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.

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.

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.