Comparisons of methods for introgressing exotic germ plasm into adapted sorghum

The incorporation of exotic germ plasm into breeding populations can broaden and diversify the genetic base of adapted genotypes. To more effectively utilize the genetic resources existing in Sorghum bicolor (L.) Moench, a rapid and efficient method of incorporating exotic genotypes into adapted populations is needed. Therefore, this study was conducted to compare the effectiveness of backcrossing to a broad-based population versus backcrossing to an inbred line for developing improved lines from adapted x exotic crosses. A wild sorghum, a cultivated landrace, and a converted sorghum line were crossed to an inbred line (CK60) and a broad-based population (KP9B). After two generations of backcrossing to the respective adapted parent, 50 F₂ lines were derived from each of the backcross generations of every mating and evaluated at three test environments. Backcrossing to an inbred line (CK60) gave fewer high-yielding segregates and generated less genetic variation than backcrossing to a population (KP9B). Also, the number of agronomically acceptable lines derived from each CK60 mating was fewer than that derived from the corresponding mating with KP9B. Overall, the use of a broad-based population as an adapted recurrent parent for introgressing exotic genotypes may provide good opportunities for developing suitable inbred lines from adapted x exotic backcrosses.Contribution no. 93-499-J from the Kansas Agricultural Experiment Station     

An Induced Sorghum Mutant Population Suitable for Bioenergy Research

The sorghum [Sorghum bicolor (L.) Moench] inbred line BTx623 has served as a parent for development of several mapping populations, also providing a source for the generation of DNA libraries for physical mapping, and as the inbred line selected for sorghum genome sequencing. Since genetic mapping, physical mapping and genome sequencing are all based on the same inbred line, these genetic resources have made the genome study of sorghum very efficient. However, in comparison with other model species, there is one important genetic resource still missing in the sorghum research community, a mutant population. A systematically annotated mutant population will facilitate many avenues of research, especially those focusing on functional genomics and bioenergy research. Here we report the generation of a sorghum mutant population derived from the inbred line BTx623 by treatment with the chemical agent ethyl methanesulfonate (EMS). The mutant population consists of 1,600 pedigreed M₃ families; each of them was derived from an independent M₁ seed. Many lines displayed traits such as brown midrib (bmr), erect leaves (erl), multiple tillers (mtl), and late flowering (lfl), characteristics useful for bioenergy research. Results from our phenotyping and genotyping studies indicate that this mutant population will be a valuable and useful genetic resource for both sorghum functional genomics and bioenergy research.     

The production of callus capable of plant regeneration from immature embryos of numerous Zea mays genotypes

In the summer of 1983, immature embryos from 101 selfed inbred lines and germplasm stocks of Zea mays L. were examined for their ability to produce callus cultures capable of plant regeneration (regenerable cultures) using a medium with which some limited success had previously been obtained. Forty-nine of the genotypes (49%) produced callus which visually appeared similar to callus previously cultured and shown to be capable of plant regeneration. After five months, 38 of these genotypes were alive in culture and plants were subsequently regenerated from 35 (92%) of them. No correlation was observed between plant regeneration and callus growth rate, the vivipary mutation (genes vp1, 2, 5, 7, 8 and 9), or published vigor ratings based on K⁺ uptake by roots. When F₁ hybrid embryos were cultured, 97% of the hybrids having at least one regenerable parent also produced callus capable of plant regeneration. No regenerable cultures were obtained from any hybrid lacking a parent capable of producing a regenerable callus culture.In the summer of 1984, immature embryos from 218 additional inbred lines and germplasm stocks were plated and examined for their ability to produce regenerable callus cultures on media containing altered micronutrient concentrations, 3,6-dichloro-o-anisic acid (dicamba), glucose, and elevated levels of vitamin-free casamino acids and thiamine. Of these genotypes 199 (91%) produced callus that was regenerable in appearance. In the 1984 study, plant regeneration was noted in many commercially important inbreds, including B73, Mo17, B84, A632, A634, Ms71, W117, H99³H95 and Cm105. Thus tissue-culture techniques are now available to obtain callus cultures capable of plant regeneration from immature embryos of most maize genotypes.Abbreviations trade names 2,4-D 2,4-dichlorophenoxyacetic acid - dicamba 3,6-dichloro-o-anisic acid     

Morphological and molecular characterization of sweet,grain and forage sorghum (Sorghum bicolor L.) genotypes grown under temperate climatic conditions

