G. Craig Yencho

Phytochemical changes in phenolics, anthocyanins, ascorbic acid, and carotenoids associated with sweetpotato storage and impacts on bioactive properties

Sweetpotato phytochemical content was evaluated in four genotypes (NCPUR06-020, Covington, Yellow Covington, and NC07-847) at harvest and after curing/storage for 4 or 8 months. Curing and storage for up to 8 months did not significantly affect total phenolic content in Covington, Yellow Covington, and NC07-847, however for NCPUR06-020, a purple-fleshed selection, total phenolic content declined mainly due to anthocyanin degradation during storage. Covington had the highest carotenoid content at harvest time (281.9 μg/g DM), followed by NC07-847 (26.2 μg/g DM), and after 8 months, total carotenoids had increased by 25% and 50%, respectively. Antioxidant activity gradually declined during storage, and freshly harvested sweetpotatoes also demonstrated higher anti-inflammatory capacity as gauged by inhibition of lipopolysaccharide-induced reactive oxygen species (ROS) in SH-SY5Y cells. Gradual changes in sweetpotato phytochemical content and antioxidant and anti-inflammatory capacity were noted during normal long-term storage, but the specific effects were genotype-dependent.

Conventional breeding, marker-assisted selection, genomic selection and inbreeding in clonally propagated crops: a case study for cassava

Key messageConsolidates relevant molecular and phenotypic information on cassava to demonstrate relevance of heterosis, and alternatives to exploit it by integrating different tools. Ideas are useful to other asexually reproduced crops.AbstractAsexually propagated crops offer the advantage that all genetic effects can be exploited in farmers’ production fields. However, non-additive effects complicate selection because, while influencing the performance of the materials under evaluation, they cannot be transmitted efficiently to the following cycle of selection. Cassava can be used as a model crop for asexually propagated crops because of its diploid nature and the absence of (known) incompatibility effects. New technologies such as genomic selection (GS), use of inbred progenitors based on doubled haploids and induction of flowering can be employed for accelerating genetic gains in cassava. Available information suggests that heterosis, non-additive genetic effects and within-family variation are relatively large for complex traits such as fresh root yield, moderate for dry matter or starch content in the roots, and low for defensive traits (pest and disease resistance) and plant architecture. The present article considers the potential impact of different technologies for maximizing gains for key traits in cassava, and highlights the advantages of integrating them. Exploiting heterosis would be optimized through the implementation of reciprocal recurrent selection. The advantages of using inbred progenitors would allow shifting the current cassava phenotypic recurrent selection method into line improvement, which in turn would allow designing outstanding hybrids rather than finding them by trial and error.

Diallel analysis of sweetpotatoes for resistance to sweetpotato virus disease

Sweetpotato virus disease (SPVD) is due to the dual infection and synergistic interaction of Sweetpotato feathery mottle potyvirus (SPFMV) and Sweetpotato chlorotic stunt crinivirus(SPCSV), and causes up to 98% yield loss in sweetpotato in East Africa. This study was conducted to determine the inheritance of resistance to SPVD in sweetpotato and to estimate the nature of genetic variance. Ten parental clones varying in reaction to SPVD were crossed in a half diallel mating design to generate 45 full-sib families. The families were graft-inoculated with SPCSV and SPFMV to induce SPVD and evaluated for resistance in a randomized complete block design at two sites in Namulonge, Uganda during 1998–2000. In serological assays for SPFMV and SPCSV,resistance to symptom development and recovery from initial systemic SPVD symptoms, characterised resistant genotypes. Genetic component analysis showed significant effects for both general combining ability (GCA) and specific combining ability (SCA) for resistance to SPVD. GCA to SCA variance component ratios were large (0.51–0.87), hence GCA effects were more important than SCA effects. Resistant parents exhibited high GCA indicating that additive gene effects were predominant in the inheritance of resistance to SPVD and recovery. Narrow-sense heritability (31–41%) and broad-sense heritability (73–98%) were moderate to high, indicating that rapid genetic gains for SPVD resistance could be accomplished by mass selection breeding techniques. Two genotypes, New Kawogo and Sowola, had high negative GCA effects and had several families in specific crosses,which exhibited rapid recovery from SPVD,and are promising parents for enhancement of SPVD resistance and recovery.

