New smut-specific primers for multilocus genotyping and phylogenetics of Ustilaginaceae

Molecular Diagnostic Assay for Rapid Detection of Flag Smut Fungus (Urocystis agropyri) in Wheat Plants and Field Soil

Flag smut incited by Urocystis agropyri has the potential to cause substantial reduction in yield and quality of wheat production. An early and precise diagnosis is a key component in the successful management of flag smut of wheat. Therefore, a simple molecular assay for the rapid detection of U. agropyri was developed for the first time. To detect U. agropyri, species specific primers were developed by comparing the partial sequences of internal transcribed spacer (ITS) DNA region of U. agropyri with related and unrelated phytopathogenic fungi. The clear amplicons of 503 and 548 bp were obtained with the two sets of designed primers (UA-17F/UA-519R and UA-15F/UA-562R) from the genomic DNA of 50 geographic distinct isolates of U. agropyri. However, no amplicon was obtained from the DNA of other 21 related and unrelated phytopathogenic fungi which showed the specificity of the primers for the U. agropyri. PCR reaction was also set up to confirm the presence of U. agropyri spores in six different wheat varieties along with eleven distinct regional soil samples as template DNA. The presence of U. agropyri in all the soil samples collected from an infected field and plant tissue of diseased plants collected at two different stages (20 and 40 days post sowing) and the absence in the soils and plants of healthy plots indicated 100% reliability for detection of U. agropyri. This simple and rapid test can be employed for the detection of U. agropyri from enormous wheat and soil samples in very short time with less man power. Thus, the reported molecular assay is very specific for U. agropyri and requires less time and man power over conventional diagnosis which is often confused by coinciding morphological features of closely related fungal pathogens, and therefore, it can be used for quarantine surveillance of flag smut.

Phylogeography and Population Structure Analysis Reveal Diversity by Gene Flow and Mutation in Ustilago segetum (Pers.) Roussel tritici Causing Loose Smut of Wheat

Ustilago segetum (Pers.) Roussel tritici (UST) causes loose smut of wheat account for considerable grain yield losses globally. For effective management, knowledge of its genetic variability and population structure is a prerequisite. In this study, UST isolates sampled from four different wheat growing zones of India were analyzed using the second largest subunit of the RNA polymerase II (RPB2) and a set of sixteen neutral simple sequence repeats (SSRs) markers. Among the 112 UST isolates genotyped, 98 haplotypes were identified. All the isolates were categorized into two groups (K = 2), each consisting of isolates from different sampling sites, on the basis of unweighted paired-grouping method with arithmetic averages (UPGMA) and the Bayesian analysis of population structure. The positive and significant index of association (I_A = 1.169) and standardized index of association (rBar_D = 0.075) indicate population is of non-random mating type. Analysis of molecular variance showed that the highest variance component is among isolates (91%), with significantly low genetic differentiation variation among regions (8%) (F_st = 0.012). Recombination (R_m = 0) was not detected. The results showed that UST isolates have a clonal genetic structure with limited genetic differentiation and human arbitrated gene flow and mutations are the prime evolutionary processes determining its genetic structure. These findings will be helpful in devising management strategy especially for selection and breeding of resistant wheat cultivars.

Ten reasons why a sequence-based nomenclature is not useful for fungi anytime soon

The large number of species still to be discovered in fungi, together with an exponentially growing number of environmental sequences that cannot be linked to known taxa, has fuelled the idea that it might be necessary to formally name fungi on the basis of sequence data only. Here we object to this idea due to several shortcomings of the approach, ranging from concerns regarding reproducibility and the violation of general scientific principles to ethical issues. We come to the conclusion that sequence-based nomenclature is potentially harmful for mycology as a discipline. Additionally, a classification based on sequences as types is not within reach anytime soon, because there is a lack of consensus regarding common standards due to the fast pace at which sequencing technologies develop.