Genetic gains from selection for drought tolerance during three breeding periods in extra-early maturing maize hybrids under drought and rainfed environments

Open Access Journal; Published online: 23 Apr 2021Genetic gain studies in a breeding program are very important for measuring the efficiency of the program over a specific period. It also provides breeders with an understanding of the outcomes of the huge investments committed to the breeding programs. This study sought to (i) estimate the gains in grain yield under drought and rainfed conditions and (ii) identify high-yielding and stable hybrids developed in the last two decades under drought and rainfed conditions. Sixty extra-early maturing hybrids developed by the International Institute of Tropical Agriculture (IITA), Ibadan, during three breeding periods: (2008–2010, 2011–2013, and 2014–2016) were assessed under managed drought and rainfed conditions across 14 environments in Nigeria to estimate the genetic gains in grain yield using linear regression analysis. Considerably high genetic gains (4.1%) per year for grain yield was obtained for the extra-early maturing hybrids under drought environments. Six of the top ten hybrids identified were from period 3, an indication of the high genetic gains from selection in period 3. Additionally, two of the top six period 3 hybrids (TZEEI 29 × TZEEI 13) × TZEEI 64 and TZdEEI 64 × TZEEI 54 were found to be the best yielding and most stable across the 14 test environments and were highly recommended for extensive evaluations to warrant their commercialization in sub-Saharan Africa (SSA)

Progress on implementation of an accelerated sweetpotato breeding scheme in Ghana.

The sweetpotato support platform for West Africa was established at the CSIR-Crops Research Institute in Kumasi, Ghana in early 2010 with the objective of supporting cultivar development in Ghana and elsewhere in West Africa through the development of adapted less sweet germplasm, and through a participatory approach. The accelerated sweetpotato breeding approach in Ghana uses multi-locational clonal evaluation of seedling families to identify promising families and genotypes, followed by 2 years of additional multi-locational evaluation in target environments. Superior early selections may be used as parents in population improvement in order to speed genetic gain for various attributes. In 2010, roughly 250 genotypes from 34 families, from Ghana, Uganda and Kenya were evaluated at 3 locations, and high yielding, virus resistant genotypes were selected, some at 2 or more locations. In 2011 selected genotypes and introduced clones from diverse sources (330 genotypes) were evaluated in replicated trials at 5 locations covering major production zones and agroecologies. At harvest, farmers were involved in assessment of performance and taste, and selections were evaluated for sugars, minerals and carotenoids using near infrared reflectance spectroscopy. Sixteen genotypes are in advanced trials in 2012.

Multi-locational assessment of some physicochemical attributes and amylase activity of sweetpotato varieties and elite materials in Ghana.

As part of the breeding objectives to select sweetpotato materials with acceptable quality attributes for adaptation and subsequent utilisation in Ghana, the total amylase activity and physicochemical attributes (flesh colour, Beta-carotene, dry matter, starch and sugars) of 13 sweetpotato genotypes across five locations were evaluated. Near Infrared Reflectance Spectrometry (NIRS), was mainly employed in the study. The flesh colour of the materials ranged from white to deep orange while thedry matter content ranged from 20% to 44%. Starch, fructose, glucose and sucrose contents were 46– 74, 0.3 - 5, 2 – 8 and 9 – 22% respectively. Apomuden, a deep orange type, recorded the highesttotal sugar content of 36% and the lowest dry matter and starch content of 20% and 46% respectively. Hi-starch variety had the highest dry matter (45%), starch (74%) and the lowest sugar (11%). Dry matter content correlated positively with starch content whilst orange colour intensity was inversely proportional to dry matter content. The outcome of the study supports the fact that sweet potato contains high extractable amylases. Amylase activity of the materials was fairly stable across locations. Okomkum, Faara, Santom Pona, Kemb, and Cemsa 74-228 recorded the highest activity while Hi-starch, Apomuden, Mohc, and 199062.1 were low. There was no correlation between raw sugars and amylase activity. The potential of individual cultivars for food industry will be discussed in relation to starch content and extractable amylases

