Traits In Cassava Research Articles

Inheritance of useful traits in cassava grown in subhumid conditions

AbstractA diallel study among nine parental clones of cassava was conducted in the subhumid environment on the northern coast of Colombia. Analysis of variance suggested significant effects for the six variables analysed: fresh‐root yield, harvest index, root dry matter content, height of first branching, reaction to thrips and plant‐type scores. General and specific combining ability effects and their interaction with the environment were significant for most of the variables as well. Results suggested that dominance plays a particularly important role in the cases of fresh‐root yield and harvest index but had relatively little importance in the reaction to thrips, dry matter content or height of first branching. Specific breeding approaches are suggested for these traits, depending on the relative importance of additive or non‐additive effects in their inheritance. The correlations among different traits were also analysed and in several cases their magnitude reached statistical and biological significance.

Within-family genetic variation and epistasis in cassava (Manihot esculenta Crantz) adapted to the acid-soils environment

Little is known about the inheritance of agronomic traits in cassava, or on the relative importance of epistasis for most crops. A group of 10 clones, adapted to the acid-soils environment was used as parents in a diallel study. Thirty genotypes were obtained from each F1 cross and cloned. Each clone was represented by six plants, which were distributed in three replications at two contrasting locations. Genetic variability concentrated in the within-family component, which was statistically significant for all the variables analyzed (fresh root yield (FRY), fresh foliage yield (FFY), harvest index, root dry matter content, and plant type score (PTS)) except for the reaction to super elongation disease (SED). Estimates of dominance variance were considerably larger than those of additive variance for fresh root and foliage yields. The reverse was observed for harvest index, dry matter content, PTS and SED score. Epistasis played an important role only for fresh root and foliage productions. These results agree with those from similar studies targeting different environments. The common assumption of absence of significant epistatic effects frequent in many quantitative genetic designs is, therefore, challenged from the results for these two variables. Alternative breeding approaches are suggested according to the results obtained from this study.

Epistasis in the Expression of Relevant Traits in Cassava (Manihot esculenta Crantz) for Subhumid Conditions

There is limited knowledge on the inheritance of agronomic traits in cassava and the importance of epistasis for most crops. A nine-parent diallel study was conducted in subhumid environments. Thirty clones were obtained from each F1 cross. Each clone was represented by six plants, which were distributed in three replications at two locations. Therefore the same 30 genotypes of each F1 cross were planted in the three replications at the two locations. Analysis of variance suggested significant genetic effects for all variables analyzed (reaction to thrips, fresh root and foliage yields, harvest index, dry matter content, and root dry matter yield). Significant epistatic effects were observed for all variables, except harvest index. Dominance variance was always significant, except for dry matter content and dry matter yield. Additive variance was significant only for reaction to thrips. Results suggested that dominance plays an important role in complex traits such as root yield. The significance of epistasis can help us understand the difficulties of quantitative genetics models and QTLs in satisfactorily explaining phenotypic variation in traits with complex inheritance. Significant epistasis would justify the production of inbred parental lines to fix favorable allele combinations in the production of hybrid cassava cultivars.

Diallel inheritance of relevant traits in cassava (Manihot esculenta Crantz) adapted to acid-soil savannas

There is a limited knowledge on the inheritance of traits with agronomic relevance in cassava. A diallel study among 10 parental clones was conducted in the acid-soils environment in the eastern savannas of Colombia. Thirty clones were obtained for each F1 cross. Each clone was represented by six plants, which were distributed in three replications at two locations. Therefore, the same 30 genotypes of each F1 cross were planted in the three replications at the two locations. Analysis of variance suggested significant effects for five of the six variables analyzed (harvest index, dry matter content, height of first branching, reaction to super elongation disease, and plant type scores). Fresh root yield showed strong genotype × environment interaction and differences between crosses reached statistical significance in only one of the two environments analyzed. General and specific combining ability effects and their interaction with the environment were significant for most of the variables as well. Results suggested that dominance plays an important role particularly in the cases of fresh root yield and harvest index.

