Characterization of Ethiopian Chickpea (Cicer Arietinum L) Genotypic Diversity Population Structure Cold Tolerance and Assessment of Change of Variability Over time
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Date
2021-12-29
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Addis Ababa University
Abstract
Plant genetic resources are valuable source of desirable agronomic traits that can be used in crop
improvement. These resources are constantly threatened by both natural and human-caused risks.
Chickpea (Cicer arietinum L.) germplasm is one of the crops affected by these factors. Regular
chickpea diversity monitoring in farmers' fields, as well as characterization and evaluation of
Ethiopian chickpea germplasm in ex-situ, are essential in order to build viable conservation
strategies and undertake breeding initiatives. However, in Ethiopia chickpea, the abovementioned
information is limited. As a result, this research began with the general objective of
determining the diversity of Ethiopian chickpea germplasm and its potential for frost resistance,
as well as determining the degree to which chickpea on-farm diversity has changed over time. In
the study, molecular analysis was conducted to determine the genetic diversity, population
structure, and relationships of 152 chickpea genotypes using simple sequence repeats (SSR)
markers. There were 133 alleles observed using 23 polymorphic SSR markers, with a mean of
5.8 alleles per locus. Pairwise population Nei's genetic distance, heterozygosity (0.4), Shannon's
information index (1.2), Gene Diversity (0.67), polymorphic information content (0.63), and
percent polymorphism (99.5%) were among the genetic-based statistics used in the study. These
studies demonstrated that there was high genetic variation within and among chickpea
genotypes. The 152 genotypes were divided into two groups on UPGMA tree developed based
on Nei's genetic distances. The exotic genotypes were all grouped together in one cluster,
showing that they are distinct from Ethiopian genotypes. However, seed exchange caused
inconsistencies in the patterns of grouping Ethiopian chickpea genotypes by geographic location.
Two separate populations were discovered using model-based population structure clustering.
These findings can be used to create efficient conservation approaches and breeding initiatives to
enhance the genetic diversity of chickpeas. To assess the potential of Ethiopian chickpea for frost
resistance, a frost screening study was carried out in a natural field and in controlled conditions.
Six hundred seventy-three genotypes were characterized for two years (2018/2019 to 2019/2020)
using an augmented design at Bakelo, Debre Birhan, Ethiopia, a place as national frost screening
site. A significant (p<0.01) variability amongst genotypes was recorded for all agronomic traits
considered. In terms of agronomic performance, 94 (12.6%) of the genotypes examined
outperformed the frost susceptible genotypes. Stem/leaf pigmented genotypes had a better
response to frost stress than non-pigmented genotypes. The majority of black seeded chickpeas
were adapted well to frost stress, when compared to brown and white seeded genotypes.
According to the freezing tolerance rate (FTR) and plant survival rate (SR), 83 (12.3%) and 85
(12.6%) genotypes were identified as frost tolerant. Grain yield had a significant (p<0.01)
correlation with FTR, SR, seed shriveling score, stem/leaf pigmentation, and seed color. Based
on the field experiment genotypes performances, 72 genotypes were selected and evaluated
further for cold tolerance variability at seedling stage under controlled environment using a
complete randomized design with two replications. The analysis of variance revealed a
significant (P<0.01) difference among genotypes for plant height, number of foliage, number of
primary branches and fresh weight. Cold tolerant genotypes had a higher growth rate than
susceptible genotypes, which had a slower growth rate or completely failed. According to SR, 31
(43.1%) genotypes scored above 0.8 values. Based on FTR, 37 (51.4%) and 31 (43.1%)
genotypes were rated at a score of 1 to 3 in freezing test 1 (T1) and freezing test 2 (T2),
respectively indicating better frost tolerance than others. Fresh biomass yields had a high
negative correlation (p<0.01) with SR, but a substantial positive correlation (p<0.01) with FTR
value. At seedling stage, based on the combined results of FTR and SR scores, 26 genotypes
were shown to be cold tolerant genotypes at temperatures as low as -5oC. Therefore, the field and
controlled environment experiments results revealed that Ethiopian chickpea landraces have a
good genetic potential for cold tolerance traits for use in breeding programs. In addition, a
diversity monitoring research was conducted to look into the differences in phenotypic diversity
between the present (2017) and prior chickpea collections (1979-1983). The experiment was
conducted using simple lattice design with two replications at Debre Zeit Agricultural Research
Center for two consecutive years (2018/2019 to 2019/2020). The result showed that chickpea has
been under genetic erosion ranging from 30.4% to 100% during the last 35 years. During this
time, estimations of Shannon-Weaver diversity index for black seeded and ivory white seeded
chickpea kinds have declined from 1.99 to 0.69 and 1.33 to 0.0, respectively. In previous
collections, 25.8% of black coated genotypes and 6.5% of white coated genotypes were found,
but these chickpea varieties are now rare (black 6.5%) or unobtainable (white 0.0%). Cluster
analysis revealed that genotypes clustered according to the time of collections regardless of their
geographic origins. The genotypes of chickpeas in the current and prior collections were
different. Landraces of black and white seeded chickpeas were vulnerable to genetic erosion and
chickpea genotypes at farmer’s field are found to be losing their variability. Black and white
seeded chickpea are missing at farmers’ fields and are under greater threat of extinction. So,
implementation of immediate restoration of chickpea landraces is required to recover and
maintain the lost chickpea landraces in the studied region and we strongly recommended revision
of the current conservation strategies.
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Keywords
Chickpea Diversity Change, Ethiopian Chickpea Germplasm, Freezing Test, Frost Survival Rate, Frost Tolerance Rate, Genetic Erosion, Germplasm Characterization, SSR Markers