Storage Root Dry Matter Content Research Articles

Adaptability of a U.S. purple-fleshed sweetpotato breeding population in Uganda

Purple-fleshed sweetpotato varieties are important for their nutraceutical value due primarily to their high anthocyanin content. These varieties also often have high dry matter content preferred by consumers and processors in sub-Saharan Africa. However, improved purple-fleshed sweetpotatoes are not available in Uganda. This study was conducted to evaluate the adaptability of purple-fleshed sweetpotato genotypes for storage root yield, dry matter and anthocyanin content in Uganda. A bi-parental population of 159 clones from the cross NCP06-020 NC09-188 introduced to Uganda from North Carolina State University was evaluated with three local checks in two sites and two seasons in Uganda. The trials were planted in two locations using alpha lattice design with two replicates and five sweetpotato vine cuttings per genotype. Storage roots and vines were harvested after five months and the agronomic characteristics were recorded. Dry matter and anthocyanin content of storage roots were analysed after harvesting. The mean storage root yield of clones across the two locations was 37.8 t/ha and 24.2 t/ha in the first season (2015A) and second season (2015B); respectively, with an overall mean of 31.0 t/ha. Storage root dry matter content ranged from 21.5 to 33.7% across locations and seasons with an overall mean of 29.1%. Storage root anthocyanin content across the two locations ranged from 0 to 12.6 mg/100g FW with the overall mean of 3.9 mg/100g FW. A total of ten genotypes showed significantly stable performance (P <= 0.001) across two locations and two seasons. Highly significant difference between genotypes for dry matter content, anthocyanin content and total storage root yields revealed significant genetic variability among the tested genotypes, which can be exploited for future crop improvement.

Combining Ability, Heterosis, and Heritability of Storage Root Dry Matter, Beta-Carotene, and Yield-related Traits in Sweetpotato

Orange-fleshed sweetpotato (OFSP) is an effective, low-priced, and sustainable source of β-carotene (provitamin A). However, most OFSP varieties have low storage root dry matter content (DMC), which influences their acceptance by small-scale farmers and hence needs to be improved. The objective of the study was to determine the combining ability, type of gene action, heterosis and heritability of storage root DMC, β-carotene content, and yield-related traits of selected sweetpotato clones for further evaluation and breeding. Crosses were conducted using a 7 × 7 half-diallel mating design and a total of 28 genotypes (seven parents and 21 crosses) were evaluated at four locations in Ethiopia using a 7 × 4 alpha lattice design with two replications. The performance of the genotypes was significantly different (P &lt; 0.01) across the four locations for storage root DMC, β-carotene content, sweetpotato virus disease (SPVD) reaction, storage root yield, and harvest index (HI). The general combining ability (GCA) and specific combining ability (SCA) mean squares were significant (P &lt; 0.01) for all traits except the SCA effect of storage root DMC. The GCA to SCA variance ratios were 0.96, 0.94, 0.74, 0.96, and 0.97 for storage root DMC, β-carotene content, SPVD, fresh storage root yield, and HI, respectively, indicating that the inheritance of these traits was controlled mainly by additive genes. Progenies of crosses involving Ukerewe × Ejumula, Ukerewe × Pipi, Resisto × Pipi, and Ejumula × Pipi exhibited high levels of positive heterosis for storage root DMC. Similarly, progenies of crosses including Resisto × Pipi and Resisto × Ogansagan had higher positive heterosis for fresh storage root yield, reflecting the breeding value of these parents. Relatively high narrow sense heritability (h2) was obtained for β-carotene content (79.8%) and HI (48.6%). However, the h2 estimates of storage root DMC, SPVD, and fresh storage root yield were relatively low at 19.0%, 14.9%, and 20.4%, respectively. Crosses with high β-carotene content such as Ukerewe × Resisto, Resisto × Ogansagan, Eumula × Pipi, and NASPOT 1 × Temesgen exhibited high storage root DMC. These families also had medium-to-high mean fresh storage root yield. Therefore, progenies derived from these families are good candidates to develop improved OFSP varieties with high storage root DMC.

Heritability, combining ability and inheritance of storage root dry matter in yam beans