Abstract

In the present study, we used 12 genotypes of sorghum originated from different countries (five sweet, four grain and three forage). These different genotypes and types of sorghum were evaluated for the agro-morphological traits that are associated with the estimated sugar and bioethanol yield to estimate their phenotypic diversity. Analysis of variance showed significant differences between different types of sorghum for all the evaluated traits. Sweet sorghum genotypes, however, showed better performance with respect to all studied traits than the other genotypes. A positive significant correlation was observed between plant height, leaf number, leaf area, biomass yield, cane and bagasse yields, and the predicted bioethanol yield. Both, cluster and principal component analysis were performed to group the genotypes according to their agro-morphological and molecular similarity coefficients. For analytical approaches, the Iranian grain and forage genotypes clustered separately from the other genotypes. The clustering patterns obtained from the molecular dominant markers had higher discriminatory power than using morphological characters to separate sweet genotypes from the forage and grain sorghum ones. The results clearly indicated that sweet sorghum can be grown in Germany and maintains its superiority in biomass production and sugar yield over grain and forage sorghum types.     

Adventitious shoot regeneration from immature embryos of sorghum

Eleven genotypes of sorghum were examined for their response in tissue culture, and the tissue culture system was optimized. The cultures were initiated from immature embryos taken approximately two weeks after flowering. The response of immature embryos varied with the genotype. `C. Kafir' and `PE932 025' showed the highest frequency of callus induction and regenerable callus formation under appropriate culture conditions. Regeneration occurred at high frequencies when cytokinins (kinetin or 6-benzyladenine) had been added in the callus induction medium, followed by regeneration medium devoid of growth regulators. The addition of proline and polyvinylpyrrolidone also enhanced shoot formation, but the addition of cytokinins to regeneration media did not improve shoot formation. On the revised culture medium, plants were regenerated from up to 100% of sorghum immature embryos.     

Improved Culture Media for Embryogenic Callus Generation in Sorghum [<i>Sorghum bicolor</i> (L.) Moench]

Many attempts on optimization of sorghum [Sorghum bicolor (L.) Moench] tissue culture induction media have been made, but the culture system remains with some bottlenecks compared to that of other crops. This study aimed at assessing the suitability of various induction media to produce embryogenic callus (yellow and friable) with high induction rates and reduced phenolic exudation. The six culture medium modifications: 3 based on Murashige and Skoog (MS) medium and one each based on Chu N6, Gamborg B5 and 190-2 media respectively were applied in the culture of mature embryos from 10 sorghum genotypes. Although there was a genotype influence on the attainment of a yellow callus, friability of the callus was determined to be dependent on the culture medium and not the genotype. Half strength MS medium with 0.2 mg/l 2,4-D with 2.8 g/l Gelrite® as the gelling agent modified with 1.0 g/l KH₂PO₄, 1.0 g/l L-proline, 1.0 g/l L-asparagine and 0.16 mg/l CuSO₄·5H₂O (type E) was found to be the most effective resulting in about 60% yellow coloured callus induction with 25% friability. Addition of CuSO₄·5H₂O, KH₂PO₄, L-proline and L-asparagine significantly reduced the phenolic production. Half strength MS medium was observed to contribute to quality callus production when compared to full strength MS media modified with the compounds. The half strength MS medium was also observed to suppress phenolic production. Medium 190-2 produced the highest regeneration frequency (40%) among the 3-regeneration media tested. The results provide information on a suitable sorghum callus induction medium necessary for embryogenesis.     

Assessment of sorghum genetic resources of Ethiopia for anthracnose (Colletotrichum sublineolum Henn.) resistance and agronomic traits

Sorghum anthracnose caused by Colletotrichum sublineolum Henn. is one of the key diseases limiting sorghum production and productivity. Development of anthracnose‐resistant sorghum genotypes possessing yield‐promoting agronomic traits is an important breeding goal in sorghum improvement programs. The objective of this study was to determine the responses of diverse sorghum genetic resources for anthracnose resistance and agronomic traits to identify desirable lines for breeding. A total of 366 sorghum collections and three standard checks were field evaluated during the 2016 and 2017 cropping seasons. Lines were artificially inoculated with a virulent pure isolate of the pathogen. Anthracnose disease severity was assessed to calculate the area under disease progress curve (AUDPC). Agronomic traits such as panicle length (PL), panicle width (PW), head weight (HW) and thousand grain weight (TGW) were measured. Lines showed highly significant differences (p < .001) for anthracnose severity, AUDPC and agronomic traits. Among the collections 32 lines developed levels of disease severity between 15% and 30% in both seasons. The following sorghum landraces were selected: 71708, 210903, 74222, 73955, 74685, 74670, 74656, 74183, 234112, 69412, 226057, 214852, 71420, 71484, 200126, 71557, 75120, 71547, 220014, 228179, 16212, 16173, 16133, 69088, 238388, 16168 and 71570. These landraces had a relatively low anthracnose severity possessing farmer‐preferred agronomic traits. The selected genotypes are useful genetic resources to develop anthracnose‐resistant sorghum cultivars.     

