Common Rust Disease Research Articles

Use of the Puccinia sorghi haustorial transcriptome to identify and characterize AvrRp1-D recognized by the maize Rp1-D resistance protein.

The common rust disease of maize is caused by the obligate biotrophic fungus Puccinia sorghi. The maize Rp1-D allele imparts resistance against the P. sorghi IN2 isolate by initiating a defense response that includes a rapid localized programmed cell death process, the hypersensitive response (HR). In this study, to identify AvrRp1-D from P. sorghi IN2, we employed the isolation of haustoria, facilitated by a biotin-streptavidin interaction, as a powerful approach. This method proves particularly advantageous in cases where the genome information for the fungal pathogen is unavailable, enhancing our ability to explore and understand the molecular interactions between maize and P. sorghi. The haustorial transcriptome generated through this technique, in combination with bioinformatic analyses such as SignalP and TMHMM, enabled the identification of 251 candidate effectors. We ultimately identified two closely related genes, AvrRp1-D.1 and AvrRp1-D.2, which triggered an Rp1-D-dependent defense response in Nicotiana benthamiana. AvrRp1-D-induced Rp1-D-dependent HR was further confirmed in maize protoplasts. We demonstrated that AvrRp1-D.1 interacts directly and specifically with the leucine-rich repeat (LRR) domain of Rp1-D through yeast two-hybrid assay. We also provide evidence that, in the absence of Rp1-D, AvrRp1-D.1 plays a role in suppressing the plant immune response. Our research provides valuable insights into the molecular interactions driving resistance against common rust in maize.

Breeding for Resistance to Biotic Stresses in Crops: Conventional to Genome Editing

Biotic stress is caused by fungi, bacteria, viruses, insects, nematodes as well weeds and it significantly reduces crop yield globally. For instance, the outbreak of a new strain of stripe rust in wheat worldwide, the emergence of white scale insect affecting mango in Ethiopia, the newly emerged Maize Lethal Necrosis viral disease in maize, and invasive fall armyworm insect are devastating maize crop and causing yield loss in Africa. To reduce the yield losses due to biotic stresses, the development of resistant variety and integrated insect pest approach is the way forward for managing disease and insects at respective agroecologies. Thus, this review paper discussed on conventional breeding methods and molecular-assisted selection for breeding resistance to foliar disease in major cereal crops. Wide array of germplasm such as landraces, recombinant inbred lines, pure lines, Double haploid lines, elite lines, multi-parent population, mutant lines, introgressed lines, hybrids, open population variety and wild relative can be used as source germplasm and should be screened under artificial inoculation and or at hotspot areas to develop disease resistance variety. Many maize inbred lines and hybrids showed resistance to turcicum leaf blight, grey leaf spot and common rust diseases and indicating that these genotypes have carrying genes/favorable alleles for multiple disease resistance and it is possible to develop variety resistance to fungi foliar disease in maize. Similarly, several advanced lines and some varieties showed resistance to strip and leaf rust in wheat. However, host plant resistance could be broken down due to new emerging race pathogens. Thus, conventional breeding and molecular screening should be integrated for resistant variety development. Indeed, Marker-assisted selection through backcrossing, gene pyramiding, combined Genome-Wide Association, and transcriptome approach is useful to identify candidate genes and resistant parents in crops. .......

Etiology, management, and host response of cold-tolerant maize germplasm for common rust disease of maize under temperate conditions

Etiology, management, and host response of cold-tolerant maize germplasm for common rust disease of maize under temperate conditions

Comparative transcriptome analysis of two contrasting resistant and susceptible Aegilops tauschii accessions to wheat leaf rust (Puccinia triticina) using RNA-sequencing

