Combining ability of cassava genotypes for cassava mosaic disease and cassava bacterial blight, yield and its related components in two ecological zones in Ghana

Breeding for resistant genotypes is the best strategy to offset the destructive effects of cassava mosaic disease (CMD) and cassava bacterial blight (CBB). Two sets of diallel parents were selected for the forest and the savannah ecological zones in Ghana based on good levels of resistance to CMD and CBB. Both sets were crossed in a half-diallel design. The first set of seven progenitors and their 21 F1 progenies were planted in a randomised complete block design (RCBD) with three replications in two different locations for two seasons in the forest ecology. The second set of five progenitors and their 10 F1 progenies were planted in a RCBD with three replications in two locations in the coastal savannah ecological zone of Ghana. Both experiments were evaluated for CMD and CBB resistance, fresh root yield, dry root yield, root number, harvest index, dry matter content, plant height at maturity and height at first branching, levels of branching and plant vigour. Results of the combined analysis of variance revealed that the environment effect was significant for all the traits. General combining ability and specific combining ability effects were significant for most of the traits. Narrow sense heritability was significant for plant vigour, root number, CMD and CBB in both the zones. CMD and root number also had a predictability ratio of close to one, indicating the importance of additive gene effects.     

Genotype by environment interaction components underlying variations in root,sugar and white sugar yield in sugar beet (<Emphasis Type="Italic">Beta vulgaris</Emphasis> L.)

The success of plant breeding programs depends on the ability to provide farmers with genotypes with guaranteed superior performance in terms of yield across a range of environmental conditions. We evaluated 49 sugar beet genotypes in four different geographical locations in 2 years aiming to identify stable genotypes with respect to root, sugar and white sugar yields, and to determine discriminating ability of environments for genotype selection and introduce representative environments for yield comparison trials. Combinations of year and location were considered as environment. Statistical analyses including additive main effects and multiplicative interactions (AMMI), genotype main effects and genotype?×?environment interaction effects (GGE) models and AMMI stability value (ASV) were used to dissect genotype by environment interactions (GEI). Based on raw data, root, sugar and white sugar yields varied from 0.95 to 104.86, 0.15 to 20.81, and 0.09 to 18.45 t/ha across environments, respectively. Based on F-Gollob validation test, three interaction principal components (IPC) were significant for each trait in the AMMI model whereas according to F ratio (F_R) test two significant IPCs were identified for root yield and sugar yield and three for white sugar yield. For model diagnosis, the actual root mean square predictive differences (RMS PD) were estimated based upon 1000 validations and the AMMI-1 model with the smallest RMS PD was identified as the most accurate model with highest predictive accuracy for the three traits. In the GGE biplot model, the first two IPCs accounted for 60.52, 62.9 and 64.69% of the GEI variation for root yield, sugar yield and white sugar yield, respectively. According to the AMMI-1 model, two mega-environments were delineated for root yield and three for sugar yield and white sugar yield. The mega-environments identified had an evident ecological gradient from long growing season to intermediate or short growing season. Environment-focused scaling GGE biplots indicated that two locations (Ekbatan and Zarghan) were the most representative testing environments with discriminating ability for the three traits tested. Environmentally stable genotypes (i.e. G21, G28 and G29) shared common parental lines in their pedigree having resistance to some sugar beet diseases (i.e. rhizomania and cyst nematodes). The results of the AMMI model were partly in accord with the results of GGE biplot analysis with respect to mega-environment delineation and winner genotypes. The outcome of this study may assist breeders to save time and costs to identify representative and discriminating environments for root and sugar yield test trials and creates a corner stone for an accelerated genotype selection to be used in sweet-based programs.     