Genetic diversity among early provitamin A quality protein maize inbred lines and the performance of derived hybrids under contrasting nitrogen environments

Open Access JournalInformation on population structure and genetic diversity of germplasm in a breeding programme is useful because it enhances judicious utilisation of genetic resources to achieve breeding objectives. Seventy early maturing provitamin A (PVA) quality protein maize (QPM) inbreds developed by the IITA- maize improvement programme were genotyped using 8171 DArTseq markers. Furthermore, 96 hybrids derived from 24 selected inbreds plus four checks were evaluated under low-N and optimal environments in Nigeria during 2016 and 2017. Genotypic and phenotypic data of inbreds and hybrids respectively, were analysed to (i) assess the level of genetic dissimilarities and population structure of the inbreds, and (ii) investigate the grain yield performance of derived hybrids under low-N, optimal and across environments

Genetic analysis of grain yield and agronomic traits of early provitamin A quality protein maize inbred lines in contrasting environments

Open Access Article; Published online: 17 Oct 2019Early-maturing provitamin A (PVA) quality protein maize (QPM) hybrids with combined drought and low soil nitrogen (low-N) tolerance are needed to address malnutrition and food security problems in sub-Saharan Africa (SSA). The current study's objectives were to (i) examine combining ability of selected early maturing PVA-QPM inbreds for grain yield and other agronomic traits under drought, low-N, optimal environments and across environments, (ii) determine gene action conditioning PVA accumulation under optimal environments, (iii) classify inbreds into heterotic groups and identify testers and (iv) assess yield and stability of hybrids across environments. Ninety-six hybrids generated from 24 inbred lines using the North Carolina Design II together with four commercial hybrid controls were evaluated under drought, low-N and optimal environments in Nigeria in 2016 and 2017. Fifty-four selected hybrids were assayed for PVA carotenoid and tryptophan content. Additive genetic effects were greater than non-additive effects for grain yield and most agronomic traits under each and across environments. The gene action conditioning accumulation of PVA carotenoids under optimal growing conditions followed a pattern similar to that of grain yield and other yield-related traits. The inbred lines were categorized into four heterotic groups consistent with the pedigree records and with TZEIORQ 29 identified as the best male and female tester for heterotic group IV. No tester was found for the other groups. Hybrid TZEIORQ 24 × TZEIORQ 41 was the highest yielding and most stable across environments and should be further tested for consistent performance for commercialization in SSA

Phenotypic characterization and validation of provitamin A functional genes in early maturing provitamin A-quality protein maize (Zea mays) inbred lines

Open Access Article; Published online: 20 Dec 2019The number of drought and low‐N tolerant hybrids with elevated levels of provitamin A (PVA) in sub‐Saharan Africa could increase when PVA genes are optimized and validated for developed drought and low‐N tolerant inbred lines. This study aimed to (a) determine the levels of drought and low‐N tolerance, and PVA concentrations in early maturing PVA‐quality protein maize (QPM) inbred lines, and (b) identify lines harbouring the crtRB1 and LcyE genes as sources of favourable alleles of PVA. Seventy early maturing PVA‐QPM inbreds were evaluated under drought, low‐N and optimal environments in Nigeria for two years. The inbreds were assayed for PVA levels and the presence of PVA genes using allele‐specific PCR markers. Moderate range of PVA contents was observed for the inbreds. Nonetheless, TZEIORQ 55 combined high PVA concentration with drought and low‐N tolerance. The crtRB1‐3′TE primer and the KASP SNP (snpZM0015) consistently identified nine inbreds including TZEIORQ 55 harbouring the favourable alleles of the crtRB1 gene. These inbreds could serve as donor parents of the favourable crtRB1‐3′TE allele for PVA breeding in maize

Breeding un-sweetpotato for West Africa: Progress on population development and improvement in Ghana and Peru.