Leaf rust, caused by Puccinia triticina Eriks., is the most common rust disease of wheat (Triticum aestivum L.) worldwide. Owing to the rapid evolution of virulent pathotypes, new and effective leaf rust resistance sources must be found. Aegilops tauschii, an excellent source of resistance genes to a wide range of diseases and pests, may provide novel routes for resistance to this disease. In this study, we aimed to elucidate the transcriptome of leaf rust resistance in two contrasting resistant and susceptible Ae. tauschii accessions using RNA-sequencing. Gene ontology, analysis of pathway enrichment and transcription factors provided an apprehensible review of differentially expressed genes and highlighted biological mechanisms behind the Aegilops–P. triticina interaction. The results showed the resistant accession could uniquely recognize pathogen invasion and respond precisely via reducing galactosyltransferase and overexpressing chromatin remodeling, signaling pathways, cellular homeostasis regulation, alkaloid biosynthesis pathway and alpha-linolenic acid metabolism. However, the suppression of photosynthetic pathway and external stimulus responses were observed upon rust infection in the susceptible genotype. In particular, this first report of comparative transcriptome analysis offers an insight into the strength and weakness of Aegilops against leaf rust and exhibits a pipeline for future wheat breeding programs.

Genomic characterization of Puccinia triticina using molecular marker technology.

Leaf rust, caused by Puccinia triticina, is the most common rust disease of wheat. The fungus is an obligate parasite capable of producing infectious urediniospores. To study the genetic structure of the leaf rust population 20 RAPD primers were evaluated on 15 isolates samples collected in Pakistan. A total of 105 RAPD fragments were amplified with an average of 7 fragments per primer. The number of amplified fragments varied from 1 to 12. GL Decamer L-07 and GL Decamer L-01 amplified the highest number of bands (twelve) and primer GL Decamer A-03 amplified the lowest number of bands i.e one. Results showed that almost all investigated isolates were genetically different that confirms high genetic diversity within the leaf rust population. Rust spores can follow the migration pattern in short and long distances to neighbor areas. Results indicated that the greatest variability was revealed by 74.9% of genetic differentiation within leaf rust populations. These results suggested that each population was not completely identical and high gene flow has occurred among the leaf rust population of different areas. The highest differentiation and genetic distance among the Pakistani leaf rust populations were detected between the leaf rust population in NARC isolate (NARC-4) and AARI-11and the highest similarity was observed between NARC isolates (NARC-4) and (NARC-5). The present study showed the leaf rust population in Pakistan is highly dynamic and variable.

General and Specific Combining Ability of Quality Protein Maize (Zea mays L.) Inbred Lines for Major Foliar Diseases, Grain Yield and Other Agronomic Traits Evaluated at Mid-altitude Agroecology of Ethiopia

Abstract: Despite the fact that maize is a crucial cereal crop for food security, several foliar diseases are the main threats and limitations maize production in Ethiopia, resulting in low yields, particularly quality protein maize (QPM). Accordingly, national maize research program of Ethiopia has released QPM maize varieties adapted to the mid-altitude, low moisture stress and highland agro-ecologies of the country. Nonetheless, the market share of these varieties is generally small due to these reason and other features that have limited their adoption by farmers. General and specific combining ability analysis is one of the powerful instruments in identifying the best combiners that may be used in crosses to accumulate biotic resistance and productive alleles. A line x tester analysis involving 36 crosses generated by crossing 9 selected maize inbred lines with 4 testers were evaluated for different desirable agronomic traits during 2019/2020 main season at Bako and Jimma. The purpose of the experiment were to determine the GCA and SCA combining ability of QPM inbred lines, adapted to mid altitude agroecology of Ethiopia for grain yield and major foliar diseases. The crosses were evaluated in alpha lattice design replicated 3 times. For analysis of days to silking interval, days to maturity, turcicum leaf blight, grey leaf spot, common rust disease severity index, and grain yield were recorded. Analyses of variances showed significant mean squares due to crosses for almost all the traits studied. GCA mean squares due to lines and testers were significant (P<0.05 or P<0.01) for most studied traits. SCA mean squares were also significant for most attributes and major foliar maize diseases across locations. The comparative importance of GCA and SCA variances observed in the current study for most studied traits. Inbred lines L1, L2, L5 and L8 exhibited negative and highly significant GCA effects for husk cover. From this conduct it can be decided that better performing hybrids, inbred lines with desirable GCA and cross combinations with desirable SCA effects for grain yield, major foliar maize diseases and other traits were successfully identified.

