Characterization of selected rice genotypes from eastern and southern Africa tolerant to salinity at seedling stage
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Date
2024-05
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Sokoine University of Agriculture
Abstract
Soil salinity stands as a prominent abiotic stress significantly
impacting rice production and food security within sub-Saharan
Africa. A promising strategy to mitigate this challenge involves the
development and deployment of salinity-tolerant rice varieties. The
objective of this study was to identify salinity-tolerant rice genotypes
suitable for integration into breeding programs, offering a viable
solution to salinity-affected soils in Eastern and Southern African
rice-growing areas. The investigation focused on both phenotypic
and genotypic characterizations of selected rice genotypes at the
seedling stage, coupled with the identification of salinity tolerance-
associated quantitative trait loci (QTLs).
This research focused on analyzing a collection of 206 rice
genotypes obtained from Tanzanian farmers' fields, along with other
genotypes from Eastern and Southern Africa. genotypes were then
subjected to phenotypic screening under a salinity level of 12 dS/m,
utilizing a hydroponic system and following the established IRRI
protocol. From this initial pool, 13 genotypes were carefully selected
based on their SES scores to undergo more detailed evaluation of
their growth and physiological characteristics. To identify the
presence of the Saltol allele, a widely recognized QTL associated
with salinity tolerance, genotypic analysis was performed using 1k-
RiCA SNP markers.
Phenotypic screening revealed salinity's adverse effects on various
growth parameters, particularly on root and shoot dry weights,
indicative of osmotic imbalance. Correlation analysis identified
sodium concentration, sodium-to-potassium ratio, and canopy
temperature as strong indicators of salinity tolerance in rice
genotypes. These variables hold as potential physiological markers
for salinity tolerance screening in breeding programs. Principal
Component Analysis (PCA) was employed to identify key variables
for salinity tolerance, revealing potassium ratio, root dry weight, shoot dry weight, shoot length, and survival as significant
contributors. Based on PCA results, genotypes were classified into
tolerant, moderately tolerant, and sensitive categories. Six
moderately tolerant genotypes (Intsindagira Bigega, K5, SATO 1,
Sukari, Terembele (LL 29), and ZX 117) exhibited promising
phenotypic tolerance, making them potential candidates for
enhancing salinity tolerance in rice varieties.
Concurrently, Genotypic evaluation at the seedling stage provided
insights into the expression of salinity-tolerant traits among the rice
genotypes. Remarkably, 36 rice genotypes were found to possess
the Saltol allele, recognized for its role in conferring salinity
tolerance. some Saltol-possessing genotypes exhibited inadequate
performance under salinity stress conditions. Interestingly, 16
genotypes lacking the Saltol allele demonstrated salinity tolerance,
suggesting the presence of other genetic factors (QTLs) contributing
to this trait beyond Saltol. Additionally, the geographical distribution
of Saltol-possessing genotypes within Tanzania revealed variations
across different Agro-ecological zones. Notably, the Coastal Zone
exhibited a higher proportion of phenotypically tolerant genotypes
compared to other zones, suggesting local farmers' continuous
selection pressure as a possible contributing factor. These findings
highlight the potential for integrating diverse salinity-tolerant rice
genotypes, possessing various genetic mechanisms, into breeding
programs. This approach could lead to the development of novel rice
varieties capable of thriving under salinity stress conditions.
Description
MSc. Dissertation
Keywords
phenotypic characterization, Eastern Africa, Southern Africa, seedling stage, salinity tolerance