Number Of Storage Roots Research Articles

Phosphorus affects storage root yield of cassava through root numbers

The objective of this study was to determine the effect of phosphorus applied through fertigation on growth and root yield of cassava. This was achieved through a greenhouse pot-experiment consisting of 1, 4, 7, 10, 20 and 30 mg P L−1. Increasing P from 1 to 30 mg P L−1 realized a 57.1 and 150.0% increase in leaf blade P in 2014 and 2015, respectively. Similarly, chlorophyll content and shoot growth increased as P concentration in solution increased. However, leaf stomatal conductance and net photosynthesis reached a maximum in 7 and 20 mg P L−1 in 2014 and 2015, respectively. This trend of stomatal conductance and net photosynthesis was consistent with that of dry root yield and storage roots numbers. Regressing dry root yield against storage root numbers showed that R2 = 0.80. Phosphorus encourages formation of storage roots and the duration of cassava’s growth affects the amount of P required for maximum root yield.

Partitioning index and non-structural carbohydrate dynamics among contrasting cassava genotypes under early terminal water stress

Cassava (Manihot esculenta Crantz.) is a storage root crop of importance in tropical regions where periodic dry season and drought affect performance. Cassava genotypes that differ in performance in ecosystems with various water regimes were subjected to water stress during storage-root initiation and early development. Plants were grown in 50 kg pots in a screen house environment under well-watered and water stress conditions for a 120-day period. Water stress had a significant effect on most traits analyzed. However, relative water content, partitioning index and non-structural carbohydrates were unaffected. Tolerant genotypes had a higher partitioning index than susceptible genotypes during water stress, associated with a larger number of storage roots initiated and larger storage root biomass, while they were shorter and had less fibrous root biomass. Tolerant lines were indistinguishable from susceptible lines in above ground biomass under stress. These findings suggest that early evaluation of storage root number, partitioning index, and associated traits at an early stage of cassava storage-root development could be an effective approach by which cassava genotypes are screened for favorable drought tolerance response.

Combining ability and heterosis of selected sweetpotato (Ipomoea batatas L.) clones for storage root yield, yield-related traits and resistance to sweetpotato virus disease

Designed crosses using genetically diverse and complementary genotypes is useful to develop sweetpotato clones with improved agronomic traits. The objective of this study was to determine combining ability and heterosis among selected sweetpotato clones for number of storage roots per plant (NRPP), storage root yield (SRY), dry matter content (DMC) and resistance to sweetpotato virus disease (SPVD) for breeding. Eight selected genotypes were crossed using an 8 × 8 half diallel mating design to generate 28 families which were evaluated along their parents under field condition at three sites using a 6 × 6 lattice design with three replications. General combining ability (GCA) and specific combining ability (SCA) effects were highly significant (P < 0.001) among families. Significant GCA × sites and SCA × sites effects indicated environmental effect on gene action and expression. Parental genotypes Simama and Gairo had positive and significant GCA effects for NRPP. The parents 03-03, Ukerewe and Simama had significant and positive GCA effects for SRY and DMC, respectively. Further, Ex-Msimbu-1 and Gairo displayed negative and significant (P ≤ 0.01) GCA effect for SPVD resistance. The genotypes Gairo, 03-03, Ukerewe, Simama and Ex-Msimbu-1 are promising parents for sweetpotato breeding to improve NRPP, SRY, DMC and resistance to SPVD. Further, the study selected best performing families namely: 03-03 × Simama, 03-03 × Resisto and Simama × Ex-Msimbu-1 which recorded the highest mean storage root yields of 16.1, 16.6 and 17.2 tons/ha combined with high DMC and resistant to SPVD for genetic advancement.

