Latest Research on Rice Genotypes: Dec 2020

Evaluation of salt tolerance in rice genotypes by multiple agronomic parameters

The lack of an effective evaluation method for salt tolerance in the screening process is one of the reasons for limited success in conventional salt tolerance breeding. This study was designed to identify useful agronomic parameters for evaluation of salt tolerance and to evaluate genotypes by multiple agronomic parameters for salt tolerance at different growth stages. Twelve genotypes were grown in a greenhouse in sand and irrigated with nutrient solutions of control and treatments amended with NaCl and CaCl2 (5:1 molar concentration) at 4.4 and 8.2 dS m-1 electrical conductivity. Wide genotypic differences in relative salt tolerance based on seedling growth were identified. The duration of reproductive growth between panicle initiation and anthesis was either reduced or increased by salinity, but the response was not strictly correlated with relative salt tolerance in seed yield among genotypes. Wide genotypic differences in relative salt tolerance based on spikelet and tiller numbers were identified. Few genotypic differences were identified for fertility and kernel weight. Spikelet and tiller numbers contributed most of the variation to seed yield among parameters investigated. When genotypes were ranked for salt tolerance based on the means of multiple parameters, dramatic changes of salt tolerance at early and seed maturity stages were observed in two genotypes, GZ5291-7-1-2 and GZ178. IR63731-1-1-4-3-2 was identified with a favourable combination of salt tolerance at early seedling and seed maturity stages. Cluster group ranking of genotypes based on multiple agronomic characters can be applied in salt tolerance breeding to evaluate salt tolerance and may have great advantage over conventional methods. [1]

Comparative Transcriptional Profiling of Two Contrasting Rice Genotypes under Salinity Stress during the Vegetative Growth Stage

Rice (Oryza sativa), a salt-sensitive species, has considerable genetic variation for salt tolerance within the cultivated gene pool. Two indica rice genotypes, FL478, a recombinant inbred line derived from a population developed for salinity tolerance studies, and IR29, the sensitive parent of the population, were selected for this study. We used the Affymetrix rice genome array containing 55,515 probe sets to explore the transcriptome of the salt-tolerant and salt-sensitive genotypes under control and salinity-stressed conditions during vegetative growth. Response of the sensitive genotype IR29 is characterized by induction of a relatively large number of probe sets compared to tolerant FL478. Salinity stress induced a number of genes involved in the flavonoid biosynthesis pathway in IR29 but not in FL478. Cell wall-related genes were responsive in both genotypes, suggesting cell wall restructuring is a general adaptive mechanism during salinity stress, although the two genotypes also had some differences. Additionally, the expression of genes mapping to the Saltol region of chromosome 1 were examined in both genotypes. Single-feature polymorphism analysis of expression data revealed that IR29 was the source of the Saltol region in FL478, contrary to expectation. This study provides a genome-wide transcriptional analysis of two well-characterized, genetically related rice genotypes differing in salinity tolerance during a gradually imposed salinity stress under greenhouse conditions. [2]

Methodology for Evaluation of Lowland Rice Genotypes for Nitrogen Use Efficiency

Rice is a staple food for more than 50% of the world’s population. Based on land and water management practices, rice ecosystem is mainly divided into lowland, upland, and deep water or floating rice. However, major area and production at global level comes from lowland or flooded rice system. In rice growing regions nitrogen (N) is one of the most yield‐limiting nutrients for rice production. Adaptation of cultivars or genotypes with high N use efficiency is a potential strategy in optimizing N requirements of crops, lowering the cost of production and reducing the environmental pollution. The objectives of this paper are to discuss rate and timing of N application, define N‐use efficiency, discuss mechanisms involved for genotypic variation in N‐use efficiency and present experimental evidence of genotypic variations in N‐use efficiency in lowland rice. Evaluation methodology and criteria for screening N‐use efficiency are also discussed. Significant variation in N use efficiency exists in lowland rice genotypes. Nitrogen use efficiency parameters (grain yield per unit of N uptake, grain yield per unit of N applied and recovery of applied N) are useful in differentiating lowland rice genotypes into efficient and non‐efficient responders to applied N. Such an evaluation could assist in identification of elite genotypes that could be used in breeding program to produce cultivars with high N use efficiency and capable of producing high yields. [3]

Genetic Variability among Egyptian Rice Genotypes (Oryza sativa L.) for Their Tolerance to Cadmium

Aim: Heavy metals are significant environmental pollutants. Cadmium (Cd) is a toxic heavy metal and is also known as one of the major environmental pollutants. Therefore, study the germination ability, seedling growth performance and genetic variability of twelve Egyptian rice (Oryza sativa L.) genotypes in response to Cd stress.

