The objective of the present study was to investigate to what extent the macroscopic phenotype of incompatible host–pathogen interactions reflects differences in fungal development and host responses at the histological level. This was done by conventional and advanced microscopic analysis of six wheat near‐isogenic lines differing by individual R genes and inoculated with an avirulent isolate of Puccinia striiformis. Wheat line AvocetYr15 had the lowest macroscopic infection type (IT) 0–1, in which fungal growth was stopped at early stages due to extensive expression of a hypersensitive response (HR) at all time points (4, 8 and 16 days post‐inoculation, dpi) without any sign of haustorial bodies. AvocetYr5 and AvocetYr1 had IT 1, in which most fungal colonies developed secondary hyphae. Many colonies were encased by HR at 16 dpi, more extensively in AvocetYr1 than AvocetYr5. In AvocetYr6 (IT 2), HR was expressed after the formation of secondary hyphae at 4 dpi, after which fungal growth and HR increased simultaneously until most colonies became encased by HR. AvocetYr27 (IT 2–3) and AvocetYr17 (IT 4–5) showed similar fungal growth and HR at 4 dpi, where HR was only weakly expressed in a few host cells. Encasement of secondary and runner hyphae increased significantly in AvocetYr27, but at 16 dpi, HR was often circumvented by large, intermingled fungal colonies in both lines. No resistance responses were observed in Avocet S (susceptible control). The very different histological patterns conferred by the six R genes suggests differences in the timing of the host–pathogen recognition and onset of host defence pathways.
Plants and their pathogen co-evolved simultaneously and therefore survive either through symbiotic or parasitic interaction. With the human civilization and increasing population, food security and food safety are of major concern. For achieving that, plants are being modified to attain maximum yield and minimum loss. Therefore, in reaction pest and pathogens also mutate themselves to evolve new tools and weapons for feeding and infection. In this race, plants have to defend for attaining yield and reproduction. Plants are blessed with many structure which minimize entry of pathogens specially cell wall, spines and thorns. Furthermore, biochemical defense in plants is highly sophisticated with many antimicrobial compounds, which trigger whole plant system to defend. Many genes incorporated in crop plants also lead to enhance biochemical defense through elicitors- receptors interaction. On the other hand, pathogens utilized toxins, enzymes, growth regulators and polysaccharides to suppress the host defense system and breakdown the resistance barriers. So its continuous race between host and pathogen but through details study and understanding of such interaction, better management strategies can be deployed.
Background: Bacterial leaf blight (BLB) of rice occupies the most significant position among various potentially important bacterial diseases all over Pakistan. The first important step towards the management of this disease is the characterization of the pathogen. Methods: Survey was conducted and disease samples were collected from 9 different locations of Punjab. Isolation and characterization by biochemical tests was done from the diseased samples under standard conditions in the laboratory. For pathogenicity and virulence characterization, all isolates were inoculated on IR-24, Basmati super and Basmati-2000 varieties. Data was recorded after three weeks of inoculation. Results: 30 isolates of Xanthomonas oryzae pv. oryzae ( Xoo ) were purified from the diseased plants of different geographical origin which had very similar morphological and biochemical characteristics. PXo-20 (causing 51.35% leaf damage) and PXo-16 (causing 50.05% leaf damage) were found most virulent for Basmati Super and Basmati-2000. Conclusion: The presence of highly virulent isolates in Sheikhupura is alarming and there is dire need to incorporate new resistance genes in commercial rice cultivars to cope with BLB.
Phytotoxic ability of aqueous extracts of new and old mango leaves at different concentrations i.e., 2.5, 5.0, 7.5 and 10% against canary grass and wheat were tested In vitro and In vivo. Results revealed that all the extracts significantly inhibited the germination and growth of canary grass In vitro as well as In vivo. Maximum inhibition i.e. more than 80% to all the parameters of canary grass was observed by 10% extract In vitro. In pot experiment 66% reduction, in the dry weight of canary grass was observed when the old leaves water extract was applied before emergence. All the treatments showed non significant results about the germination of wheat In vivo. Old mango leaves extract was found better as compared to new ones, because it moderately enhanced the wheat germination and growth, while new mango leaves induced some reduction regarding the shoot length and grain weight of wheat. Total phenolic contents were higher in new mango leaves as compared to old ones. 4-hydroxybenzaldehyde, m-coumaric, p-coumaric, 4-hydroxy benzoic, vanillic, caffeic, gallic and protocatechuic acids were phenolic compounds identified through Mass Spectrometry and High Performance Liquid Chromatography analyses of mango leaves. It has been concluded that old mango leaves extract could be used as a herbicide to suppress canary grass and to enhance wheat growth.