Yield, Quality, and Performance of Organic Sweetpotato Slips Grown in High Tunnel Compared with Open Field

Sweetpotatoes (Ipomoea batatas) are nutritious, easily stored, and well adapted to a variety of organic farming operations. This widely consumed root crop is propagated through the use of cuttings, known as slips. Slips are commercially grown primarily in the southeastern United States, and growers in the central United States still have limited access to sweetpotato planting material. Production of organic slips in high tunnels (HTs) could be a profitable enterprise for growers in the central United States given the season extension afforded by controlled-environment agriculture, which could allow growers to diversify their operations and facilitate crop rotation. In trials conducted in 2016 and 2017 at two research stations in northeast and south central Kansas, a systems comparison was used to evaluate the yield and performance of organic sweetpotato slips grown in HT as compared with the open field (OF), with four to six replications at each location. Propagation beds planted with ‘Beauregard’ seed roots in 2016 and ‘Orleans’ in 2017 were established in HT and OF under similar cultural methods and planting schedules. Slips were harvested from both treatment groups and transplanted to field plots to investigate the impact of production system on transplant establishment and storage root production. Slip yield from HT was greater than OF at both locations in 2016 (P ≤ 0.001), but this trend was inconsistent in 2017. Slips grown in HT were on average 12% less compact (slip dry weight per centimeter length) with fewer nodes than their OF counterparts in 2016. Nonetheless, mean comparisons for vine length, stem diameter, and total marketable storage root yield were not significant between HT and OF treatments (1.7 and 2.1 lb/plant, respectively). Similarly, the number of marketable storage roots for HT and OF groups was comparable (3.4 and 3.8 storage roots/plant, respectively). Although more research is needed to evaluate the feasibility of slips grown in HT and to determine recommendations for seed root planting densities, results from this study suggest that HT organic sweetpotato slip production could be a viable alternative to OF production as it relates to slip performance. According to this study, HT production could be a useful mechanism for growing sweetpotato slips, which could provide regional growers more control over planting material. Furthermore, HT slip production could promote the adoption of an underused vegetable crop that can be grown throughout many parts of the United States.

Pemberian Biochar Jengkok Tembakau untuk Meningkatkan Hasil Ubijalar pada Lahan Kering Sub-Optimal

Indawan et al, 2019. Increasing Sweet Potato Yield on Biochar Amendment Application on Sub-Optimal Dry Land. JLSO 8(1):47-56. Biochar is a soil amendment that can improve soil fertility, increase crop yield and can reduce contamination. This study aim to evaluate the sweet potato response to biochar application from tobacco industry waste. The combination of cultivar and dose of biochar implemented using a Split Plot Experiment Design with three replications. The cultivars placed 0n main plots and biochar doses on sub-plots. The thirteen cultivars covering 7 varieties (Kuningan Putih, Beta 1, Beta 2, Kuningan Merah, Sari, Boko, and Jago) plus six accession from Unitri and Brawijaya University collections (BIS OP-61-OP-22 , 73-6 / 2, 73 OP-8, BIS OP-61, 73 OP-5, and BIS OP-61-♀-29). The biochar dose used was B0 (0 t / ha) and B1 (5 t / ha). The experimental unit is measuring 5 m x 0.6 m, consisting of single row and planted with a spacing of 25 cm in row or 20 cuttings/row). The storage root numbers, storage root weight, % dry matter, Harvest Index (HI) and yields estimation are ditermined. The results showed that sweet potato cultivars gave a significant response to biochar application on fresh storage root weight, dry storage root weight, biomass dry weight, HI and storage root yields, but no interaction between cultivars and biochar doses. Storage root yield range of 8 - 21 t / ha without biochar and 10 - 23 t / ha with biochar 5 t / ha, except for Beta 1 and Boko. The use of biochar of 5 t / ha can increase storage root yields ranging from 8 - 45%.

Influence of Two Nitrogen Forms on Hormone Metabolism in Potential Storage Roots and Storage Root Number of Sweetpotato

In this study, we investigated the effects of two N forms on sweetpotato [Ipomoea batatas (L.) Lam.] root growth and development, zeatin riboside (ZR) and indole‐3‐acetic acid (IAA) concentrations in potential storage roots, and storage root number per plant. During the period 2015 to 2016, field experiments were performed using the sweetpotato cultivars ‘Shangshu 19’ and ‘Jixu 23’, which involved the following three treatments: no application of N fertilizer, application of 60 kg N hm−2 ammonium N, and application of 60 kg N hm−2 amide N. Our results indicated that during storage root formation, compared with the control treatment, the ammonium N treatment led to a significantly higher number of thick roots. However, the ammonium N treatment significantly reduced the average diameter of thick roots during early storage root formation and increased the average diameter during late storage root formation. Compared with the control treatment, ammonium N treatment inhibited the expression of Ibkn1, Ibkn2, and SRD1 genes during the early stage of storage root formation and also reduced the activities of IAA oxidase, peroxidase, and polyphenol oxidase enzymes, thereby ultimately reducing the ZR and IAA concentrations in potential storage roots. The opposite pattern was observed during the late stage of storage root formation. During the canopy closure period, compared with the control treatment, ammonium N treatment significantly increased the number of storage roots with diameters of 0.5 to 5.0 cm but decreased the number of storage roots with diameters &gt;5.0 cm. At harvest, the ammonium N treatment had resulted in the highest storage root yield and storage root number per plant.

