Number Of Storage Roots Research Articles

English

This study was conducted to evaluate the growth and yield stability of cassava mosaic disease (CMD) resistant breeding populations clones against early drought. Field trials were planted using 200 CMD resistant clones and 7 local landraces in a randomised complete block design with 3 replicates at the International Institute of Tropical Agriculture (IITA) station, Sendusu in Namulonge (Central Uganda) during the second rains of 2006 (2006B) and the first rains of 2007 (2007A). The 2007A crop suffered from drought stress in the first 4 months after planting (MAP). Data were taken on the leaf lobe length and width at 6 MAP and plant height at 12 MAP. Harvest was done at 12 MAP during which the number of storage roots per plant and storage root yield were recorded. Data were analysed using the Mann-Whitney U test to compare crop performance between the 2 seasons. The 2006B crop had significantly (P<0.01) longer leaf lobes, taller plant heights, higher number of storage roots per plant and higher storage root yield than the 2007A crop. There was no significant difference in the leaf lobe width. In this experiment, it was observed that the CMD resistant breeding clones were susceptible to early drought and thus it was recommended that selections should be done for higher water use efficiency. Key words: Abscisic acid, Manihot esculenta Crantz, Stomatal conductance, water use efficiency, Uganda.

Comparison of Root Characteristics and Sugar Components in Root and Leaf at Early Growth Phase of Sweet Potato Varieties with Significant Difference in Valid Storage Root Number

Starch sweet potato varieties Shangshu 19 and Jixu 23 differing in valid storage root number per plant significantly were used to investigate root characteristics, sugar components in root and leaf at early growth phase and their relationship with the formation of storage root per plant at top cover stage. The results showed that, Shangshu 19 with higher valid storage root number regrew quickly with more new roots after seedling transplanting, developed fiberous roots mainly in the whole early growth phase, and formed a stable rate of top biomass/total root system biomass (T/TR) at 15 and 30 days after planting. Jixu 23 achieved the steady number of adventitious root and valid storage root at 15 and 30 days after planting, respectively. Meanwhile, Jixu 23 showed the lower rate of top biomass/storage root biomass (T/SR) at top cover stage (45 days after planting). On the other hand, in point of metabolism of sucrose and hexoses, and the formation of stored polysaccharide polymers, Shangshu 19 had sig- nificantly lower rate of sucrose/hexoses in the whole early growth phase, formed the greater sucrose concentration gradient be- tween leaves and roots, and had 1-kestose and nystose in roots at 15 and 30 days after planting. Its starch content in leaf was sig-

Adventitious root primordia formation and development in stem nodes of 'Georgia Jet' sweetpotato, Ipomoea batatas.

• Yield in sweetpotato is determined by the number of storage roots produced per plant. Storage roots develop from adventitious roots (ARs) present in stem cuttings that serve as propagation material. Data on the origin of sweetpotato ARs and the effect of nodal position on AR establishment and further development are limited.• We anatomically described root primordium initiation using stem sections and measured number of root primordia formed at different nodal positions using light microscopy and correlated nodal positions with AR number and length 14 d after planting (DAP).• Primordia for ARs initiate at the junction of the stem pith ray and the cambium, on both sides of the leaf gap, and they are well developed before emerging from the stem. The number of ARs that develop from isolated stem nodes 14 DAP corresponded to the number of AR primordia detected inside the stem. The total length of established roots at nodes 9-13 from the apex is about 2-fold longer than at nodes 5-8.• Nodal position (age) has a significant effect on the developmental status and number of root primordia inside the stem, determining the number and length of ARs that have developed by 14 DAP. Adventitious roots originating from nodes 9-13 possess similar AR systems and develop better than those originating from younger nodes 3-8. The mechanism regulating AR initiation in nodes is discussed. This system can serve for studying the effect of environmental conditions on AR initiation, development, and capacity to form storage roots.