Genetic variability of cassava progenies developed through introgression of cassava mosaic disease resistance into Ghanaian landraces

Availability of genetic diversity is important in selecting suitable cultivars for crop improvement. Progenies of crosses between 19 farmer-preferred cassava landraces and Cassava Mosaic Disease (CMD)-resistant cultivar TME 11 were evaluated and compared with their maternal parents to assess their genetic variability and genetic gains based on CMD tolerance, some growth variables and root yield. The combined analysis of variance for the traits showed significant genotypic differences amongst the progenies and the parents. Apart from a few instances, the differences in replications and years were also significant. Genetic variability components showed high heritability ranging from 92.3 to 99.6% and moderately high genetic gains of 54.1 to 99.6% for the parental cultivars. Apart from canopy spread and plant height, heritability and genetic gains of the progenies were slightly lower than the parents indicating high variability within families of the progenies. The phenotypic coefficient of variation was slightly greater than genotypic coefficient of variation indicating minimal influence of environment on the genotypes. For most of the characters evaluated, the mean performance of the progenies was higher than their corresponding parental lines. Although the genotypes differed significantly (P < 0.001) for all traits evaluated, cultivars such as Afebankye, Bosome nsia, Cedi bankye, 262 Debor, Kwadaso 25, Nkaakom 57 and Sisipe were found to constitute a pool of germplasm with adequate variability. The negative correlation between CMD incidence and other traits evaluated showed significant progress made in the breeding program.     

Performance of Diploids and Induced Autotetraploids of Catharanthus roseus under Different Levels of Nitrogen and Plant Spacings

Two bulk experimental strains of induced autotetraploids,‘Purple tetraploid bulk’ (PTB) and ‘White tetraploid bulk’ of Catharanthus roseus were evaluated along with the diploid ‘Purple’ variety (PDB) and a diploid pure line selection PS-3 in four environments consisting of combinations of two levels each of plant spacing and nitrogen at Bangalore and Hyderabad during 1983—84 and in two additional environments at Bangalore during 1984—85. PTB, in general, performed better than PDB at closer plant spacings, especially in the absence of nitrogen application. The highest increase in economic yield (leaf + root yield) over PDB was recorded by PTB with 45 × 30 cm plant spacing and no nitrogen fertilization. The highest economic yield of PTB (obtained with 30 × 30 cm spacing and 100 kg N per ha) was 26 % higher than the highest economic yield of PDB. There were no significant differences between PTB and PDB for content of total alkaloids in leaves within all the environments during both years. Strain × environment interactions were significant for content of total alkaloids in roots during 1983—84. During 1984—85, PTB and PDB did not significantly differ from each other for content of total alkaloids in roots.     

Impact of different environments in Europe on yield and quality of sugar beet genotypes

Sugar beet (Beta vulgaris L.) yield and quality are determined by genotype and environment. This study aimed at analysing the relative importance of the environment for yield and quality of sugar beet genotypes and at assessing parameters which could give essential improvement for beet quality if included as additional selection criteria. For that purpose, root yield and quality (sugar, K, Na, amino N, total soluble N, betaine, glutamine, invert sugar, raffinose) of 9 sugar beet genotypes were investigated in 52 environments (25 sites in 2003 and 27 sites in 2004) in randomised field trials across Europe.The environment accounted for about 80% of the total variance for all parameters. Effects of the tested genotypes were larger for the content of betaine (8.5%) and sugar (7.6%) than for other parameters (1–5%). With the exception of invert sugar and amino N, the genotype by environment interaction was about 3% and thereby lower than the main effect of genotypes. Interactions resulted in an increase of the differences between genotypes which can be used to select genotypes in the most discriminating environments. The response of genotypes in sugar content was contrasting to other parameters and points to a physiological limit for sugar storage at about 20%. As no crossover interaction occurred for root yield or any quality parameter, there seemed to be no specific suitability of the tested genotypes to certain environmental stress conditions. This is probably due to the fact that the harvested beetroot is a vegetative storage organ and has no growth stages susceptible to unfavourable environmental conditions such as flowering and grain filling which are important for final yield in cereals. Invert sugar showed the largest relative differences between genotypes which were strongly enhanced in southern and some south-eastern European environments. Because of its importance during processing, considering invert sugar in breeding could improve technical quality for processing considerably for those extreme environments.     