PRODUTIVIDADE E QUALIDADE DE RAÍZES DA MANDIOQUINHA-SALSA EM DIFERENTES NÍVEIS DE ADUBAÇÃO NPK

The storage roots of arracacha have high nutritional value, being rich in carbohydrates, minerals, vitamins A and C, and starch of high digestibility. However, in this crop one of the decisive factors for the production of roots with higher nutritional value is the balanced fertilization. The aim of this study was to evaluate the yield and nutritional quality of storage roots of arracacha, grown at increasing levels of NPK fertilization. The experiment was conducted in the randomized blocks design, with eight replications. The treatments consisted of three NPK levels (AD0 = unfertilized cultivation, AD1 = cultivation with 50% of recommended fertilization, and AD2 = cultivation with 100% ofrecommended fertilization). It was observedthat higher levels of NPK fertilization increase the number, size and marketable yield of storage roots of arracachacrop. NPK fertilization also increases the size and contentsof K, Mg, and Mn of storage roots, without interfering with the pulp pH and contentsof protein, Ca, Cu, and Fe. However, when the increase in root size is not accompanied by an increase in dry matter content, the starch, P, and Zn contents of the roots reduce with increasing levels of NPK fertilization.

Low and high-temperature effects on sweetpotato storage root initiation and early transplant establishment

Abstract Temperature is considered as a major environmental factor upon which the storage behavior of sweetpotatoes depends. To quantify shoot and root vigor responses during sweetpotato early transplant establishment, an experiment was conducted using sunlit environmental growth chambers at three day/night temperatures, 22/14 (low), 30/22 (optimum), 38/30 °C (high). Ten sweetpotato cultivars were transplanted in pots for 20 days and several shoot and root morphological and physiological traits were assessed. Sweetpotato cultivars varied significantly for many traits measured particularly root components. High and low temperatures significantly decreased the production of storage root number. Low temperature caused a marked decrease in vine length, node number, leaf area, total biomass, and net photosynthesis causing 95, 70, 78, 66, and 36% reduction compared to the optimum temperature. At high temperature, average leaf area was seven times more than optimum indicating strong temperature effects on leaf number, size, and leaf area development. Principal component analysis was used to classify sweetpotato cultivars to low and high-temperature tolerant, intermediate, and sensitive groups. The sweetpotato cultivars O’henry and Bonita were identified as tolerant, Evangeline, B14, Vardaman, and Covington as intermediate tolerant, and NC05198 and Travis as sensitive to both low and high temperatures. A poor correlation was observed between low and high temperature response indices indicating that cold and heat tolerance mechanisms are different and the selection has to be made independently in developing tolerance to low and high temperatures. The identified low and high temperature tolerant cultivars and their associated morpho-physiological characteristics may be useful for breeders to develop new cultivars that could withstand variable temperatures projected to occur in future climates aiming to increase storage root yield.

Effects of nitrogen forms on carbohydrate metabolism and storage‐root formation of sweet potato