Genetic variation and association among factors influencing storage root bulking in cassava

SUMMARYCassava (Manihot esculenta Crantz) is an important storage root crop with largely unexplored and unexplained potentially valuable genetic variability. Genetic variability is important in selecting suitable genotypes for crop improvement. The present study was aimed at assessing the extent of variability in cassava storage root bulking, based on fresh storage root yield accumulated over time. Twelve cassava genotypes were evaluated in a randomized complete block design at three contrasting locations in Uganda. Assessments were done from 5 to 13 months after planting at intervals of 2 months. Genotype, harvest time, location and their interactions were significantly different for fresh storage root yield and most of the other traits assessed. Estimates of variance components revealed that a large portion of the phenotypic variance was accounted for by the genotypic component for all traits assessed indicative of substantial genetic variability among the genotypes evaluated. This genetic variability is important in a hybridization and/or selection programme because it implies that significant genetic gain through phenotypic selection is possible for the traits assessed. Fresh storage root yield was positively and significantly correlated with storage root girth, harvest index, shoot mass and storage root number. The information generated will inform future breeding initiatives to develop early-bulking cassava genotypes with farmer-preferred traits in Uganda.

Combining ability and heterosis for yield and drought tolerance traits under managed drought stress in sweetpotato

Drought is among sweetpotato production constraints in sub-Saharan Africa. Two studies were conducted on 15 F1 sweetpotato families (G1-G15) generated using a half-diallel mating scheme of six parents. The first experiment was conducted at Kenya Agricultural Research Institute (KARI), Kiboko, using split plot design under drought stress and no drought stress replicated twice and repeated thrice between January 2012 and June 2013. The second study was conducted in the screen house at KARI, Muguga using randomized complete block design. General combining ability (GCA) and specific combining ability (SCA) effects for storage root yield (FSR), total biomass (BIO), harvest index (HI), marketable number of storage roots (MNR) and root dry matter (%RDM) were significant (P ≤ 0.05) under both conditions. GCA/SCA ratio for FSR, HI, and %RDM under both conditions, ranged 0.51–0.76, thus, additive gene effects were more important than non-additive genes effects. G15, G5 and G7 had the highest significant (P ≤ 0.05) FSR SCA effects under drought stress while G15, G7, and G12 had the highest under no drought stress. Progenies G8-8, G15-5 and G15-8, had the highest FSR mid and best parent heterosis ranging 117.8–269.6 % under drought. Drought susceptible parents P3, P4 and P5 had the highest yielding crosses under drought,which were also high yielding under no drought [G15 (P3 × P5) and G5 (P4 × P5)]. Thus, these parents probably were carriers of the drought tolerant genes (heterozygous recessive). This suggests that the drought tolerance alleles could be homozygous recessive, which may be confirmed in further studies.

Combining Ability Analysis of Storage Root Yield and Related Traits in Cassava at the Seedling Evaluation Stage of Breeding

Selection of genotypes at the seedling evaluation stage of cassava breeding for advancement is largely based on high heritability traits. Moreover, combining ability and family data at this stage are rarely analyzed, leading to a loss of potential genetic information. This study was conducted to estimate the general combining ability (GCA) of nine cassava parents and specific combining ability (SCA) of their crosses for storage root yield (SRY) and related traits, as well as to determine the gene action controlling these traits. Thirty-six full-sib cassava families were developed from a 9 x 9 half-diallel mating design and evaluated in a 6 x 6 triple lattice design. The family mean squares (MS) were significantly different for all traits assessed, suggesting significant differences among families for all traits. The GCA MS were significant for all traits, whereas SCA MS were significant for only storage root number (SRN). Percentage sum of squares attributable to GCA accounted for >50.0% of variability expressed by families in five of the seven traits studied, indicating predominance of additive gene effects in controlling expression of most traits. Parent CT4 was the best general combiner for SRY, SRN, and resistance to cassava brown streak and mosaic diseases, while crosses NASE3 x CT2, CT5 x CT3, and NASE3 x CT4 had desirable SCA effects for SRY. Correlation analysis indicated a possibility of selecting for SRY and quality traits simultaneously. Simultaneous selection of these traits at the seedling generational stage of cassava breeding could reduce the cassava breeding cycle.

