Genetic enhancement of sorghum for yield-related traits and drought tolerance through induced mutagenes.
Loading...
Date
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
Sorghum (Sorghum bicolor [L.] Moench) is the foundation crop in the world's dry regions, for
food, feed, and bioenergy feedstock. There has not been a systematic breeding program and
farmers-preferred varieties of the crop in Namibia due to several constraints. There is a need
to develop high-yielding and farmer-preferred sorghum varieties with drought-adaptive traits
to boost sorghum productivity in the country. The overall goal of this study was to contribute
to the national sorghum breeding program aimed at improving sorghum production and
productivity through the development and deployment of climate-smart cultivars preferred by
farmers and markets in Namibia via induced mutagenesis. The specific objectives of the study
were: (1) to assess the present state of sorghum production in northern Namibia and
document farmers’ perceived production constraints and trait preferences in new varieties to
guide drought-tolerance breeding; (2) to determine the optimum doses of a single and
combined use of gamma radiation and ethyl methanesulfonate (EMS) for effective mutation
breeding in sorghum; (3) to determine the genetic profile of elite sorghum lines developed via
gamma radiation using diagnostic simple sequence repeat (SSR) markers and phenotypic
traits for selection; and (4) to determine the Genotype by environment interaction (GEI) of
newly-developed mutant and traditional sorghum lines for grain yield and yield related traits
for drought-prone areas of Namibia.
In the first study, a survey was conducted using a participatory rural appraisal in the following
six selected sorghum-growing constituencies: Kapako and Mpungu (Kavango West Region),
Eenhana and Endola (Ohangwena Region), and Katima Mulilo Rural and Kongola (Zambezi
Region). Data were collected using a structured questionnaire involving 198 farmers in 14
sampled villages across the regions. An equal proportion of male and female respondent
farmers cultivate sorghum, suggesting the value of the crop to both genders in Namibia. Most
respondent farmers (63.6%) were in productive age groups of <40 years old. In the study
areas, low-yielding landrace varieties, namely Ekoko, Okambete, Makonga, Kamburo, Nkutji,
Katoma, Fuba, Dommy, Kawumbe, and Okatombo, were widely cultivated, and most of the
farmers did not use chemical fertilizers to cultivate sorghum. Farmers’ perceived sorghum
production constraints in the study areas included recurrent drought, declining soil fertility,
insect pest damage, high cost of production inputs, unavailability of improved seed, lack of
alternative improved varieties with farmers’ preferred traits, lack of organic manure, limited
access to market and limited extension service. The key farmers’ preferred traits in a new
sorghum variety included high grain yield, early maturity, and tolerance to drought and storage
pests. The study recommends genetic improvement and new variety deployment of sorghum
with the described farmers-preferred traits to increase the sustainable production of the crop
in Namibia.
In the second study, two concurrent experiments were conducted as follows: in experiment I,
the seeds of four sorghum genotypes (Parbhani Moti, Parbhani Shakti, ICSV 15013, and
Macia) were treated using five gamma radiation doses (0, 300, 400, 500 and 600 Gray [Gy]),
and three EMS doses (0, 0.5 and 1.0%), and gamma radiation followed by EMS (0 and 300
Gy and 0.1% EMS; 400 Gy and 0.05% EMS). In experiment II, the seeds of two sorghum
genotypes (Macia and Red sorghum) were treated with only seven doses of gamma radiation
(0, 100, 200, 300, 400, 500 and 600 Gy). The combined applied doses of gamma radiation
and EMS are not recommended due to poor seedling emergence and seedling survival rate
below LD50. The best dosage of gamma radiation for genotypes Red sorghum, Parbhani Moti,
Macia, ICSV 15013 and Parbhani Shakti ranged between 392 and 419 Gy, 311 and 354 Gy,
256 and 355 Gy, 273 and 304 Gy, and 266 and 297 Gy, respectively. The optimum dosage
ranges of EMS for genotypes Parbhani Shakti, ICSV 15013, Parbhani Moti and Macia were
between 0.41% and 0.60%, 0.48% and 0.58%, 0.46% and 0.51%, and 0.36% and 0.45%,
respectively. The above dose rates are useful for induced mutagenesis and creating genetic
variation in the tested sorghum genotypes for breeding programs.
In the third study, 20 mutant lines (which were at mutation generation 7 [M7]) were developed
using gamma-irradiation at 350 Gy from the seed of the variety Macia (SDS 3220). Also, five
check varieties were used for the comparative study. DNA extraction was carried out on young
and fresh leaves samples per test line 20 days after sowing. Seventeen SSR markers
amplified a total of 50 alleles, which varied from 2 to 5 (mean = 2.94). The number of effective
alleles per locus varied from 1.08 to 2.53, with a mean of 1.96. The observed heterozygosity
ranged from 0.00 to 0.21 (mean = 0.09). The mean expected heterozygosity value was 0.45
indicating moderate genetic differentiation of the tested lines for selection and hybridization.
Cluster analysis classified the genotypes into three main groups. Moderate to high genetic
distance (≥ 0.50) was displayed between drought-tolerant and high-yielding genotypes that
aided in selecting mutant lines such as ‘ML2, ML3, ML4, ML7 and ML14’ compared with the
check varieties ‘Macia, Kotovara, ICSR 137, and ICSV 17004’. The selected lines are a useful
source of genetic variation for breeding high-yielding and drought-tolerant varieties suited for
the drought-prone environments of Namibia.
In the fourth study, 50 sorghum genotypes, including 10 newly-developed mutant lines (M9),
33 landraces, two sorghum varieties widely grown in Namibia, and five standard check
varieties were evaluated under field conditions using a 10 x 5 alpha lattice design with three
replications. The experiments were carried out in four environments with two growing seasons
in Namibia. Data were collected on grain yield and related traits and subjected to the Additive
Main Effects and Multiplicative Interaction (AMMI) model. The AMMI model showed that
93.9% of the total genetic variation was attributed to days to 50% flowering (DF), while 94.04%
of the variation was due to plant height (PH), 86.52% to panicle weight (PW), 70.67% to
thousand-grain weight (TGW), and 90.68% to grain yield (GY). The larger variations attributed
to genotypic effects for PL (36.3%), TGW (33.2%) and PH (20.7%) are useful for genotype
selection for yield-related traits. Based on a multi-trait biplot and Best Linear Unbiased
Prediction (BLUPs) analyses of the GEI data across all drought-prone testing environments,
the medium maturity mutant line designated as L7P9-13 was selected as the best yielding (2
tons/ha) and recommended for the drought-prone areas of Namibia.
In summary, the study identified sorghum production systems, key farmers’ perceived
production constraints and trait preferences in new varieties in Namibia. Also, the best dosage
of gamma radiation and EMS were determined for increasing the genetic diversity in sorghum
for genetic enhancement. Newly developed mutant lines ML2, ML3, ML4, ML7 and ML14
displayed moderate to high genetic distance useful for breeding high-yielding and droughttolerant
varieties suited for the drought-prone environments of Namibia. The medium maturity
and drought-tolerant mutant line designated as L7P9-13 was the best yielding (2 tons/ha) and
recommended for large-scale production in the country.
Description
Doctoral Degree. University of KwaZulu-Natal, Pietermaritzburg.