Design: Twelve Egyptian rice genotypes are investigated for their tolerance to cadmium stress at seedling stage. Four cadmium chloride concentrations are applied i.e., 0, 0.01, 0.02 and 0.04 mg/ml to the germinated rice seeds. Five traits are studied i.e., germination percentage, germination index, root length, shoot length and root/shoot ratio.

Results: The results show that the most affected trait is root length in response to Cadmium stress, while germination percentage is the lowest affected trait. The studied rice genotypes show highly significant variability in their response to cadmium stress at seedling stage. The most tolerant genotypes are Giza 177 and Giza 178 for germination percentage, under cadmium stress. While, all studied Egyptian rice genotypes are highly sensitive to cadmium stress at high concentrations for all traits.

Conclusion: It can be concluded that, highly genetic variability are observed among studied Egyptian rice genotypes for tolerance to cadmium stress. Moderate tolerance is observed for germination percentage trait, while the most sensitive trait to cadmium stress is root length. [4]

Partitioning of Rice (Oryza sativa L.) Genotypes Based on Morphometric Diversity

Aims: The Objectives of this study were to partition the rice genotypes into different clusters, identification of heterotic groups, and most important traits contributing to divergence to utilize them for specific objective-oriented breeding programs in future.

Study Design: The experiment was set out in randomized complete block design with three replications.

Place and Duration of Study: The experiment was carried out at experimental farm of Department of Genetics and Plant Breeding, Bangladesh Agricultural University, Bangladesh during Aus (Kharif) season of 2012.

Methodology: The diversity among sixty rice genotypes and contribution of thirteen traits towards diversity were analyzed using Mahalanobis’s D2 statistics and principal component analysis.

Results: Analysis of variance showed highly significant variation among the genotypes for all the traits. Cluster analysis based on D2 values exhibited seven distinct clusters. The highest intra-cluster distance (21.95) was observed in cluster II whereas that was lowest (7.62) for cluster VI. Maximum inter-cluster distance was observed between cluster III & VII (46.75) followed by cluster II & VII (42.91), cluster V & VII (38.48), and cluster III & VI (30.87). In all cases inter-cluster distance was higher than the intra-cluster distance suggesting wider diversity among the genotypes. All the short duration genotypes with high yield, high tiller number per hill and more filled grain per panicle were grouped in cluster VII whereas tall, long duration genotypes with low yield, wider flag leaf area, long panicle and more unfilled grain per panicle were grouped in cluster II. Cluster III composed of long duration & moderate yielded genotypes, but cluster V composed of genotypes with long duration and high yield. First three principal components explained about 81% of the total variation. Results of PCA suggested that traits such as number of filled grains per panicle, number of unfilled grains per panicle, flag leaf area, plant height and days to maturity were the principal discriminatory characteristics.

Conclusion: The studied rice genotypes showed considerable divergence for most of the traits. These results can now be used by the breeders to develop rice varieties having desirable characteristics and new breeding strategies for rice improvement. [5]

Reference

[1] Zeng, L., Shannon, M.C. and Grieve, C.M., 2002. Evaluation of salt tolerance in rice genotypes by multiple agronomic parameters. Euphytica, 127(2), pp.235-245.

[2] Walia, H., Wilson, C., Condamine, P., Liu, X., Ismail, A.M., Zeng, L., Wanamaker, S.I., Mandal, J., Xu, J., Cui, X. and Close, T.J., 2005. Comparative transcriptional profiling of two contrasting rice genotypes under salinity stress during the vegetative growth stage. Plant physiology, 139(2), pp.822-835.

[3] Fageria, N.K. and Baligar, V.C., 2003. Methodology for evaluation of lowland rice genotypes for nitrogen use efficiency. Journal of Plant nutrition, 26(6), pp.1315-1333.

[4] F. Ghidan, W., M. Elmoghazy, A., M. Yacout, M., Moussa, M. and E. Draz, A. (2015) “Genetic Variability among Egyptian Rice Genotypes (Oryza sativa L.) for Their Tolerance to Cadmium”, Journal of Applied Life Sciences International, 4(2), pp. 1-9. doi: 10.9734/JALSI/2016/23094.

[5] Hoque, A., Begum, S. N., Robin, A. H. K. and Hassan, L. (2015) “Partitioning of Rice (Oryza sativa L.) Genotypes Based on Morphometric Diversity”, Journal of Experimental Agriculture International, 7(4), pp. 242-250. doi: 10.9734/AJEA/2015/15687.

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