Genotype × environment interaction effects on early fresh storage root yield and related traits in cassava

Cassava (Manihot esculenta Crantz) is an important root crop worldwide. It exhibits substantial differential genotypic responses to varying environmental conditions, a phenomenon termed genotype×environment interaction (GEI). A significant GEI presents challenges in the selection of superior genotypes. The objective of this study was to examine the effect of genotype, environment and GEI on early fresh storage root yield (FSRY) and related traits in cassava. Accordingly, 12 cassava genotypes were evaluated in a randomised complete block design at three contrasting locations (Jinja, Nakasongola and Namulonge) in Uganda. Trials were harvested nine months after planting and the data collected were analysed using the additive main effects and multiplicative interaction (AMMI) model. The AMMI analysis of variance showed significant variation among genotypes for early FSRY and all other traits assessed. Locations were significantly different for all traits except for cassava brown streak disease root necrosis. The GEI effect was non-significant for early FSRY, but significant for other traits. For early FSRY, 48.5% of the treatment sum of squares was attributable to genotypes, 27.3% to environments, and 24.1% to GEI, indicating a predominance of genotypic variation for this trait. Predominance of genotypic variation was also observed for all the other traits. A majority of the genotypes (67%) had low interaction effects with locations for early FSRY, with Akena, CT2, CT4 and NASE14 being the most stable genotypes for the trait. Significant negative correlation was observed between cassava mosaic disease severity and early FSRY and storage root number, indicating significant negative effects of cassava mosaic disease on early FSRY and stability in cassava. The information generated will inform future selection initiatives for superior early-yielding cassava genotypes combining resistance to cassava mosaic and brown streak diseases in Uganda.

English

Thirty-eight high and low cyanide cassava genotypes were evaluated for growth and yield. The experiment was fitted in a randomized complete block design with three replications. Analysis of variance (ANOVA) revealed significant difference (P<0.05) in growth and yield parameters, indicating strong genetic variations among the genotypes. Significant (P<0.05) highest average storage root weight of 1.5 and 1.8 kg were obtained from TMS 94/0035 (high cyanide cassava genotype) and TMS 98/0505 (low cyanide cassava genotype), respectively. Correlation analyses indicated significant (P<0.05) and positive associations between number of storage roots per plant, average storage root weight and root yield in the two types of cassava genotypes tested, indicating that the parameters are good indices that can be improved upon during breeding and selection to enhance root yield. Four high cyanide cassava genotypes (TMS 99/2123, TMS 96/1642, TMS 98/0068 and TMS 94/3200i´? were outstanding in fresh root yield performance. To improve fresh root yield in cassava, the inter-relationships among the various agronomic character of the cassava genotypes demands appropriate attention. The study gives more information on the improvement of fresh storage root yield of cassava. Key words: High cyanide cassava genotypes, low cyanide cassava genotypes, correlations, growth, yield.

Genotype x Environment Interaction Effect on Farmer Preferred Traits of Cassava Varieties Adapted to the Tropical Climatic Conditions of Western Kenya

Presence of farmer preferred traits and understanding their sensitivity to heterogeneous environments is important and critical to variety adoption. The study aimed at determining genotype x environment interaction (GEI) effect and heritability of farmers preferred cassava traits. A 5 x 2 α-lattice design with two replicates was used. Ten cassava varieties were evaluated at Kenya Agricultural Research Institute farms in Kakamega and Alupe and on-farm in Mumias, Busia and Teso between 2009 and 2011. Data were collected on; plant height (PT), height of first branching (HB), internode length (IL), Branching level (BL) per plot, total number of storage roots per plant (NR) and Fresh storage roots yield (RY) converted to yield per hectare. Four stability analyses parameters; Finlay and Wilkinson’s regression coefficient (β1), mean squares deviations from the regression (Sdi), Wricke’s ecovalence (Wi) and Additive Main effects and Multiplicative Interaction stability value (ASV) were used. Heritability was estimated as the proportion of phenotypic variances that is due to genetic differences among varieties. GEI effects were significant (p=0.05) for all traits evaluated except PT and NR. Traits related to plant architecture had fairly high heritability as compared to RY and NR with heritability of 6.9% and 13.6%, respectively. W i, Sdi , and ASV significantly (p=0.05) correlated for all Original Research Article American Journal of Experimental Agriculture, 4(6): 686-702, 2014 687 the traits evaluated. However, βi did not significantly (p=0.05) correlate with all the other procedures except with Sdi for height of first branching with Spearman’s rank correlation coefficient of 0.74. For effective cassava evaluation, traits related to plant type which has high heritability should be evaluated early when planting materials is still a hindrance to carry out multi-location replicated trials. Later, with enough planting materials, evaluation should focus on yield and yield related traits with low heritability in multi-location replicated trials. The presence of GEI implies cassava variety selection should be based on both mean performance and stability. Any one of the Wi, Sdi or ASV stability analysis methods can be used.