Segregation of leptine glycoalkaloids and resistance to Colorado potato beetle (Leptinotarsa decemlineata (Say)) in F2Solanum tuberosum (4x) ×S. chacoense (4x) potato progenies

Solanum chacoense Bitter is resistant to the Colorado potato beetle (CPB),Leptinotarsa decemlineata (Say). Resistance has been associated with the presence of a rare class of glycoalkaloids, the leptines. In this study, seven tetraploid, F2S. tuberosum xS. chacoense families were evaluated for foliar production of leptines I and II, leptinines I and II, and α-solanine and α-chaconine; and screened for resistance to CPB in the laboratory and field. Resistance was correlated with the concentrations of glycoalkaloids on a family and an individual basis. Leptine concentrations ranged from undetectable to a high of 18.0 mg/g dry weight. All of the progeny produced solanine and chaconine. Family 9623 had the highest mean leptine concentration and the lowest mean leaf disk feeding and CPB defoliation levels. Family 9616 had the lowest mean glycoalkaloid concentration and ranked as one of the most susceptible families. Regression analyses of solanine + chaconine, leptine I and II, and leptinine I and II foliar concentrations versus leaf disk consumption and field defoliation revealed that only increased foliar levels of leptines resulted in decreased CPB feeding. The regression models for leptines versus leaf disk consumption and field defoliation were highly significant, accounting for 17% and 26% of the variation in consumption and defoliation, respectively. To the best of our knowledge, this is the first work reporting the impact of leptine and leptinine concentrations on CPB feeding in tetraploid,S. tuberosum xS. chacoense potato hybrids. Results are discussed within the context of breeding for resistance to CPB.ResumenSolanum chacoense Bitter es resistente al escarabajo de la papa (CPB),Leptinotarsa decemlineata (Say). La resistencia ha sido asociada con la presencia de una clase rara de glicoalcaloides, los leptinos. En este estudio, siete familias tetraploides, F2S. tubero-sum x S. chacoense fueron evaluadas por la producción foliar de leptinos I y II, leptininos I y II, y α-solanina y ochaconina, y revisadas por su resistencia al escarabajo de la papa en el laboratorio y el campo. La resistencia fue correlacionada con las concentraciones de glicoalcaloides sobre una base familiar e individual. Concentraciones de leptinos se extendieron de no percibidas hasta un máximo de 18.0 mg/g peso seco. Toda la progenie producía solanina y chaconina. La familia 9623 tenía el promedio de concentración más alto de leptinos, y el promedio más bajo tanto para el consumo de discos de hoja, como en los niveles de defoliación por el escarabajo de la papa. La familia 9616 demostro el promedio de concentración más bajo de glicoalcaloides, y se mostró como una de las familias mas susceptibles. Los análisis de regresión de solanina + chaconina, y las concentraciones foliares de leptino I y II, y leptinino I y II contra el consumo de discos de hoja y la defoliación en campo, revelaron que solo los niveles foliares aumentados de leptinos resultaron en una alimentación reducida de parte del escarabajo de la papa. Los modelos de regresión para leptinos contra el consumo de discos de hoja, y la defoliación en el campo, fueron sumamente signifcantes, y explicaron el 17% y el 26% de la variación en el consumo y la defoliación, respectivamente. Que sepamos, este es el primer trabajo que informa del impacto de concentraciones de leptinos y leptininos sobre el consumo que realiza el escarabajo de la papa de los híbridos de papa tetraploides 5.tuberosum x S. chacoense. Los resultados se evalúan dentro del contexto de la crianza para la resistencia al escarabajo de la papa.