Diallel inheritance of relevant traits in cassava (Manihot esculenta Crantz) adapted to acid-soil savannas

There is a limited knowledge on the inheritance of traits with agronomic relevance in cassava. A diallel study among 10 parental clones was conducted in the acid-soils environment in the eastern savannas of Colombia. Thirty clones were obtained for each F1 cross. Each clone was represented by six plants, which were distributed in three replications at two locations. Therefore, the same 30 genotypes of each F1 cross were planted in the three replications at the two locations. Analysis of variance suggested significant effects for five of the six variables analyzed (harvest index, dry matter content, height of first branching, reaction to super elongation disease, and plant type scores). Fresh root yield showed strong genotype × environment interaction and differences between crosses reached statistical significance in only one of the two environments analyzed. General and specific combining ability effects and their interaction with the environment were significant for most of the variables as well. Results suggested that dominance plays an important role particularly in the cases of fresh root yield and harvest index.     

5个木薯品种生理特性与主要农艺性状的研究

对木薯品种西选07、桂垦09-11、辐选01、南植199和华南205的生理特性和主要农艺性状进行比较研究。结果表明,5个木薯品种的叶片叶绿素、蔗糖、可溶性糖含量、农艺性状、产量和淀粉含量有显著差异。西选07块根产量最高,其次是桂垦09-11和辐选01;南植199淀粉含量最高,其次是辐选01和西选07;西选07淀粉产量最高,其次是辐选01和桂垦09-11;西选07单株块根数、块根长、块根粗和块根重最高,其次是桂垦09-11和辐选01;南植199叶片蔗糖和可溶性糖含量最高,其次是西选07和辐选01。叶片蔗糖、可溶性糖含量均与块根淀粉含量呈极显著正相关,可作为高淀粉木薯品种评价的生理指标。淀粉产量综合反映木薯淀粉生产能力,可作为木薯品种品质评价的指标。     

Genotype × environment interaction and yield stability in a cowpea-based cropping system

Twenty-four cowpea genotypes were evaluated under sole cropping or additive series intercropping with sorghum from 2004 to 2005 at four sites representative of the Guinea and Sudan savannah ecologies in Ghana. The aim was to determine whether cowpea breeding programs that emphasize selection under sole-crop conditions have the potential to produce cultivars that are effective under additive series intercropping. Genotype × cropping systems interaction was significant for days to 50% flowering but not for grain yield, biomass and other studied traits. Genotypic yield reaction to cropping systems indicated that bridging the yield gap between sole cropping and intercropping systems is best addressed by agronomic interventions that reduce stress on intercrop cowpea rather than by selecting for specifically adapted genotypes for intercropping. Significant genotype × environment interactions were observed for all traits when data was pooled over cropping systems. Partitioning of the genotype × environment interaction variance indicated that days to 50% flowering was dominated by heterogeneity of genotypic variance, whereas genotype × environment interactions for grain yield and biomass was mainly due to imperfect correlations. Large differences in genotypic yield stability were observed as estimated by the among-environment variance, regression of yield on the environmental index, Kataoka’s index, and by partitioning of genotype × environment interaction sum of squares into components attributable to each genotype. The results suggest that in regions where genotype × environment interaction for yield frequently causes re-ranking across environments, genotypes with the least contribution to the interaction sum of squares are likely to be most productive. On the whole, the results support the contention that breeding under sole-crop conditions has the potential to produce cultivars effective under intercropping conditions.     

Association and Path Coefficients Analysis of Fresh Root Yield of High and Low Cyanide Cassava (Manihot esculenta Crantz) Genotypes in the Humid Tropics

Thirty-eight high- and low-cyanide cassava genotypes were examined in the 2004 and 2005 cropping seasons at Umudike, southeastern Nigeria using RCBD with three replications. Simple correlation associations and path coefficients analyses were computed among agronomic characters with the aim of understanding the interrelationships of these characters and the extent of their contribution to the root yield of cassava. There was a significant (P 2 0.05) positive correlation between root yield and number of roots plant-1 with correlation coefficients (r) of 0.57, average weight of root (r = 0.58) in high-cyanide cassava genotypes, while in low cyanide cassava genotypes, fresh root yield was highly significantly (P 2 0.01) correlated with average weight of root (r = 0.74). Path analysis showed that average weight of root had the highest direct effect in high (0.66) and in low cyanide (0.67) cassava genotypes. Also, the number of roots plant-1 in both types of cassava exerted a positive direct effect on fresh root yield, however, a minimum effect was obtained by number of leaves plant-1 (0.22) in high-cyanide cassava and number of stems plant-1 (-0.13) in lowcyanide cassava genotypes. Average weight of roots in high- and low-cyanide cassava genotypes had 98 and 89% direct effects, respectively, on yield of cassava. The results indicated the importance of average weight of roots and other characters such as number of roots plant-1, plant height, and number of leaves plant-1 in determining increased yield hence priority must be accorded it during selection aimed at increasing cassava root yield.     

