Phenotypic and Molecular Characterization of Rice Genotypes’ Tolerance to Cold Stress at the Seedling Stage

Agro-morphological and structural diversity of rice germplasm revealed by SSR markers in Benin Republic

BACKGROUND

In developing countries, rice is a staple food and cash crop for the people. In Benin Republic, paddy rice production has increased over time. Accordingly, local varieties were replaced by improved varieties, leading unfortunatley to a loss of the diversity of Beninese rice germplasm.

METHODS AND RESULTS

The investigation focused on the structure and genetic diversity of 72 rice accessions collected throughout 22 villages using 13 quantitative traits and 17 SSR markers. The descriptive analysis of the 13 quantitative parameters showed a significant difference among the accessions, with a grouping in three clusters. Group I (16.66% of samples) was composed of accessions with long, wide and thick grains alongside with four controls TOG5681, TOG5307, Azucena and Moroberekan. Group II (7% of samples) contained accessions with late vegetative cycle. Group III contained most of the accessions (76.39% of the samples), including accessions such as the CG14 and Nipponbare control lines, and almost all the improved varieties. The molecular analysis revealed a significant diversity (mean number of alleles: 4.47 with polymorphism information content of 0.633). Population structure based on molecular markers showed three primary populations with a mixture of phenotypic groupings at ΔK, K = 3.

CONCLUSION

This study showed that Beninese rice germplasm was divided into two structures: phenotypically similar cultivars but genotypically distinct (homonyms), and phenotypically different cultivars but genotypically similar (synonyms). Some local cultivars such Bagou19, Bagou20 and Koud44 can be used for large scale production due to their agronomics and molecular traits. The molecular structure obtained in this investigation might be used for future conservation and breeding programs.

Screening Technique Based on Seed and Early Seedling Parameters for Cold Tolerance of Selected F2-Derived F3 Rice Genotypes under Controlled Conditions

The cold tolerance studies were carried out in a bi-parental F2 population of a cross between tolerant and susceptible parents (SKUA-529 and HEERA, respectively). The purpose was to screen the individuals of a population for primary cold-tolerance-related attributes. The information generated has a direct application and use in identifying cold tolerance quantitative trait loci (QTLs) and further can be used for genotyping with an appropriate marker system. The screening was carried out on F2-derived F3 seeds and F3 plants for seedling and agronomic traits, respectively. Two tests measuring cold tolerance were conducted. In experiment I, seeds were germinated for 28 days at 13 °C and 7 days at 28 °C, and in experiment II, the seeds were germinated for 72 h at 28 °C, 96 h at 13 °C, and once more for 72 h at 28 °C. Coleoptile length, germination percentage, and radical reduction percentages were all measured in experiment I. The radicle and coleoptile regeneration in experiment II were measured after the cold period. The improvement in cold tolerance was achieved through radicle regrowth, as evidenced by the difference between the second and first measurements. The individual lines from the F2:3 population that recorded high germination (%) were #21, #13, #14, and #15. The percentage of coleoptile length (PERCOL %) was observed to be between the ranges of 23.33% to 53.00%. The reduction in coleoptile length (REDCOL %) was also obtained, and there was less reduction in #15, #16, and #14 and it had a range between 38.46% and 75%. Radicle regrowth (REDRAG) was high at 13 °C in #7, #11, #30, #35, and #36. Survival of the seedling range was between 33.33% and up to 100%, and the highest survival rate was observed in #16. The main objective of this rotation in temperature was to emulate field conditions where there has been a drop in temperature. The evaluations were done for primary cold stress tolerance traits, and it was found that most of these traits exhibited high variability. The mapping population developed may be utilized to generate a linkage map and locate QTLs for tolerance to cold stress in rice. Further, the identified donors for cold tolerance may be utilized for breeding programs aimed at the transfer of low-temperature stress tolerance into susceptible backgrounds. In general, a genotype with improved seedling germination rates, growth rates, and leaf yellowing scores; high seedling survival; lesser reduction in coleoptile length and in radicle development; and recovery following a cold shock at the seedling stage demonstrated its cold resistance. Genotypes with a low germination percentage, a greater number of days to germination, slow growth rate and higher leaf yellowing score, high reduction in coleoptile and radicle growth, and reduced seedling survival indicated cold susceptibility.