Abstract
Root and tuber crops (RTCs) produce a variety of edible belowground organs constituting the second most important source of carbohydrates to humans and the most important in sub-Saharan Africa. This review focuses on the development of adventitious roots (ARs), differentiation of storage roots and the growth and decay of non-storage roots. The root systemof RTCs comprises ARs but the storage organs differ; confusingly, much of the literature refers to them all as tubers. Swelling of ARs to form storage roots (SRs) in cassava and sweet potato results from expansion of root cambium and proliferation of starch storage tissue with starch biosynthesis genes highly expressed, and lignin biosynthesis genes down regulated. Several genes play a role
in SR development in sweet potato including two MADS-box transcription factors and in cassava, potato and sweet potato storage organ initiation and developmentis related to KNOX1 activity. The small number of studies makes generalization difficult, but several show thatmaximum length coincides with the start of rapid growth of storage roots/tubers. Different patterns of growth may reflect differences in soil water and nutrient availability. Many ARs appear to be short-lived. Typically the rooting depth of potato was <1m with a maximum root length of 7–12km/m2 while for cassava, rooting depth was deeper (>1m), but root length was less (1–2.84km/m2). We highlight the paucity of studies of RTCs, the inconsistent use of terms to describe roots and
storage organs and the need to characterize the longevity and functionality of different root types especially SRs.

Elsevier Inc. All rights reserved.
Advances in Agronomy, Volume 161 2020
ISSN 0065-2113
https://doi.org/10.1016/bs.agron.2020.01.001

his study investigates the sustainable fertilization of cassava using localized struvite application, a fertilizer recovered from wastewater, which is rich in nitrogen, phosphorus, and magnesium.

Abstract

Cassava is a root storage crop that is important to the starch industry and food security. We studied sustainable fertilization of cassava using local placement of struvite, a fertilizer recovered from wastewater, rich in nitrogen, phosphorus, and magnesium. We asked if struvite is a suitable fertilizer for cassava, if it is likely to spread through the substrate (leach), and if roots can proliferate and utilize a concentrated placement of struvite. Cassava was grown in rhizoboxes under different fertilizer placement strategies: unfertilized control, homogenous fertilizer distribution in the top 20 cm (‘homogenized’), a strip placement (‘layer’) at 20 cm depth, and a localized ‘depot’at the same depth. Shoot and root growth responses were monitored over 8 weeks. Cassava growth was significantly improved with struvite fertilization. The fertilizer remained localized, with minimal spread during the 8 weeks of experimentation. Both the ‘layer’and ‘homogenized’struvite placements resulted in comparable biomass production, significantly greater than the unfertilized treatment. Plants in the ‘depot’placement initially grew similar to the unfertilized treatment as roots took time to locate and proliferate into the fertilizer depot. Afterwards, plants in the ‘depot’treatment grew quickly resulting in an intermediate biomass at harvest. Notably, cassava exhibited strong root proliferation in response to concentrated struvite, which did not compromise deep rooting but instead appeared to enhance it, increasing specific root length. These findings suggest that strip fertilization with struvite may offer a sustainable fertilization strategy for cassava, warranting further investigation in field trials.

This study models the architecture of cassava root systems and explores the dynamics of carbon allocation between shoots and roots during the early stages of storage root bulking.

Background and aims
Plants store carbohydrates for later use during, e.g., night, drought, and recovery after stress. Carbon allocation presents the plant with tradeoffs, notably between growth and storage. We asked how this tradeoff works for cassava (Manihot esculenta) pre- and post-storage root (SR) formation and if manipulation of the number of storage organs and leaf growth rate might increase yield.
Methods
We developed a functional-structural plant model, called MeOSR, to simulate carbon partitioning underlying cassava growth and SR formation in conjunction with the root system's three-dimensional (3D) architecture (RSA). We compared the model results to experimental data and simulated phenotypes varying in the number of SR and leaf growth rate.
Results
The simulated 3D RSA and the root mass closely represented those of field-grown plants. The model simulated root growth and associated carbon …

This publication focuses on analyzing cassava storage root development, which is critical for improving yields in South America, Africa, and Asia.

Abstract: Storage roots of cassava plants crops are one of the main providers of starch in many South American, African, and Asian countries. Finding varieties with high yields is crucial for growing and breeding. This requires a better understanding of the dynamics of storage root formation, which is usually done by repeated manual evaluation of root types, diameters, and their distribution in excavated roots. We introduce a newly developed method that is capable to analyze the distribution of root diameters automatically, even if root systems display strong variations in root widths and clustering in high numbers. An application study was conducted with cassava roots imaged in a video acquisition box. The root diameter distribution was quantified automatically using an iterative ridge detection approach, which can cope with a wide span of root diameters and clustering. The approach was validated with virtual root models of known geometries and then tested with a time-series of excavated root systems. Based on the retrieved diameter classes, we show plausibly that the dynamics of root type formation can be monitored qualitatively and quantitatively. We conclude that this new method reliably determines important phenotypic traits from storage root crop images. The method is fast and robustly analyses complex root systems and thereby applicable in high-throughput phenotyping and future breeding.

Increasing cassava production could mitigate one of the global food insecurity challenges by providing a sustainable food source. To improve the yield potential, physiological strategies (i.e., the photosynthetic efficiency, source-to-sink carbon partitioning, and intracellular carbon metabolism) can be applied in breeding to screen for superior genotypes. However, the influences of source-to-sink carbon partitioning and carbon metabolism on the storage root development of cassava are relatively little understood. We hypothesized that carbon partitioning and utilization vary modulating the distinctive storage root yields of high and low-yielding cassava varieties, represented in this study by varieties Kasetsart 50 (KU50) and Hanatee (HN), respectively.

Abstract: AbstractMain conclusion The efficiency of suberized plant/environment interfaces as transpiration barriers is not established by the suberin polymer but by the wax molecules sorbed to the suberin polymer.Abstract Suberized cell walls formed as barriers at the plant/soil or plant/atmosphere interface in various plant organs (soil-grown roots, aerial roots, tubers, and bark) were enzymatically isolated from five different plant species (Clivia miniata, Monstera deliciosa, Solanum tuberosum, Manihot esculenta, and Malus domestica). Anatomy, chemical composition and efficiency as transpiration barriers (water loss in m s −1 ) of the different suberized cell wall samples were quantified.Results clearly indicated that there was no correlation between barrier properties of the suberized interfaces and the number of suberized cell layers, the amount of soluble wax and the amounts of suberin. Suberized interfaces of C. miniata roots, M. esculenta roots, and M. domestica bark periderms formed poor or hardly any transpiration barrier. Permeances varyingbetween 1.1 and 5.1 × 10 −8 ms −1 were very close to the permeance of water (7.4 × 10 −8 ms −1 ) evaporating from a water/ atmosphere interface. Suberized interfaces of aerial roots of M. deliciosa and tubers of S. tuberosum formed reasonable transpiration barriers with permeances varying between 7.4 × 10 −10 and 4.2 × 10 −9 m s −1 , which were similar to the upperrange of permeances measured with isolated cuticles (about 10 −9 ms −1 ). Upon wax extraction, permeances of M. deliciosa and S. tuberosum increased nearly tenfold, which proves the importance of wax establishing a transpiration barrier. Finally,highly opposite results obtained with M. esculenta and S. tuberosum periderms are discussed in relation to their agronomicalimportance for postharvest losses and tuber storage.Keywords Bark · Diffusion barrier · Periderm · Suberization · Storage root · Transpiration · Tuber · Water loss · Wax