Characterization of resistance of cassava genotypes to bacterial blight by evaluation of leaf and systemic symptoms in relation to yield in different ecozones

Twenty-two improved and local cassava genotypes were evaluated for their bacterial blight symptom types in reaction to infection by Xanthomonas axonopodis pv. manihotis under field conditions in the forest, forest savanna transition and wet savanna zones of Togo. High genotype × environment interactions in development of each symptom type were observed. Combining data on environments and genotypes, spot, blight and wilt symptoms were positively correlated. Analysing genotype reactions across environments, indications for independent mechanisms of resistance on leaf and stem level, varying by genotype, were found. Genotypes Main27 with resistance to spot and blight symptoms and TMS4(2)1425 with resistance to wilt symptoms are recommended to breeders to introgress their resistance characteristics. Significant negative correlations were generally observed between blight and wilt symptom development and root yield across ecozones, with blight being more important under lower, and wilt under higher inoculum pressure. Genotypes TMS30572, CVTM4, TMS92/0429 and TMS91/02316 showed low spot, blight and wilt symptoms combined with high root yield across ecozones.     

Genotypic Variability in Adaptation Responses of Selected Clones of Cassava to Drought Stress in the Sudan Savanna Zone of Nigeria

Identification of drought‐tolerant and ‐resistant varieties of cassava is of paramount importance for the maximization of productivity potential in drought‐prone areas. Nine improved cassava varieties developed in humid and subhumid agro‐ecologies were evaluated for their growth responses and adaptability in the dry savannas of Nigeria. Field trials were set up in two cropping seasons at three different locations. Parameters evaluated included fresh root yield (FRY), fresh shoot yield (FSY), cumulative leaves formed (CLF), cumulative leaf scars (CLS), root dry‐matter content (DMC), harvest index (HI), and root cyanogenic potential (CNp). Results demonstrated that varietal response differed with water table site, implying different adaptation responses of varieties to the water regime. Variations in all characters studied were significantly (P<0.05) influenced by genotype, suggesting a strong genetic basis for the phenotypic differences amongst varieties. Compared with variation attributable to location, the genotypic components were strong for FRY, FSY, CLF, CLS, HI and DMC. HI and DMC were not significantly affected by location. CNp tended to increase with increasing drought stress. The significance of genotype × environment effects for FRY suggested that genotypes may be selected for specific adaptation for drought‐prone environments. The poor adaptability responses of the majority of the varieties implied that an agro‐ecologically targeted breeding scheme for the dry savanna would be a more appropriate approach for the development of drought‐tolerant varieties.     

Assessing the agronomic potential of linseed genotypes by multivariate analyses and association mapping of agronomic traits

High prices of fish oil make linseed attractive for aquaculture and animal feed. To ensure a constant supply of linseed, the development of stable cultivars is of strategic importance. In this study, 35 linseed genotypes were evaluated in five Chilean environments (E) from 2009 to 2012. The additive main effect and multiplicative interaction analysis (AMMI), genotype (G) plus genotype by environment (GE) interaction (GGE) biplot analysis and three stability parameters were tested with the aim of identifying adapted genotypes for the development of linseed cultivars. An association mapping (AM) analysis was also conducted for four agronomic traits and the stability of the associated markers was evaluated using the QQE (QTL main effect and QTL by environment interaction) approach. Combined analysis of variance for yield, seeds per boll (SPB), plant height (PH) and days to flowering (DTF) were significant for G, E and GE (P < 0.001). The combined stability analysis identified some Canadian, Argentinean and Chilean accessions to be the best adapted and highest yielding genotypes. Coancestry analysis indicated that crossing Canadian and Chilean genotypes could maximize transgressive segregation for yield. Significant associations for DTF, PH and SPB explained up to 59 % of the phenotypic variation for these traits. The QQE and AM analyses were consistent in identifying marker LGM27B as the most stable and significant across all environments with the largest effect in reducing DTF. The combined application of the stability, AM and QQE analyses could accelerate the development of marketable linseed cultivars adapted to Southern Chile.     

