Abdul Aziz Napar

An overview of stripe rust of wheat (Puccinia striiformis f. sp. tritici) in Pakistan

Stripe rust (yellow rust) caused by Puccinia striiformis f. sp. tritici has been an important disease of wheat in the Indian subcontinent since 1786. Currently, it prevails across all the wheat growing areas from north to south in the country. Due to the favourable weather conditions, the northern uplands have been historically hit by the severe disease epidemics. These epidemics caused significant losses to national wheat production. Acquisition of broader virulence pattern by the pathogen poses a serious threat to national agriculture. Although the deployed national wheat varieties have adequate resistance, these are developed around few major genes and are vulnerable to the new evolving strains of the pathogen. Utilisation of race non-specific durable resistance and seedling resistance via gene pyramiding, based on the current virulence scenario of the pathogen should provide sustainable control. This review focuses on the national milestones that recognise the economic significance of the disease and current status of stripe rust and its management in Pakistan.

Stripe rust analysis of D-genome synthetic wheats (2n = 6x = 42, AABBDD) and their molecular diversity

Stripe or yellow rust caused by Puccinia striiformis f. sp. tritici is a threat to many of the existing cultivars of Pakistan. Many attempts are being made to evolve new varieties resistant to stripe rust to reduce the losses caused by this disease. For this purpose, novel genes are needed to incorporate into the existing cultivars. These genes are found in the wild progenitors of wheat that are D-genome donors to wheat. As a result of extensive research, wheat synthetic hexaploids have been developed. These synthetics have resistances against biotic as well as abiotic stresses including the yellow rust. A group of such synthetics has been identified which seems resistant to this destructive disease. This group was tested under field conditions to identify resistance against stripe rust. The same population was analysed at molecular level to explore the genetic diversity for rust resistance. Genetic diversity among 34 selected synthetic hexaploid wheats was studied by random amplified polymorphic DNA (RAPD) analysis. A set of 12 RAPD primers was applied, and the level of polymorphism was found to be 46.67%. The coefficients in the range of 71–100% were detected by genetic similarity matrix based on Nei and Lis index. These coefficients were used for constructing a dendrogram using unweighted pair group of arithmetic means. Synthetic hexaploid line 34 was found to exhibit maximum genetic distances among the 34 selected lines. The same accession also showed excellent phenotypic characters with above average grain weight. These synthetic hexaploids carrying genetic potential for stripe rust resistance and morphological traits should be useful for improvement of existing wheat cultivars.

QTL Analysis in Plants: Ancient and Modern Perspectives

Quantitative traits exhibit continuous variation, indicating their control through multiple genes. Segregating populations are used to mine out associations between phenotypic and genotypic variations. Phenotyping performed for a specific trait and its variation in the population is justified with genotypic variation obtained through genetic markers application. A snapshot of genotypic variation is strictly dependent on the number and density of the markers applied. Parental and marker information is required to correlate genetic and phenotypic data for quantitative trait loci (QTL) analysis. For many years (now becoming obsolete), it has been of core importance to identify QTL with such methodology. Failure had to be faced by the researcher because the DNA region identified for phenotypic variation was much wider, and needed to be narrowed down by further dense marker application in that area to obtain required and accurate results. Nowadays the focus is on high-throughput technologies to obtain genome-wide resolution: high-throughput sequencing (HTS) is one of them. A comprehensive map of genomic variations can be produced with resequencing or reference genome sequences. Along with expression profiling, new molecular markers can be searched out with QTL analysis. Genomic-assisted breeding by studying the evolutionary variations in crops has many applied aspects as well. As compared to the conventional biparental population, presently the focus is on raising multiparent advanced generation inter-cross (MAGIC) populations to explore the genetic basis of quantitative traits. Probabilities of alleles of interest across the whole genome are calculated through the Hidden Markov Model (HMM). Different software packages (such as R-package, Qgene) are used for the estimates. Such whole-genome approaches in QTL analysis are a powerful and recently used technique. In this chapter, all these recent and modified modern techniques are reviewed with the most recent upcoming details. Traditional and modern QTL analyses have clearly been differentiated on applicable grounds.

Cytological, Phenological and Molecular Characterization of B (S)-Genome Synthetic Hexaploids (2n = 6x = 42; AABBSS)

The B(S) genome diploids (2n = 2x = 14) are a unique reservoir of genetic diversity that can provide wheat breeders a rich source of allelic variation for stress traits that limit productivity. Restricted in practical use essentially due to their complex chromosomal behavior, these diploids have been in limited practical usage. The classic utilization example has been the suppression activity of the Ph locus and role in alien genetic transfer aspects that has been a standard in cytogenetic manipulation studies. For applied efforts focusing on Aegilops speltoides researchers in CIMMYT initiated an ambitious program to make AABBBB(SS) synthetics and made progress by generating over 50 such synthetics. Of these 20 were available for this study in which phenology and powdery mildew screening were evaluated. Four of these 20 synthetics appeared to be useful sources for further exploitation in breeding. These were entries 6, 9, 10 and 11 suited for exploitation in pre-breeding, with positive phenological characters particularly high thousand-kernel weight and are cytologically near euploid at 2n = 6x = 42. The subtle hyper (43) and hypoploid number would not negate their applied use potential. Preference however goes to genotypes 9 and 11.

Biological screening of Albizia lebbek L. and Mimosa himalayana Gamble (Mimosaceae)

Methanolic leaf extracts of two medicinal plant species of family Mimosaceae: Albizia lebbek L. and Mimosa himalayana Gamble, were used to evaluate their antibacterial and antifungal activity using agar diffusion method. Extractions from leaves of selected plants were carried out by simple maceration process. The methanolic extracts of these plants were tested against four strains of bacteria (one strain was gram positive that is, Bacillus subtilis and three were gram negative that is, Ecscherichia coli, Pseudomonas aeruginosa and Klebsiella pneumoniae) and two strains of fungi (Aspergillus niger and Aspergillus flavus). At 15 mg/ml extract concentration, the maximum inhibitory zones observed in A. lebbek L. and M. himalayana Gamble were12.5 and 27 mm, respectively. A. lebbek L. and M. himalayana gave response against A. niger by producing 36.2 and 0.86% inhibition, respectively. No antifungal activity was reported by A. lebbeck L. and M. himalayana Gamble against A. flavus. Key words: Mimosaceae, antibacterial, antifungal, methanol extracts, medicinal plants.