Cassava storage roots (SRs) are a crucial staple food and industrial resource worldwide. However, SRs are highly susceptible to postharvest physiological deterioration (PPD) after harvest, characterized by blue-brown vascular discoloration. This discoloration results from the accumulation of polyphenolics, mainly quinones and coumarins, produced by enzymes such as polyphenol oxidase (PPO). We identified a MePPO gene in the cassava (Manihot esculenta) genome and performed a comparative analysis of PPO homologs across various plant species. Their physicochemical characteristics, evolutionary relationships, gene structures, chromosomal localizations, conserved motifs, cis-acting elements, gene duplications, and synteny relationships were thoroughly compared and analyzed. Expression profiling revealed that MePPO was predominantly transcribed in the roots and leaves of cassava. Virus-induced gene silencing (VIGS) of MePPO significantly delayed the occurrence and progression of cassava PPD in SRs, particularly on the 6th and 9th days postharvest. Silenced lines displayed substantially reduced PPO transcript levels and enzymatic activity, accompanied by a marked decrease in scopoletin, a key coumarin implicated in PPD at 3 days postharvest. Notably, the accumulation of cassava flavanols (catechins) was enhanced in the silenced lines. In summary, these findings establish that targeted suppression of MePPO effectively mitigates PPD in cassava SRs.

木薯原产热带美洲,是世界热区重要的粮食作物,也是世界近十亿人的食粮.然而木薯基因组高度杂合、后代分离严重,定向选育难度大、育种周期长,这些因素严重制约着木薯产业的发展.因此,缩短育种周期、定向选育出木薯优良品种是当今育种工作的重点.近年来,随着测序技术的发展以及多组学、基因编辑、遗传转化等核心技术在育种中的应用,木薯育种工作取得了重大突破.本文综述了木薯育种的最新进展,包括木薯种质资源重要农艺性状评价已从传统表型评价发展到表型与基因型的精准评价、木薯参考基因组的组装与注释及关键性状基因资源的发掘、木薯现代育种策略的发展等.此外,本文还讨论了今后木薯育种的研究方向,这将对推动木薯产业发展、服务国家“一带一路”倡议,以及解决世界热区粮食安全和饲料有效供给具有重要意义.

As a starchy and edible tropical plant, cassava (Manihot esculenta Crantz) has been widely used as an industrial raw material and a dietary source. However, the metabolomic and genetic differences in specific germplasms of cassava storage root were unclear. In this study, two specific germplasms, M. esculenta Crantz cv. sugar cassava GPMS0991L and M. esculenta Crantz cv. pink cassava BRA117315, were used as research materials. Results showed that sugar cassava GPMS0991L was rich in glucose and fructose, whereas pink cassava BRA117315 was rich in starch and sucrose. Metabolomic and transcriptomic analysis indicated that sucrose and starch metabolism had significantly changing metabolites enrichment and the highest degree of differential expression genes, respectively. Sugar transport in storage roots may contribute to the activities of sugar, which will eventually be exported to transporters (SWEETs), such as (MeSWEET1a, MeSWEET2b, MeSWEET4, MeSWEET5, MeSWEET10b, and MeSWEET17c), which transport hexose to plant cells. The expression level of genes involved in starch biosynthesis and metabolism were altered, which may result in starch accumulation. These results provide a theoretical basis for sugar transport and starch accumulation and may be useful in improving the quality of tuberous crops and increasing yield.

BACKGROUND:Magnesium chelatase plays an important role in photosynthesis, but only a few subunits have been functionally characterized in cassava. RESULTS:Herein, MeChlD was successfully cloned and characterized. MeChlD encodes a magnesium chelatase subunit D, which has ATPase and vWA conservative domains. MeChlD was highly expressed in the leaves. Subcellular localization suggested that MeChlD:GFP was a chloroplast-localized protein. Furthermore, the yeast two-hybrid system and BiFC analysis indicated that MeChlD interacts with MeChlM and MePrxQ, respectively. VIGS-induce silencing of MeChlD resulted in significantly decreased chlorophyll content and reduction the expression of photosynthesis-related nuclear genes. Furthermore, the storage root numbers, fresh weight and the total starch content in cassava storage roots of VIGS-MeChlD plants was significantly reduced. CONCLUSION:Taken together, MeChlD located at the chloroplast is not only required for chlorophyll biosynthesis and photosynthesis, but also affecting the starch accumulation in cassava. This study expands our understanding of the biological functions of ChlD proteins.