First report of stem rust, caused by Puccinia graminis, and crown rust, caused by Puccinia coronata var. avenae f. sp. avenae, on tall fescue (Festuca arundinacea) in Georgia, USA.

Stem rust, caused by Puccinia graminis, and crown rust, caused by P. coronata, are common rust diseases on cool-season grasses (Karakkat et al. 2018), for which long-distance spore dispersal was recorded in northern US (Harder and Haber 1992). During the summers of 2019 and 2020, severe infection of stem rust and crown rust was observed on > 60% of tall fescue (Festuca arundinacea) germplasm plants in a breeding nursery located at the University of Georgia, Griffin GA. Rust-infected leaves first presented uredinia pustules, then black telia towards the end of the season. The uredinia pustules of stem rust and crown rust were brick-red and, yellow and arranged along the host veins, respectively. The urediniospores were one-celled, round to ovoid and measured from 20.75±2.44 μm (crown rust) to 27±3.60 μm long (stem rust). The teliospores were two-celled and measured from 45.75±10.14 μm (stem rust) to 51.60±4.0 μm long (crown rust) (Leonard et al. 2005; Cummins 1971). Urediniospores of both rusts were collected from infected plants in the field in April of 2020 using a Piston vacuum pump (Welch by Gardner Denver Ltd.) and stored at -80 °C in 1.5 ml Eppendorf tubes. Genomic DNA was extracted by grinding the urediniospores in liquid nitrogen using mortar and pestle, followed by the cetyltrimethylammonium bromide method (Doyle and Doyle 1987). The internal transcribed spacer (ITS) region of the ribosomal DNA was amplified using the ITS5-ITS4 primers (White et al. 1990). BLASTn and phylogenetic analyses revealed that the sequence of stem rust (GenBank acc. no. MW430963) and crown rust (GenBank acc. no. MW431324) pathogens had >99% similarity with P. graminis (GenBank acc. no. HQ317538) and P. coronata var. avenae f. sp. avenae (clade V; Liu and Hambleton 2013) (GenBank acc. no. EU014044), respectively. Pathogenicity tests were conducted on the tall fescue cultivar 'Bandit'. For each rust, 12 pots (10 cm × 10 cm) were planted, each containing 13 seeds in a Sungro professional growing mix soil (Sun Gro Horticulture Distribution Inc.). The plant materials were kept in the greenhouse at 20°C/ 25°C (night/day),15-hrs of light, and watered twice a week for 4-weeks. Urediniospores were recovered from -80°C and allowed to acclimate at room temperature for 1 h. For each rust, 20 ml of suspension containing 1×105 urediniospores ml-1 and 5 μl of Tween-twenty (Agdia Inc. Elkhart, IN) were used to inoculate 6 pots; while 6 control pots were sprayed with sterile water. After inoculation, plants were allowed to dry for 1 h and then transferred to a dark chamber at 20°C and 90% of humidity for 12-15 h. At 10-days post inoculation, all inoculated plants developed rust symptoms identical to those observed in the field, whereas control plants had no symptoms. Stem and crown rust pathogens were re-isolated from the artificially inoculated tall fescue plants. Based on form, size, color and numbers of cells forming the spores, a 1947 Festuca elatior specimen from Georgia mentioning Puccinia coronata (Hanlin 1966), held at the Julian H. Miller Mycological Herbarium (Catalog No. GAM00013162), was discarded as an earlier record of P. coronata var. avenae and could have been misdiagnosed. Due to the fragile integrity of the original infected plant sample as well as the incipient infection, DNA identification was unsuccessful. To our knowledge, this is the first morphological, genetic and taxonomic report of P. graminis and P. coronata var. avenae f. sp. avenae on tall fescue in Georgia, USA.

