Drought effects on root and tuber production: A meta-analysis

Chapter 13 - Update on phytoplasma diseases associated with starchy root and tuber crops in Asia

This paper attempts to explore the status of tuber crops cultivation with regard to area, production and productivity across countries and exports of cassava and sweet potatoes from India. The result indicated that among various tuber crops, potatoes were vastly cultivated and consumed by Europe and Asia. At the same time, cassava and sweet potatoes were generally grown and consumed by Africa and Asia. In India, cassava and sweet potatoes are the most important tuber crops due to their large scale and varied uses. The growth rate analysis showed that the area under cassava (-1.38 percent) and sweet potatoes (-0.70 percent) as a whole showed a declining trend in India due to various agro-climatic conditions and socioeconomic constraints. In the context of climate change and considering the importance of root and tuber crops for food and nutritional security, it would be a smart move to bring more area under tuber crops cultivation to achieve 'self-reliance' and ' Make in India Mission'.

The term “root and tuber crops” is a very general “catch-all” for a wide cross-section of subterranean storage organs of which there are approximately 38 root, 23 tuber, 14 rhizome, 11 corm, and 10 bulb crops. The most important among them are potato, sugar beet, carrot, onion, and garlic (temperate root and tuber crops) and cassava, sweet potato, yams, and aroids (tropical root and tuber crops). Pre and postharvest losses of these crops are very high and, depending on the species cultivated and the storage environment, may be of the order of 30–60%. Bacterial control has been emerging as a promising alternative to chemical fungicide to control many pre- and postharvest diseases of these crops. The underlying mechanisms include antibiosis, competition for nutrients and space, and systemic resistance. The various strategies for use of antagonists and field uses (i.e., seed treatment, soil application, foliar spray, antagonistic mixture) have been discussed. In addition, certain mechanisms to improve performance of antagonists, such as addition of nutrients, use of antagonist mixture, and formulation of antagonist have been emphasized in this chapter.

Tropical root and tuber crops are gaining more importance presently due to their climate-the word climate resilience is very important for tuber crops resilient nature and irreplaceable role in assuring food security, especially in the developing countries. The major tropical root and tuber crops are cassava/tapioca (Manihot esculenta), sweet potato (Ipomoea batatas), yams (Dioscorea spp.), taro (Colocasia esculenta), elephant foot yam (Amorphophallus paeonifolius) and tania (Xanthosoma sagittifolium). Storage ability of tubers provides an opportunity to market the product, safeguards year-round supply and helps the growers realize better prices. Many viruses and fungi infection of tuber crops cause great loss to growers. The postharvest invasion of various pathogens takes the lead in increasing the loss. Postharvest pathogens make their way to the tuber through wounds or injury that occurs during harvest, transportation, packaging operations and storage processes. The pathogens belonging to the genera Alternaria, Aspergillus, Botrytis, Fusarium, Geotrichum, Gloeosporium, Mucor, Monilinia, Penicillium and Rhizopus cause the most important postharvest diseases in tuber crops. Many physical methods, chemicals, bioagents and botanicals are being utilized for minimizing and managing postharvest diseases. Tuber crops are clonally propagated and thus storage is an essential factor. Minimizing postharvest losses increases food availability to the growing human population, decreases the area needed for production and conserves natural resources. Correct information is essential in formulating an effective and eco-friendly management strategy and thus ensuring tubers that are safe to eat at affordable prices. Precise identification of the pathogens responsible for various diseases, preharvest and postharvest environmental conditions that favour the disease along with proper handling and curing helps in alleviating the huge postharvest loss encountered.

Limited annotated data often constrain accurate yield prediction in underrepresented crops. To address this challenge, we developed a cross-crop deep transfer learning (TL) framework that leverages potato (Solanum tuberosum L.) as the source domain to predict sweet potato (Ipomoea batatas L.) yield using multi-temporal uncrewed aerial vehicle (UAV)-based multispectral imagery. A hybrid convolutional–recurrent neural network (CNN–RNN–Attention) architecture was implemented with a robust parameter-based transfer strategy to ensure temporal alignment and feature-space consistency across crops. Cross-crop feature migration analysis showed that predictors capturing canopy vigor, structure, and soil–vegetation contrast exhibited the highest distributional similarity between potato and sweet potato. In comparison, pigment-sensitive and agronomic predictors were less transferable. These robustness patterns were reflected in model performance, as all architectures showed substantial improvement when moving from the minimal 3 predictor subset to the 5–7 predictor subsets, where the most transferable indices were introduced. The hybrid CNN–RNN–Attention model achieved peak accuracy (R2≈0.64 and RMSE ≈ 18%) using time-series data up to the tuberization stage with only 7 predictors. In contrast, convolutional neural network (CNN), bidirectional gated recurrent unit (BiGRU), and bidirectional long short-term memory (BiLSTM) baseline models required 11–13 predictors to achieve comparable performance and often showed reduced or unstable accuracy at higher dimensionality due to redundancy and domain-shift amplification. Two-way ANOVA further revealed that cover crop type significantly influenced yield, whereas nitrogen rate and the interaction term were not significant. Overall, this study demonstrates that combining robustness-aware feature design with hybrid deep TL model enables accurate, data-efficient, and physiologically interpretable yield prediction in sweet potato, offering a scalable pathway for applying TL in other underrepresented root and tuber crops.