Storage root dry matter content (RDM) is central to the improvement of consumer and industrial attributes of root crops. Yam bean ( Pachyrhizus species) is a legume root crop newly introduced in Uganda, but its adoption may be constrained by low RDM. The objective of this study was to investigate the magnitude of variance for general combining ability (GCA) and specific combining ability (SCA) effects, heritability estimates and inheritance of RDM in yam beans. Progenies of sixteen crosses, generated using the North Carolina (NCII) mating scheme, were evaluated in F 1 and F 2 field experiments, with three replications at the National Crops Resources Research Institute (NaCRRI), Namulonge in Central Uganda, during the first cropping seasons of April, 2013 and 2014, respectively. Significant (p<0.001) mean squares for general combining ability (GCA), and specific combining ability (SCA) were observed in F 1 and F 2 generations, demonstrating additive and non-additive genetic inheritance of RDM. High Baker’s ratio in F 1 (0.76) and F 2 (0.78), and large σ 2 GCA / σ 2 SCA (3.13) indicate predominance of additive gene effects. Narrow sense heritability was high in both F 1 (0.74) and F 2 (0.75), implying that RDM can be improved in yam beans through selection. The results provide a basis for selection of suitable parents for hybridisation and breeding programmes to develop high dry matter yam bean varieties in Uganda. Keywords: Baker’s ratio, gene action, Pachyrhizus species

Genetic variability in storage root bulking of cassava genotypes under irrigation and no irrigation

Early bulking in cassava (Manihot esculenta Crantz) is a very important trait in semi-arid ecologies of the tropics. Farmers tend to select early-maturing cassava varieties to escape terminal drought and destruction by domestic animals during the dry season. However, early harvesting is associated with yield penalty due to unavailability of high-yielding early-maturing cassava varieties. In order to develop early-bulking cassava varieties for the savanna ecologies, this study was carried out to assess genetic variation in the pattern of storage root bulking and as well as traits associated with early storage root bulking under moisture stress and well-watered conditions. Twenty cassava genotypes were arranged in a randomised complete block design with three replications under irrigation and no irrigation. The genotypes were sequentially harvested at 6, 8, 10 and 12 months after planting to study their pattern of dry matter accumulation. Irrigation water was supplied using a drip irrigation system with a discharge capacity of 1.6 l/h. Analysis of variance indicated significant effect of genotype, harvesting time and irrigation on most of the yield traits studied. The interaction between genotype and irrigation effect was significant for all traits except mean storage root weight, storage root girth, storage root length and storage root dry matter content. Apart from storage root girth and storage root dry matter content, genotype × harvesting time interaction was not significant. Pearson correlation analysis of root yield at different times showed significant positive correlation between early storage root yield and final root yield indicating the possibility of selecting early-bulking genotypes with high yield potential. The study indicated that dry matter is partitioned more for root elongation than expansion in root girth under moisture stress conditions compared with irrigation, resulting in high storage root length: girth ratio. This ratio can be used to study the pattern of photosynthates accumulation in cassava roots under stress conditions. The study helped to provide improved understanding of the genetic basis and the mechanism of storage root bulking in cassava under moisture stress conditions, which can be exploited to develop high-yielding cassava varieties for drought-prone areas to ensure food security.

Altered carbohydrate metabolism in the storage roots of sweetpotato plants overexpressing the SRF1 gene, which encodes a Dof zinc finger transcription factor

In order to characterize the functions of the sweetpotato SRF1 gene, which encodes a Dof zinc finger transcriptional factor preferentially expressed in the storage roots, we isolated its full length cDNA and produced transgenic sweetpotato plants with altered SRF1 expression levels. The isolated cDNA of SRF1 encoded a polypeptide of 497 amino acids and was closely related to the cyclic Dof factors of Arabidopsis and the ascorbate oxidase binding protein of pumpkin. SRF1 was most highly expressed in storage roots, although some expression was also observed in other vegetative tissue. Transgenic plants overexpressing SRF1 showed significantly higher storage root dry matter content compared to the original cultivar Kokei No. 14 or control transgenic plants. In these plants, the starch content per fresh weight of the storage roots was also higher than that of the wild-type plants, while the glucose and fructose content drastically decreased. Among the enzymes involved in the sugar metabolism, soluble acid invertase showed a decreased activity in the transgenic plants. Gene expression analysis showed that the expression of Ibbetafruct2, which encodes an isoform of vacuolar invertase, was suppressed in the transgenic plants overexpressing the SRF1 gene. These data suggest that SRF1 modulates the carbohydrate metabolism in the storage roots through negative regulation of a vacuolar invertase gene.

Comparison of methods for phenotypic stability analysis of cassava (Manihot esculenta Crantz) genotypes for yield and storage root dry matter content

The objective of this work was to compare different phenotypic stability methods by using yield and storage root dry matter content data of eight cassava genotypes, assessed in eight environments in northwest of Paraná State, Brazil. All the methodologies applied showed to be able to study the stability of cassava genotypes, but each with its peculiarities. The methodologies of Eskridge, Annicchiarico and Lin and Binns were the most appropriated on situation with smaller effect of G x E interaction. The AMMI analysis and the Toler and Burrows methodology were the most specific on detailing specific adaptations of cassava genotypes to favorable and unfavorable environments. It could be suggested to use simultaneous AMMI analysis and Toler and Burrows methodology. The clone IAC 190-89 was the most promising.