AbstractIn this study, we examined the effects of different forms of nitrogen (N) fertilizer on carbohydrate metabolism and storage root formation in sweet potato [Ipomoea batatas L. (Lam.) cv. Shangshu 19 and cv. Jixu 23] in 2015–2016. Two fertilizer treatments, ammonium nitrogen (AN) and amide nitrogen (XN), were applied at 60 kg ha−1 in a two‐factor split‐plot design. The effects of nitrogen form on the morphology of adventitious roots, carbohydrate metabolism in potential storage roots, and number of storage roots per plant in sweet potato were investigated. The results show that during the early growth phase, the AN treatment significantly increased the number of adventitious roots, root tips, root length density, and fresh weight of roots (in pot trials). This treatment also significantly decreased the sucrose concentration of potential storage roots and increased the activities of cell wall, vacuolar, and cytoplasmic invertases. However, XN‐treated potential storage roots showed a relatively high starch concentration, activities of sucrose synthase and ADP‐glucose pyrophosphorylase, and transcription of sporamin genes. At the canopy closure period, the AN treatment significantly increased the number of storage roots of 0.5–5.0 cm in diameter and decreased the number of those &gt; 5 cm in diameter compared to the control. The XN treatment induced the opposite effects. In the harvesting period, the AN treatment produced the highest storage root yield and number of storage roots per plant. Thus, in field trials the AN treatment induced a greater increase in production by increasing the number of storage roots.

Root zone temperature alters storage root formation and growth of sweetpotato

AbstractLarge mounds amended with plant residues are a common cultivation method for sweetpotato (Ipomoea batatas) in the western parts of the Papua New Guinea highlands, with a suggested benefit of elevated root zone temperature (RZT) from decomposition. This study aimed to evaluate whether RZT affects the formation and growth of sweetpotato storage roots. Experiments evaluated the effects of a constant elevated RZT on the Beauregard cultivar and of a short‐term increase in RZT on the Beauregard and Northern Star cultivars. Plants were grown in 18‐L pots divided into a control compartment (constant RZT at 20°C) and a treated compartment (RZT at 30, 40 or 50°C). Constant elevated RZT was maintained until harvest, while short‐term increase in RZT occurred in weeks 2 and 3 only. Constant elevated RZT did not affect the total number of storage roots, but RZT of 30°C and above reduced the dry‐biomass of storage roots. The short‐term increase in RZT did not alter the total number or dry‐biomass of storage roots in Beauregard, while both of these attributes were reduced at RZT of 40°C or above in Northern Star. Elevated RZT inhibited dry‐biomass accumulation of storage root, with a more pronounced impact at constant elevated RZT. These results demonstrate that any benefits of the mound culture on sweetpotato yield production do not arise through the influence of temperature elevation.

Responses of root physiological characteristics and yield of sweet potato to humic acid urea fertilizer.

Humic acid (HA), not only promote the growth of crop roots, they can be combined with nitrogen (N) to increase fertilizer use efficiency and yield. However, the effects of HA urea fertilizer (HA-N) on root growth and yield of sweet potato has not been widely investigated. Xushu 28 was used as the experimental crop to investigate the effects of HA-N on root morphology, active oxygen metabolism and yield under field conditions. Results showed that nitrogen application alone was not beneficial for root growth and storage root formation during the early growth stage. HA-N significantly increased the dry weight of the root system, promoted differentiation from adventitious root to storage root, and increased the overall root activity, total root length, root diameter, root surface area, as well as root volume. HA-N thus increased the activity of superoxide dismutase (SOD), peroxidase (POD), and Catalase (CAT) as well as increasing the soluble protein content of roots and decreasing the malondialdehyde (MDA) content. HA-N significantly increased both the number of storage roots per plant increased by 14.01%, and the average fresh weight per storage root increased by 13.7%, while the yield was also obviously increased by 29.56%. In this study, HA-N increased yield through a synergistic increase of biological yield and harvest index.

‘Covington’ Sweetpotato Plant Survival and Yield Response to Preplant Irrigation, Planting Depth, and Transplant Size

A research gap exists on the effects of irrigation, transplant (nonrooted stem cuttings) size, and planting depth on sweetpotato (Ipomoea batatas) plant survival and storage root yield. Field studies were conducted in 2012 and 2013 to determine the effects of preplant irrigation, planting depth, and transplant size on sweetpotato plant stand, storage root number, and yield. Treatments included four transplant sizes (3.7, 6.3, 8.5, and 10.7 inches), two planting depths (2 and 6 inches), and preplant irrigation or nonirrigation. Overall, plant stand, storage root number, and yield were greater when transplants of size ≥6.3 inches were planted 6 inches deep as compared with transplants planted 2 inches deep. The use of preplant irrigation had an overall positive impact on plant stand, storage root number, and yield under dry soil conditions. When moisture was readily available, neither plant stand nor storage root numbers were affected by the application of irrigation as observed in 2013. However, sweetpotato yields were greater during both years when preplant irrigation was used. Irrigation during the root initiation phase of plant establishment or extended periods of no rainfall would be beneficial for improving plant stands and yields.