Internal Heat Necrosis of Potato—A Review

Non-pathogenic necroses of potato tubers have been described in the literature since the early 20th century using different names including internal rust spot, internal browning, physiological internal necrosis, internal brown fleck, chocolate spot, internal brown spot and internal heat necrosis. These reports very likely describe either the same, or a collection of similar disorders, falling under the general umbrella of “internal necrosis”, with the expression of symptoms being significantly altered via genotype by environment interactions. A number of widely-grown cultivars (e.g. ‘Russet Burbank’, ‘Atlantic’ and ‘Yukon Gold’) are susceptible to internal necrosis, making it an economically significant problem. In Atlantic, this syndrome has been termed internal heat necrosis (IHN) in the eastern United States by several investigators because heat and drought are believed to be important triggers of this condition. Investigators in the midwestern and western United States term this same or similar disorder internal brown spot (IBS). IHN and IBS are an internal physiological disorder of potato characterized by brownish red necrotic patches of parenchymal tissue that typically, though not always, occur along and/or inside the vascular ring. Several reports indicate that IHN is most commonly associated with the vascular ring tissue near the apical end of the tuber, but IHN may form anywhere in the tuber. In many cases, it is very difficult to distinguish between IHN and IBS, and several overlapping environmental factors are associated with each of these disorders. High day and night temperatures early in the growing season, combined with low rainfall, have been shown to increase the frequency and severity of IHN and IBS in several cultivars. Considerable research has examined the role of calcium in ameliorating IHN and IBS expression. Much of this work suggests an important role for calcium in the development of IHN, but other biotic and abiotic factors undoubtedly affect IHN and IBS expression. The biochemistry and genetics behind internal necroses of potato have historically been the least-researched facets of this problem. Research has shown that enzymes involved in protecting cells from oxidative damage may be involved, and heritability studies have demonstrated that broad-sense heritability for IHN resistance is high. This review seeks to outline previous work on physiological internal necroses of potato due to high temperatures, summarize our current knowledge of IHN, and point to new areas of investigation to develop IHN resistant potato varieties.ResumenDesde comienzos del siglo 20 se han descrito en la literatura unas necrosis no patogénicas del tubérculo de papa, usando diferentes nombres, como herrumbre interna, oscurecimiento interno, necrosis fisiológica interna, punto oscuro interno, mancha chocolate, mancha marrón interna y necrosis interna por calor. Estos nombres parecen describir ya sea la misma enfermedad o una colección de desórdenes similares que caen dentro de la descripción general “necrosis interna”, con la expresión de los síntomas significativamente alterada, a través de interacciones genotipo ambiente. Varios de los cultivares ampliamente cultivados (tales como Russet Burbank; “Atlantic” y ‘Yukon Gold’) son susceptibles a la necrosis interna, haciéndola un problema económicamente significativo. En Atlantic, este síndrome ha sido llamado necrosis interna por calor (IHN) en la parte oriental de los Estados Unidos por varios investigadores porque se cree que el calor y la sequía son importantes factores desencadenantes para esta condición. Los investigadores en el medio oeste y oeste de los Estados Unidos llaman a este o similares desórdenes mancha parda interna (IBS). El IHN y el IBS son desórdenes fisiológicos internos de la papa, caracterizados por parches necróticos marrón rojizos de tejido parenquimático del tubérculo que típicamente, aunque no siempre, se presentan a lo largo o dentro de anillo vascular. Varios informes indican que IHN está asociado más comúnmente con el tejido de anillo vascular cerca de extremo apical, pero puede estar localizado en cualquier parte de tubérculo. En muchos casos, es muy difícil distinguir entre IHS e IBS y varios otros factores ambientales asociados con estos desórdenes. Las temperaturas altas diurna y nocturna al inicio de la etapa del cultivo, combinadas con poca lluvia, han demostrado incrementar la frecuencia y severidad de IHN e IBS en varios cultivares. Se ha hecho investigación considerable para examinar el rol del calcio en disminuir expresión de IHN e IBS. Mucho de este trabajo sugiere el rol importante del calcio en disminuir el desarrollo de IHN, pero indudablemente otros factores bióticos y abióticos afectan la necrosis interna de la papa. La bioquímica y genética detrás de la necrosis interna han sido las facetas históricamente menos investigadas del problema. La investigación ha demostrado que las enzimas involucradas en la protección de las células contra el daño oxidativo pueden estar involucradas y los estudios de heredabilidad han demostrado que la herencia de sentido amplio es alta para resistencia al IHN. Esta revisión busca resumir el trabajo previo sobre la necrosis fisiológica interna de la papa debida a altas temperaturas, resume el conocimiento actual de IHN y señala las nuevas áreas de investigación para desarrollar variedades resistentes de papa al IHN.

