Performance based grouping of adapted and exotic drought tolerant maize (Zea mays L) inbred lines under stressed and nonstressed conditions

Knowledge of the heterotic responses of elite adapted and exotic maize inbred lines can facilitate their utilization for population improvement and hybrid development. In the present study, a line x tester mating design was used to determine the combining ability of 20 elite drought-tolerant maize inbred lines developed at CIMMYT and IITA and to classify them into heterotic groups under diverse growing conditions. The 20 lines were crossed each with two inbred line testers representing the tropical and temperate heterotic pattern established in West and Cental Africa (WCA), to generate 40 testcrosses. A trial comprising the 40 testcrosses along with the cross between the two testers and three hybrid checks were evaluated at two environments in the dry season and at six environments in the rainy season. GCA effects were more important than SCA effects in controlling grain yield in both seasons. Two exotic lines in the dry season and four exotic lines in the rainy season had significantly positive GCA effects. Only EXL22 was identified as a superior line in the two seasons. Only two adapted lines had significantly positive GCA effects in either or both seasons while three adapted lines consistently had significantly negative GCA effects in both seasons. Hybrid between EXL22 and tester 9071 showed broad adaptation to all test environments. The two testers separated some of the lines into two main heterotic groups. the lines in each heterotic group and the good combiners will be utilized for developing populations for extracting new improved inbred lines

Evaluation of sweetpotato accessions for end-user preferred traits improvement

This study assessed the genetic diversity and differentiation in sweetpotato accessions in Ghana to guide selection for genetic improvement on beta-carotene, dry matter and sugar contents to promote increased utilization. One hundred and fifteen sweetpotato accessions from four different sources, which were the International Potato Centre (CIP) collection, local collection from farmers’ field, local improved varieties, and local and exotic collections from the National Agricultural Research Programmes were studied using 40 agro-morphological and physico-chemical traits, and 25 SSR markers. Variability was obtained for 13 agro-morphological traits and all the physico-chemical traits. Significant genetic diversity indicates existence of a high degree of agro-morphological and physicochemical variation. Within Group variation (97%) accounted for most of the diversity indicating a broad genetic base. The divergence indicates that breeders can form different populations with significant levels of genetic variation to exploit heterosis and improvement of populations. A strong negative relationship was found for sugar content and dry matter content and indicates a possible development of non-sweet high dry matter sweetpotato varieties. However, developing non-sweet, high dry matter and high beta-carotene sweetpotato varieties could be challenging due to the strong negative association between dry matter content and beta-carotene content, and the positive association existing between beta-carotene and sugar content. This study has in addition confirmed the breeding potential of sweetpotato accessions in Ghana and the probability of providing useful genetic variation for the development of farmer preferred cultivar

Constraints and breeding priorities for increased sweetpotato utilization in Ghana

Sweetpotato is used in various food preparations in place of rice, cassava, yam and plantain in Ghana. In spite of this it does not have the same importance in Ghanaian diet as other root and tuber crops. Consumer taste, preference and acceptance are critical in determining the suitability of sweetpotato cultivars to any locality. A study was carried out in some selected communities of Ghana where sweetpotato is popular which span all five ecozones of Ghana in February, 2012. The main objective was to investigate why sweetpotato has low utilization compared with other root and tuber crops and to increase its utilization through breeding. The study employed Focus Group Discussion (FGD) followed by administration of Semi-structured Questionnaire (SSQ). Data collected were analysed using Genstat and Statistical Package for Social Sciences. Seventy-nine people consisting of 63% males and 37% females, and 178 people consisting of 52% female and 48% males were involved in the FGD and SSQ, respectively. Majority (94%) of farmers’ ranked sweetpotato from 1 to 5 among 24 cultivated crops. Only about 28% of consumers ate sweetpotato at least six days per week. The survey revealed that consumers in Ghana desired non-sweet, high dry matter sweetpotato cultivars. Therefore, there is need for Research and Development to adjust sweetpotato breeding objectives and selection procedures to develop high dry matter non-sweet sweetpotato varieties in Ghan

Identification of QTLs for grain yield and other traits in tropical maize under high and low soil-nitrogen environments.