Sweetness of sweetpotato is considered to be a significant constraint to demand for this crop in West Africa where starchy staple root crops with low flavor impact are important. Un-sweetpotato populations and varieties which may have use both for fresh consumption and in processed forms are therefore under development at the Sweetpotato Support Platform for West Africa, and drawing on a global genetic resource base at CIP headquarters in Lima, Peru. In Ghana base populations were assembled from locally adapted regional germplasm, including released varieties, farmers' varieties, breeding lines from IITA reported to be un-sweet, and from exotic germplasm reported to be unsweet. Seed populations were also introduced for assessment from Sweetpotato Support Platforms in Uganda and Mozambique, and from Japan and the USA. Introduced germplasm was evaluated in field trials in production zones/agroecologies where sweetpotato is important in Ghana, and farmers participated in selection based on field performance and taste. Sugars of raw samples were measured using near-infrared reflectance spectrometry, and cooked samples were tasted to assess sweetness. In Peru, a large breeding population was screened for un-sweet taste (low flavor impact) and these materials, presumed to be Beta-amylase nulls, were crossed with a population of breeding lines developed at IITA and presumed to have good adaptation to West African conditions. Seed from the Peruvian crossing block has been sent to Ghana for evaluation and selection. Together, West African and exotic populations are expected to provide a solid foundation for developing un-sweetpotato and for expanding the range of options available to sweetpotato producers and consumers in West Africa and elsewhere

Genetic diversity, population structure and inter-trait relationships of combined heat and drought tolerant early-maturing maize inbred lines from west and central Africa

Open Access Journal; Published online: 04 Sept 2020Adequate knowledge and understanding of the genetic diversity and inter-trait relationships among elite maize inbred lines are crucial for determining breeding strategies and predicting hybrid performance. The objectives of this study were to investigate the genetic diversity of 162 early maturing white and yellow tropical maize inbred lines, and to determine the population structure, heterotic groups and inter-trait relationships among the lines. Using 9684 DArT single nucleotide polymorphism (SNP) markers, a gene diversity (GD) of 0.30 was recorded for the inbred lines with polymorphic information content (PIC) ranging from 0.08 to 0.38. The genetic relatedness among the inbred lines evaluated revealed six different groups based on the history of selection, colour of endosperm and pedigree. The genotype-by-trait (GT) biplot analysis identified inbred 1 (TZEI 935) as outstanding in terms of combined heat and drought (HD) tolerance with the base index analysis identifying 15 superior inbreds in the HD environment. A wide range of genetic variability was observed among the inbred lines, indicating that they are an invaluable resource for breeding for HD tolerance in maize breeding programmes, especially in West and Central Africa

Genetic enhancement of early and extra-early maturing maize for tolerance to low-soil nitrogen in sub-Saharan Africa

Open Access ArticleTo increase and improve food crop production and crop management for sustainable agricultural development, the Maize Improvement Program (MIP) of the International Institute of Tropical Agriculture (IITA) has, in partnership with national and international organizations, focused attention on the genetic improvement of maize (Zea mays L.) for tolerance/resistance to abiotic and biotic stresses constraining maize grain production. One of the abiotic stresses into which new technologies have been established for crop protection and sustainable natural resource management is low soil nitrogen (N). Nitrogen, an important plant nutrient required for growth and productivity, is not readily available and little quantity or none is applied by farmers for maize production. Because of long periods of bush fallow, the absence of N was not noticeable at the initial stages of maize production in West and Central Africa (WCA). However, with the fallow period gradually reducing and totally disappearing, it has become imperative for external supply of N in maize production. Taking a cue from the International Maize and Wheat Improvement Centre (CIMMYT), IITA has been breeding low-N tolerant maize and several low-N-tolerant maize varieties and hybrids are now available to farmers. Reviewed in this manuscript are the efforts used to develop low-N tolerant early and extra-early maturing maize by the MIP of IITA. The review covers the objectives, methodology, and output of the research, including the genetics of tolerance, ongoing conventional and molecular approaches, and the gaps that new research could fill