Development and Validation of a Near-Infrared Spectroscopy Method for the Prediction of Acrylamide Content in French-Fried Potato

This study investigated the ability of near-infrared spectroscopy (NIRS) to predict acrylamide content in French-fried potato. Potato flour spiked with acrylamide (50-8000 μg/kg) was used to determine if acrylamide could be accurately predicted in a potato matrix. French fries produced with various pretreatments and cook times (n = 84) and obtained from quick-service restaurants (n = 64) were used for model development and validation. Acrylamide was quantified using gas chromatography-mass spectrometry, and reflectance spectra (400-2500 nm) of each freeze-dried sample were captured on a Foss XDS Rapid Content Analyzer-NIR spectrometer. Partial least-squares (PLS) discriminant analysis and PLS regression modeling demonstrated that NIRS could accurately detect acrylamide content as low as 50 μg/kg in the model potato matrix. Prediction errors of 135 μg/kg (R(2) = 0.98) and 255 μg/kg (R(2) = 0.93) were achieved with the best PLS models for acrylamide prediction in Russet Norkotah French-fried potato and multiple samples of unknown varieties, respectively. The findings indicate that NIRS can be used as a screening tool in potato breeding and potato processing research to reduce acrylamide in the food supply.

Plant cell calcium‐rich environment enhances thermostability of recombinantly produced α‐amylase from the hyperthermophilic bacterium Thermotoga maritime

In the industrial processing of starch for sugar syrup and ethanol production, a liquefaction step is involved where starch is initially solubilized at high temperature and partially hydrolyzed with a thermostable and thermoactive α‐amylase. Most amylases require calcium as a cofactor for their activity and stability, therefore calcium, along with the thermostable enzyme, are typically added to the starch mixture during enzymatic liquefaction, thereby increasing process costs. An attractive alternative would be to produce the enzyme directly in the tissue to be treated. In a proof of concept study, tobacco cell cultures were used as model system to test in planta production of a hyperthermophilic α‐amylase from Thermotoga maritima. While comparable biochemical properties to recombinant production in Escherichia coli were observed, thermostability of the plant‐produced α‐amylase benefited significantly from high intrinsic calcium levels in the tobacco cells. The plant‐made enzyme retained 85% of its initial activity after 3 h incubation at 100°C, whereas the E. coli‐produced enzyme was completely inactivated after 30 min under the same conditions. The addition of Ca2+ or plant cell extracts from tobacco and sweetpotato to the E. coli‐produced enzyme resulted in a similar stabilization, demonstrating the importance of a calcium‐rich environment for thermostability, as well as the advantage of producing this enzyme directly in plant cells where calcium is readily available. Biotechnol. Bioeng. 2009; 104: 947–956.

Chemical Constituents of Sweetpotato Genotypes in Relation to Textural Characteristics of Sweetpotato French Fries.

