Search

Species of the genus Cynodon are among the most cultivated forage crops in the world due to their high yield and nutritional quality, and its use in cattle feeding has been associated with gains in animal weight and increased milk production. The objective of this study was to model covariance structures in Cynodon spp. clones and study the changes in ranking of the selected genotypes, since it is believed that affects the ranking of genotypes. A total of 202 genotypes were evaluated in an experiment conducted in an augmented block design with four replications and four harvests. The genotypes were assessed for plant height, green weight, percentage of dry matter, and plant vigor. Nineteen repeated measures models with different covariance structures were tested. The best-fitted model adopts the CORH covariance structure for the genetic effects. Correct modeling of the covariance structure affected the ranking of genotypes in all variables evaluated. [ABSTRACT FROM AUTHOR]

Forage plant breeders often use visual scores to assess agronomic traits because of the costs associated with in-depth phenotyping in the initial stages of breeding cycles. The aim of this study was to investigate the impact of the number of graders on the effectiveness of indirect selection of high-yielding genotypes and determine an optimal number of graders in the early-stage trials of Urochloa ruziziensis. For that purpose, five graders assessed 2.219 U. ruziziensis genotypes in an augmented block design. Biomass production and vigor scores were evaluated in two cuts and were analyzed using a linear mixed model approach. Vigor scores were analyzed considering each grader's score and the combinations of two, three, four, and five graders. Genetic variance was significant for both traits. Visual evaluation was effective in identifying productive genotypes based on the statistical criteria. The optimal number of graders for indirect selection of high-yielding U. ruziziensis genotypes is three. [ABSTRACT FROM AUTHOR]

Perennial grass hybrids of Urochloa are evaluated for at least two years during the screening stage trials (SS) and advanced trials (AD) in breeding programs, an expensive and time-consuming process. In this study, we aimed to evaluate the potential for early selection of cultivars in this breeding scheme. We used multiple measurements of agronomic and nutritive value traits of Urochloa humidicola and Urochloa decumbens in the SS, and Urochloa ssp. in the AD. Repeatability coefficient, genetic correlation, selection efficiency (SE), and Spearman correlations were estimated. The results indicated that reliable early selection could be applied, decreasing the evaluation period to one year and a half for SS, and to one year for AD. These results were confirmed by high genetic and rank correlations, and overall SE above 50%. This proposed change in the breeding scheme could save considerable time, labor, and resources and accelerate the release of improved cultivars. [ABSTRACT FROM AUTHOR]

The objective of this work was to estimate genetic parameters for agronomic traits and resistance to spittlebugs in B. decumbens hybrids and to select the ones with best performance. For that, 324 hybrids were evaluated in field plots for agronomic traits and in the greenhouse for resistance to spittlebugs. Genetic variability amongst the hybrids was observed for all traits analyzed. The heritability estimates between genotypes means were higher than 0.52 for all agronomic traits and 0.98 and 0.99 for nymphal survival and nymphal period duration respectively. Hybrids with better performance than cultivar Basilisk for each individual trait were identified and also through a selection index combining all traits. Assigning weights to the different traits in the selection index did not significantly alter the rank for superior hybrids. Those were selected to continue on to the next phases of the breeding program. [ABSTRACT FROM AUTHOR]

The objectives of this study were to detect genetic variability among genotypes of Brachiara humidicola, study the genetic diversity and identify redundant variables in the discrimination of hybrids. Fifteen genotypes were evaluated for morphological, agronomic and nutritive characteristics in a randomized block design with six replications, in Rio Branco, Acre. Analysis of variance was performed, followed by the Scott-Knott test. Different techniques of multivariate analysis were used to study genetic diversity. Significant differences in plant performance were observed for agronomic and morphological characteristics, but not for nutritive value. There was consistency between the different clustering techniques. Four redundant characteristics were identified that can be discarded. The existence of divergent and superior hybrids that can be used in recurrent selection (sexual) programs or can be released as new (apomictic) cultivars after testing for animal response was confirmed. The lack of genetic variability in bromatological traits indicates the need for differentiated selection strategies. [ABSTRACT FROM AUTHOR]

The aim of this study was to evaluate the resistance of B. ruziziensis clones to the spittlebug species Deois schach and Mahanarva spectabilis. Together with the cultivar Marandu (B. brizantha) and the progenies 77s, 85s and 106s as controls, 71 B. ruziziensis clones were evaluated in a randomized block design. Six spittlebug eggs about to hatch were artificially infested and 40 days later evaluated for the percentage of surviving nymphs and plant damage based on a rating scale. Analysis of variance identified significant differences for nymph survival and plant damage of both spittlebug species. Since nymph survival and damage scores of the clones 100, 95, 19, 42, 93, 4, 92, 47, 26, 63, and 58 were similar to Marandu, these can be considered resistant to insect pests. These results, besides demonstrating the existence of genetic variability for a possible selection, offer hope for an identification of B. ruziziensis spittlebug-resistant genotypes. [ABSTRACT FROM AUTHOR]