木薯主要农艺性状的遗传变异、相关性和主成分分析

对广西14个主要木薯品种的9个农艺性状进行了遗传变异分析、相关性分析和主成分分析。结果表明,块根长,块根鲜重、块根数的变异系数较大,分别为13.95%、11.33%、10.22%,块根干物质率和茎径的变异系数最小,分别为7.00%和6.57%;在相关性上,产量与块根数呈极显著的正相关,块根干物质率与块根淀粉含量呈极显著的正相关;主成分分析结果表明,前4个主成分对变异的贡献率达85.69%。在性状选择上,首先对变异大的性状进行选择是非常重要的。在品种选择时,应注意选择产量和淀粉含量均高的品种。     

Genotype by environment interactions (GEIs) for barley grain yield under salt stress condition

Changes in the relative genetic performance of genotypes across environments are referred to as genotype × environment interactions (GEIs). GEIs can affect barley breeding improvement for salt tolerance because it often complicates the evaluation and selection of superior genotypes. The present study evaluated the GEIs over 60 barley genotypes for yield components and grain yield in six salinity environments in North Delta, Egypt. Data were analyzed using the additive main effects and multiplicative interaction (AMMI) and Tai’s stability parameters. GEIs effects on yield explained 20.3, 20.1, 14.6, and 33.0% of the total variation besides, the first two principal components account for 67.3, 56.3, 64.3, and 83.7% of the explained variance in the four sets, respectively. Six genotypes namely G-4, G-7, G-20, G-34, G-36, and G-39 were found to be most stable and high yielding across environments (GY >2.00 t ha^-1), and located close to zero projection onto the AEC ordinate. Tai’s stability parameters demonstrated that these genotypes were more responsive to the environmental changes. The genotypes G-50 and G-53 showed perfect/static stability (α = -0.95, -0.91, respectively). In contrast, the genotype; G-36 had α = 0 and λ = 1.10, indicating parallel with the environmental effects followed by G-44. Overall, we found that GEIs for grain yield are highly significant in all sets, suggesting that responded differently across environments. This interaction may be a result of changes in genotypes’ relative performance across environments, due to their differential responses to various abiotic factors.     

不同间作绿肥替代化肥模式对木薯性状和产量的影响

通过探讨秸秆还田与化肥减施下间作绿肥对木薯产量性状的影响,着力解决连作木薯土壤肥力提高与改良相关技术的协调增效。于2019-2020年,以木薯品种“南美1号”为供试材料,设置8个处理,调查每个小区的木薯茎径、叶绿素（SPAD）、块根直径、块根长、单株茎秆鲜重、单株块根鲜重、株高、单片叶重、单株块根数以及小区产量等农艺性状。结果表明,处理5（木薯秆还田+化肥减量12.5%+12.5%营养元素当量黑豆绿肥还田）的木薯产量最高,并得到拟合方程。绿肥秸秆还田以及间作绿肥从整体上改良了土壤肥力,并通过显著影响木薯块根、单片叶重以及单株块根数而影响最终产量。     

Evaluation of cassava germplasm for drought tolerance under field conditions

The development of cassava (Manihot esculenta Crantz) with a high yield under water-deficit conditions is one of the goal of the breeding programs. The objective of this study was to evaluate the performance and to select cassava accessions based on drought tolerance indices and productive potential under water stress. Forty-nine accessions were evaluated for five agronomic traits (plant height—PH, root yield—RoY, shoot yield—ShY, harvest index—HI; and dry matter content of roots—DMC) under full irrigation conditions and drought stress (DS). The accessions were selected based on: (i) high yield under drought conditions (HY-DS) and (ii) high drought tolerance (Dr-To) based on six different indices. Overall, water stress dramatically reduced the traits’ means (RoY—72.98%, ShY—54.95%, DMC—26.15%, HI—31.05%, and PH—32.95%). Low coincidence among the top ten accessions was identified based on HY-DS and Dr-To criteria. Therefore, considering only the most important traits (RoY and ShY), five accessions (BGM0815, BGM0598, 9624-09, BGM0818, and BRS Formosa) presented high HY-DS. In contrast, to Dr-To criterion, eight and nine accessions were selected for high yield of the aerial part (ShY and PH) and roots (RoY and DMC), respectively. The mean productivity, geometric mean productivity, and drought tolerance indices were the most promising to identify genotypes with high agronomic attributes, while drought susceptibility index, susceptibility, and yield stability index were suitable to identify the most drought tolerant accessions. This set of selected accessions can be used in breeding programs aimed at high yield and drought tolerance.     