Sweetpotato French fries (SPFF) are growing in popularity, however limited information is available on SPFF textural properties in relation to chemical composition. This study investigated the relationship between chemical components of different sweetpotato varieties and textural characteristics of SPFF. Sixteen sweetpotato genotypes were evaluated for (1) chemical constituents; (2) instrumental and sensory textural properties of SPFF; and (3) the relationship between chemical components, instrumental measurements, and sensory attributes. Dry matter (DM), alcohol-insoluble solids (AIS), starch, sugar, and oil content, and also α- and β-amylase activities were quantified in raw sweetpotatoes and SPFF. Peak force and overall hardness describing instrumental textural properties of SPFF were measured using a texture analyzer. Descriptive sensory analysis was conducted and 10 attributes were evaluated by a trained panel. Results showed that DM, AIS, and starch content in raw sweetpotatoes were significantly correlated (P < 0.05) with instrumental peak force and overall hardness (r = 0.41 to 0.68), and with sensory surface roughness, hardness, fracturability, and crispness (r = 0.63 to 0.90). Total sugar content in raw sweetpotatoes was positively correlated with sensory smoothness and moistness (r = 0.77), and negatively correlated with instrumental peak force and overall hardness (r = -0.62 to -0.69). Instrumental measurements were positively correlated with sensory attributes of hardness, fracturability, and crispness (r = 0.68 to 0.96) and negatively correlated with oiliness, smoothness, moistness, and cohesiveness (r = -0.61 to -0.91). Therefore, DM, AIS, starch, and total sugar contents and instrumental measurements could be used as indicators to evaluate sweetpotato genotypes for SPFF processing. PRACTICAL APPLICATION In recent years, sweetpotato French fries (SPFF) have grown in popularity, but limited information is available on SPFF textural properties in relation to the differences in chemical constituents among sweetpotato varieties. This study demonstrated that sensory texture attributes of SPFF varied widely and were significantly correlated with chemical components such as dry matter, starch, and total sugar contents of raw sweetpotatoes and instrumental texture measurements of SPFF. The knowledge generated from this study will benefit the food industry and breeding programs with the selection of sweetpotato varieties for improved SPFF quality.

Genetic variance partitioning and Genome-Wide prediction with allele dosage information in autotetraploid Potato

As one of the world’s most important food crops, the potato (Solanum tuberosum L.) has spurred innovation in autotetraploid genetics, including in the use of SNP arrays to determine allele dosage at thousands of markers. By combining genotype and pedigree information with phenotype data for economically important traits, the objectives of this study were to (1) partition the genetic variance into additive vs. nonadditive components, and (2) determine the accuracy of genome-wide prediction. Between 2012 and 2017, a training population of 571 clones was evaluated for total yield, specific gravity, and chip fry color. Genomic covariance matrices for additive (G), digenic dominant (D), and additive × additive epistatic (G#G) effects were calculated using 3895 markers, and the numerator relationship matrix (A) was calculated from a 13-generation pedigree. Based on model fit and prediction accuracy, mixed model analysis with G was superior to A for yield and fry color but not specific gravity. The amount of additive genetic variance captured by markers was 20% of the total genetic variance for specific gravity, compared to 45% for yield and fry color. Within the training population, including nonadditive effects improved accuracy and/or bias for all three traits when predicting total genotypic value. When six F1 populations were used for validation, prediction accuracy ranged from 0.06 to 0.63 and was consistently lower (0.13 on average) without allele dosage information. We conclude that genome-wide prediction is feasible in potato and that it will improve selection for breeding value given the substantial amount of nonadditive genetic variance in elite germplasm.

Sweetpotato (Ipomoea batatas L.).

Sweet potato has traditionally been viewed as a “poor person’s crop” or “orphan crop,” and it has attracted limited attention compared to other staple crops. However, during the last decade, this perception has changed, and it is widely acknowledged that sweet potato has great potential to contribute to the alleviation of malnutrition and hunger in the developing world. Orange-fleshed sweet potato, in particular, with its high provitamin A content, has become a prominent example of the effectiveness of biofortified staple crops to combat vitamin A deficiency. Similarly, increasing awareness of the nutritional value of sweet potato is driving consumer demand among health-conscious consumers globally, and its potential use in a wide range of value-added human and animal products is widely recognized. As the public and private sectors learn more about the benefits and opportunities of sweet potato, they have invested more in crop improvement; thus our understanding of the importance and potential of the crop is increasing.