C4 plants can be divided into three groups based on differences in activities of three decarboxylating enzymes: NADP-malic enzyme, NAD-malic enzyme, and phosphopyruvate carboxykinase.In the Gramineae the three C4 groups are distinguished by anatomical and ultrastructural characteristics of bundle-sheath chloroplasts. NADP-malic enzyme species lack well-developed grana in bundle-sheath chloroplasts (grana reduced) and the bundle-sheath chloroplasts are in the centrifugal position. NAD-malic enzyme species have bundle-sheath chloroplasts in the centripetal position and contain grana. Phosphopyruvate carboxykinase species have bundle-sheath chloroplasts in the centrifugal position and they contain grana. NADP-malic enzyme species of the Gramineae have only been found in the subfamilies Aristidoideae and Panicoideae. With the exception of the genera Panicum, and Urochloa, NAD-malic enzyme species and phosphopyruvate carboxykinase species have only been found in the subfamily Eragrostoideae. C4 species of the genus Panicum are found among all three of the C4 groups.The dicotyledonous C4 species examined fall into two groups: those having high NADP-malic enzyme and those having high NAD-malic enzyme. No phosphopyruvate carboxykinase C4 species have been found among the dicotyledons. The NADP-malic enzyme C4 species of the dicotyledons like NADP-malic enzyme species of the Gramineae have bundle-sheath chloroplasts with reduced grana but in contrast to NADP-malic enzyme species of the Gramineae the bundle-sheath chloroplasts are in the centripetal position. The NAD-malic enzyme species of the dicotyledons like the NAD-malic enzyme species of the Gramineae have bundlesheath chloroplasts in the centripetal position with well developed grana.The results are discussed in terms of evolutionary and functional diversification of C4 plants.

Key messageConsolidates relevant molecular and phenotypic information on cassava to demonstrate relevance of heterosis, and alternatives to exploit it by integrating different tools. Ideas are useful to other asexually reproduced crops.AbstractAsexually propagated crops offer the advantage that all genetic effects can be exploited in farmers’ production fields. However, non-additive effects complicate selection because, while influencing the performance of the materials under evaluation, they cannot be transmitted efficiently to the following cycle of selection. Cassava can be used as a model crop for asexually propagated crops because of its diploid nature and the absence of (known) incompatibility effects. New technologies such as genomic selection (GS), use of inbred progenitors based on doubled haploids and induction of flowering can be employed for accelerating genetic gains in cassava. Available information suggests that heterosis, non-additive genetic effects and within-family variation are relatively large for complex traits such as fresh root yield, moderate for dry matter or starch content in the roots, and low for defensive traits (pest and disease resistance) and plant architecture. The present article considers the potential impact of different technologies for maximizing gains for key traits in cassava, and highlights the advantages of integrating them. Exploiting heterosis would be optimized through the implementation of reciprocal recurrent selection. The advantages of using inbred progenitors would allow shifting the current cassava phenotypic recurrent selection method into line improvement, which in turn would allow designing outstanding hybrids rather than finding them by trial and error.

Cassava (Manihot esculenta Crantz) is an important security crop that faces severe yield loses due to cassava brown streak disease (CBSD). Motivated by the slow progress of conventional breeding, genetic improvement of cassava is undergoing rapid change due to the implementation of quantitative trait loci mapping, Genome-wide association mapping (GWAS), and genomic selection (GS). In this study, two breeding panels were genotyped for SNP markers using genotyping by sequencing and phenotyped for foliar and CBSD root symptoms at five locations in Uganda. Our GWAS study found two regions associated to CBSD, one on chromosome 4 which co-localizes with a Manihot glaziovii introgression segment and one on chromosome 11, which contains a cluster of nucleotide-binding site-leucine-rich repeat (NBS-LRR) genes. We evaluated the potential of GS to improve CBSD resistance by assessing the accuracy of seven prediction models. Predictive accuracy values varied between CBSD foliar severity traits at 3 months after planting (MAP) (0.27–0.32), 6 MAP (0.40–0.42) and root severity (0.31–0.42). For all traits, Random Forest and reproducing kernel Hilbert spaces regression showed the highest predictive accuracies. Our results provide an insight into the genetics of CBSD resistance to guide CBSD marker-assisted breeding and highlight the potential of GS to improve cassava breeding.