Epistasis in Cassava Adapted to Midaltitude Valley Environments

Little is known about the inheritance of agronomic traits in cassava (Manihot esculenta Crantz). The vegetative multiplication of cassava allows cloning of individual genotypes, and separates environmental from genetic variation in the within‐family variation. Knowing the magnitude of between‐ and within‐family variation is important for defining breeding strategies and for measuring different components of genetic variances, particularly the seldom‐estimated epistasis. A group of nine genotypes, adapted to midaltitude environments, was used for a diallel study. Thirty clones were obtained from every F1 cross (each clone was represented by six plants), and planted in three replications at two locations. Statistical differences among crosses were found for fresh‐root yield, harvest index, root dry‐matter content, and reaction to mites (Mononychellus tanajoa Bondar) and to whiteflies (Aleurotrachelus socialis Bondar). General combining ability (GCA) was significant for all traits except fresh‐root yield and dry‐matter content, and specific combining ability (SCA) was significant for all traits except whitefly damage score. Fresh‐root yield was the only trait with significant epistatic effects, which, combined with a large dominance variance, suggested a prevalence of nonadditive effects. The introduction of inbreeding would be one approach for the efficient exploitation of these nonadditive effects found for fresh‐root yield. For the remaining traits, epistasis was negligible and current schemes exploiting additive effects may suffice.

Two cassava promoters related to vascular expression and storage root formation.

Cassava ( Manihot esculenta Crantz) storage roots, organs accumulating large amounts of starch, develop from primary roots via secondary growth. The availability of promoters related to storage-root formation is a prerequisite for engineering root traits in cassava. Two cDNAs, c15 and c54, were identified from a storage-root cDNA library of cassava MCol1505 via differential screening. The transcripts of c15 and c54 were detected in storage roots but not in leaves by Northern analysis. Homology analysis of the deduced amino acid sequences showed that C15 is likely to be related to cytochrome P450 proteins, which are involved in the oxidative degradation of various compounds, while C54 may be related to Pt2L4, a cassava glutamic acid-rich protein. The promoter regions of c15 and c54 were isolated from the corresponding clones in a cassava genomic library. A 1,465-bp promoter fragment ( p15/1.5) of c15 and a 1,081-bp promoter region ( p54/1.0) of c54 were translationally fused to the uidA reporter gene, and introduced into cassava and Arabidopsis thaliana (L.) Heynh. The expression patterns of p15/1.5::uidA and p54/1.0::uidA in transgenic plants showed that both promoters are predominantly active in phloem, cambium and xylem vessels of vascular tissues from leaves, stems, and root systems. More importantly, strong beta-glucuronidase activity was also detected in the starch-rich parenchyma cells of transgenic storage roots. Our results demonstrate that the two promoters are related to vascular expression and secondary growth of storage roots in cassava.

Distribuição da diversidade isoenzimática e morfológica da mandioca na agricultura autóctone de Ubatuba

A diversidade fenotípica de quatro sistemas isoenzimáticos e doze caracteres morfológicos em mandioca (Manihot esculenta Crantz) foi quantificada através do índice de Shannon-Weaver para quatro roças de mandioca pertencentes a dois agricultores autóctones no município de Ubatuba-SP. A diversidade total foi repartida entre diversidade dentro de roças e diversidade entre roças, mostrando que a maior parte da diversidade se concentra dentro de roças para a maioria dos caracteres. Entrevistas foram realizadas para verificar se os agricultores reconhecem a existência de plantas de mandioca originadas por semente e a existência de bancos de semente.

Cassava-based intercropping: a review

This paper reviews intercropping research for a particular case: cassava-based crop combinations. Cassava is dominated in combination with maize while it is the dominating species in combination with low-growing species. Combinations with maize or legumes show a real biological advantage over the sole crops reflected in (modified) Area × Time Equivalency ratio (ATER) values above unity. This is not the case with sweet potatoes. Success of maize+cassava mixtures depends on time and rate of recovery of cassava after maize harvest. Biological advantage tends to disappear when maize yield exceeds about 3.5 t ha −1. Under growing conditions or practices which result in high maize yield, intercropping cassava with maize is not biologically advantageous Biological advantage of intercropping with legumes decreases with the legumes' growth duration, which should not exceed 90 days. Physiological traits of cassava for successful intercropping with maize or with legumes are probably not the same, but their nature is not clear. Moderate early vigour and a high partitioning of dry matter to the storage roots after harvest of the associated crops seem important in both cases. Cassava breeding for sole cropping has resulted in varieties with good performance in intercropping. Whether varieties can be selected with better adaptation to intercropping cannot be concluded from the literature. Dry-matter distribution, in particular after harvest of the associated crop, seems important but more growth analytical studies are required. Usefulness of currently available crop models in the study of intercropping is doubtful.