Precision genome editing, particularly using Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/CRISPR-associated protein 9 (Cas9), is advancing crop improvement by enabling targeted and efficient genetic modifications. Root and tuber crops such as potato, cassava, sweet potato, and yam are vital for global food and nutritional security but remain highly vulnerable to climate change, pests, diseases, and limited genetic diversity. Genome editing technologies facilitate the development of improved traits, including enhanced disease resistance, tolerance to abiotic stress, improved nutritional quality, and extended shelf life. This review synthesizes recent advances in genome editing for root and tuber crops across global production systems, including illustrative examples from Sub-Saharan Africa, where active genome editing initiatives are being implemented. It further examines key technical constraints, such as low efficiency of plant transformation and regeneration, and highlights regulatory challenges arising from differing policy frameworks across countries. Emerging solutions are discussed, including genotype-independent editing strategies and DNA-free approaches that avoid the integration of foreign genetic material. Addressing these challenges will be critical for developing resilient and sustainable food systems. Unlike previous reviews, this study integrates mechanistic insights with cross-crop synthesis and proposes next-generation genome editing strategies for engineering complex traits in polyploid root and tuber crops.

BackgroundPolypyrimidine-tract binding proteins (PTBs) are ubiquitous RNA-binding proteins in plants and animals that play diverse role in RNA metabolic processes. PTB proteins bind to target RNAs through motifs rich in cytosine/uracil residues to fine-tune transcript metabolism. Among tuber and root crops, potato has been widely studied to understand the mobile signals that activate tuber development. Potato PTBs, designated as StPTB1 and StPTB6, function in a long-distance transport system by binding to specific mRNAs (StBEL5 and POTH1) to stabilize them and facilitate their movement from leaf to stolon, the site of tuber induction, where they activate tuber and root growth. Storage tubers and root crops are important sustenance food crops grown throughout the world. Despite the availability of genome sequence for sweet potato, cassava, carrot and sugar beet, the molecular mechanism of root-derived storage organ development remains completely unexplored. Considering the pivotal role of PTBs and their target RNAs in potato storage organ development, we propose that a similar mechanism may be prevalent in storage root crops as well.ResultsThrough a bioinformatics survey utilizing available genome databases, we identify the orthologues of potato PTB proteins and two phloem-mobile RNAs, StBEL5 and POTH1, in five storage root crops - sweet potato, cassava, carrot, radish and sugar beet. Like potato, PTB1/6 type proteins from these storage root crops contain four conserved RNA Recognition Motifs (characteristic of RNA-binding PTBs) in their protein sequences. Further, 3´ UTR (untranslated region) analysis of BEL5 and POTH1 orthologues revealed the presence of several cytosine/uracil motifs, similar to those present in potato StBEL5 and POTH1 RNAs. Using RT-qPCR assays, we verified the presence of these related transcripts in leaf and root tissues of these five storage root crops. Similar to potato, BEL5-, PTB1/6- and POTH1-like orthologue RNAs from the aforementioned storage root crops exhibited differential accumulation patterns in leaf and storage root tissues.ConclusionsOur results suggest that the PTB1/6-like orthologues and their putative targets, BEL5- and POTH1-like mRNAs, from storage root crops could interact physically, similar to that in potato, and potentially, could function as key molecular signals controlling storage organ development in root crops.

The aim of this study was to investigate the effect of micronization on the physicochemical properties of the peels of root and tuber crops, including yam (Dioscorea alata L.), taro (Colocasia esculenta L.) and sweet potato (Ipomea batatas L.). Two continuous milling sections, including hammer milling and ball milling, were applied to three samples to obtain micro-sized particles of root and tuber peels. The micronization by ball-milling treatment for 10 h was carried out to investigate the distribution of particle sizes and the changes in physiochemical properties. The results indicate that the peels of three crops appeared to be significantly decreased in particle size after 10 h of ball-milling treatment. Moreover, the ball-milling treatments resulted in the redistribution of fiber components from insoluble fiber to soluble fiber. The micronization treatments decreased the bulk density but increased the solubility and water-holding capacities of the micronized peels. Our findings suggested that micronization treatments can improve functional properties of the fiber components of micronized peels, which provide a good source of dietary fiber in food applications.

