Marcos de Araújo Rodovalho

Componentes genéticos de médias e depressão por endogamia em populações de milho-pipoca

Ten popcorn populations (PR 038, PR 079, RR 046, SC 016, PR 017, BRS ANGELA, SC 002, PR 009, PR 023 and SE 013) were evaluated to estimate inbreeding depression and average genetic components. The experiment was a split plot in a randomized complete block design with three replications. The plots were the inbreeding levels (S1 and S0) and the sub-plots were the populations in two locations (Maringa and Iguatemi-PR) during the 2001/2002 grown season. Plant and ear height, grain yield and popping expansion were evaluated. It was observed lower values of inbreeding depression and predominance of additive effects for popping expansion in relation to yield. The sucess of getting high popping expansion inbred lines is higher with BRS ANGELA and SC 002 populations.

Evaluation of Top-Cross Popcorn Hybrids Using Mixed Linear Model Methodology

The market for popcorn (Zea mays L.) has been continuously growing in Brazil fact has required the development of cultivars adapted to local environmental conditions. For this reason, the analytical objectives of this study were to evaluate top-cross popcorn hybrids in relation to popping expansion and grain yield in three different ecogeographic regions of Brazil, in order to estimate variance components using Restricted Maximum Likelihood (REML) and predict breeding values using Best Linear Unbiased Prediction (BLUP). Genetic evaluation considered a linear model with heterogeneous residual (environmental) variances. The Restricted Likelihood Ratio Test (RLRT) evidenced significant differences (p < 0.01) for the genotypic effect. Grain yield showed a moderate heritable trait (h2 = 0.26-0.39). A higher additive genetic control was evidenced for popping expansion (h2 = 0.58-0.85). Genetic correlations and Spearman coefficient between both traits were negative, indicating that selection based on grain yield would have a negative effect on popping expansion. The top-cross hybrids showed an adequate grain yield, whereas the quality of the popcorn was lower than commercial standards.

Influência do estresse hídrico sobre o desempenho fisiológico de sementes de híbridos simples de milho-pipoca

Objetivou-se, neste trabalho, avaliar o efeito do estresse hidrico induzido por polietileno glicol, na qualidade fisiologica das sementes de catorze hibridos simples de milho-pipoca. Para tanto, foi conduzido um experimento em que as sementes foram colocadas para germinar em substrato de papel-toalha, umedecido com solucoes de polietileno glicol (PEG 6000), nos niveis de potencial osmotico de zero (controle) e -0,3 MPa. A qualidade fisiologica das sementes foi avaliada por meio do teste de germinacao (primeira contagem e contagem final), do comprimento da raiz primaria e da parte aerea das plântulas e da biomassa seca das plântulas. A diminuicao do potencial hidrico do substrato e prejudicial a germinacao das sementes e, principalmente, ao crescimento das plântulas de milho-pipoca. Os decrescimos nas variaveis analisadas dependeram dos hibridos avaliados. Os hibridos G e K foram os que se mostraram mais tolerantes ao estresse hidrico, enquanto que o hibrido M foi mais susceptivel a seca. A tolerância ao estresse hidrico independe da qualidade inicial das sementes de milho-pipoca.

Heredabilidad de la sobrevivencia en 169 familias de maíz-roseta de granos blancos: Un enfoque Bayesiano

M.A. Rodovalho, F. Mora, E.M. Santos, C.A. Scapim, and E. Arnhold. 2008. Survival heritability in 169 families of white grain popcorn: A Bayesian approach. Cien. Inv. Agr. 35(3):303-309. During the genetic evaluation of 169 half-sib families of white grain popcorn (Zea mays), at the beginning of a breeding program conducted in southern Brazil (Cycle I), signifi cant differences in family survival were detected (p < 0.01). Consequently, plant survival was incorporated into the breeding program. The main objective of this study was to examine genetic parameters for plant survival, and their association with other traits of agronomic interest. A Bayesian approach was used for this purpose, implemented by Gibbs sampling (for individual plant selection) and independence chain algorithms (for family selection). The survival (measured as a binary trait) varied from 48 to 100% at the family level. Heritability (h 2 ) was signifi cant and high for this trait, with a posterior mean of h 2 =0.63 and Bayesian credible interval of 0.53-0.74. The genetic gain was 14.5% (selection intensity: 20%). Survival was correlated positively and signifi cantly with grain yield (p < 0.01), indicating that family selection based on survival alone would have a positive effect on yield and vice versa. The Spearman correlation coeffi cient calculated between survival and popping expansion was not signifi cantly different from zero, indicating that selection for family based on popping expansion would not have a signifi cant effect on survival.

Genetic analysis of tropical rust resistance in popcorn lines

The objectives of this study were to identify promising popcorn lines and hybrids for genetic resistance to tropical rust (Tr, Physopella zeae) in diallel crosses of nine lines derived from a large part of Brazilian popcorn germplasm and to estimate genetic parameters for Tr resistance. Crosses and checks were tested in a random block design, with artificial inoculations under greenhouse conditions. Plots consisted of a single 14-L pot, with four plants. Tr was measured by severity and area under the disease progress curve. Data was analyzed by Griffings diallel model, and genetic parameters were estimated. Heritability estimates to Tr resistance was medium. Specific combining ability-SCA had significant effects (P 0.10). This indicated the major importance of non additive gene effects. In general, breeding possibilities for resistance was restricted. The line 9 (L7.4) had the most outstanding GCA for resistance to Tr, and hybrids 1×7 and 3×6 had outstanding SCA and were recommended for breeding.