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.
Path Analyses of Yield and Yield-Related Traits of Fifteen Diverse Rice GenotypesLiterature on the path analyses of grain yield and at least 14 yield related traits in a path diagram that is organized with at least second order variables has been lacking. The objectives of this study were to obtain and interpret information on the nature of interrelationships between first-, second-, and third-order yield-related traits and rice (Oryza sativa L.) grain yield. Fifteen rice genotypes were used in this study to represent the combinations of low and high levels of four traits that were identified as important yield determinants — maximum number of tillers, grain size, panicle node number, and panicle size. ‘Lemont’ and ‘Teqing’ were two of these genotypes. The remaining genotypes were F9 lines from a Lemont × Teqing cross. Field experiments were conducted during the 1994 and 1995 cropping seasons at the Texas A&M University Agricultural Research and Extension Center near Beaumont, TX. The 1994 path coefficient (p) of panicle weight on grain yield (p = 0.72; r2 = 0.93) was used to predict the 1995 grain yield (r2 = 0.90). Based on a path analysis of the combined 1994 and 1995 data, the following traits had positive path coefficients on grain yield: panicle weight (p = 0.84), number of filled grains per panicle (p = 0.67), panicle density (p = 0.52), maximum filler density (p = 0.34), number of spikelets per panicle (p = 0.34), and 100-grain weight (p = 0.23). The panicle node number has a negative path coefficient on grain yield (p = −0.23). These results may be useful to rice breeders for the indirect selection of grain yield during the early segregating generations when yield tests are not yet being conducted.
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.
Genetic Variability and Inter Relationship between Yield and Yield Components in Some Rice Genotypes
The study was conducted at the Sudan University of Science and Technology; College of Agricultural Studies, Shambat farm during the season 2009/10 to study genetic variability and correlation between yields, yield components in some rice genotypes. The experiment was laid out in a randomized complete block design (RCBD) with three replications. Seven characters were measured including yield, yield components. Phenotypic () and genotypic () variances, phenotypic (PCV) % and genotypic (GCV) %, coefficients of variation were estimated. Phenotypic and genotypic correlation between characters was determined. The results showed that there were highly significant differences (p≤0.01) between the most of the characters under study except for percentage of unfilled grains per panicle (%). The highest values of phenotypic and genotypic variance were recorded by yield kgha-1 Also grain yield was attained the highest values of phenotypic and genotypic coefficients of variation. Positive phenotypic and genotypic correlation coefficient was detected between grain yield and number of filled grains per panicle, harvest index, panicle length and number of grains per panicle. The present study revealed that there was highly genetic variability among the tested genotypes, indicating that it could be used for further improvement in rice breeding.
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.
Reference 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.
 PB. Samonte, S.O., Wilson, L.T. and McClung, A.M., 1998. Path analyses of yield and yield‐related traits of fifteen diverse rice genotypes. Crop Science, 38(5), pp.1130-1136.
 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.
 Idris, A.E., Justin, F.J., Dagash, Y.M.I. and Abuali, A.I., 2012. Genetic variability and inter relationship between yield and yield components in some rice genotypes. Journal of Experimental Agriculture International, pp.233-239.
 Ghidan, W.F., Elmoghazy, A.M., Yacout, M.M., Moussa, M. and Draz, A.E., 2016. Genetic variability among Egyptian rice genotypes (Oryza sativa L.) for their tolerance to cadmium. Journal of Applied Life Sciences International, pp.1-9.