Root and tuber crops (RTCs) play an important role in alleviating poverty, improving health and nutrition, and providing excellent opportunities for improving the livelihoods of smallholder farmers in countries like sub-Saharan Africa. Starch roots and tubers are edible starch materials that are stored in the subterranean stems, roots (cassava and sweet potatoes), rhizomes (canna and arrow roots), corms (taros and cocoyams), and tubers (potatoes and yams) (Chandrasekara and Kumar, 2016). RTCs are second in importance to cereal crops in terms of calories, food security, and industrial purposes.

Sweet potato is an important food crop throughout much of sub-Saharan Africa with the important attribute as a dual-purpose crop. While tuberous crops are grown for human consumption, the sweet potato can also provide substantial vine biomass suitable for feeding animals without competing for human feed resources. Sweet potato is generally low in nutrient other than carbohydrate. The newly developed orange-fleshed varieties of sweet potato, high in beta-carotene yield large quantities of vines with very little exploration of their agronomic attributes to date. Intermediate vine harvesting (ratooning) has been promoted as a strategy to further increase the value of sweet potato as a dual-purpose human/animal feed crop. The results of this practice on yields of other types of sweet potato have been equivocal or highly variable. Production effects on three new orange-fleshed dual-purpose sweet potato (Kenspot 1, SPK 013, SPK 117) developed by the International Potato Centre (CIP), of intermediate plus final (INT) versus final only (FIN) vine harvesting were assessed in a randomized block with a split plot trial. Cultivar SPK013 produced the greatest vine, tuber and total biomass yield of the three varieties tested, but also the greatest decline in tuber yields after intermediate vine harvesting. While intermediate harvesting increased vine yield in all varieties (p<0.05), in cultivar SPK013, it caused a 58% decline in tuber yield (p<0.05). The variation in performance between cultivars assessed in this study, reflects what is seen in the general literature. What is clear from the present study is that, there is a substantial interaction between environment/cultural practice and genotype. As such, it seems impossible to generalize that Intermediate vine harvesting is beneficial for vine production in the cultivars studied. It should be borne in mind that this practice may also be associated with a substantial decline in tuber yield in some cultivars. Thus, results should not be extrapolated to other varieties without investigation.

The physicochemical composition and microbial quality of 7 different water sources (Umudike ukwu bore hole (B5), Umuariaga borehole (B3), Nidoro spring water (S2), Umudike bore hole (B4), Umudike school borehole A (B7), Umudike school bore hole B (B6) and Ahiaeke bore hole (B9) used for root and tuber crop processing in Umudike, Nigeria were investigated using standard techniques. The chloride, sulphate, phosphate, dissolved substances, hardness of water, ammonium nitrate and conductivity in all the water samples, fell within the range recommended by the Nigerian Industrial Standard (NIS) or the World Health Organization (WHO) while the values obtained for pH and nitrites were lower than the range given by WHO and NIS. Most of the samples had higher organic carbon contents than permitted. In terms of dissolved oxygen (D) and total hydrogen (TH), S2 had the highest, B5 and B6 had the least for DO (P > 0.05) while B6 had the least in addition for TH. The biochemical oxygen demand (BOD) of B3 was the highest among the water samples analyzed (P 0.05). Sensory evaluation of the samples showed that they were clear, tasteless and odorless. Microbial analysis carried out indicated the presence of coliforms in the water samples although this does not give any cause for concern as they fell within the standards for coliform in water. The total plate count of the samples ranged from 8.00 to 19.09cfu/100ml with B9 having the highest while B7 had the least. Some of the microorganisms isolated include: E.coli, salmonella, shigella, fungi and staphylococcus, indicating microbial contamination of these water samples and thus highlights the need for their urgent sterilization. The absence of Vibrio cholerea in all the water samples indicate the non-prevalence of cholera in the study area. Finally, most of the water sources used by these communities in processing their root and tuber crops did not meet the recommended standards for nitrites, biochemical oxygen demand, organic carbon and nitrites in water, underscoring the need for regular checks and on these water sources. Key words: Water, microbial, coliform, physicochemical, root crops, tuber crops.