Identification of QTLs for eight agronomically important traits using an ultra-high-density map based on SNPs generated from high-throughput sequencing in sorghum under contrasting photoperiods

The productivity of sorghum is mainly determined by agronomically important traits. The genetic bases of these traits have historically been dissected and analysed through quantitative trait locus (QTL) mapping based on linkage maps with low-throughput molecular markers, which is one of the factors that hinder precise and complete information about the numbers and locations of the genes or QTLs controlling the traits. In this study, an ultra-high-density linkage map based on high-quality single nucleotide polymorphisms (SNPs) generated from low-coverage sequences (~0.07 genome sequence) in a sorghum recombinant inbred line (RIL) population was constructed through new sequencing technology. This map consisted of 3418 bin markers and spanned 1591.4 cM of genome size with an average distance of 0.5 cM between adjacent bins. QTL analysis was performed and a total of 57 major QTLs were detected for eight agronomically important traits under two contrasting photoperiods. The phenotypic variation explained by individual QTLs varied from 3.40% to 33.82%. The high accuracy and quality of this map was evidenced by the finding that genes underlying two cloned QTLs, Dw3 for plant height (chromosome 7) and Ma1 for flowering time (chromosome 6), were localized to the correct genomic regions. The close associations between two genomic regions on chromosomes 6 and 7 with multiple traits suggested the existence of pleiotropy or tight linkage. Several major QTLs for heading date, plant height, numbers of nodes, stem diameter, panicle neck length, and flag leaf width were detected consistently under both photoperiods, providing useful information for understanding the genetic mechanisms of the agronomically important traits responsible for the change of photoperiod.     

Genetic dissection of sorghum grain quality traits using diverse and segregating populations

Key message

Coordinated association and linkage mapping identified 25 grain quality QTLs in multiple environments, and fine mapping of the Wx locus supports the use of high-density genetic markers in linkage mapping.

Abstract

There is a wide range of end-use products made from cereal grains, and these products often demand different grain characteristics. Fortunately, cereal crop species including sorghum [Sorghum bicolor (L.) Moench] contain high phenotypic variation for traits influencing grain quality. Identifying genetic variants underlying this phenotypic variation allows plant breeders to develop genotypes with grain attributes optimized for their intended usage. Multiple sorghum mapping populations were rigorously phenotyped across two environments (SC Coastal Plain and Central TX) in 2 years for five major grain quality traits: amylose, starch, crude protein, crude fat, and gross energy. Coordinated association and linkage mapping revealed several robust QTLs that make prime targets to improve grain quality for food, feed, and fuel products. Although the amylose QTL interval spanned many megabases, the marker with greatest significance was located just 12 kb from waxy (Wx), the primary gene regulating amylose production in cereal grains. This suggests higher resolution mapping in recombinant inbred line (RIL) populations can be obtained when genotyped at a high marker density. The major QTL for crude fat content, identified in both a RIL population and grain sorghum diversity panel, encompassed the DGAT1 locus, a critical gene involved in maize lipid biosynthesis. Another QTL on chromosome 1 was consistently mapped in both RIL populations for multiple grain quality traits including starch, crude protein, and gross energy. Collectively, these genetic regions offer excellent opportunities to manipulate grain composition and set up future studies for gene validation.

     

The effect of parental genotype on initiation of embryogenic callus from elite maize (Zea mays L.) germplasm

Summary Embryogenic callus consisting of both Type 1, firm, compact, translucent, relatively slow growing callus and Type 2, highly friable, rapidly growing callus with well-formed somatic embryos, were observed in elite maize germplasm, notably B73 and hybrids with B73. Parental genotype is very important in the ability to identify and isolate embryogenic callus after 14 and 28 days in culture. A partial diallel analysis revealed that a large proportion of the genotypic variation was of the additive type although heterosis did positively increase culture response in most cases. A significant negative maternal effect for culture response was noted for inbred B73 from Reid-type germplasm while four lines sampled from Lancaster germplasm showed similar response whether used as male or female. Although significant media differences were observed in some genotypes, culture media did not preclude observation of Type 1 or Type 2 embryogenic cultures in this study after 14 and 28 days. Plants could be regenerated from all genotypes in this study after 14-days of culture, but not all genotypes were capable of sustained subculture and plant regeneration. Plant regeneration from Type 2 cultures of B73 and B73 hybrids has been obtained up to a year after initiation.     

