Breeding groundnut for drought tolerance.
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Date
2021
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Abstract
Groundnut (Arachis hypogaea L.) is one of the world’s most important grain legumes for its
quality edible oil and higher protein content. It is the major cash crop in the semiarid tropics
where production is mainly under rain-fed condition. Recurrent drought is the major cause of
low yields of groundnut in sub-Saharan Africa (SSA). Farmers in SSA grow unimproved groundnut
varieties which are vulnerable to drought stress and insect pests and disease attack. Therefore,
there is need to develop drought tolerant, locally adapted and high yielding groundnut varieties
for sustainable production of the crop. Breeding groundnut for drought tolerance requires
inexpensive, reproducible and high throughput screening systems. Understanding the agromorphological,
physiological and molecular bases of drought tolerance aid in the development
and release of new varieties with drought tolerance. Therefore, the objectives of this study were:
(1) to assess farmers’ perceived production constraints, variety choice, and preferred traits of
groundnut in eastern Ethiopia to guide future groundnut variety development and release, (2) to
determine drought tolerance, kernel and fodder yield and quality amongst diverse groundnut
genotypes for direct production or breeding, (3) to assess the genetic diversity and population
structure among 100 groundnut genotypes using agronomic traits and high density single
nucleotide polymorphism (SNP) markers, (4) to determine the combining ability effects of eight
selected drought tolerant groundnut parental lines and their F2 families under drought-stressed
(DS) and non-stressed (NS) conditions to select best performing parents and families for drought
tolerance breeding.
In the baseline work, participatory rural appraisal studies were conducted in two major
groundnut-producing districts (Babile and Fedis) in eastern Ethiopia. The following data were
collected involving 150 participant farmers: demographic descriptors, groundnut farming system,
farmers’ knowledge about improved groundnut varieties, constraints to groundnut production,
market access, and varietal trait preference. Chi-square and t-test analyses were conducted to
determine statistical significance among the parameters across districts. Participant farmers
identified drought stress (reported by 90% of respondents), poor soil fertility (88%), poor seed
supply systems (67%), pre-harvest diseases (root rot and leaf spot) (59.5%), low yielding varieties
(52.5%), low access to extension services (41.5%), low access to credit (21.5%) and limited
availability of improved varieties (18.5%) as the major groundnut production constraints. The
study identified the following farmer-preferred traits: high shelled yield (reported by 27.67% of
respondents), early maturity (16.84%), and tolerance to drought stress (13.67%), market value
(11.17%), good grain quality (10%), adaptability to local growing conditions (5.8%), and resistance
to diseases (5.17%). Therefore, the aforementioned production constraints and farmer-preferred
traits are key drivers that need to be integrated into groundnut breeding and variety release
programs in eastern Ethiopia.
In the second study, 100 groundnut genotypes were evaluated at the International Crops
Research Institute for the Semi-Arid Tropics (ICRISAT)/India during 2018/19 and 2019/20 under
drought-stressed (DS) and non-stressed (NS) conditions using a 10 x 10 alpha lattice design with
two replications. Seed and haulm samples collected at physiological maturity from DS and NS
experiments to estimate Kernel and haulm quality parameters using near infrared spectroscopy
(NIRS). Data were collected on kernel yield (KY), oil content (OC), oil yield (OY), protein content
(PC), palmitic acid content (PAC), stearic acid content (SAC), oleic acid content (OAC) and linoleic
acid content (LAC), haulm yield (HY) and fodder quality parameters such as the contents of dry
matter (DM), ash, nitrogen (NC), neutral detergent fiber (NDFDM), acid detergent fiber (ADFDM),
acid detergent lignin (ADLDM), in vitro digestibility (IVOMD) and metabolizable energy (ME). Data
were subjected to parametric and non-parametric statistical analyses. Combined analysis of
variance revealed significant (P< 0.05) genotype differences for all assessed traits. Genotype ×
water regime interaction effects were significant for KY, OC, ash content, NC, NDFDM and
ADLDM. Kernel yield positively and significantly (P<0.05) correlated with oil yield (r = 0.99), LAC
(r = 0.13), ash (r = 0.32), NDFDM (r = 0.54) under DS condition. Haulm yield was positively and
significantly (P<0.05) correlated with OC (r = 0.24), NDFDM (r = 0.19), ADFDM (r = 0.18) and
ADLDM (r = 0.17) under DS condition. Cluster analysis grouped the test genotypes into 12 distinct
genetic groups. The study identified genotypes, ICGV 10178, ICGV 01260, ICGV 06175 and ICGV
10379 with high kernel and haulm yields, and CGV 181017, ICGV 01491, ICGV 15019, ICGV
181026, ICGV 16005 and ICGV 181063, with high oleic acid content. Furthermore, genotypes,
ICGV 7222, ICGV 10143, ICGV 6040, ICGV 03042, ICGV 06175, ICGV 01260, ICGV 99241, ICGV
96266, ICGV 171027 and ICGV 01491, were selected with relatively better drought tolerance. The
selected genotypes are recommended for further breeding and variety release under drought
stress environments.