Automatic Fuzzy Logic-Based Maize Common Rust Disease Severity Predictions with Thresholding and Deep Learning.

Many applications of plant pathology had been enabled by the evolution of artificial intelligence (AI). For instance, many researchers had used pre-trained convolutional neural networks (CNNs) such as the VGG-16, Inception, and Google Net to mention a few, for the classifications of plant diseases. The trend of using AI for plant disease classification has grown to such an extent that some researchers were able to use artificial intelligence to also detect their severities. The purpose of this study is to introduce a novel approach that is reliable in predicting severities of the maize common rust disease by CNN deep learning models. This was achieved by applying threshold-segmentation on images of diseased maize leaves (Common Rust disease) to extract the percentage of the diseased leaf area which was then used to derive fuzzy decision rules for the assignment of Common Rust images to their severity classes. The four severity classes were then used to train a VGG-16 network in order to automatically classify the test images of the Common Rust disease according to their classes of severity. Trained with images developed by using this proposed approach, the VGG-16 network achieved a validation accuracy of 95.63% and a testing accuracy of 89% when tested on images of the Common Rust disease among four classes of disease severity named Early stage, Middle stage, Late Stage and Healthy stage.

Preliminary Screening of Maize Accessions Against Common Rust Disease (<i>Puccinia sorghi</i> Schw) in Arsi Negele District, Ethiopia

Maize is one of the most important crops in Ethiopia. The production of the crop is threatened by a number of biotic and a biotic factor. Among biotic factors, common rust caused by Puccinia sorghi Schw, is one of destructive foliar diseases of maize in Ethiopia. A study was conducted during the main cropping season (April to November, 2016) in the field at Arsi Negele research farm, Ethiopia with the objective of screening 92 maize accessions and 2 farmer’s verities checks against common rust disease. The experiment was laid out in augmented design with no replications. Disease assessment was done as percentage of leaf area infected on individual plant at 15 days intervals starting from 55 days after planting to cropping season for 5 times. The mean values of disease incidence, severity and AUDPC were calculated and yield recorded. The higher disease percent severity and AUDPC, least yield and thousand seed weight were observed from accessions, AN-239620, AN-9195, AN-9988, AN-9991, AN-15459, AN-15460, AN-16021, AN-18121, AN-18122 and Check-1 with mean values (63.94%, 1694.5%-in days, 3.04 to 3.69 t/ha and 240 to 297g) respectively and categorized in moderately susceptible group. Conversely, the minimum percent disease severity, AUDPC, higher yield and thousand seed weight were recorded from accessions, AN-16559, AN-9987, AN-16571, AN-18104, AN-18106, AN-18121, AN2-4297, AN-913, AN-15325 AN-15326, AN-15461, AN-16276, AN-16278, AN-241584 and AN-162383, with mean values of (31.01%, 720.4%-in days, 4.81 to 5.59 t/ha and 380 to 442g) respectively and grouped in resistant category. Therefore, accessions recorded low percent disease severity and AUDPC values could be used as the resistant varieties and source of resistance to common rust for varietal development of maize.

Benefits of maize resistance breeding and chemical control against northern leaf blight in smallholder farms in South Africa

