Predominantly symplastic phloem unloading of photosynthates maintains efficient starch accumulation in the cassava storage roots (Manihot esculenta Crantz)

Background Cassava (Manihot esculenta Crantz) efficiently accumulates starch in its storage roots. However, how photosynthates are transported from the leaves to the phloem (especially how they are unloaded into parenchymal cells of storage roots) remains unclear. Results Here, we investigated the sucrose unloading pattern and its impact on cassava storage root development using microstructural and physiological analyses, namely, carboxyfluorescein (CF) and C14 isotope tracing. The expression profiling of genes involved in symplastic and apoplastic transport was performed, which included enzyme activity, protein gel blot analysis, and transcriptome sequencing analyses. These finding showed that carbohydrates are transported mainly in the form of sucrose, and more than 54.6% was present in the stem phloem. Sucrose was predominantly unloaded symplastically from the phloem into storage roots; in addition, there was a shift from apoplastic to symplastic unloading accompanied by the onset of root swelling. Statistical data on the microstructures indicated an enrichment of plasmodesmata within sieve, companion, and parenchyma cells in the developing storage roots of a cultivar but not in a wild ancestor. Tracing tests with CF verified the existence of a symplastic channel, and [14C] Suc demonstrated that sucrose could rapidly diffuse into root parenchyma cells from phloem cells. The relatively high expression of genes encoding sucrose synthase and associated proteins appeared in the middle and late stages of storage roots but not in primary fibrous roots, or secondary fibrous roots. The inverse expression pattern of sucrose transporters, cell wall acid invertase, and soluble acid invertase in these corresponding organs supported the presence of a symplastic sucrose unloading pathway. The transcription profile of genes involved in symplastic unloading and their significantly positive correlation with the starch yield at the population level confirmed that symplastic sucrose transport is vitally important in the development of cassava storage roots. Conclusions In this study, we revealed that the cassava storage root phloem sucrose unloading pattern was predominantly a symplastic unloading pattern. This pattern is essential for efficient starch accumulation in high-yielding varieties compared with low-yielding wild ancestors.

Assessing the Efficiencies and Competitiveness of the Fresh Cassava Storage Root Production Systems in Sierra Leone

The Policy Analysis Matrix (PAM) was used to assess the efficiencies and competitiveness of fresh cassava storage root production systems in Sierra Leone. Proportional random sampling was used to select study samples. Information was collected using structured questionnaire from a total of 1,880 producer households. Out of the 36 potential storage root production systems identified, only 6 systems are mainly used by producers. The PAM was based on one hectare of land for production and Leone (SSL) as money to evaluate costs and revenues. The analysis indicates that, all the 6 fresh cassava storage root production systems present a Domestic Resource Cost Ratio of less than 1 (DRC < 1) and Cost-Benefit Ratio (RCB) also less than 1 (RCB within 0.14 to 0.42). Discounting potential revenue from stems and cassava leaves in storage root production systems that use improved varieties and fertilizer have higher comparative and competitive advantages. The systems are also profitable, even though producers are not protected from tradable and taxed inputs. Production systems also remain profitable with 25% and 50% yield loss. This was also confirmed by Abiodun and Adefemi (2016). It is therefore better to produce cassava locally in Sierra Leone than import for processing or consumption. This study proposes recommendations to improve cassava productivity in Sierra Leone.

Genetic variation and association among factors influencing storage root bulking in cassava

SUMMARYCassava (Manihot esculenta Crantz) is an important storage root crop with largely unexplored and unexplained potentially valuable genetic variability. Genetic variability is important in selecting suitable genotypes for crop improvement. The present study was aimed at assessing the extent of variability in cassava storage root bulking, based on fresh storage root yield accumulated over time. Twelve cassava genotypes were evaluated in a randomized complete block design at three contrasting locations in Uganda. Assessments were done from 5 to 13 months after planting at intervals of 2 months. Genotype, harvest time, location and their interactions were significantly different for fresh storage root yield and most of the other traits assessed. Estimates of variance components revealed that a large portion of the phenotypic variance was accounted for by the genotypic component for all traits assessed indicative of substantial genetic variability among the genotypes evaluated. This genetic variability is important in a hybridization and/or selection programme because it implies that significant genetic gain through phenotypic selection is possible for the traits assessed. Fresh storage root yield was positively and significantly correlated with storage root girth, harvest index, shoot mass and storage root number. The information generated will inform future breeding initiatives to develop early-bulking cassava genotypes with farmer-preferred traits in Uganda.

The Effects of Calcium on the In Vitro Cassava Storage Root Formation

Calcium can affect in vitro cassava storage roots formation and starch accumulation. Low concentration of calcium stimulates to induce in vitro cassava storage roots formation and the accumulation of starches. With the addition of calcium concentration, the diameter of the in vitro cassava storage roots was increased, but the induction rate and starch content was decreased. The scanning electron microscope observations SC124 in vitro cassava storage roots starch and field cultivation of cassava root starch, starch grains formed by these two different ways is very similar in size and shape. Our findings show that, apply tissue culture techniques to study the cassava starch synthesis mechanism is feasible.