A study was done to determine the levels of minerals (Calcium, Magnesium, Iron, Potassium and Zinc) in three different cultivars of yams (D. alata and D. esculenta), Xanthosoma sp and four different cultivars of sweet potatoes (Ipomea batatas Lam) from different regions in Sri Lanka. Yams (Rajala, Hingurala and Kukulala), Xanthosoma sp (Kiriala) and sweet potatoes (Swp3, Swp4, Swp5 and Swp7) were prepared for analysis 2 – 3 days after harvesting. Flour samples were subjected to ashing using AOAC (1980) method and mineral constituents were analysed using Atomic Absorption Spectrophotometer (AAS). Variation in mineral constituents on dry weight basis were analysed using ANOVA, Tukey‟s HSD test (p< 0.05) Minitab. All three cultivars of yams had significant levels (p< 0.05) of Calcium and Iron and high level of Magnesium was observed in Kiriala (45.27± 0.31 mg 100g-1). A significantly high level of Iron and Potassium (p<0.05) was observed in Rajala and Sweet potatoes respectively. Swp5 cultivar contained a comparatively high amount of Calcium and Magnesium while Swp3 and Swp7 contained a high level of iron (p<0.05). Comparatively high level of Zinc was present in Hingurala, Swp3 and Swp7 cultivars. Key words: Dioscorea , Ipomea batatas, minerals, Xanthosoma sp

Sweetpotato (Ipomoea batatas), is a tuberous root crop native to South America and cultivated by the ancient Incas in Peru. Sweetpotato is one of the ground provisions grown in the Caribbean. Consumers want their sweet potatoes to be sweet. Sweetpotatoes require a postharvest curing to set the skin prior to storage. The objective of this study was to determine the influence of time and temperature on the postharvest sugar content of ten sweetpotato varieties. Soluble sugar content was determined at harvest using a garlic press and refractometer. The tuberous roots were cured at room temperature for five days then place at 40oF, 60oF and room temperature (~80oF). Nine varieties had a soluble sugar content of 4-6% Brix while ‘VIP’ was at 8.5% brix at harvest. The soluble sugar content more than doubled after two weeks of storage. There was only a small change in sugar content between the second and fourth weeks. While all three temperatures resulted in increased sugar content the room temperature and 60oF resulted in higher soluble sugars than 40oF. Postharvest storage of sweetpotato results in a significant increase in sugar content within two weeks. This research was supported by USDANIFA-Regional Hatch.

ABSTRACTIn the relay intercropping of maize and sweet potato, maize brought 40–70 days of shading stress on sweet potato; thus, sweet potato yield was reduced. Morphological and physiological impacts of weak light or shading stress on sweet potato in the early stage are not known. We hypothesised that shading stress would change morphogenesis and physiology of sweet potato in the early stage that leads to low yield. To test this hypothesis, we simulated the shading stress using weak light and applied the shade stress onto two sweet potato cultivars, Yushu‐17 and Qianshu‐8. Results showed that 45‐day weak light caused abnormal growth of sweet potato seedlings. The weak light triggered a smaller diameter, longer internodes and extended length of the main vines on both cultivars. The fresh weight of stems and leaves was less than that under normal light. It was also found that weak light promoted the accumulation of proline (Pro) and malondialdehyde (MDA) that influence osmotic status of the vines. Weak light elevated the activities of both superoxide dismutase (SOD) and catalase (CAT). Although weak light enhanced the content of chlorophyll, it inhibited the net photosynthetic rate (Pn) and sucrose phosphate synthase (SPS), and delayed root development. The yield loss was not reversed by resuming normal light after 60 days of weak light. We conclude that weak light in the early stage impedes normal morphogenesis by disturbing osmotic status and adversely impacting antioxidant and photosynthetic enzymes that led to abnormal growth of the main vines and roots, thus causing yield reduction. These findings may explain the negative impact of the shading stress by maize on the yield of sweet potato in the field.

Root and tuber crops (RTCs) are an essential source of food for many developing and underdeveloped countries, providing a substantial part of the world’s food supply. With the global population projected to reach 9.8 billion by 2050, the importance of RTCs is likely to increase. These crops are not only a cheap source of food and energy but also exhibit high biological efficiency and can withstand biotic and abiotic challenges. RTCs namely sweet potato, cassava, yams, and taro are rich in nutrients. The bioactive compounds present in these crops have been shown to have medicinal properties. The glutin free, and low glycemic indices of RTCs make them suitable foods for celiac and diabetic patients. These crops are able to grow under different climatic conditions and fit well with different cropping systems for year-round production and employment generation in lower economic populace. This review highlights the importance of RTCs as a sustainable food and industrial corps and their potential to alleviate malnutrition and improve public health.