Maize underpins food security in South Africa. An annual production of more than 10 million tons is a combination of the output of large-scale commercial farms plus an estimated 250 000 ha cultivated by smallholder farmers. Maize leaves are a rich source of nutrients for fungal pathogens. Farmers must limit leaf blighting by fungi to prevent sugars captured by photosynthesis being ‘stolen’ instead of filling the grain. This study aimed to fill the knowledge gap on the prevalence and impact of fungal foliar diseases in local smallholder maize fields. A survey with 1124 plant observations from diverse maize hybrids was conducted over three seasons from 2015 to 2017 in five farming communities in KwaZulu-Natal Province (Hlanganani, Ntabamhlophe, KwaNxamalala) and Eastern Cape Province (Bizana, Tabankulu). Northern leaf blight (NLB), common rust, Phaeosphaeria leaf spot, and grey leaf spot had overall disease incidences of 75%, 77%, 68% and 56%, respectively, indicating high disease pressure in smallholder farming environments. NLB had the highest disease severity (LSD test, p<0.05). A yield trial focused on NLB in KwaZulu-Natal showed that this disease reduced yields in the three most susceptible maize hybrids by 36%, 71% and 72%, respectively. Eighteen other hybrids in this trial did not show significant yield reductions due to NLB, which illustrates the progress made by local maize breeders in disease resistance breeding. This work highlights the risk to smallholder farmers of planting disease-susceptible varieties, and makes recommendations on how to exploit the advances of hybrid maize disease resistance breeding to develop farmer-preferred varieties for smallholder production.
 Significance:
 
 Northern leaf blight, grey leaf spot, Phaeosphaeria leaf spot and common rust diseases were widespread in KwaZulu-Natal and Eastern Cape smallholder maize fields where fungicides were not applied.
 NLB was the most severe maize leaf disease overall.
 NLB caused maize leaf blighting, which reduced grain yields by 36–72% in susceptible maize hybrids.
 Maize resistance breeding has produced locally adapted hybrids that do not have significant yield losses under NLB disease pressure.

Agronomic performance and severity of common rust in maize under different nitrogen sources

Nitrogen is the most required and complex management element in maize crop, promoting the highest responses in crop yield. The objective of this work was to verify the effect of different N sources on topdressing in minimum tillage and conventional tillage systems on the agronomic performance of the Pioneer 32R22YHR single cross and on the severity of common rust disease. Two experiments were carried out in a randomized block design (DBC) in the 2013/14 crop in minimum tillage and conventional tillage systems. The treatments were: control without nitrogen, ammonium sulfate, urea, ammonium nitrate, a physical mixture of nitrate (70%) and ammonium sulfate (30%) and a chemical mixture of these same sources in the same proportion just explained. Nitrogen sources had no significant effect on plant height, ear insertion height, ear prolificacy, grain yield and leaf severity of common rust, regardless of the sowing system. Under conventional tillage, the plants presented higher plant height, ear insertion and grain yield. There was no effect of sowing systems on prolificacy. With the exception of nitrogen free treatment, for all others, the severity of common rust was higher in minimum tillage system.

Potential occurrence of Puccinia sorghi in corn crops in Paraná, under scenarios of climate change.

In the face of climate change scenarios, it is important to evaluate the possibility of an increase in the incidence of corn crop diseases and to promote studies aimed at creating mitigation measures. This paper aims to study the impacts that regional climate changes may have on the potential occurrence of corn common rust (Puccinia sorghi), in the region of Castro, Paraná (Brazil). The Eta climate model was driven by the global model CanESM2. We use the Historical simulation of the EtaCanESM2 model from 1981 to 2005, and future projections from 2046 to 2070 to simulate the occurrence of common rust. The criteria was adopted to simulate the common rust disease favored in environments with the minimum temperature lower than 8 °C, the maximum temperature higher than 32 °C, average temperature between 16 and 23 °C, and relative humidity higher than 95%. In Brazil, there are two different seasons for corn crop (Normaland Safrinha). Results show that relative humidity and minimum temperature simulated by the model presented good skills, approaching the observed data. Compared to the Historical simulation, the projections show a tendency to increase of maximum and minimum temperature in the future, and a tendency to decrease relative humidity. There is an increase in the number of days with the potential for the occurrence of the disease. The distribution of days with favorable conditions to rust disease tends to change in the future. In the Normaland Safrinhaseasons, there is a tendency to increase the number of days with favorable conditions to common rust occurrence. The influence of planting time is greater in Historical simulation when compared to future scenarios. The Safrinhaseason may present more days with the potential for the occurrence of common rust in the future than the Normalseason.