Evaluation of the Storage Root‐Forming Legume Yam Bean (Pachyrhizus spp.) under West African Conditions

The yam bean (Pachyrhizus spp.) contains three closely related cultivated species: P. tuberosus (Lam.) Sprengel, P. erosus (L.) Urban, and P. ahipa (Wedd.). Its storage root dry matter content (SRDM) is usually low, although genotypes with a high SRDM have been identified (‘Chuin’ accessions). Flowers are often removed through flower pruning (FP) to increase storage root fresh matter yield (SRFY). The main objectives of this study were to investigate the potential for use in Benin (West Africa), to estimate the effect of FP, and to test whether roots could be processed into gari In total, 34 accessions were tested at one drought‐stress and one irrigated location. Means and genetic variance components were estimated for 33 agronomic traits. Without FP, the SRFYs of P. tuberosus, P. erosus, and P. ahipa were 13.9, 23.4, and 12.4 t ha−1, respectively, and the seed yields were 2.2, 5.2, and 2.1 t ha−1, respectively. The FP caused SRFY to increase by 48, 91, and 61% in P. tuberosus, P. erosus, and P. ahipa, respectively. The storage root dry matter yield (SRDY) of P. erosus was only slightly higher (∼8.5 t ha−1) than that of the Chuin accessions (∼8.0 t ha−1). Under drought, the SRDY was least affected in P. erosus Early‐maturing P. ahipa accessions were identified. All species could be used to make gari, which contained, on average, 5.5% protein, 58.5% starch, and 23.8% total dietary fiber. The crop has the potential for use in West Africa and has a large genetic variation for genetic improvement.

Variance component estimations and allocation of resources for breeding sweetpotato under East African conditions

AbstractIn Africa, average sweetpotato storage root yields are low and breeding is considered to be an important factor in increasing production. The objectives of this study were to obtain variance component estimations for sweetpotato in this region of the world and then use these to determine the efficiency of variety trials and breeding systems. From an incomplete series of variety trials in Kenya and Uganda (comprising 15 genotypes, three locations, two crop durations and three seasons) variance components were estimated ‐ using the REML method ‐ for the following traits: storage root yield, biomass production, harvest index, storage root dry matter and the Elston index which was used to aggregate all four traits. The storage root yield of clones across all 12 environments ranged from 15.2 to 33.0 t/ha. The variance components were significant for all traits, except the genotype by season interactions for storage root dry matter. The efficiency of selection systems was determined for total test capacities of 450 and 900 plots and using not more than five locations. Two‐stage selection was 17‐81% more efficient than one‐stage selection after two seasons of testing. Two‐stage selection was optimized under the restriction of using at least two locations at step 1. Trials with two locations and one replication at step 1 and five locations and two replications at step 2 were appropriate both for selecting for storage root yield and for simultaneously selecting for storage root yield, biomass production, harvest index and storage root dry matter content by using the Elston index. There are indications that such an allocation of resources for breeding sweetpotato is also appropriate for other regions in Sub‐Saharan Africa.

Selecting a Peruvian sweetpotato core collection on the basis of morphological, eco-geographical, and disease and pest reaction data

Sweetpotato [Ipomoea batatas (L.) Lam.] ranks among the seven most important food crops of the world. The International Potato Center (CIP) holds one of the largest sweetpotato (2n=6x=90) genebanks with more than 5000 cultivated accessions from America, Africa, Asia and the Pacific. This collection is clonally maintained because it comprises farmer-selected cultivars that have been asexually propagated for many years. Because of this, numerous duplicate accessions of the same cultivar are to be expected. Considering that almost 30% of the sweetpotato accessions assembled in this collection were from Peru, the first step to select a sweetpotato core collection was to identify duplicates in this group. Duplicate identification, using detailed comparisons of morphological characters and electrophoretic banding patterns of total proteins and esterases, reduced the number of Peruvian accessions in the collection from 1939 to 673. The number of duplicates of the same cultivar ranged from 1 to 99 accessions. A Peruvian sweetpotato core collection was selected to enhance the utilization of this germplasm. A total of 21 morphological descriptors were scored in all the different Peruvian cultivars. The unweighted pair-group method using an arithmetic average (UPGMA) determined the pairwise distance for members of distinct clusters based on these morphological descriptors. A core subset was selected considering the square root of the number of accessions for each Peruvian department and respective cluster, as defined by UPGMA. The original core collection consists of 85 accessions (12.6%) from all Peruvian departments, except that of Madre de Dios, where sweetpotato was never collected, and from all agro-ecological zones except Paramo, which has only 0.5% of the accessions of the entire collection. The sampling for this core collection was appropriate as determined by comparisons of means and frequency distributions for all morphological descriptors. Furthermore, this sampling was validated by the partial assessment of this sweetpotato germplasm for resistance to diseases and pests, tolerance to salt, storage root dry matter content, and vegetative period.