Effect of Acute Gamma Irradiation onCurcuma alismatifoliaVarieties and Detection of DNA Polymorphism through SSR Marker

The effects of eight different doses (0, 10, 20, 25, 35, 40, 60, and 100 Gy) of acute gamma irradiation on 44 (three varieties of Curcuma alismatifolia: Chiang Mai Red, Sweet Pink, Kimono Pink, and one Curcuma hybrid (Doi Tung 554) individual plants were investigated. Radiation sensitivity tests revealed that the LD50 values of the varieties were achieved at 21 Gy for Chiang Mai Red, 23 Gy for Sweet Pink, 25 Gy for Kimono Pink, and 28 Gy for Doi Tung 554. From the analysis of variance (ANOVA), significant variations were observed for vegetative traits, flowering development, and rhizome characteristics among the four varieties of Curcuma alismatifolia and dose levels as well as the dose × variety interaction. In irradiated plants, the leaf length, leaf width, inflorescence length, the number of true flowers, the number of pink bracts, number of shoots, plant height, rhizome size, number of storage roots, and number of new rhizomes decreased significantly (P < 0.05) as the radiation dose increased. The cophenetic correlation coefficient (CCC) between genetic dissimilarity matrix estimated from the morphological characters and the UPGMA clustering method was r = 0.93, showing a proof fit. In terms of genetic variation among the acutely irradiated samples, the number of presumed alleles revealed by simple sequence repeats ranged from two to seven alleles with a mean value of 3.1, 4.5, and 5.3 alleles per locus for radiation doses of 0, 10, and 20 Gy, respectively. The average values of the effective number of alleles, Nei's gene diversity, and Shannon's information index were 2.5–3.2, 0.51–0.66, and 0.9–1.3, respectively. The constructed dendrogram grouped the entities into seven clusters. Principal component analysis (PCA) supported the clustering results. Consequently, it was concluded that irradiation with optimum doses of gamma rays efficiently induces mutations in Curcuma alismatifolia varieties.

Characterisation of proteins in the storage organs of Curcuma alismatifolia Gagnep.

SummaryCurcuma alismatifolia rhizomes are exported to world markets for ornamental use. Rhizome size and the number of storage roots affected shoot sprouting, plant growth, and inflorescence yield and quality, indicating an important role for storage food reserves such as the carbohydrates and proteins in these organs. An understanding of the proteins used for growth and development in rhizomes and in storage roots is lacking, so changes in the storage proteins in these organs were investigated at the planting stage, the sprouting stage, the second-leaf stage, the flowering stage, and the dormancy stage. The protein concentrations in both these organs decreased rapidly until the flowering stage in order to support the initial growth of roots and shoots. The intensity of Coomassie Brilliant Blue staining of tissues was stronger in rhizomes than in storage roots. Protein staining was present in the cytosol and in the cell walls in rhizomes, and was intense in small particle-like protein bodies in the cytosol. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) profiles showed that peptides of 10.6 kDa and 12.0 kDa were the two major soluble proteins in rhizomes and were different from the proteins in storage roots.The 10.6 kDa and 12.0 kDa bands contained five peptides and one peptide, respectively, when separated by 2D-PAGE. The amino acid sequences of these six peptides were not homologous to any known proteins using BLASTP or FASTA analysis. The N-terminal amino acid sequences of these two polypeptides did not start with methionine, indicating that they had undergone posttranslational modification. Knowledge of the major storage proteins in the rhizomes and storage roots of C. alismatifolia may provide information to improve N-fertilisation.