Sweetpotato Transplant Holding Duration Effects on Plant Survival and Yield

Studies were conducted in North Carolina to determine the effect of holding durations (HDs) [0, 1, 3, 5, and 7 days before planting (DBP)] of ‘Covington’ sweetpotato (Ipomoea batatas) transplants on plant stand and storage root numbers and yield in production fields. In a second field study, the effect of preplant irrigation (PI) treatments (PI and nonirrigation) were evaluated along with the transplant HD on plant stand, storage root numbers, and yield. Transplants held for 7 DBP did not survive as well as the other treatments (lower plant stands) and had lower no. 1, marketable, and total storage root numbers and yields than other holding treatments. HD of 1 or 3 DBP resulted in higher plant stands, and no. 1, marketable, and total numbers of storage roots and yields than holding for 0, 5, or 7 DBP. This study affirms the importance of soil moisture at and shortly after planting for transplant survival and yield. Holding transplants for 1–3 DBP can improve stand establishment and yields when dry conditions occur either before or soon after planting. However, holding transplants for 7 DBP can result in reduced plant stands and yields when stress/dry conditions occur soon after planting.

Physiological, Morphological Changes and Storage Root Yield of Sweetpotato [Ipomoea batatas (L.) Lam.] under PEG-Induced Water Stress

Sweetpotato is an important tuberous root crop rich in nutrients such as vitamins and carbohydrates, and can grow well in arid regions with less water consuming crop. The aim of this research was to evaluate the storage root yields, physiological, biochemical and morphological traits in sweetpotato cv. ‘Japanese Yellow’ subjected to polyethylene glycol (PEG)-induced water deficit. At harvest (4 months after planting) the number of storage roots per plant and storage root fresh weight in sweetpotato treated with 5% PEG (-0.54 MPa) in nutrient solution of hydroponic culture declined by 20.0% and 47.4% compared to the control without PEG, respectively. Leaf area and leaf dry weight significantly decreased by 85.6% and 95.3%, respectively when exposed to water deficit stress. Sucrose content (114.7 mg g-1 dry weight; DW) in storage roots of sweetpotato grown under PEG-induced water deficit conditions was enriched by 2.2 fold of control (52.5 mg g-1 DW) and was greater than in storage roots derived from soil culture (70.3 mg g-1 DW). Total soluble sugar in the root and storage root tissues was enriched and may play a key role as osmotic adjustment (OA) in PEG-induced water stressed plants. Free proline and sucrose contents were also dominated in the leaf tissues to maintain the leaf osmotic potential in water stressed plants. In addition, chlorophyll degradation, chlorophyll fluorescence diminution and stomatal closure were found in plants grown under PEG-induced water deficit conditions, leading to reduction in net photosynthetic rate (Pn) and subsequently lesser amounts of glucose and fructose contents in the leaf tissues. Sucrose and free proline in the roots of sweetpotato play a key role as major osmotic adjustment when subjected to PEG-induced water deficit condition. Basic knowledge gained from this research will further be investigated the drought defense mechanism in sweetpotato via osmoregulation system.

Growth and yield response of glasshouse- and field-grown sweetpotato to nitrogen supply

Nitrogen (N) is an essential element for producing optimum crop yields, but negative responses to high N supply are commonly reported in sweetpotato (Ipomoea batatas) production. This study assessed contrasting responses of sweetpotato yield as a result of N application rates of 0, 30, 60, 90, 130, 160 and 230 kg ha−1 in a glasshouse trial, and rates of 0, 50, 100, 150, 200 and 250 kg ha−1, equivalent to 160, 210, 260, 310, 360 and 410 kg ha−1 when soil N supply is included. The glasshouse-grown sweetpotato produced a maximum number and dry-biomass of storage roots, aboveground biomass and leaf area at 130 kg N ha−1, while leaf N concentration peaked at 90 kg N ha−1. Further increasing N application to 230 kg ha−1 did not result in significant change in any of these attributes. In field-grown sweetpotato, leaf and storage root N concentrations increased with increasing N supply. Although N supply had no effect on the number of storage roots, total yield peaked at 260 kg ha−1. Further increase of N supply reduced the total yield by up to 14% of the maximum yield. With increasing N supply, the glasshouse-grown sweetpotato yield linearly increased with leaf area; the arrangement of the trial permitting light interception to exceed the pot surface area. The yield reduction in field-grown plants was attributed to excess growth of aboveground parts, beyond that needed for efficient light capture. Respirational demand of the aboveground growth occurred at the expense of storage root yields.