Article purchased; Published online: 03 Nov 2017Low soil Nitrogen (low-N) is one of the most important abiotic stresses responsible for significant yield losses in maize (Zea mays. L.). The development and commercialization of low N tolerant genotypes can contribute to improved food security in developing countries. However, selection for low N tolerance is difficult because it is a complex trait with strong interaction between genotypes and environments. Marker assisted breeding holds great promise for improving such complex traits more efficiently in less time, but requires markers associated with the trait of interest. In this study, 150 BC2F1 families of CML 444 x CML 494 were evaluated at two location for two consecutive seasons to identify SNP markers associated with quantitative trait loci (QTLs) for yield and other agronomic traits under low- and high-N environments. A total of 13 QTLs were identified with 158 SNP markers, of which nine and four QTLs were detected under low- and high-N environments, respectively. Five QTLs one each for grain yield (qgy-1), days to silking (qdts-1) and anthesis- silking interval (qasi-6), and two for stay green characteristic (qsg-1 and qsg-4) were close to their adjacent markers, with an interval of 0.7 to 5.2 cM between them and explained phenotypic variance of 9 to 21%. These QTLs would be invaluable for rapid introgression of genomic regions into maize populations using marker assisted selection (MAS) approaches. However, further validation of these QTLs is needed before use in MAS

Mapping chromosomal regions associated with anther indehiscence with exerted stigmas in CRI-48 and Jasmine 85 cross of rice (Oryza sativa L)

Anther indehiscence in certain wide crosses combines male sterility with stigma exertion, a phenomenon that is desirable for hybrid rice seed production. This study sought to identify chromosomal region(s) that combine anther indehiscence with exerted stigmas. A mapping population consisting of 189 BC1F1 plants was derived from a cross between CRI-48 and Jasmine 85 and backcrossing the resulting F1 to Jasmine 85. Contrary to the three complementary genes mode of inheritance reported earlier, a single locus (AI6-1) was mapped on chromosome 6 at 27.4 cM for anther indehiscence with exerted stigmas through a mixed model-based composite interval mapping (MCIM). This locus was flanked by two single nucleotide polymorphism (SNP) markers, K_ID6002884 and K_ID6003341 within a range of 23.1–28.9 cM. The allele at the locus was contributed by the CRI-48 parent which has Oryza glaberrima ancestry. This locus is suggested to control anther indehiscence and stigma exertion through pleiotropic gene action or cluster of genes

Genetic diversity and inter-trait relationships among maize inbreds containing genes from Zea diploperennis and hybrid performance under contrasting environments

Open Access Journal; Published online: 27 Sep 2020Accurate estimation of genetic variability present in tropical maize inbreds with varying reactions to Strigahermonthica infestation is essential for efficient and sustainable utilization to ensure increased genetic gain in a breeding program. Thirty-six early maturing maize inbred lines and 156 single cross hybrids were evaluated under Striga-infested and non-infested conditions in Nigeria during the 2014 and 2015 cropping seasons. Under Striga infestation, grain yield ranged from 1134 kg ha−1 for TZEI 26 × TZEI 5 to 5362 kg ha−1 for TZdEI 173 × TZdEI 280. The average yield reduction of the hybrids under Striga infestation was 44% relative to the performance under non-infested environments. Using 4440 high-quality DArT markers, clustering and population structure analyses separated the inbred lines into three distinct groups based on the genetic distance indicating high level of genetic variability among the lines. The base index of the International Institute of Tropical Agriculture (IITA) identified 50% of the inbred lines as Striga resistant. The genetic diversity study provided an opportunity for selecting divergent parents for tagging candidate genes and quantitative trait loci for marker-assisted introgression of Striga resistance genes into early maturing tropical maize breeding populations. The most reliable secondary trait for indirect selection for grain yield under Striga infestation was the ear aspect

