Molecular Characterization and Target Prediction of Candidate miRNAs Related to Abiotic Stress Responses and/or Storage Root Development in Sweet Potato

Sweet potato is a tuberous root crop with strong environmental stress resistance. It is beneficial to study its storage root formation and stress responses to identify sweet potato stress- and storage-root-thickening-related regulators. Here, six conserved miRNAs (miR156g, miR157d, miR158a-3p, miR161.1, miR167d and miR397a) and six novel miRNAs (novel 104, novel 120, novel 140, novel 214, novel 359 and novel 522) were isolated and characterized in sweet potato. Tissue-specific expression patterns suggested that miR156g, miR157d, miR158a-3p, miR167d, novel 359 and novel 522 exhibited high expression in fibrous roots or storage roots and were all upregulated in response to storage-root-related hormones (indole acetic acid, IAA; zeaxanthin, ZT; abscisic acid, ABA; and gibberellin, GAs). The expression of miR156g, miR158a-3p, miR167d, novel 120 and novel 214 was induced or reduced dramatically by salt, dehydration and cold or heat stresses. Moreover, these miRNAs were all upregulated by ABA, a crucial hormone modulator in regulating abiotic stresses. Additionally, the potential targets of the twelve miRNAs were predicted and analyzed. Above all, these results indicated that these miRNAs might play roles in storage root development and/or stress responses in sweet potato as well as provided valuable information for the further investigation of the roles of miRNA in storage root development and stress responses.

Stem portion and number of stakes influence on growth and yield of cassava variety in the South East, Nigeria

Investigations were conducted to study the effect of stem portion and number of stakes per stand on crop establishment, growth and yield of cassava variety NR 8082 in Umudike Southeastern Nigeria during the 2016/17 and 2017/18 cropping seasons. In each year, the experiment was laid out as a 3 × 3 factorial, in randomized complete block design with three replications. Treatments consisted of three stem portions of different physiological ages (top, middle and basal) and three numbers of stakes per stand (1, 2 and 3). The middle and basal stem portions significantly increased percent establishment, plant height and leaf area index at 3 months after planting (MAP) but had no effect on number of storage roots per plant. The best stem portion for storage root yield was, however, the top portion which produced the highest yield on average. Number of stakes per stand did not significantly affect stem girth, number of nodes per plant and leaf area index, but the use of 1 stake per stand increased number of storage roots per plant, root weight and storage oot yield in 2017/2018 cropping season. Number of stakes per stand did not significantly influence storage root yield across the two seasons of evaluation. Interactions between stem portion and number of stakes per stand did not significantly affect storage root yield of NR 8082 high cassava variety in both cropping seasons. Based on the findings, the use of 1 stake per stand is recommended for high root yields of NR 8082 cassava variety under conditions of low soil fertility in Umudike, South East Nigeria. Although the top portion enhanced root yield, farmers could use any of the stem portions, since the middle and basal parts gave satisfactory yields and had better establishment than the former.

High yield and pest resistant genotypes of sweet potato (Ipomoea batatas (L.) Lam.) for cultivation in Umudike, Southeastern, Nigeria

Newly developed progenies of sweet potato were evaluated to identify promising genotypes with high storage root yield, dry matter, starch content and susceptibility to Cylas spp. at the National Root Crops Research Institute, Umudike, Southeastern Nigeria during the 2015 and 2016 cropping seasons to evaluate variation among crosses of different sweet potato families, namely: LigriXFaara (17), LigriXApomoen (9) and LigrixSauti (8), including two check varieties (Umuspo 3 and TIS 87/0087). Analysis of variance, correlation and principal component analysis were employed for data analysis. In this study, four genotypes; LigriXFaara/3 (16.02t/ha), LigriXFaara/2 (14.67t/ha), LigriXFaara/1 (13.66t/ha) and LigriXFaara/6 (10.33t/ha) produced higher fresh storage root yield than the national check (TIS 87/0087). Four genotypes recorded starch content above 50mg100-1; LigriXApomoden/1 (69.71mg100-1), LigriXApomoden/3 (62.98mg100-1), LigriXApomoden/2 (60.89mg100-1), LigriXApomoden/4 (57.53 mg100-1). Among the thirty-four genotypes evaluated, twenty-nine genotypes were susceptible to the attack of C. puncticollis. LigriXFaara/1 recorded the highest attack of C. puncticollis, followed by LigriXApomoden/5, LigriXFaara/4, LigriXApomoden/3, LigriXSauti/3, LigriXFarra/5 while five genotypes; LigriXFaara/4, LigriXFaara/5, LigriXSauti/5, LigriXFaara/8, LigriXFaara/7 and LigriXFaara/14 did not show any sign of vulnerability of C. puncticollis. Promising genotypes that recorded high yield, dry matter and resistance to Cylas spp. could be subjected to advanced yield trail and incorporated into further breeding program.