The use of humic acid urea fertilizer for increasing yield and utilization of nitrogen in sweet potato

Humic acid urea fertilizer (HA-N) is a new type of slow-release nitrogenous fertilizer that can enhance utilization rate of urea, and consequently increases crop yield. However, there were few researches about the effect of HA-N on the nitrogen absorption and utilization in sweet potato production. Hence, the effect of HA-N on nitrogen accumulation and distribution, nitrogen use efficiency (NUE), and yield of sweet potato was studied in the field using the &lt;sup&gt;15&lt;/sup&gt;N tracer technique. Results showed that HA-N significantly increased the number of storage roots per plant and the average fresh weight per storage root, as well as the yield increased by 29.6% compared with urea fertilizer. Furthermore, nitrogen accumulation of total plant was higher under the HA-N. In addition, HA-N significantly increased nitrogen production efficiency of fertilizer and nitrogen production efficiency. Results of a &lt;sup&gt;15&lt;/sup&gt;N tracer experiment revealed that the percentage of nitrogen absorbed by plant from fertilizer increased from 31.1% to 38.7% and NUE increased from 33.5% to 44.8% with application of HA-N when compared with single N treatment, respectively. HA-N significantly increased sweet potato storage root yield, nitrogen absorption and NUE, as well as it reduced the loss of nitrogen fertilizer.

The use of humic acid urea fertilizer for increasing yield and utilization of nitrogen in sweet potato

Humic acid urea fertilizer (HA-N) is a new type of slow-release nitrogenous fertilizer that can enhance utilization rate of urea, and consequently increases crop yield. However, there were few researches about the effect of HA-N on the nitrogen absorption and utilization in sweet potato production. Hence, the effect of HA-N on nitrogen accumulation and distribution, nitrogen use efficiency (NUE), and yield of sweet potato was studied in the field using the &lt;sup&gt;15&lt;/sup&gt;N tracer technique. Results showed that HA-N significantly increased the number of storage roots per plant and the average fresh weight per storage root, as well as the yield increased by 29.6% compared with urea fertilizer. Furthermore, nitrogen accumulation of total plant was higher under the HA-N. In addition, HA-N significantly increased nitrogen production efficiency of fertilizer and nitrogen production efficiency. Results of a &lt;sup&gt;15&lt;/sup&gt;N tracer experiment revealed that the percentage of nitrogen absorbed by plant from fertilizer increased from 31.1% to 38.7% and NUE increased from 33.5% to 44.8% with application of HA-N when compared with single N treatment, respectively. HA-N significantly increased sweet potato storage root yield, nitrogen absorption and NUE, as well as it reduced the loss of nitrogen fertilizer.

Herbicides and polythene mulching effects on yield of cassava

A field experiment was conducted to study the effects of weed management practices on cassava under irrigated conditions in Bhubaneswar (Odisha), India for consecutive three years (2010–11 to 2012–13). The results revealed that four rounds of manual weeding at 1, 2, 3 and 4 months after planting (MAP) and black polythene mulching resulted in taller plants, more number of nodes and leaves per plant, maximum number of storage roots per plant, maximum length and girth of storage roots as well as fresh storage roots yield per plant with lower weed biomass. Mean fresh root yield due to black polythene mulching was at par with four rounds of manual weeding (at 1, 2, 3 and 4 MAP). Black polythene mulching resulted in higher dry matter partitioning efficiency and soil microbial population. The root yield decreased by 9.6%, due to pre-emergence application of oxyfluorfen + two rounds of manual weeding (at 2 and 3 MAP) treatment and 10.1% in two rounds of manual weeding (at 1 and 2 MAP) + post-emergence application of glyphosate (at 3 MAP) compared to four rounds of manual weeding (at 1, 2, 3 and 4 MAP).