Genetic analysis of gain yield of IITA and CIMMYT earlymaturing maize inbreds under Strigainfested and lowsoil nitrogen environments

Accepted paper, posted 17 November, 2014Breeding maize (Zea mays L.) hybrids resistant to Striga and tolerant to low soil nitrogen (low-N) will reduce grain yield losses due to stresses in West Africa (WA). Studies were conducted to determine if selection for Striga resistance and/or drought tolerance in early-maturing maize populations improved low-N tolerance in hybrids derived from selected inbreds from International Institute of Tropical Agriculture (IITA) and International Centre for Maize and Wheat Improvement (CIMMYT) under Striga-infested, low-N and optimum environments in Nigeria. One hundred and fifty hybrids developed from crosses involving 30 lines using North Carolina Design II plus six checks were evaluated at two locations each under low-N, artificial Striga infestation, and optimum environments for 2 yr. Lines with combined resistance or tolerance to Striga as well as low-N were identified. Striga-resistant– as well as low-N–tolerant hybrids with outstanding performance under both stress environments could be obtained through the accumulation of favorable alleles for resistance or tolerance in both parental lines. Although selection for Striga resistance and/or drought tolerance resulted in improved performance of genotypes under low-N, it is important to test genotypes under low-N to identify those with outstanding performance under the target stress. ENT 11 × TZEI 4 and TZEI 65 × ENT 11 were identified as the most stable and high-yielding hybrids

Genetic control of dry matter, starch and sugar content in sweetpotato

Sweetpotato (Ipomoea batatas L. (Lam)) is a nutritious food security crop for most tropical households, but its utilisation is very low in Ghana compared to the other root and tuber crops due to lack of end-user-preferred cultivars. Knowledge on the genetic control of important traits such as dry matter, starch and sugar content of sweetpotato storage roots in a breeding population is critical for making breeding progress in developing sweetpotato varieties preferred by farmers and consumers. This study used diallel mating design to elucidate general combining ability and specific combining ability, to determine the gene action controlling storage root dry matter, starch and sugar content in sweetpotato and the heterotic potential of the traits to facilitate the crop’s improvement for increased utilisation. A general model for estimating genetic effects, GEAN II, was used to analyse the data. Genetic variability was seen for dry matter, starch and sugar content of sweetpotato and much of this genetic variation was additive in nature. The study also revealed significant heterosis in sweetpotato which offers opportunity for breeding non-sweet, high dry matter sweetpotato varieties that are preferred by farmers and consumers in Ghana

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

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

Genetic analysis of drought tolerance in adapted X exotic crosses of maize inbred lines under managed stress conditions

Abstract Introduced maize (Zea mays L.) germplasmcan serve as sources of favorable alleles toenhance performance in new maize varieties andhybrids under drought stress conditions. In the presentstudy, the combining abilities of 12 exotic maizeinbred lines from CIMMYT and 12 adapted maizeinbred lines from IITA were studied for grain yield andother traits under controlled drought stress. The inbredlines from each institution were separated into groupsusing SSR-based genetic diversity and were intercrossedusing a factorial mating scheme to generate 96hybrids. These hybrids were evaluated under bothcontrolled drought stress and well-watered conditionsat Ikenne in Nigeria in 2010 and 2011. Average meanyields of hybrids under drought stress represented23 % of the average yield of hybrids under fullirrigation. General combining ability (GCA) effectsaccounted for 49–85 % of the observed variation forseveral traits recorded under both well-watered anddrought stress conditions. Specific combining abilityeffects for grain yield, though positive in most hybrids,were not significant under drought stress conditions.All the twelve exotic and nine adapted lines hadpositive GCA effects (female, male, or both) for grainyield under either drought stress or full irrigation, orboth environments. EXL03 and EXL15 that hadpositive and significant female and male GCA effectsfor grain yield under both environments can be used toimprove their adapted counterparts for grain yield anddrought tolerance. Normalized difference vegetationindex had weak but significant correlation with grainyield