Pre-breeding of sorghum [sorghum bicolor (L.) moench] for drought tolerance in the semi-arid zones of Nigeria.
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Date
2023
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Abstract
Sorghum [Sorghum bicolor (L.) Moench] is a staple food crop serving millions of people
in Africa and Asia's arid and semi-arid agro-ecologies. Sorghum is widely cultivated in Northern
Nigeria, serving diverse value chains, including the food and feed sectors and the brewery industry.
However, the potential production and productivity of sorghum in Africa, including Northern
Nigeria, is constrained by severe drought stress associated with climate change. Furthermore,
smallholder farmers in Nigeria still cultivate low-yielding and drought-susceptible unimproved
sorghum landraces. Developing drought-tolerant sorghum cultivars adapted to semi-arid regions
would enhance yield gains and stability with desirable product profiles according to the needs of
the farmers and the marketplace. Therefore, the overall objective of this study was to improve
sorghum productivity in Nigeria by developing new generation, locally adapted and droughttolerant
varieties. The specific objectives of this study were to: (1) present the current opportunities
and constraints to sorghum production in Nigeria and make recommendations as a guide to new
variety design and sustainable production, (2) determine drought tolerance and genotype-byenvironment
interaction (GEI) effect on grain yield of a population of African sorghum genotypes
to identify high-yielding and drought-adapted genotypes for production and breeding, (3) assess
the genetic diversity and deduce the population structure among 200 sorghum accessions to guide
the selection of contrasting parents for pre-breeding and breeding of drought-tolerant sorghum
cultivars and (4) determine the combining ability, heterosis and gene action conditioning
agronomic traits and grain yield among sorghum genotypes to select genetically superior and
contrasting parental genotypes and new families for drought tolerance breeding, cultivar release
and commercialization.
In the first chapter, a participatory rural appraisal (PRA) study was conducted in three
selected sorghum growing zones in Northern Nigeria involving 250 farmers. Socio-economic data
were collected through surveys and focus group discussions. Results showed that sorghum was
cultivated mainly by males (80%) who had grade 6-12 level of education (31.3%), with a
productive age of 21-45 years (75.7%) and a household family size of below five members
(52.3%). Low-yielding landrace varieties such as Kaura (37.4%) and Fara-fara (29.3%) were the
most widely cultivated types across the study zones due to their good grain quality. The major
farmers' preferred traits from a sorghum variety were high yield, drought tolerance and Striga
resistance. The study recommends integrated sorghum technology development incorporating the
described preferences of the farmers for sustainable production and economic gains of the crop.
The second chapter examined 225 sorghum genotypes assembled from diverse origins to
determine drought tolerance and GEI effects on grain yield. The collections were evaluated under
non-stressed (NS), pre-anthesis drought stress (PreADS), and post-anthesis drought stress
(PoADS) conditions under field and greenhouse environments. The additive main effect and
multiplicative interaction (AMMI) analysis revealed that genotype (G), environment (E), and GEI
were significant (p<0.05) and accounted for 38.7, 44.6, and 16.6% of the total explained variation
in grain yield, in that order. AMMI 4 was the best-fitting model for genotype selection with better
grain yield. Based on AMMI 4 and the Best Linear Unbiased Predictors (BLUPs) analyses,
genotypes Yar Lazau and Dangama Wulchichi, with a grain yield of 5.6 t/ha and 6.3 t/ha, were
selected as being suitable for non-stressed conditions, respectively. Genotypes ICNSL2014-022-4
and Takumbo with BLUPs of 2.5 t/ha and 2.6 t/ha were best-suited for pre-anthesis drought stress
conditions, whereas genotypes Danyar Bana and Gagarau - 4 with BLUPs of 4.2 t/ha and 4.3 t/ha
are recommended for post-anthesis drought-prone environments, respectively. The identified
sorghum genotypes are valuable genetic resources to develop novel drought tolerance cultivars or
for production in dry agro-ecologies of sub-Saharan Africa characterized by pre-and-post anthesis
drought stress.
