four checks were randomly allocated within each block. Plots consisted of 15 m long rows containing 6 plants spaced 3 m apart. The girth at breast height (cm/plant) was evaluated at 19 and 26 months of age. Variance analyses were performed according to the following methods: lattice design, randomized complete block design, augmented block design, Papadakis method, moving means method, and check plots. Comparisons among different methods were based on the magnitude of experimental errors and precision of the estimates of genetic and phenotypic parameters. General results indicated that augmented block design is useful to evaluate progenies and clones in early selection in eucalyptus breeding programs using moderate and low selection intensities. However, this design is not suitable for estimating genetic and phenotypic parameters due to its low precision. Check plots, nearest neighbour, Papadakis (1937), and moving means methods were efficient in removing the heterogeneity within blocks. These efficiencies were compared to that in lattice analysis for estimation of genetic and phenotypic parameters.

Predicting performance of soybean populations using genetic distances estimated with RAPD markers

Abstract In order to verify whether genetic distance (GD) is associated with population mean (PM), genetic variance (GV) andthe proportion of superior progenies generated by each cross in advanced generations of selfing (PS), the geneticdistances between eight soybean lines (five adapted and three non-adapted) were estimated using 213 polymorphicRAPD markers. The genetic distances were partitioned according to Griffing’s Model I Method 4 for diallel analysis,i.e.,GD ij =GD+ GGD i + GGD j + SGD ij . Phenotypic data were recorded for seed yield and plant height for 25 out of 28populations of a diallel set derived from the eight soybean lines and evaluated from F 2:8 to F 2:11 generations. Nosignificant correlation for seed yield was detected between GD and GV, while negative correlations were detectedbetween GD and PM and between GD and PS (r = -0.74** and -0.75**, respectively). Similar results were observedfor the correlation between GGD i + GGD j and PM and between GGD i + GGD j and PS (r = -0.78** and -0.80**,respectively). No significant correlation was detected for plant height. The magnitudes of the correlations for seedyield were high enough to allow predictions of the potential of the populations based on RAPD markers.

Heterose e distâncias genéticas moleculares para a produção de grãos em soja

1 em Abstract Heterosis has been reported for grain yield in soybeans, and despite the fact that hybrid cultivars have not been used yet, the knowledge of heterosis magnitude is very important for a previous selection of crosses, since heterosis is related to parental divergence. However, the obtention of enough F 1 seeds for experimental evaluation in plots is a time-consuming task, and thus, other indicators of the occurrence of heterosis could be very useful. The objective of this work was to evaluate heterosis and its relationship with AFLP molecular genetic distance (DG). Six F hybrids, derived from parents with different levels of genetic distances (DG) and their respective parents, were evaluated in completely randomized block designs, with four replications. Heterosis estimates were very different among different crosses, varying from 6.29 to 56.50% for mid-parent heterosis ( mg h ) and from -0.34 to 51.30% for high-parent heterosis ( gs h ). Besides, the correlation between heterosis and genetic distances (DG) were very high (0.83 and 0.60, respectively, for mg h and gs h ), which indicates that DG can be used as indicative of more divergent crosses, and thus, as one criterion for selection of more divergent parents.

Avaliação de cultivares de mamona em cruzamentos dialélicos parciais

Castor bean (Ricinus communis L.) is a very important crop in northeastern Brazil. Nowadays it became also important in other regions of Brazil, due to the Brazilian Biodiesel Program. The objective of the present work was to estimate general and specific combining ability for seed yield and agronomic traits in castor bean, in order to obtain a better understanding of the genetic control of these traits of breeding purposes. Two groups of cultivars were studied: Group 1, composed by five short stature cultivars, and Group 2, composed by five tall cultivars. The two groups were crossed according to a partial diallel design, giving rise to 25 hybrid evaluated in a 5 x 5 lattice design with four replications. Plots comprised of a nine meters single row spaced three meters apart (27 m2) with 10 plants. Seed yield (PR), days to flowering (DF), plant height (AP), height up to the primary raceme (AC), and length of primary raceme (TU) were evaluated. General combining ability (GCA) was significant for all traits within each group, while specific combining ability (SCA) was significant only for DF and TU. The GCA sum of squares was higher than SCA sum of squares for all traits, indicating that additive effect loci were more important than dominant effect loci. In both groups there are cultivars with favorable alleles for yield and agronomic traits.

Avaliação de progênies f2:4 e f4:6 de soja e perspectivas do uso de teste precoce para a produção de grãos

The objective of this work was to evaluate the perspectives of using early generation testing for grain yield in soybeans. The base material comprises a population derived from a two-way cross between lines 14 and 38, divergent for grain yield. One hundred progenies F2:4 and one hundred progenies F4:6 were derived from this population and evaluated in the 2006/07 growing season, using a lattice design with 4 replications, in two locations, at Piracicaba, SP. Plots consisted of 2 meter long rows spaced 0,5 meter apart, with 35 plants after thinning. The components of variance, coefficients of heritability on a plot mean basis and expected response to selection were estimated for grain yield from the joint analysis of variance, for F2:4 and F4:6 generations. Estimates of expected response to selection were about 60% higher in the F4:6 generation; however this superiority would probably be offset by the larger time to complete a cycle. General results indicate that early generation testing for grain yield in soybeans can be effective for moderate selection intensities.