Resequencing of 388 cassava accessions identifies valuable loci and selection for variation in heterozygosity

Background Heterozygous genomes are widespread in outcrossing and clonally propagated crops. However, the variation in heterozygosity underlying key agronomic traits and crop domestication remains largely unknown. Cassava is a staple crop in Africa and other tropical regions and has a highly heterozygous genome. Results We describe a genomic variation map from 388 resequenced genomes of cassava cultivars and wild accessions. We identify 52 loci for 23 agronomic traits through a genome-wide association study. Eighteen allelic variations in heterozygosity for nine candidate genes are significantly associated with seven key agronomic traits. We detect 81 selective sweeps with decreasing heterozygosity and nucleotide diversity, harboring 548 genes, which are enriched in multiple biological processes including growth, development, hormone metabolisms and responses, and immune-related processes. Artificial selection for decreased heterozygosity has contributed to the domestication of the large starchy storage root of cassava. Selection for homozygous GG allele in MeTIR1 during domestication contributes to increased starch content. Selection of homozygous AA allele in MeAHL17 is associated with increased storage root weight and cassava bacterial blight (CBB) susceptibility. We have verified the positive roles of MeTIR1 in increasing starch content and MeAHL17 in resistance to CBB by transient overexpression and silencing analysis. The allelic combinations in MeTIR1 and MeAHL17 may result in high starch content and resistance to CBB. Conclusions This study provides insights into allelic variation in heterozygosity associated with key agronomic traits and cassava domestication. It also offers valuable resources for the improvement of cassava and other highly heterozygous crops.

Variation in Boron Availability Alters Root Architecture Attributes at the Onset of Storage Root Formation in Three Sweetpotato Cultivars

The primary objective of this work was to generate species-specific information about root architectural adaptation to variation in boron (B) availability at the onset of storage root formation among three sweetpotato [Ipomoea batatas (L.) Lam] cultivars (Beauregard = BX; Murasaki = MU; Okinawa = OK). Three B levels were used: 0B (B was omitted in the nutrient solution, substrate B = 0.1 mg·kg−1), 1XB (sufficient B; 0.5 mg·kg−1), and 2XB (high B; 1 mg·kg−1). The check cultivar BX showed evidence of storage root formation at 15 days in 0B and 1XB, whereas cultivars MU and OK failed to show evidence of root swelling. The 1XB and 2XB levels were associated with 736% and 2269% increase in leaf tissue B in BX, respectively, relative to plants grown in 0B. Similar magnitudes of increase were observed in MU and OK cultivars. There were no differences in adventitious root (AR) count within cultivars but OK showed 25% fewer AR numbers relative to BX across all B levels. 0B was associated with 20% and 48% reduction in main root length in BX and OK, respectively, relative to plants grown in 1XB and 2XB. 2XB was associated with a 10% increase in main root length in MU relative to plants grown in 0B and 1XB. 0B was associated with reduced lateral root length in all cultivars but the magnitude of responses varied with cultivars. These data corroborate findings in model systems and well-studied crop species that B deficiency is associated with reduced root growth. These data can be used to further understand the role of cultivar-specific responses to variation in B availability in sweetpotato.

General and specific combining ability studies of yield and yield character of sweet potato weevil in predominant and non-predominant environments

Combining ability for marketable sweet potato root yield were carried out using ten sweet potato varieties and their F1 hybrids in Cylasformicarius endemic (Landmark University, Omu Aran) and free (University of Ibadan) environments during 2012 cropping season. Both general combining ability and specific combining ability play significant role on traits such as marketable root yield, non- marketable root yield, and total number of storage root/plant and marketable storage root, root size, percentage of tuber damage and weight of total roots, as well as the incidence and severity were generally low, suggesting the role of additive and dominant gene action in tolerances to Cylasformicarius. Hybrids from the parents Resisto, TIS 87/0087 displayed high performance in term of Cylasformicarius tolerance. These parents and their hybrids appeared to have gene pools for Cylasformicarius tolerance that can be manipulated for developing promising hybrids in South west, Nigeria.