BackgroundCassava (Manihot esculenta Crantz) is widely planted in tropical and several subtropical regions in which drought, high temperatures, and other abiotic stresses occur. Metallothionein (MT) is a group of conjugated proteins with small molecular weight and rich in cysteine. These proteins play a substantial role in response to physiological stress through the regulation of reactive oxygen species (ROS). However, the biological functions of MT genes in cassava are unknown.ResultsA total of 10 MeMT genes were identified in the cassava genome. The MeMTs were divided into 3 groups (Types 2-4) based on the contents and distribution of Cys residues. The MeMTs exhibited tissue-specific expression and located on 7 chromosomes. The MeMT promoters contain some hormones regulatory and stresses responsiveness elements. MeMTs were upregulated under hydrogen peroxide (H2O2) treatment and in respond to post-harvest physiological deterioration (PPD). The results were consistent with defense-responsive cis-acting elements in the MeMT promoters. Further, four of MeMTs were selected and silenced by using the virus-induced gene silencing (VIGS) method to evaluate their functional characterization. The results of gene-silenced cassava suggest that MeMTs are involved in oxidative stress resistance, as ROS scavengers.ConclusionWe identified the 10 MeMT genes, and explore their evolutionary relationship, conserved motif, and tissue-specific expression. The expression profiles of MeMTs under three kinds of abiotic stresses (wounding, low-temperature, and H2O2) and during PPD were analyzed. The tissue-specific expression and the response to abiotic stresses revealed the role of MT in plant growth and development. Furthermore, silenced expression of MeMTs in cassava leaves decreased its tolerance to ROS, consistent with its predicted role as ROS scavengers. In summary, our results suggest an important role of MeMTs in response to physiological stress as well as species adaptation via the regulation of ROS homeostasis.

As a starchy and edible tropical plant, cassava (Manihot esculenta Crantz) has been widely used as an industrial raw material and dietary source. However, the metabolomic difference in different colors of cassava storage root is unclear. In this study, two specific germplasms WFSR with white flesh of storage root and PFSR with pink flesh of storage root were used as research materials. A previous study found that WFSR was rich in sucrose and fructose, PFSR was rich in starch and glucose. Combined metabolomic and transcriptomic analysis indicated that sucrose and starch metabolism had SCMs enrichment and highest degree of DEGs, respectively. Sugar allocation of storage roots may contribute to sugar transporters SWEETs activities (MeSWEET1a, MeSWEET2b, MeSWEET4, MeSWEET5, MeSWEET10b and MeSWEET17c), which transport hexose in plant cell-to-cell during source-to-sink process. The expression levels of the starch biosynthetic and metabolic genes were altered may result in starch content accumulation. These results provide a theoretical basis for source-to-sink, and then improve quality and increase yield of tuberous crops.

This study aimed to synthesize packaging films using bioactive ingredients. The composite film was prepared by blending octenyl succinate cassava starch ester (OSCS) with chitosan (CS) nano-ZnO and then adding ε-polylysine (ε-PL). The study also explored the effect of different concentrations of ε-PL on OSCS/CS/ZnO films. Fourier infrared spectroscopyand fluorescence microscopy revealed that the composite film was formed by both hydrogen bonding and a Schiff base reaction. The diffraction peaks of the original materials in X-ray diffraction disappeared after film formation, indicating good miscibility between the materials. Scanning electron microscope showed that the density of its structure increased with increasing the ε-PL content. The thermogravimetric analysis showed that the addition of ε-PL improved the thermal stability of the composite film to some extent. When used in cherry preservation, the bio-based modified starch film effectively reduced cherry decay, stem dryness, and weight loss, maintained surface color, and increased the soluble solid content.

