Adel H. Abdel-Ghani

Genotypic variation and relationships between seedling and adult plant traits in maize (Zea mays L.) inbred lines grown under contrasting nitrogen levels

Genotypes with better root development have good nutrient acquisition capacity and may yield better under limited nitrogen (N) conditions and consequently can help reduce the N fertilization rate and hence mitigate some economic and ecological problems. This study focused on the genotypic variation among diverse maize inbred lines for seedling and adult plant traits under contrasting N levels. Seventy-four lines were screened under high and low N levels in a climate chamber and in the field. High phenotypic diversity was observed for seedling and adult plant traits together with moderate to high broad-sense heritability estimates. Seedling total root length and root dry weight were significantly correlated with other root traits in maize. Of the adult plant traits evaluated in the field, the anthesis-silking interval and the leaf chlorophyll contents were significantly correlated with grain yield under both low and high N levels. In one location, the seminal root length was correlated with grain yield both under low and high N levels and the root dry weight was correlated with grain yield under high N. Selection indices based on secondary root traits along with grain yield could lead to an increase in selection efficiency for grain yield under N stress condition. By identifying lines with better root development, particularly lines with longer SRL, it may be possible to select inbred lines with higher grain yield particularly under low N condition.

Association analysis of single nucleotide polymorphisms in candidate genes with root traits in maize (Zea mays L.) seedlings

Several genes involved in maize root development have been isolated. Identification of SNPs associated with root traits would enable the selection of maize lines with better root architecture that might help to improve N uptake, and consequently plant growth particularly under N deficient conditions. In the present study, an association study (AS) panel consisting of 74 maize inbred lines was screened for seedling root traits in 6, 10, and 14-day-old seedlings. Allele re-sequencing of candidate root genes Rtcl, Rth3, Rum1, and Rul1 was also carried out in the same AS panel lines. All four candidate genes displayed different levels of nucleotide diversity, haplotype diversity and linkage disequilibrium. Gene based association analyses were carried out between individual polymorphisms in candidate genes, and root traits measured in 6, 10, and 14-day-old maize seedlings. Association analyses revealed several polymorphisms within the Rtcl, Rth3, Rum1, and Rul1 genes associated with seedling root traits. Several nucleotide polymorphisms in Rtcl, Rth3, Rum1, and Rul1 were significantly (P<0.05) associated with seedling root traits in maize suggesting that all four tested genes are involved in the maize root development. Thus considerable allelic variation present in these root genes can be exploited for improving maize root characteristics.

Diversity of germination and seedling traits in a spring barley ( Hordeum vulgare L.) collection under drought simulated conditions

This research evaluated the genotypic variation in a diverse set of 233 barley genotypes including 57 landraces in the context of early drought tolerance using polyethylene glycol-(PEG) induced osmotic stress on germinating seeds. The effect of PEG treatment ranged from accelerating to delaying the germination rate. PEG showed inhibitory effects on all seedling traits. Expressions of root and shoot traits recorded under optimum and under PEG-induced drought stress were positively and significantly correlated. Combined analysis of variance over experiments and treatments showed intermediate to high broad sense heritability values ranging from 0.42 to 0.76 for germination rate and seedling traits. Higher heritability values were obtained under optimum conditions as compared to PEG-induced drought stress conditions, indicating that the selection for genotypes with a more vigorous root system would be more efficient under optimum conditions. The extensive genetic variation for root morphology-related traits found in this diverse collection opens the opportunity to further investigate the analyzed root traits as selection criteria to improve barley performance under drought stress and to reveal the genetic basis for the observed stress tolerance by a genome-wide association study.

Association analysis of genes involved in maize (Zea mays L.) root development with seedling and agronomic traits under contrasting nitrogen levels

A better understanding of the genetic control of root development might allow one to develop lines with root systems with the potential to adapt to soils with limited nutrient availability. For this purpose, an association study (AS) panel consisting of 74 diverse set of inbred maize lines were screened for seedling root traits and adult plant root traits under two contrasting nitrogen (N) levels (low and high N). Allele re-sequencing of RTCL, RTH3, RUM1, and RUL1 genes related to root development was carried out for AS panel lines. Association analysis was carried out between individual polymorphisms, and both seedling and adult plant traits, while controlling for spurious associations due to population structure and kinship relations. Based on the SNPs identified in RTCL, RTH3, RUM1, and RUL1, lines within the AS panel were grouped into 16, 9, 22, and 7 haplotypes, respectively. Association analysis revealed several polymorphisms within root genes putatively associated with the variability in seedling root and adult plant traits development under contrasting N levels. The highest number of significantly associated SNPs with seedling root traits were found in RTCL (19 SNPs) followed by RUM1 (4 SNPs) and in case of RTH3 and RUL1, two and three SNPs, respectively, were significantly associated with root traits. RTCL and RTH3 were also found to be associated with grain yield. Thus considerable allelic diversity is present within the candidate genes studied and can be utilized to develop functional markers that allow identification of maize lines with improved root architecture and yield under N stress conditions.

Evaluation of genetic diversity among Jordanian pomegranate landraces by fruit characteristics and molecular markers.

The level of variation in various fruit traits was described among 14 Jordanian pomegranate landraces and the genetic relatedness was investigated using RAPD and SSR markers. Euclidean distances among studied landraces ranged from 3.33 to 12.01, with a mean of 7.65. Fruit and aril traits explained the variation in the first component (28.92%), while other traits were present in the second (17.615) and third (12.81%) components, and therefore contributed less to the variability. Genetic distances based on RAPD scores ranged from 0.24 to 0.66, indicating that considerable level of divergence exists among studied pomegranate landraces. The set of SSR markers used in this study was monomorphic, which might be due to the fact that available SSR markers are too few to identify polymorphic SSR markers to differentiate between landraces present within a small geographic area. Multivariate analysis showed that dendrograms constructed based on fruit related traits as compared with that based on RAPD scores were not consistent. Pomegranate landraces displayed high variability in fruit and aril related traits, which could be considered a valuable source of genes for commercial uses. Results revealed the presence of small seeded variety that has large arils. High morphological and RAPD variation exist among Jordanian pomegranate landraces could be exploited in pomegranate breeding.