Diversity of virulence phenotypes among annual populations of Puccinia triticina originating from common wheat in Israel during the period 2000–15

Leaf rust, caused by the fungus Puccinia triticina, is the most common rust disease of wheat in wheat‐producing areas worldwide. The Israeli population of P. triticina has been consistently monitored since 1993. A total of 784 single urediniospore isolates from Triticum aestivum were analysed during 2000–15. The structure of the pathogen population has changed to a large extent since 2000. The annual populations of P. triticina were separated into two distinct groups, 2000–11 and 2012–15, while populations of 2000–5 and 2006–12 were differentiated to a lesser extent. The change in the population originating from T. aestivum during the period 2000–15 is less significant compared to changes in the 1990s described previously. Diversity within the annual populations of P. triticina was rather stable during the period studied. Three new pathotypes, characterized by virulences on Lr3ka and Lr30 genes, became dominant between 2012 and 2015, while all but one prevailing pathotypes in 2000–11 were avirulent on these two genes. Significant changes in virulence frequencies on a number of Lr genes (Lr2c, Lr3ka, Lr15, Lr21, Lr23, Lr26, Lr30) and pairwise associations of virulences (mainly with Lr2c and Lr26) were registered in 2012–15 or earlier. It is postulated that the composition and pathotype structure of the P. triticina population in Israel is determined by wind‐disseminated urediniospores from neighbouring regions, where the migration of P. triticina from the eastern part of the Mediterranean Sea and from the Horn of Africa seem to have the greatest influence.

Application of High Density Linkage Map Derived from Genotyping by Sequencing for Detection of QTL Conferring Resistance to Leaf Rust Races Spread in Egypt

Wheat is a major source of carbohydrates in Egypt, leaf rust disease is known to be the most common rust disease affected wheat genotypes. This study aimed to apply a constructed high density linkage map through Genotyping-by- sequencing (GBS) for detection of QTL resistant to important leaf rust races spread in Egypt. The applied map contained 3,641 markers distributed on 21 chromosomes and spanned 1,959 cM with an average distance of 1.8 cM between markers. A mapping population of 204 RILs (F6:8) obtained from the cross between two parents of winter wheat ‘Harry’ x ‘Wesley’ through single seed decent method was used to identify QTL region associated with leaf rust resistance genes in wheat. Under the Green house condition in Egypt leaf rust pathotypes i.e NTTJT, PTTGS, PTTTT, TTTBT and TTTTT were used. High-density linkage map based on GBS derived SNPs were applied in this study for QTL mapping. The wheat genotype Harry was resistant to all tested pathotype while, the wheat genotype Wesley was susceptible to all tested pathotype. One major stable QTLs, for race NTTJT was identified on chromosome 6A flanked by markers XSNP3958 and XSNP3957 with a LOD 4.22. The identified SNP marker may be used to screen for resistance to specific races of leaf rust found in Egypt in further spring wheat breeding programs as marker assisted selection.

English

The genetic potentials of resistance to turcicum leaf blight (TLB), grey leaf spot (GLS), and common rust (CR) disease, grain yield and selected agronomic trait were studied in 45 F1 hybrids from a half diallel following Griffing’s Model 1, Method 4. The 45 hybrids excluding parents were evaluated in 5 × 9 alpha lattice designs with three replications. The study was carried out at Jimma Agricultural Research Center during 2015 cropping season with the objective to evaluate combining ability for turcicum leaf blight, grey leaf spot, common rust disease, grain yield and selected agronomic trait in maize inbred lines. For analysis of variance, days to 50% anthesis, days to 50% silking, turcicum leaf blight, grey leaf spot, common rust disease severity index, days to maturity and grain yield data were collected. Mean square due to general combining ability (GCA) was highly significant (P ≤ 0.01) for all traits, while specific combining ability (SCA) mean square was non-significant except for grain yield, days to 50% tasseling, days to 50% of silking, and days to maturity. This study showed the importance of additive types of gene action in controlling the inheritance of the traits. Among ten inbred lines, L7 and L10 were best combiners for GLS tolerance with the highest negative value of GCA effects and inbred line L7 was the best combiner for TLB and CR tolerance with the highest negative value of GCA effect. Inbred lines L2 and L9 were best combiner for grain yield with the highest positive GCA effect value. Therefore, maize breeding program can engage in hybridization and synthetic variety formation based on the information of inbred lines with high negative value GCA effect for diseases tolerant and high GCA for grain yield. Key words: Combining ability, general combining ability (GCA), inbred lines, specific combining ability (SCA).