Strategies for overcoming genotypic limitations of in vitro regeneration and determination of genetic components of variability of plant regeneration traits in sorghum

Development of suitable strategy to overcome genotypic limitations of in vitro regeneration in sorghum would help utilize high yielding but poor tissue culture responsive genotypes in genetic manipulation programmes. A factorial experiment was conducted with two explants (immature embryos and inflorescences), eight genotypes (five Sorghum sudanense and three Sorghum bicolor genotypes), three levels of 2,4-D (1 mg l⁻¹, 3 mg l⁻¹, and 5 mg l⁻¹), and two levels of kinetin (0.0 mg l⁻¹ and 0.5 mg l⁻¹). The induced callus was transferred to the regeneration media with factorial combinations of IAA (1.0 mg l⁻¹ and 2.0 mg l⁻¹) and kinetin (0.5 mg l⁻¹ and 1.0 mg l⁻¹). S. sudanense regenerated at significantly higher frequency (38.91%) and produced shoots more intensely (2.2 shoots/callus) than S. bicolor (26.93%, 1.26 shoots/callus). Immature inflorescences regenerated at a much higher frequency (46.48%) and produced significantly more number of shoots (2.71 shoots/callus) than immature embryos (22.35%, 0.99 shoots/callus). Moreover, differences for plant regeneration between genotypes of the same species were minimal when using immature inflorescences. Increase in the 2,4-D concentration in callus induction media exhibited inhibitory effect on callus induction, growth, shoot induction and number of shoots/callus but inclusion of kinetin in callus induction media improved these responses. Use of immature inflorescence explant and inclusion of kinetin in callus induction media could overcome genotypic limitations of plant regeneration to a large extent. The extent of variability, heritability and expected genetic advance was more in plant regeneration traits than in callus induction traits. This indicated that the variability in respect of these attributes in the genotypes may be due to the additive gene action and selection of genotypes for these characters would be rewarding.     

A genetic analysis of cell culture traits in tomato

Summary Tomato genotypes superior in regenerating plants from protoplast and callus cultures were obtained by transferring regeneration capacity from Lycopersicon peruvianum into L. esculentum by classical breeding. The genetics of regeneration and callus growth have been studied in selfed and backcross progenies of a selected plant (MsK93) which has 25% L. peruvianum in its ancestry. Segregation data showed that the favourable cell culture traits of L. peruvianum are dominant. Regeneration capacity from established callus cultures was controlled by two dominant genes. Callus growth on primary expiants, callus growth of established cultures and shoot regeneration from explants had high heritabilities (0.47, 0.78, 0.87, respectively). Callus growth and regeneration capacity were not correlated within the populations studied.     

Identification of QTLs associated with tissue culture response through sequencing-based genotyping of RILs derived from 93-11 × Nipponbare in rice (Oryza sativa)

Key message

The performance of callus induction and callus differentiation was evaluated by 9 indices for 140 RILs; 2 major QTLs associated with plant regeneration were identified.

Abstract

In order to investigate the genetic mechanisms of tissue culture response, 140 recombinant inbred lines (RILs) derived from 93-11 (Oryza sativa ssp. indica) × Nipponbare (Oryza sativa ssp. japonica) and a high quality genetic map based on the SNPs generated from deep sequencing of the RIL genomes, were used to identify the quantitative trait loci (QTLs) associated with in vitro tissue culture response (TCR) from mature seed in rice. The performance of callus induction was evaluated by indices of induced-callus color (ICC), induced-callus size (ICS), induced-callus friability (ICF) and callus induction rate (CIR), respectively, and the performance of callus differentiation was evaluated by indices of callus proliferation ability (CPA), callus browning tendency (CBT), callus greening ability (CGA), the average number of regenerated shoots per callus (NRS) and regeneration rate (%, RR), respectively. A total of 25 QTLs, 2 each for ICC, ICS, ICF, CIR and CBA, 3 for CPA, 4 each for CGA, NRS and RR, respectively, were detected and located on 8 rice chromosomes. Significant correlations were observed among the traits of CGA, NRS and RR, and QTLs identified for these three indices were co-located on chromosomes 3 and 7, and the additive effects came from both Nipponbare and 93-11, respectively. The results obtained from this study provide guidance for further fine mapping and gene cloning of the major QTL of TCR and the knowledge of the genes underlying the traits investigated would be very helpful for revealing the molecular bases of tissue culture response.     