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Breeding maize (Zea mays L.) hybrids resistant to Striga and tolerant to low soil nitrogen (low‐N) will reduce grain yield losses due to stresses in West Africa (WA). Studies were conducted to determine if selection for Striga resistance and/or drought tolerance in early‐maturing maize populations improved low‐N tolerance in hybrids derived from selected inbreds from International Institute of Tropical Agriculture (IITA) and International Centre for Maize and Wheat Improvement (CIMMYT) under Striga‐infested, low‐N and optimum environments in Nigeria. One hundred and fifty hybrids developed from crosses involving 30 lines using North Carolina Design II plus six checks were evaluated at two locations each under low‐N, artificial Striga infestation, and optimum environments for 2 yr. Lines with combined resistance or tolerance to Striga as well as low‐N were identified. Striga‐resistant– as well as low‐N–tolerant hybrids with outstanding performance under both stress environments could be obtained through the accumulation of favorable alleles for resistance or tolerance in both parental lines. Although selection for Striga resistance and/or drought tolerance resulted in improved performance of genotypes under low‐N, it is important to test genotypes under low‐N to identify those with outstanding performance under the target stress. ENT 11 × TZEI 4 and TZEI 65 × ENT 11 were identified as the most stable and high‐yielding hybrids.

Rice has become an important staple in Ghana in recent years but most consumption is met by imports. In this study, farmers' preferences for rice varietal traits especially grain quality and the relationship of grain quality with consumer acceptability of locally produced rice was investigated in the Ashanti region of Ghana. Both formal and informal survey approaches were employed to collect data. The farmers preferred rice varieties with high yield potential and excellent grain quality. Jasmine 85 was the most popular variety because of its good taste and pleasant aroma. Other important traits that farmers consider in choosing a variety included plant height, threshability, disease resistance and weed competitiveness but these were site specific. Most consumers preferred imported to locally produced rice because the former had better appearance, cooking and eating qualities. Surprisingly, consumers' perceptions on various grain quality attributes were generally lower than those of farmers. However, quality attributes were considered by both farmers and consumers to be important for making choices for rice varieties and their specific preferences largely coincided. Most consumers and farmers prefer long grain aromatic rice that cooks soft and fluffy. The results of the survey emphasizes the need for Rice breeders in Ghana and the West African sub-region in general to focus more on breeding for improved grain quality in addition to high yield potential and tolerance to biotic and abiotic stresses.

Twenty cassava genotypes were arranged in a randomised complete block design with three replications and assessed for growth and yield stability using the additive main effect and multiplicative interaction (AMMI) analysis. Highly significant (P<0.001) effects of genotype, environment, and genotype ⁎ environment interaction were observed for all traits studied. The AMMI analysis of variance indicated that genotype accounted for 51% of the total sum of squares for height at first branching followed by environment (33%) and interaction (15%). For fresh root yield, environment effects accounted for 37% of the total sum of squares, whilst genotype and interaction accounted for 32% and 29%, respectively. Genotypic variances for harvest index (HI), plant height, storage root yield, and dry matter content contributed a greater proportion of the phenotypic variance indicating stronger genetic control. This suggests better chance of progress in the genetic improvement of these traits. Genotype MM96/1751 combined high yield with stability according to the yield stability index ranking across environments. On the other hand genotypes UCC 2001/449 and 96/1708 though high yielding were unstable according to AMMI stability value scores. However they can be tested further in more environments to ascertain their specific adaptability for release to farmers for cultivation to boost cassava production and ensure food security.

BackgroundGenetic diversity provides the capacity for plants to meet changing environments. It is fundamentally important in crop improvement. Fifty-nine local maize lines developed at INERA and 41 exotic (temperate and tropical) inbred lines were characterized using 1057 SNP markers to (1) analyse the genetic diversity in a diverse set of maize inbred lines; (2) determine the level of genetic diversity in INERA inbred lines and patterns of relationships of these inbred lines developed from two sources; and (3) examine the genetic differences between local and exotic germplasms.ResultsRoger’s genetic distance for about 64% of the pairs of lines fell between 0.300 and 0.400. Sixty one per cent of the pairs of lines also showed relative kinship values of zero. Model-based population structure analysis and principal component analysis revealed the presence of 5 groups that agree, to some extent, with the origin of the germplasm. There was genetic diversity among INERA inbred lines, which were genetically less closely related and showed a low level of heterozygosity. These lines could be divided into 3 major distinct groups and a mixed group consistent with the source population of the lines. Pairwise comparisons between local and exotic germplasms showed that the temperate and some IITA lines were differentiated from INERA lines. There appeared to be substantial levels of genetic variation between local and exotic germplasms as revealed by missing and unique alleles.ConclusionsAllelic frequency differences observed between the germplasms, together with unique alleles identified within each germplasm, shows the potential for a mutual improvement between the sets of germplasm. The results from this study will be useful to breeders in designing inbred-hybrid breeding programs, association mapping population studies and marker assisted breeding.Electronic supplementary materialThe online version of this article (doi:10.1186/s12863-014-0127-2) contains supplementary material, which is available to authorized users.