In the third study, 99 of the test genotypes were profiled with 16, 363 SNP markers. The following
phenotypic data collected during the second study were used for complementing the SNP data:
days to 50% flowering (DF), SPAD chlorophyll meter reading (SCMR), Plant height (PH), number
of primary branches (PB), specific leaf area (SLA), leaf relative water content (LRWC), total
biomass (TBM), pod yield (PY), harvest index (HI), hundred seed weight (HSW), shelling
percentage (SHP) and kernel yield per plant (KY) and days to maturity (DM). Analysis of variance,
Pearson’s correlation coefficient, principal component and stress tolerance index were
calculated. Pod yield per plant (PY), seed yield per plant (SY) and harvest index (HI) were
significantly (p < 0.05) affected by genotype × environment interaction effects. Genotypes, ICGV
07222, ICGV 06040, ICGV 01260, ICGV 15083, ICGV 10143, ICGV 03042, ICGV 06039, ICGV 14001,
ICGV 11380 and ICGV 13200, exhibited higher pod yield under both drought-stressed and nonstressed
conditions. Pod yield exhibited significant (p < 0.05) correlation with SY, HI and total
biomass (TBM) under both test conditions. Based on the principal component analysis, PY, SY,
HSW, SHP and HI contributed maximum variability for yield under the two water regimes. Hence,
selection of these traits could be successful for screening of groundnut genotypes under droughtstressed
and non-stressed conditions. Model-based population structure analysis grouped the
studied genotypes into three sub-populations, whilst cluster analysis resolved the collections into
five clusters based on pedigree, selection history, and market type. Cluster III and Cluster V
consisted of the Spanish bunch types, late leaf spot (Phaeoisariopsis personata) and rust (Puccinia
arachidis) resistant, and drought-tolerant genotypes. Analysis of molecular variance revealed
that 98% of the total genetic variation was attributed to among individuals, while 2% of the total
variance was due to variation among the subspecies. The genetic distance between the Spanish
bunch and Virginia bunch types ranged from 0.11 to 0.52. Genotypes, ICGV 13189, ICGV 95111,
ICGV 14421, and ICGV 171007, were selected for further breeding based on their wide genetic
divergence. Data presented in this study will guide groundnut cultivar development emphasizing
economic traits and adaptation to water-limited agro-ecologies including in Ethiopia.
The fourth study examined the combining ability effects of eight selected drought tolerant
groundnut parental lines and their F2 populations under drought-stressed (DS) and non-stressed
(NS) conditions under glasshouse and field conditions at ICRISAT in 2020 rainy season. Data were
collected on days to 50% flowering (DF), number of primary branches (PB), plant height (PH) (cm),
SPAD chlorophyll meter reading (SCMR), specific leaf area (SLA) (cm2/g), pod yield (PY) (g plant-
1), shelling percentage (SHP) (%), kernel yield (KY) (g plant-1 ), total biomass (TBM) (g plant-1) and
harvest index (HI) (%). ICGV 10178 was the best combiner genotype to increase SCMR, PY, SHP,
KY, TBM and HI and, reduce SLA. The general combining ability (GCA) effects of parents were
significant (P<0.05) for all assessed traits under all testing conditions except for PB under DS and
NS conditions in the glasshouse. The specific combining ability (SCA) effects of progenies were
significant (P<0.05) for all assessed traits except for PH across all testing environments and PB
under field condition. Genotype ICGV 10178 was the best general combiner with positive
contribution to SCMR, PY, SHP, KY, TBM and HI and reduced SLA. Crosses, ICGV 10178 X ICGV
11369, ICGV 10373 x ICGV 15083, ICGV 98412 x ICGV 15094 and ICGV 10178 X ICGV 98412, were
the best specific combiners for enhanced pod yield and drought tolerance. Higher GCA: SCA
rations were recoded for PY, KY and TBM across all the testing environments suggesting the
predominant role of additive genes conditioning the inheritance of these traits. Therefore, the
above new families are recommended for genetic advancement through single seed descent
selection method to develop improved pure line groundnut varieties with high pod yield and
drought tolerance.
Description
Doctoral Degree. University of KwaZulu-Natal, Pietermaritzburg.