English

Leaf rust (Puccinia triticina Eriks) is the most common rust disease of wheat in wheat-producing areas of Ethiopia. The use of cultivars with durable resistance is the most economical way of controlling the disease. Field experiments were conducted at Ambo Plant Protection Research Center, Ethiopia during 2013 to 2014 main cropping seasons to reveal variability for field based slow rusting resistance to leaf rust among 18 improved wheat cultivars grown in Ethiopia. Parameters used as criteria to identify slow rusting included final rust severity (FRS), coefficient of infection (CI), relative area under disease progress curve (rAUDPC) and infection rate (Inf-rate). Among these parameters, FRS, CI and rAUDPC were found to be reliable to assess slow rusting in the cultivars. The results revealed that wheat cultivars Pavon 76, Africa Mayo, Bonny, Galili, Qulqulu, Hawi and Senqegna had low disease severities ( 30%) and CI (< 20) and were identified to have good level of slow rusting resistance. Cultivars Kubsa, Galama and PBW 343 had moderate values for slow rusting parameters and were identified as possessing moderate level of slow rusting. The slow rusting cultivars identified from the current study can be used for further manipulation in wheat improvement programs. Key words: Leaf rust, Puccinia triticina, resistance, slow rusting, wheat.

English

Common rust incited by Puccinia sorghi Schw. is the most destructive fungal foliar disease of maize worldwide. It is reported that common rust diseases can greatly reduce grain yield of maize in susceptible genotypes by 40% on an average. Foliar disease management in maize often involves indiscriminate use of chemicals or total reliance on host plant resistance (HPR). Integrated disease management (IDM) have clearly demonstrated that when moderate levels of HPR are combined with field treatment and affordable levels of chemical control, expected yields and economic returns are higher than obtained with chemical control of susceptible genotypes. Local agronomic practices were followed during the same period of investigation. Foliar application of Tebuconazole @ 0.1% at 35 and 50 DAS, that is, T1 was significantly superior and highly effective in reducing the disease severity (19.74%) and gave maximum grain yield (66.87 q/ha). The next best treatment was foliar application of Hexaconazole @ 0.1% at 35 and 50 DAS (28.23%) followed by foliar application of Tebuconazole @ 0.1% at 35 DAS and Neemazole F 5% at 50 DAS. The study suggests that any technology developed for maize should offer a clear yield and foliar disease resistance advantage over farmers’ current practices. Key words: Botanicals, common rust, field evaluation, fungicides, integrated disease management, Puccinia sorghi, Zea mays.

Molecular Detection of Resistance Genes to Leaf Rust Lr34 And Lr37 in Wheat Germplasm

Abstract Leaf rust, caused by Puccinia triticina , is the most common rust disease of wheat. Using molecular markers technology, with a wide variety of approaches, can improve the efficiency of the selection strategies in wheat breeding programs. One of the most known resistance gene to leaf rust is Lr34 , involved in adult plant resistance (APR) or “slow rusting” type. In order to obtain cultivars with good levels of protection several resistant gene complexes need to be combined. Another gene that confers resistance to a wide range of races of Puccinia triticina , is Lr37 , originated from Triticum ventricosum , 2NS chromosome. Our study was focused on detection of the Lr34 and Lr37 genes in 50 wheat breeding lines using molecular markers. The molecular assay showed the presence of Lr34 resistance allele in 62% (homozygous genotypes) while the Lr37 resistance allele was detected in 40% of the total genotypes analysed. Also, we found one line that carries both resistance alleles.