In the third chapter, diversity arrays technology (DArT) –derived single nucleotide
polymorphism (SNP) markers were used to assess the genetic diversity and discern the population
structure of 200 sorghum accessions to select complementary lines for breeding. The markers have
moderate discriminatory power, with the polymorphism information content ranging between 0.09
to 0.38. The average gene diversity value (0.32) was high, while the average observed
heterozygosity (0.15) was relatively low, a typical value for autogamous crop species like
sorghum. The population structure and cluster analyses revealed four main clusters with a high
level of genetic diversity among the accessions studied. The variation within populations (41.5%)
was significantly higher than that among populations (30.8%) and between samples within a
structure (27.7%). The high genetic variation within the population could be attributed to the
preservation of sorghum landraces by farmers and differences in the genetic constitution,
adaptation and parentage. The study identified distantly related sorghum accessions such as
Samsorg 48, Kaura Red Glume (from Cluster 1); Gadam, AS 152 (Cluster 2); CSRO1,
ICNSL2014−062 (Cluster 3); and Yalai, Kafi Mori (Cluster 4) useful in developing new gene
pools and novel genotypes for the West and Central Africa (WCA) sorghum breeding programs.
Based on the phenotypic and genotypic data, 12 contrasting parents were selected for breeding
population development with high yield and drought tolerance.
In the last chapter, 12 contrasting sorghum parents were selected from a diverse set of 225
genotypes exhibiting variable agronomic traits, including high grain and drought tolerance and
farmer-preferred attributes. The 12 parents were crossed using a half-diallel mating design to
create 66 F1 progenies. The F1 progenies, the parents, and two check varieties were evaluated under
three environments in Nigeria. The results revealed the presence of significant variations amongst
test genotypes allowing the selection of suitable parents and hybrids for traits of interest. The
contribution of the specific combining ability (SCA) variance to total variance was higher than
that of the general combining ability (GCA) for most of the studied traits, indicating that nonadditive
gene action was more dominant in conditioning trait inheritance. GCA x environment and
SCA x environment interaction effects were significant (p<0.05) for days to anthesis, aboveground
biomass and grain yield. Parental genotypes Samsorg 7, Masakwa, and SSV2008091,
recorded significant and positive GCA effects for grain yield and are useful germplasm resources
for breeding high-yielding cultivars. Crosses AS 152 x SSV2008091, Samsorg 7 x Kurumbasau,
AS 152 x ICNSL2014-022-8, and Masakwa x Hindatu exhibited high and positive SCA effects
and were the top performers recording above-ground biomass yield of 29.3, 23.4, 27.2 and 16.5
t/ha and grain yield of 6.4, 6.6, 6.6 and 6.5 t/ha, in that order. The crosses exhibited high parent
heterosis for grain yield and other agronomic traits, revealing that hybrid breeding is an effective
strategy for boosting sorghum production. The newly selected F1 progenies had higher yields than
the local checks and are recommended for hybrid or pure line breeding and variety release in
Nigeria's drought-prone areas and similar sub-Saharan Africa (SSA) agro-ecologies after
continuous selection and multi-environment testing.
Overall, the study identified drought stress as the most critical sorghum production
constraint in Northern Nigeria. Also, the study highlighted significant genetic diversity among the
test genotypes. Best performing genotypes Yar Lazau, ICNSL2014-022-4 and Danyar Bana were
selected as suitable for non-stressed, pre-anthesis and post-anthesis drought stress conditions,
respectively. The selected genotypes are recommended for production or breeding in droughtprone
areas. In addition, the study identified drought-tolerant and early-maturing genotypes (e.g.,
Samsorg 7, Masakwa, and SSV2008091) with good general combining ability effects for breeding
population development and heterosis breeding in the semi-arid region of Northern Nigeria.
Description
Doctoral Degree. University of KwaZulu-Natal, Pietermaritzburg.