Genetic parameters, path analysis and indirect selection of agronomic traits of cassava germplasm.

This study aimed to estimate genetic parameters and correlations between morphological, agronomic and root quality traits of cassava plants, as well as to study cause and effect relationships through path analysis. A total of 814 genotypes were evaluated from 2011 to 2015. The joint analysis of the data was performed by the mixed models approach. The predicted genetic values of the genotypes were used to estimate the genetic correlations among as well the path analysis. The estimates of heritability of the genotype means ranged from 0.31 (commercial fresh root yield - CRY) to 0.62 (plant height - PLH). The highest genetic correlation coefficient estimates were observed for starch yield (STY) × total fresh root yield (FRY) (0.97). The results of the path analysis showed that FRY had the highest direct effect on STY, but the indirect selection based on FRY was not efficient to improve the gain of STY.

Productive potential of cassava plants (Manihot esculenta Crantz) propagated by leaf buds.

New techniques of rapid multiplication of cassava (Manihot esculenta Crantz) have been developed, requiring technical support for large-scale use. This work main to evaluate the agronomic performance of plantlets obtained by leaf buds technique against stem cuttings in the field conditions. The work was conducted using the randomized block design in a factorial scheme with 3 varieties (BRS Kiriris, 98150-06, 9624-09) × 4 origins of the plantlets (conventional - stem cuttings of 20 cm length, leaf buds of the upper, middle and inferior stem part) × 2 agrochemicals (control and treated). There was a remarkable decrease in some agronomic traits that ranged from 23% (number of branches) to 62% (shoot weight) when using leaf buds plantlets. The treatment of plantlets with agrochemicals promoted significant increases in all traits, ranging from 26% (number of roots per plant) to 46% (shoot weight). The plantlets originating from leaf buds of the upper and middle parts were able to generate stem-like plants similar to stem-derived ones. Despite its lower agronomic performance under field conditions, multiplication by leaf buds may generate five times the number of propagules in comparison with the conventional multiplication, and therefore it could be a viable alternative for rapid cassava multiplication.

Molecular marker assisted selection for increasing inbreeding in S1 populations of cassava.

The objective of the present work was to use MAS in self-pollinated cassava populations for obtaining individuals with high inbreeding (f) aimed at rapid development of partial inbred lines. Three progenies (F0222, F1378 and F1662) were self-pollinated, generating a total of 233 S1 individuals. The progenies and the S1 individuals were evaluated in the seedlings and clonal evaluation trials (CETs). In the CET, plants were evaluated for the following traits: plant height (PH), root dry matter content (DMC), above ground yield (AGY), root (RY) and starch yield (SY). Twenty-seven microsatellites and five minisatellites were used to determine the level of inbreeding of the S1 individuals. Inbreeding (f) values varied from 0.15 to 0.89 within progenies, whereas most of the S1 individuals presented f values above 0.50. In average, 25% of the S1 individuals were selected, which resulted in a 38% inbreeding increase in the cassava progenies. In contrast, phenotypic selection showed no differences in inbreeding increase. Furthermore, there was no correlation between the level of inbreeding and agronomic traits. MAS was efficient for the identification and selection of cassava S1 individuals, with higher inbreeding values contributing to the decrease in the breeding cycles necessary to obtain new cassava inbred lines.

Comparative pollen morphological analysis in the subgenera Passiflora and Decaloba.

The genus Passiflora is the most diversified of the Passifloraceae, and its palynology presents wide morphological variability. The objective of the study was to evaluate the pollen morphology of 18 Passiflora species in order to identify informative pollinic characteristics to contribute to the taxonomic classification of the genus. The morphology of the pollen grains and the exine structure were investigated using light microscopy and scanning electron microscopy. Differences in the pollen morphology were found in the studied species, mainly in terms of shape, pollen aperture and ornamentation pattern of the exine. Most of the species belonging to the subgenus Passiflora presented ornamented 6-syncolpate pollen grains with an oblate-spheroidal shape and an exine with large lumens. In the subgenus Decaloba the pollen grains were 6-colporate, 12-colpate and 12-colporate, with subprolate to prolate-spheroidal shape, as well as an exine with smaller lumen size and few ornamented. The pollen morphology of the species of the subgenera Passiflora and Decaloba has shown palynological characteristics that have specific diagnostic value, thus allowing a better understanding of the taxonomy of the genus Passiflora.

Development and characterization of microsatellite markers for the wild South American Passiflora cincinnata (Passifloraceae).

PREMISE OF THE STUDY: We developed the first set of microsatellite markers for the passion fruit, Passiflora cincinnata, to provide tools for further study of its genetic diversity and to support current conservation and genetic studies. METHODS AND RESULTS: We used a microsatellite-enriched library approach to isolate and characterize 25 new molecular markers. Seven primer pairs successfully amplified polymorphic microsatellite regions, with an average of five alleles per locus. The mean values of expected and observed levels of heterozygosity were 0.516 and 0.525, respectively. CONCLUSIONS: The microsatellite markers identified in this study may be valuable tools for population genetic studies, and this set of markers also may be useful in the design of a genetic conservation strategy, mating system, and hybridization studies.