Early-season Soil Moisture Deficit Reduces Sweetpotato Storage Root Initiation and Development

Sweetpotato [Ipomoea batatas (L.) Lam.] storage root formation is a complex developmental process. Little quantitative information is available on storage root initiation in response to a wide range of soil moisture levels. This study aimed to quantify the effects of different levels of soil moisture on sweetpotato storage root initiation and to develop functional relationships for crop modeling. Five levels of soil moisture, 0.256, 0.216, 0.164, 0.107, and 0.058 m3·m−3 soil, were maintained using sensor-based soil moisture monitoring and semiautomated programmed irrigation. Two commercial sweetpotato cultivars, Beauregard and Evangeline, were grown in pots under greenhouse conditions and treatments were imposed from transplanting to 50 days. Identification of storage roots was based on anatomical, using cross-sections of adventitious roots, and visual features harvested at 5-day intervals from 14 to 50 days after transplanting (DAT). Recorded time-series storage root numbers exhibited sigmoidal responses at all soil moisture levels in both cultivars. Time to 50% storage root initiation and maximum storage root numbers were estimated from those curves. Rate of storage root development was determined as a reciprocal of time to 50% storage root formation data. Time to 50% storage root initiation declined quadratically from 0.05 to 0.15 m3·m−3 soil moisture and increased slightly at the higher soil moisture levels in both the cultivars. Cultivars differed in time to 50% storage root initiation and the storage root developmental rate. Soil moisture optima for storage root initiation were 0.168 and 0.199 m3·m−3 soil, equivalent to 63% and 75% field capacity for cultivars Beauregard and Evangeline, respectively. The data and the inferences derived from the functional algorithms developed in this study could be used to advise growers to schedule irrigation more precisely, make planting decisions based on available soil moisture, and to develop sweetpotato crop models for field applications.

Bulked segregant analysis identifies molecular markers associated with early bulking in cassava (Manihot esculenta Crantz)

Late root bulking is a major factor leading to rejection and abandoning of improved cassava genotypes in sub-Saharan Africa. Early bulking (EB) varieties shorten the growth period from planting to harvesting, better fit into environments with short rainy season, and reduce exposure to biotic and abiotic stresses thereby increasing productivity. This study was carried out to identify molecular markers linked to EB in cassava. Nine cassava hybrid populations (COB-1–COB-9) were developed using six elite varieties (TMS 30572, TMS 97/2205, TMS 98/0505, TMS 30555, NR 8212 and NR 8083) from the African cassava germplasm as parents. The progeny in each of the nine populations (101–272 genotypes per population) were evaluated for EB at 7 months after planting at seedling, clonal, and preliminary stages of breeding evaluation at Umudike. The parameters measured are fresh root yield, harvest index, fresh shoot weight and number of storage roots per plant. The progeny in each of the nine populations were genotyped at 542 simple sequence repeat (SSR) marker loci. Bulked segregant analysis was used to identify the SSR markers associated with EB in the populations. Nine SSR markers (SSRY 106, (ESTs)SSRY 292, SSRY 239, (ESTs)SSRY 7, NS 194, (ESTs)SSRY 47, SSRY 63, SSRY 250, and NS 323) were found to be closely linked (r = 0.3–0.5; p < 0.05) to EB in six of the nine hybrid populations. Seven of the markers with 10 % or more coefficient of determination (R2) were linked to major quantitative trait loci associated with EB in cassava. The molecular markers identified in this study provide useful materials to select for EB in cassava and for further target-traits-improvement by pyramiding.

IMPROVING STORAGE ROOT PROTEIN CONTENT IN SWEET POTATO THROUGH OPEN-MATING POLLINATION

Normal 0 false false false IN X-NONE X-NONE MicrosoftInternetExplorer4 Normal 0 false false false EN-US X-NONE X-NONE A field experiment was conducted at the Research Station of Brawijaya University from April to August 2009. An augmented, r andomi z e d complete block design with seven blocks was utilized with seven parental clones as standard treatment s and seven half-sib families as augmented treatmen ts . E ach block consisted of seven parental clones plus one randomly assigned family of half-sibs. In addition , the first block contained 29 accessions, the 2 nd block had 120, the 3 rd block had 194, the 4 th block had 45, the 5 th block had 28, the 6 th block had 186, and the 7 th block had 108. Ten cuttings of each parental clone was planted in each block, along with a single plant of each accession at a spacing of 75 cm in the row and 100 cm between the rows. There were five improved clones identified with high protein content and high yield . Broad-sense heritability and genetic advance of storage root weight, storage root number, percentage dry matter and protein content were high, whereas vegetative biomass and harvest index were low. The result s showed that storage root weight, storage root number, percentage dry matter and protein content could be used as the basis for a crop improvement program in sweet potato. Keywords: broad sense heritability, expected genetic advance, improved clones, high yied, protein content , sweet potato