Genotypic variation in abscisic acid content,carbon isotope ratio and their relationship with cassava growth and yield under moisture stress and irrigation

This study was carried out to assess genotypic variability in abscisic acid content, carbon isotope ratio, and their relationship to storage root yield and yield components in cassava under irrigation and moisture stress. The study involved 20 cassava genotypes arranged in randomized complete block design with three replications. Irrigation water was applied using a drip irrigation system with a discharge rate of approximately 5.33 L m^-2 hr^-1. Significant (P < 0.05) genotypic variability was observed for all physiological, growth, and yield traits assessed. Abscisic acid content was higher under stress than irrigation and negatively correlated with root yield (r = -0.45), harvest index (r = -0.43), and above-ground biomass yield (r = -0.20) indicating that it can be used as indirect selection criteria against unproductive genotypes. Carbon isotope ratio was significantly and positively correlated with above-ground biomass yield (r = 0.20) but not root yield (r = 0.09). Estimates of genotypic variability indicated high values for most of the growth and yield components but low heritability values for abscisic acid content, carbon isotope ratio, stomatal conductance, and root yield under stress conditions. However, higher estimates were recorded under irrigation and in the combined analysis. It was also found from this study that carbon isotope ratio influences above-ground biomass but not storage root yield under stress conditions. The results from this study provide useful information on the relationship between abscisic acid content, carbon isotope discrimination, and storage root yield in field-grown cassava.     

Inheritance of useful traits in cassava grown in subhumid conditions

A diallel study among nine parental clones of cassava was conducted in the subhumid environment on the northern coast of Colombia. Analysis of variance suggested significant effects for the six variables analysed: fresh‐root yield, harvest index, root dry matter content, height of first branching, reaction to thrips and plant‐type scores. General and specific combining ability effects and their interaction with the environment were significant for most of the variables as well. Results suggested that dominance plays a particularly important role in the cases of fresh‐root yield and harvest index but had relatively little importance in the reaction to thrips, dry matter content or height of first branching. Specific breeding approaches are suggested for these traits, depending on the relative importance of additive or non‐additive effects in their inheritance. The correlations among different traits were also analysed and in several cases their magnitude reached statistical and biological significance.     

Performance of cowpea varieties under <Emphasis Type="Italic">Striga gesnerioides</Emphasis> (Willd.) Vatke infestation using biplot analysis

Striga gesnerioides (Willd) Vatke, is a major destructive parasitic weed of cowpea (Vigna unguiculata (L.) Walp.) which causes substantial yield reduction in West and Central Africa. The presence of different virulent races within the parasite population contributes to significant genotype × environment interaction, and complicates breeding for durable resistance to Striga. A 3-year study was conducted at three locations in the dry savanna agro-ecology of Nigeria, where Striga gesnerioides is endemic. The primary objective of the study was to identify cowpea genotypes with high yield under Striga infestation and yield stability across test environments and to access suitability of the test environment. Data collected on grain yield and yield components were subjected to analysis of variance (ANOVA). Means from ANOVA were subjected to the genotype main effect plus genotype × environment (GGE) biplot analysis to examine the multi-environment trial data and rank genotypes according to the environments. Genotypes, environment, and genotypes × environment interaction mean squares were significant for grain yield and yield components, and number of emerged Striga plants. The environment accounted for 35.01%, whereas the genotype × environment interaction accounted for 9.10% of the variation in grain yield. The GGE biplot identified UAM09 1046-6-1 (V7), and UAM09 1046-6-2 (V8), as ideal genotypes suggesting that these genotypes performed relatively well in all study environments and could be regarded as adapted to a wide range of locations. Tilla was the most repeatable and ideal location for selecting widely adapted genotypes for resistance to S. gesnerioides.