Diversity of virulence phenotypes among annual populations of wheat leaf rust in Israel from 1993 to 2008

Leaf rust, caused by the fungus Puccinia triticina, is the most common rust disease of wheat in wheat‐producing areas worldwide. The Israeli population of wheat leaf rust has been consistently monitored since 1993. A total of 840 single urediniospore isolates from Triticum aestivum (567), T. dicoccoides (119) and T. durum (154) were analysed during 1993–2008. The structure of the pathogen population has changed to a large extent since 1993. The annual populations of P. triticina were separated into two distinct groups: 1993–1999 and 2000–2008. Differentiation among the annual pathogen populations, as well as between the overall populations of the 1990s and 2000s, could be mainly attributed to the following forces: (i) migration of leaf rust urediniospores from neighbouring regions; and (ii) selection pressure of new yellow rust‐resistant wheat cultivars that have been introduced into Israel since 1997. Genetic multiplicity of wild emmer contributes to P. triticina variability in Israel. Leaf rust populations collected from common wheat, wild emmer and durum wheat differed. The population that originated from T. durum was rather stable during the years of the survey, whereas that from T. aestivum changed significantly from the 1990s to the 2000s. Diversity within the annual populations of P. triticina was highest in 1994 when many new pathotypes and associations between virulences were observed. Single‐step derivatives of the new pathotypes became dominant after 2000. Significant changes in virulence frequency to a number of Lr genes (e.g. Lr2a, Lr15, Lr17, Lr21, Lr26) were also registered in 2000–2008.

Random amplified polymorphic DNA (RAPD) polymorphism in Puccinia sorghi Schw. causing common rust of maize

An experiment was conducted at University of Agricultural Sciences, Dharwad, Karnataka to detect molecular variation in Puccinia sorghi Schw. through molecular tool viz., random amplified Polymorphic DNA (RAPD). In this study, molecular variation in the pathogen served as a guideline for breeding suitable maize varieties against common rust disease which seriously affects maize productivity. It was reported that losses in total yield ranged from 0 in the more resistant entries to nearly 50% in more susceptible entries. Losses in total yield in late-planted sweet corn were 18, 26, and 49% for cv. Sugarloaf (most resistant), cv. Jubilee (intermediate) and cv. Style Pak (most susceptible), respectively. Results revealed that a variety of polymorphic bands were found from the specimens by polymerase chain reaction (PCR) amplification using 10 primers: OPA-19, OPB-08, OPB-15, OPB-17, OPC-08, OPD-07, OPD-13, OPD-18, OPF-02 and OPG-05. These bands were used to construct unweighted pair group method with arithmetic mean (UPGMA) dendogram, which cluster analysis divided the 15 specimens into major 2 groups: Groups A and B. Out of 10 primers used, 3 primers viz., OPA-19 (11.11%), OPB-17 (20%) and OPF-2 (14%) showed polymorphism. The similarity coefficient values revealed that, the least similarity (81%) was between Tamil Nadu-Andhra Pradesh, Haryana-Tamil Nadu and Madhya Pradesh-Haveri isolates. The maximum similarity (100%) was found between Andhra Pradesh-Haryana and Belgaum-Jammu and Kashmir isolates. Bihar isolate formed entirely separate cluster within Group A, whereas Tamil Nadu-Maharashtra and Bijapur-Haveri isolates formed separate clusters within Group A. In Group B, Sikkim, Uttar Pradesh, West Bengal and Bengaluru isolates formed entirely separate clusters, respectively. Key words: Genetic variability, Zea mays, common rust, Puccinia sorghi, random amplified polymorphic DNA (RAPD).