EFFECT OF CHEMICAL, BIO AND ORGANIC FERTILIZER TREATMENTS ON YIELD AND YIELD COMPONENTS OF SWEET POTATO (Ipomea batatas)

Field experiments of the present study were carried out during the two successive seasons of 2008 and 2009 at Research Farm of Faculty of Agriculture, Minia University, EL - Minia, Egypt. Sweet potato c.v. Mabrouka was cultivated to study effect of the chemical NPK, bio and organic fertilizers on its yield and yield components under EL-Minia growing conditions. Eight treatments were studied with some possible combinations among the used fertilizers. The obtained results of the present study could be summarized as follow: Number of storage - roots/plant was significantly affected by fertilizers treatments in both seasons. The highest numbers of roots were produced from plants fertilized with compost only in the first season, while from the combined application of compost + half rate of the recommended NPK fertilizers + bio-fertilizers in the second season. The highest values of average root fresh weight were obtained from plants fertilized with half recommended rate of dose NPK + compost in the first season and the half recommended rate of the chemical NPK fertilizer in the second season. Data declared that the highest values of root dry weight per plant were obtained from plants fertilized with compost + bio-fertilizers in the first season and compost only in the second season . Significant effect on total dry weight per plant in both seasons was detected. The highest value in the first season was obtained from plants fertilized by half NPK + compost, while plants fertilized with the bio-fertilizers only gave the highest value, in the second season. Highest value of harvest index in the first season, was given with using the bio-fertilizers only, while half rate of NPK only produced the highest value in the second season. In general , the effects of organic and bio-fertilizers on most of the studied yield characters indicate the possibility of replacing or reducing the amount of the chemical NPK fertilizers required for sweet potato ( c.v. Mabrouka) production. Furthermore, Compost + bio-fertilizers treatments exceeded the recommended NPK treatment of some economically important studied characters such as number of storage roots / plant and average root fresh weight/ Plant.

Determination of Sweetpotato [Ipomoea batatas (L.) Lam.] Genotypes Suitable to The Aegean Region of Turkey

A total of ten sweetpotato genotypes were grown in a field trial in 2003 and 2004 and certain agronomi cal and quality characteristics were determined. Local variety Hatay Kirmizi (Hatay Red) was selected as suitable to th e Aegean Region for storage root number (7.7) and storage ro ot yield (8.1 tons /ha ) as well as acceptable qual ity characteristics: dry matter content: 41.8 %; sugar content: 2229.3 mg /kg; seta carotene 7.03 mg/100 g; vitamin A: 1171 6.3 IU; vitamin C: 38.6 Mg /100 g. Another introduced variety Regal was also selected for yield (6.6 ton /ha) and starch content (31.1 g/100 g), seta carotene (7.04 mg /100 g) and vitamin A (11745 IU) for the Aegean Region.

Yielding of Asparagus Depending on Harvest Ending Date

Yielding of Asparagus Depending on Harvest Ending Date The field experiment focused on the determination of yielding of asparagus cv. ‘Thielim’ in relation to harvest duration: traditional (until June 20th), shortened (June 10th) and prolonged (30th June) harvests. The variation in harvest ending dates did not have a significant influence on the total, marketable and non-marketable yields as well as on the crown weight and the number of storage roots. However, the extension of harvest time until June 30th resulted in an increase in the number of spears in the total and marketable yields, accompanied by a decrease in their diameter. Also prolonging harvest affected negatively the summer stalk size. During harvest until June 10th asparagus plants probably did not use their full yielding potential, because of too short harvest time. It resulted in increased height, weight, light absorption of summer stalks, leaf area index (LAI) and the total of cross-section areas of summer stalks (PPPA) with no significant differences in yield.

Divergência genética entre acessos de mandioca-de-mesa coletados no município de Cianorte, região Noroeste do Estado do Paraná

The objective of this work was to evaluate the genetic divergence among 43 accesses of sweet cassava (Manihot esculenta Crantz), collected in urban area of Cianorte county – PR, were used 12 quantitative morph-agronomic descriptors. For clustering analysis, the methods of Tocher Optimization and the Nearest Neighbor both based on the Euclidian mean distance standardized were applied to data set. The highest genetic divergence was observed among UEM-38 and UEM-130 accesses, besides UEM-38 and UEM-154, whereas the lowest genetic divergence was observed among UEM-53 and UEM-79, and among UEM-53 and UEM-68. Both clustering methods presented similarity in relation to discrimination of the accesses groups. Traits that better evidenced the higher genetics divergences were length of storage roots, length of blades and number of storage roots per plant, whereas the height of plants, height of first ramification and diameter of storage roots showed the lowest contributions to genetic divergence.