RAPD and ISSR analyses of regenerated pea Pisum sativum L. plants

Long-term pea callus cultures of different genotypes (mutants R-9 and W-1 and cultivar Viola) were used to regenerate plants (generation R0). The regenerants displayed changes both in qualitative and in quantitative traits. The most dramatic morphological alterations and complete sterility were observed in regenerants of the cultivar Viola. To estimate the genetic differences, regenerants were compared with the original lines with the use of RAPD (random amplified polymorphic DNA) and ISSR (inter simple sequence repeat) analyses. The extent of divergence varied among regenerants and depended mostly on the original genotype. The genetic difference from the original line was no more than 1% in W-1 regenerants, 0.7-5.3% in R-9 regenerants, and 10-15% in sterile regenerants of the cultivar Viola. The genetic variation of plants regenerated from a callus culture maintained for ten years did not exceed that of plants obtained from a culture maintained for two years.     

Yield Results and Stability Analysis from the Sorghum Regional Biomass Feedstock Trial

Sorghum [Sorghum bicolor (L.) Moench] is one of four herbaceous dedicated bioenergy crops the U.S. Department of Energy identified as critical to annually produce one billion tons of dry biomass. Of these four crops, sorghum is unique as it is a drought-tolerant, annual crop established from seed that is readily tractable to genetic improvement. The purpose of this study was to assess the yield potential and stability of sorghums grown across diverse production environments in the USA. For this study, six sorghum genotypes (one cultivar, five hybrids) were grown in yield trials in seven locations in six states for 5 years (2008–2012). Variation in dry and fresh yield was attributable to not only genotypes, but also to the effects of year, location, and year × location. Even with the highest yielding genotype, environmental conditions were a major factor in determining the yield in a given year. This variability affects the consistency of the biomass supply for ethanol production. In general, the southeastern USA had the highest mean yields for fresh weight and dry weight, indicating that this area may be the most reliable for biomass production. A significant variation was detected among genotypes for fresh weight, dry weight, moisture content, and brix, revealing that sufficient variation within sorghum exists for continued improvement and that certain hybrids are more tractable for biomass/bioenergy production. With dedicated bioenergy sorghum germplasm and proper production environments, sorghum will be a valuable tool in the goal of the sustainable production of one billion tons of dry biomass each year in the USA.     

SNP genotyping for the genetic monitoring of laboratory mice by using a microarray-based method with dualcolour fluorescence hybridisation

Ensuring the genetic homogeneity of the mice used in laboratory experiments contributes to the Reduction aspect of the Three Rs, by maximising the quality of the data obtained from any animals that are used for these purposes, and ultimately reducing the numbers of animals used. Single nucleotide polymorphism (SNP) genotyping is especially suitable for use in the analysis of the genetic purity of model organisms such as the mouse, because bi-allelic markers remain fully informative when used to characterise crosses between inbred strains. Here, we attempted to apply a microarray-based method for a SNP marker to monitor the genetic quality of inbred mouse strains, so as to validate the reliability, stability and applicability of this SNP genotyping panel. The amplified PCR products containing four different SNP loci from four inbred mouse strains were spotted and immobilised onto amino-modified glass slides to generate a microarray. This was then interrogated through hybridisation with dual-colour probes, to determine the SNP genotypes of each sample. The results indicated that this microarray-based method could effectively determine the genotypes of the four selected SNPs with a high degree of accuracy. We have developed a new SNP genotyping technique for effective use in the genetic monitoring of inbred mouse strains.     

Heterosis Is Prevalent for Multiple Traits in Diverse Maize Germplasm

Background

Heterosis describes the superior phenotypes observed in hybrids relative to their inbred parents. Maize is a model system for studying heterosis due to the high levels of yield heterosis and commercial use of hybrids.

