Characterization of selected Rice (Oryza sativa L.) genotypes tolerance to anaerobic stress during germination
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Date
2024-04
Authors
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Sokoine University of Agriculture
Abstract
Rice is a major food and cash crop in Tanzania, cultivated on
approximately 1.5 million hectares, making it the second largest crop
after maize. The cultivation of rice in Tanzania is primarily carried
out in three major ecosystems: rainfed lowland (71%), rainfed
upland (20%), and irrigated (9%). The majority of rice production
comes from smallholder farmers practicing rainfed agriculture,
accounting for around 90% of the country's total output. Direct
seeding is a widely used, cost-effective, and labor-efficient method
for crop establishment among these farmers. However, Tanzania is
facing the adverse effects of climate change, resulting in a decline inachieve the overall objective, two specific objectives were
formulated: first, to identify potential rice donors for anaerobic stress
tolerance during germination using genomic estimated breeding
values, and second, to explore the degree of coleoptile variability of
directly seeded rice cultivars when subjected to flooding.
To achieve the first objective, we screened 208 rice genotypes,
including four known tolerant and four susceptible checks, for
anaerobic germination in a screenhouse at Sokoine University of
Agriculture (SUA). The screening involved direct seeding of the
seeds and applying 7 cm of standing water above the soil level for
twenty-one days. In the non-flooded (control) treatment, the soil was
appropriately moistened for optimal germination and subsequently
maintained with 2 cm of standing water. Six traits were measured,
including germination and seedling height at 14 and 21 days after
seeding, as well as culm diameter, root length, shoot dry matter, and
root dry matter at 21 days. A multitrait selection index based on the
genomic estimated breeding values (GEBVs) obtained from each
trait was able to identify ten potential genotypes that exhibited
tolerance to anaerobic stress during germination. These genotypes
include Afaa Mwanza 1/159, Rojomena 271/10, Kubwa jinga,
Wahiwahi, Magongo ya Wayungu, Mpaka wa bibi, Mwangaza,
Tarabinzona, IB126 (Bug 2013A), and Kanamalia.
In the second objective, variations in coleoptile elongations of 44 rice
genotypes were explored and characterized for flooding adaptability.
The 44 genotypes were only a subset of the 208 genotypes initially
screened for the first objective. To identify the subset, genotypes
were chosen based on their anaerobic germination performance.
Specifically, 33 genotypes exhibited an average percentage
germination of at least 70%, indicating their relatively high tolerance
to anaerobic conditions. The remaining 11 genotypes demonstrated
low anaerobic germination percentages, with values below 20%.
This subset of genotypes was then subjected to coleoptile
elongation measurement. The purpose of this analysis was to
agricultural productivity.
Flooding is one of the major weather events highlighted by farmers
affecting rice production. Future projections indicate an increase in
the frequency and intensity of floods in Tanzania, linked to the
heightened risk of erratic rainfall patterns. Riverine flooding
particularly poses a devastating stress for agriculture in lowland
areas. Consequently, farmers using direct seeding face challenges
such as hypoxia and anoxia, which lead to poor germination and
significant crop losses. While rice exhibits some degree of flood
tolerance compared to other cereal crops, this attribute is dependent
on the variety. Moreover, coleoptile elongation is reported as a major
determinant that can be observed and used for the selection of
donor parents, which has never been characterized for effective
germplasm utilization. Therefore, there is a need to identify rice
genotypes that can germinate under flood stress conditions provided
that Tanzania has vast rice cultivars, particularly landraces, of
untapped potential for this stress.
To address this research gap, we formulated the overall objective
aiming to contribute to the availability of donor parents by screening
and identifying rice genotypes that exhibit tolerance to anaerobic
stress during germination for direct-seeded rice cultivation. Then, toachieve the overall objective, two specific objectives were
formulated: first, to identify potential rice donors for anaerobic stress
tolerance during germination using genomic estimated breeding
values, and second, to explore the degree of coleoptile variability of
directly seeded rice cultivars when subjected to flooding.
To achieve the first objective, we screened 208 rice genotypes,
including four known tolerant and four susceptible checks, for
anaerobic germination in a screenhouse at Sokoine University of
Agriculture (SUA). The screening involved direct seeding of the
seeds and applying 7 cm of standing water above the soil level for
twenty-one days. In the non-flooded (control) treatment, the soil was
appropriately moistened for optimal germination and subsequently
maintained with 2 cm of standing water. Six traits were measured,
including germination and seedling height at 14 and 21 days after
seeding, as well as culm diameter, root length, shoot dry matter, and
root dry matter at 21 days. A multitrait selection index based on the
genomic estimated breeding values (GEBVs) obtained from each
trait was able to identify ten potential genotypes that exhibited
tolerance to anaerobic stress during germination. These genotypes
include Afaa Mwanza 1/159, Rojomena 271/10, Kubwa jinga,
Wahiwahi, Magongo ya Wayungu, Mpaka wa bibi, Mwangaza,
Tarabinzona, IB126 (Bug 2013A), and Kanamalia.
In the second objective, variations in coleoptile elongations of 44 rice
genotypes were explored and characterized for flooding adaptability.
The 44 genotypes were only a subset of the 208 genotypes initially
screened for the first objective. To identify the subset, genotypes
were chosen based on their anaerobic germination performance.
Specifically, 33 genotypes exhibited an average percentage
germination of at least 70%, indicating their relatively high tolerance
to anaerobic conditions. The remaining 11 genotypes demonstrated
low anaerobic germination percentages, with values below 20%.
This subset of genotypes was then subjected to coleoptile
elongation measurement. The purpose of this analysis was to assess the variation in coleoptile elongation among the selected
genotypes and determine its association with tolerance to anaerobic
stress during germination. Significant variations in coleoptile
elongation were observed among the 44 selected and studied
genotypes (P<0.05). The genotypes were classified based on the
magnitude of coleoptile elongation, ranging from high to very low
elongating rice. Association analysis revealed a significant positive
and moderately strong correlation between coleoptile elongation and
anaerobic germination. Among the genotypes, NERICA 7,
Kanamalia, Wahiwahi, Rojomena 271/10, Kubwa jinga, Faya
mafuta, and Mwasungo exhibited the highest elongation. In general,
most of the genotypes that exhibited high average percentage
anaerobic germination had an intermediate to high degree of
coleoptile elongation, consistently demonstrating a significant
connection between coleoptile elongation and tolerance to anaerobic
stress during germination.
Overall, these results obtained four top test genotypes: Kanamalia,
Kubwa Jinga, Wahiwahi, and Rojomena 271/10. These genotypes
were consistently selected for a greater selection index for anaerobic
germination and significant coleoptile elongation. The results provide
valuable insights into the significant variations among rice cultivars
regarding their ability to germinate and adapt under flooded
conditions. Further analysis, including starch breakdown and
identification of genes associated with tolerance and coleoptile
elongations, is imperative to confirm and broaden the scope of
tolerance in these genotypes.
Description
Master of Science in Crop
Science
Keywords
Rice, Oryza sativa L., Genotypes Tolerance, Anaerobic Stress, Germination