Efficient elimination of sweetpotato little leaf phytoplasma from sweetpotato by cryotherapy of shoot tips

Shoot tips with 3–4 leaf primordia were excised from in vitro‐grown sweetpotato plants (Ipomoea batatas) infected with little leaf phytoplasma (Candidatus Phytoplasma aurantifolia) and subjected to cryotherapy. All plants regenerated from the cryo‐treated shoot tips were free of phytoplasma, whereas shoot tip culture or dehydration of shoot tips without subsequent cryotherapy resulted in phytoplasma‐free plants at a frequency of only 7–10%. Histological and ultrastructural studies with light and transmission electron microscopy, respectively, indicated that cryotherapy was lethal to all cells except those in the apical dome of the meristem and the two youngest leaf primordia. These surviving parts of the shoot tip contained vascular tissue and sieve elements, but electron microscopy showed no phytoplasma in them. In contrast, an abundance of phytoplasma was found in sieve elements located at the lower, non‐surviving parts of the shoot tip 1·0 or 1·5 mm from the apical dome. In the greenhouse, the plants in which phytoplasmas were not detected were healthy‐looking, grew vigorously and were readily distinguished from the infected plants that exhibited little leaf and chlorosis symptoms, proliferation of axillary shoots and roots, stunting, and heavily reduced number and size of storage roots. In this study efficient elimination of phytoplasma and production of pathogen‐tested plant stocks were achieved with the novel cryotherapy‐based approach. The proposed advantage of the technique is that it can be simultaneously used for long‐term storage of plant germplasm and for production of pathogen‐free plants.

Response of cassava to nematicide application and plant-parasitic nematode infection in East Africa, with emphasis on root knot nematodes

Cassava (Manihot esculenta Crantz( is attacked by numerous species of plant-parasitic nematodes, among which, Meloidogyne spp. are the most damaging. However, data on the level of damage occurring under field and farm conditions are largely lacking. To examine the impact, upon cassava production, of plant-parasitic nematodes, field experiments were conducted at four sites in East Africa in Uganda (Serere and Sendusu( and Kenya (Mtwapa and Msabaha( during 2002 and 2003. We focused on Meloidogyne spp. (mainly M. incognita and M. javanica(, attacking two popular cultivars in each country. Nematicide (Nemacur® [fenamiphos]( was used against nematodes in control plots. Meloidogyne spp. were the most common nematodes encountered and caused galling damage at harvest at all sites, with Scutellonema spp. and Pratylenchus spp. being the next most commonly observed. The highest root densities of Meloidogyne spp. were recorded at Serere, while Mtwapa had the highest galling damage and intensity. At harvest, nematicide-treated plots had significantly lower densities of the most commonly occurring nematodes and fewer galls on feeder roots (galling intensity(. However, the root galling index score (damage( was not significantly lower compared with untreated plots. The majority of crop growth and yield variables measured at harvest across experiments were unaffected by nematicide application, but fewer storage roots suffered rot. The overall number of variables was minimized using Principal Components Analysis, which identified three major groups. A bivariate plot of the two larger groups across experiments showed that galling intensity, Pratylenchus spp. and Meloidogyne spp. density were negatively correlated with cassava yield (tonnes/ha( and marketable storage root number. Linear regression analysis showed that Meloidogyne spp. density at harvest was negatively associated with yield (tonnes/ha( for cv. Migyera and cv. SS4 in Uganda, but not for cv. Mtwapa1 or cv. Kibendameno (which was positively correlated( at Kenya sites. A strong negative correlation between marketable tuber number and Meloidogyne spp. for cv. Migyera was observed in Uganda, but not for cv. SS4. Meloidogyne spp. density and total nematode species density were each negatively correlated with non-marketable storage root number on both cultivars in Uganda, but not for either cultivar in Kenya.