Methods

The inbred lines from an association mapping panel were crossed to a common inbred line, B73, to generate nearly 300 hybrid genotypes. Heterosis was evaluated for seventeen phenotypic traits in multiple environments. The majority of hybrids exhibit better-parent heterosis in most of the hybrids measured. Correlations between the levels of heterosis for different traits were generally weak, suggesting that the genetic basis of heterosis is trait-dependent.

Conclusions

The ability to predict heterosis levels using inbred phenotype or genetic distance between the parents varied for the different traits. For some traits it is possible to explain a significant proportion of the heterosis variation using linear modeling while other traits are more difficult to predict.     

QTL for fibre-related traits in grain × sweet sorghum as a tool for the enhancement of sorghum as a biomass crop

Compared to maize and temperate grasses, sorghum has received less attention in terms of improving cell wall components. The objectives of this study were to identify quantitative trait loci (QTL) with main effects, epistatic and pleiotropic effects along with QTL × environment (QE) interactions controlling fibre-related traits in sorghum. Neutral detergent fibre (NDF), acid detergent fibre (ADF), acid detergent lignin (ADL), cellulose, hemicellulose, fresh leaf mass, stripped stalk mass, dry stalk mass, fresh biomass and dry biomass were analysed from a population of 188 grain × sweet sorghum recombinant inbred lines. A genetic map consisting of 157 DNA markers was constructed, and QTL were detected using composite interval mapping (CIM). CIM detected more than 5 additive QTL per trait explaining 7.1–24.7% of the phenotypic variation. Abundant co-localization of these QTL was observed across all chromosomes, and the highest cluster was identified on chromosome 6. Searching for candidate genes using the confidence interval of our QTL clusters reveals that these clusters might comprise a set of genes that are tightly linked. Some QTL showed multiple effects; however, the allele for each trait was favouring the parent with the increasing effect. QE interactions were observed for QTL showing multiple effects. Additive × additive interaction was observed for 7 out of 10 traits, indicating the importance of epistatic analysis. However, the phenotypic variation explained by digenic interactions was lower compared to the individual QTL. Our results indicate that various genetic components contribute to fibre-related traits and should be considered during the enhancement of sorghum for lignocellulosic biomass.     

Quantification of yield losses caused by leaf anthracnose on sorghum in Brazil

The leaf anthracnose disease in sorghum, caused by Colletotrichum sublineolum (Henn. ex Sacc. & Trotter), is widely distributed throughout its Brazilian cultivation areas. The disease can cause significant losses in grain yield and quality. This study aimed to quantify the effects of leaf anthracnose on grain yield of different sorghum genotypes. Two elite inbred lines of sorghum, BR009 (susceptible) and BR008 (moderately resistant), and the hybrids, BR304 and MR43 (susceptible), BRS310 and DKB599 (moderately resistant) and BRS308 and AG1060 (resistant), were planted in a complete randomized block design with three replicates. The disease severity (DS) was evaluated weekly, starting from the onset of the first foliar symptoms, and yield losses were estimated using linear regression analysis. Leaf anthracnose significantly reduced sorghum yields in the susceptible genotypes. The highest yield loss of 86% was observed in the inbred line BR009, when the disease severity reached 100%. For the hybrids, the grain yield loss varied from 35% (BRS310) to 72% (BRS308). According to the adjusted model, a grain yield reduction of 23.48 kg/ha for BR304, 14.57 kg/ha for BRS310 and 15.91 kg/ha for DKB599 was observed for every 1% increase in disease severity. We demonstrate for the first time the effect of leaf anthracnose disease on grain sorghum yields under Brazilian conditions. The results from this study provide a starting point for developing new strategies for the integrated disease management of sorghum anthracnose.     

Epistasis in the expression of relevant traits in cassava (Manihot esculenta Crantz) for subhumid conditions

There is limited knowledge on the inheritance of agronomic traits in cassava and the importance of epistasis for most crops. A nine-parent diallel study was conducted in subhumid environments. Thirty clones were obtained from 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 genetic effects for all variables analyzed (reaction to thrips, fresh root and foliage yields, harvest index, dry matter content, and root dry matter yield). Significant epistatic effects were observed for all variables, except harvest index. Dominance variance was always significant, except for dry matter content and dry matter yield. Additive variance was significant only for reaction to thrips. Results suggested that dominance plays an important role in complex traits such as root yield. The significance of epistasis can help us understand the difficulties of quantitative genetics models and QTLs in satisfactorily explaining phenotypic variation in traits with complex inheritance. Significant epistasis would justify the production of inbred parental lines to fix favorable allele combinations in the production of hybrid cassava cultivars.