Resources are the basis for breeding,while evaluation for resources is the prerequisite for breeding,and also the key point for speeding up breeding.In this study,54 samples that introduced from Colombia were evaluated by field experiment (1 year) in order to determine the production characteristics,the indexes including plant height,diameter,fresh weight,dry rate,starch content,amylopectin content and others.The results showed that CM837,CM2399-4,Colombia 16P,19S,SG424-19,SM2300-1,SM2323-6,CMR34-11-3,CMR35-70-1 and CMR35-70-1 were the best material for breeding;starch content and growth of CM385-6,CM837,CM3993-9,CM4054-40,PER557,CMR26-07-15,CMR36-40-9,CMR37-14-9 were better but the yield were low,which would be used as breeding materials with high starch content and feeding;yield and quality of CM92-56-1,CM901,CM7595-1 and SM28-80-3 were better,which are able to be used as breeding material for harvesting target.

为分析海南岛木薯主产区产量的限制因素,找出缩减产量差的途径.研究调查海南岛木薯主产区典型乡村木薯种植管理情况,确定各级木薯产量差,从种植密度、连作年数、养分管理、产投结构等方面分析产量差的贡献因素.结果显示:不同产量等级间木薯产量差异显著,基于高产农户的产量差YGT、高产纪录的产量差YGB、模型模拟的产量差YGM分别为15.59、30.98、37.82 t/hm2;25％最低产农户平均种植密度和连作年数均高于其余农户,其K2O总施用量、基肥中N、K2O的施用量及追肥中K2O的施用量均低于其余农户;现有管理水平条件下,N、P2O5、K2O对产量差的贡献率分别为6.3％、11.0％、6.3％,达到高产高效施肥水平的农户仅4.69 ％～6.45％;产投结构中,产量达到65.15 t/hm2时产投比最大,此后随产量增加,报酬递减,人工成本尤其收获成本是最大限制因素.缩减木薯产量差的途径为合理密植,减少连作年数,增施钾肥,调整基追肥比例,增施氮钾基肥,追肥增钾,为节约劳动力成本,推广全程机械化,尤其是收获环节.

A new cassava cultivarSC 10originated from crossbreeding betweenCM4042as the female parent andCM4077as the male parent in 1988 and was approved by National Grass Variety Approval Committee in 2006.SC 10had high yield,good adaptability and strong resistance to wind.Its root yield was about 38.87 t/hm2 and 46.06% more than the dominant varietySC205(CK).SC 10possessed 41.44% dry content in storage root,2.04 percentage points higher than CK,and the average rupture rate was only 4.4%,15.2 percentage points lower than CK.The fingerprint mapping of the variety was also established by microsatellite markers.

As a effect of 12 different NPK fertilizer rate on fresh root yield and economic benefit of cassava variety South China 5 in Hainan Island,China in 2004～2005.The same N and K2O ratio,or a litter higher N ration than K2O,also moderate fertilizer was beneficial to increase fresh cassava root yield and income.It suggested that N∶P2O5∶K2O ratio was 2～3∶1∶2～3 for continues cassava production,and their recommendation fertilizer per year for moderate fertility soil was N∶P2O5∶K2O=60～90∶30∶ 60～90 kg/hm2.

The advanced trial for 17 new cassava breeding lines was carried out,and local dominant variety SC205 was used as the CK.The results showed that the yield of breeding line B16 was significantly higher than that of SC205,and the fresh tuber yield was 51.83 t/hm2 and increased by 73.52%.The dry matter and starch content of B103、B86、B171、B165、B16、B81 and B74 were significantly higher than those of SC205,and those of B107 was significantly higher than those of the control.Moreover,seven breeding lines including B16、B74、B1、B161、B83、B160 and B103 had stronger resistance to stress.Therefore,according to the agronomic traits of these lines,B16 is a new one worth to be tested in further productive trial.

中国热带农业科学院热带作物品种资源研究所长期致力于木薯的杂交育种工作,从数千个杂交组合和数万个单株中选育出了一批优良品系.经过无性系统评选,育成了华南5号等木薯新品种,并通过边区试、边审定品种、边增殖扩繁、边生产试种和示范推广的方法,为我国提供了高产优质的系列木薯新品种,改善了我国木薯品种单一退化的状况.