The Expression of IbMYB1 Is Essential to Maintain the Purple Color of Leaf and Storage Root in Sweet Potato [Ipomoea batatas (L.) Lam]

IbMYB1 was one of the major anthocyanin biosynthesis regulatory genes that has been identified and utilized in purple-fleshed sweet potato breeding. At least three members of this gene, namely, IbMYB1-1, -2a, and -2b, have been reported. We found that IbMYB1-2a and -2b are not necessary for anthocyanin accumulation in a variety of cultivated species (hexaploid) with purple shoots or purplish rings/spots of flesh. Transcriptomic and quantitative reverse transcription PCR (RT-qPCR) analyses revealed that persistent and vigorous expression of IbMYB1 is essential to maintain the purple color of leaves and storage roots in this type of cultivated species, which did not contain IbMYB1-2 gene members. Compared with IbbHLH2, IbMYB1 is an early response gene of anthocyanin biosynthesis in sweet potato. It cannot exclude the possibility that other MYBs participate in this gene regulation networks. Twenty-two MYB-like genes were identified from 156 MYBs to be highly positively or negatively correlated with the anthocyanin content in leaves or flesh. Even so, the IbMYB1 was most coordinately expressed with anthocyanin biosynthesis genes. Differences in flanking and coding sequences confirm that IbMYB2s, the highest similarity genes of IbMYB1, are not the members of IbMYB1. This phenomenon indicates that there may be more members of IbMYB1 in sweet potato, and the genetic complementation of these members is involved in the regulation of anthocyanin biosynthesis. The 3′ flanking sequence of IbMYB1-1 is homologous to the retrotransposon sequence of TNT1-94. Transposon movement is involved in the formation of multiple members of IbMYB1. This study provides critical insights into the expression patterns of IbMYB1, which are involved in the regulation of anthocyanin biosynthesis in the leaf and storage root. Notably, our study also emphasized the presence of a multiple member of IbMYB1 for genetic improvement.

The assessment of yield and quality traits of sweet potato (Ipomoea batatas L.) genotypes in middle Black Sea region, Turkey

Sweet potato (Ipomoea batatas L.) cultivation in Turkey is concentrated in one province situated in Mediterranean region only, which would not fulfill the domestic needs of the country soon. Therefore, cultivation of the crop in other provinces/climatic regions should be initiated to fulfill the domestic needs. The cultivation in other provinces requires thorough assessment of yield and quality traits of target crop. Therefore, yield and quality characteristics of four sweet potato genotypes (i.e., ‘Hatay Kırmızısı’, ‘Hatay Yerlisi’, ‘Havuc’ and ‘Kalem’) were assessed in the current study in Kazova and Niksar counties of Tokat province of the country having middle Black Sea climate in field experiments during 2018 and 2019. The cuttings of the genotypes were planted in Niksar during the second fortnight of April and first week of May in Kazova. The planting density was kept 90 × 45 cm. Data relating to number of storage roots, storage root weight, storage root yield per hill and storage root yield per hectare were recorded. Furthermore, quality traits, including dry matter ratio (%), protein ratio (%) and antioxidant ratio (%) of storage roots were also determined. The highest total storage root yield was recorded for ‘Havuc’ genotype during both years and locations, followed by ‘Hatay Yerlisi’ and ‘Hatay Kırmızısı’ genotypes. Overall, storage root yield (60.06 and 62.40 tons ha-1 during first and second year) recorded for the experiment at Niksar was higher than the storage root yield recorded for Kazova experiment (53.50 and 52.84 tons ha-1 during first and second year, respectively). The highest dry matter was produced by ‘Kalem’ and ‘Hatay Yerlisi’ genotypes during both years and at both locations, followed by ‘Hatay Kırmızısı’ and ‘Havuc’ genotypes. The storage roots of the tested genotypes accumulated higher dry matter at Kazova during both years. The highest protein content was obtained from the ‘Kalem’ genotype, and the protein contents of the ‘Hatay Yerlisi’ and ‘Hatay Kırmızısı’ genotypes were close to the ‘Kalem’ genotype. The results indicated that tested genotypes can successfully be cultivated in middle Black Sea climate. Therefore, production of sweet potato can be initiated in the future to meet the domestic needs for sweet potato in the country.

Evaluation of Morphological Characters and Yield Variability of Some Elite Cassava (Manihot Esculenta Crantz) in Uyo, Southeastern Nigeria

Field experiment was carried out at Uyo to evaluate some morphological traits and yield variability of some elite cassava varieties with aim of making innovative recommendation to farmers. The experiment laid out in a complete block design, replicated three times. The treatments were six cassava varieties; TMS 30572, TME 419, TMS 98/0505, TMS 98/0581, TMS 01/1412 and local variety known as Obubit Okpo. Data collected from growth and yield was subjected to analysis of variances. Significant means were compares using least significant difference (LSD) at 5% probability level. Among the cassava varieties; TMS 98/0581 had superiority over in four characters namely; leaf area, storage root length, storage root circumference and yield. Also TMS 01/1412 was superior in terms of number of leaves per plant and number of storage roots per plant while TME 419 was superior in terms of plant height. Since TMS 98/0581 had four major characters, it could be disseminated to farmers in Uyo, Akwa Ibom State, while the other varieties TMS 01/1412, and TME 419 which were superior in two and one characters respectively could be incorporated into breeding programme with TMS 98/0581 to produce hybrid varieties with higher yield for the study area. Keywords: Cassava, characters, breeding and yield.