Failure Analysis under Electric Lights: Growth and Yield of Sweetpotato in Response to 14 Days of Prolonged Darkness

Two sweetpotato [Ipomoea batatas (L.) Lam] genotypes (TU-82-155 and NCC-58) were grown hydroponically and subjected to a temporary loss of lighting in the form of 14 days of prolonged darkness compared with a lighted control under standard daily light periods to determine the impact on growth responses and storage root yield. Vine cuttings of both genotypes were grown in rectangular channels. At 65 days after planting, lights were turned off in the treatment chambers and replaced by a single incandescent lamp, providing between 7 and 10 µmol·m−2·s−1 photosynthetic photon flux (PPF) for 18 hours, and the temperature lowered from 28/22 °C light/dark, to a constant 20 °C. Plants remained under these conditions for 14 days after which the original light level was restored. Growth chamber conditions predark included, a PPF mean provided by 400-W metal halide lamps, of 600 ± 25 µmol·m−2·s−1, an 18-hour light/6-hour dark cycle and a relative humidity of 70% ± 5%. The nutrient solution used was a modified half-Hoagland with pH and electrical conductivity (EC) maintained between 5.5–6.0 and 1000–1200 μS·cm−1, respectively, and was adjusted weekly. Storage root number and fresh weight were similar regardless of treatments. Plants exposed to prolonged darkness produced 10.5% and 25% lower fibrous root fresh and dry mass, respectively, but similar foliage yield and harvest index (HI). ‘NCC-58’ produced an average of 31% greater storage root yield than that of ‘TU-82-155’ but the number of storage roots as well as % dry matter (%DM) were similar. ‘NCC-58’ also produced 31% greater fibrous root dry weight, whereas ‘TU-82-155’ produced a 44% greater HI. The significant interaction between prolonged darkness and cultivars for %DM of the storage roots showed that DM for ‘TU-82-155’ was 18.4% under prolonged darkness and 17.9% in the light. That for ‘NCC-58’ was 16.4% under prolonged darkness compared with 19.4% (14.8% greater) for plants that were not subjected to prolonged darkness. The evidence that there were no adverse impacts on storage root yield following the exposure to prolonged darkness suggests that the detrimental effects were below the detectable limits for these cultivars in response to the short perturbation in the available light and that sweetpotatoes would be hardy under short-term failure situations.

Early storage root bulking index and agronomic traits associated with early bulking in cassava

One of the attempts by farmers in counteracting the devastating effects of cassava brown streak disease (CBSD) on yield and quality of cassava is early harvesting. However, most varieties grown by farmers are often late bulking which increases the disease severity while on the other hand early harvesting results in significant yield losses. Farmers, therefore, need early storage root bulking cassava varieties in order to reduce the time to harvest leading to a faster rate of return to investment, while at the same time avoiding devastating effects of CBSD on yield and quality of cassava. The study was, therefore, conducted to identify high-yielding and early storage root bulking cassava genotypes as well as traits associated with early storage root bulking and estimate yield loss if any due to early harvesting. The overall aim was to generate information that would guide future improvement programmes for high-yielding and early-bulking cassava varieties in Malawi and other countries facing similar challenges. Trials were implemented using a square lattice design with three replications at two locations for two growing seasons with three harvest intervals (6, 9 and 12 months after planting, MAP). High yields were obtained of up to 9.5t/ha at 6 and 17.8t/ha at 9 MAP. Furthermore, the study revealed that yields obtained at 9 MAP were higher than those obtained at 12 MAP for some genotypes which suggests that such genotypes would be considered as early storage root bulking. Simple correlation analysis identified harvest index, storage root number, storage root diameter and storage root length as the selection criteria to achieve high fresh storage root yield (t/ha) and dry mass yield (t/ha). Path coefficient analysis allocated harvest index and shoot mass as the major selection criteria in improving fresh storage yield and dry mass yield. The study suggests that both source and sink capacities were important for determining early yield. Therefore, these two traits are the key determinants of early storage root bulking and should be used when selecting early-bulking cultivars and indirectly selecting for storage root number, storage root diameter and storage root length.