Bacterial leaf blight (BLB) of rice, the most notorious and horrendous disease of rice, caused by Xanthomonas oryzae pv. oryzae (Xoo) andcontinue to evolve covering more area and rice cultivars. Keeping in view the escalating virulence in pathogen population, current study was conducted to determine the genetic diversity in pathogen population and to search new sources of resistance in rice germplasm. The samples collected during the survey from different rice growing areas of Punjab were provided by the Rice Pathology group of NIAB. Then these samples were plated to isolate and purify the pathogen causing bacterial blight disease Xanthomonas oryzae pv. oryzae. The genetic diversity of the pathogens from different areas of the Punjab was determined through the repetitive DNA element with primers JEL1 and JEL2. During this study, twenty seven (27) varieties/lines were screened for resistance under artificial inoculation conditions against BLB. Plants were artificially inoculated by clipping method with the Xoo culture. After isolation and purification of pathogen, 9 isolates were selected for genetic diversity. DNA-Fingerprinting of 9 local isolates of Xoo generated with IS1112 based primers Jel1and Jel2, reveal great variability among themselves. The dendrogram showed two main groups A and B. In group A isolates 1, 3 and 5 have 86% similarity while in group B isolates 9 and 8 are 100% similar and 90% similar to 7 and isolate 6 is 87% similar to 4. Where isolate 2 is 82% similar to isolates 4,6,7,8 and 9. In comparison of group A and B they are 65% similar to each other. In search of resistance source against BLB, none of the variety/line out of 27 was found immune, highly resistant, resistant or moderately resistant to bacterial leaf blight disease. Only one variety/line was moderately susceptible, five were susceptible and twenty one were highly susceptible to BLB disease. The results of this study seem to be very helpful for deploying effective management of BLB disease. The information can be utilized in controlling the bacterial leaf blight disease in Pakistan that can save the economic and production losses of rice crop that are increasing every year.
Background : Barley yellow dwarf in wheat is an important viral disease among wheat cultivating areas of the world. It is gradually progressing as a major threat to wheat crop in Pakistan due to availability of favorable environmental conditions. The use of resistant cultivar is environmentally safest method for disease control so, it is necessary to develop resistant cultivars before epidemic outbreaks. Methods: The most commonly used wheat variety Inqilab91 was crossed with BYDV / CYDV resistant variety TC14. F1 generation obtained from the P1 cross was then allowed to self-cross. 61 plants were selected from F2 generation on THE BASIS OF disease tolerance or susceptibility and only tolerant plants were included for further experiments in the study. The presence of BDV2 among F2 generation was confirmed by sequence characterized amplified region (SCAR) markers in 6 (91, 96, 110, 119, 121 and 131) out of 61 genotypes which were then backcrossed with recurrent parent. Advance analysis regarding the presence of resistance source among the selected F2 generation was carried out using ELISA. Moreover, appearance of symptoms, agronomic values for different parameters, green house and field responses were also kept under consideration to characterize and confirm the presence of BDV2 among plants. Results: Results indicated that majority of F2 segregating population showed less yellowing, low viral titer and good agronomic values. ELISA value, glasshouse and field analysis showed that seven genotypes (30, 81, 89, 91,101,110 and 121) were resistant, and twenty-four genotypes were found moderately resistant. Tolerance was detected in genotypes 31, 47, 48, 50, 52, 56, 57, 60, 61, 94, 103, 106, 113, 115, 127, 140 and 413. Conclusion: Wheat lines containing Bdv2 genes showed resistance in both field and glasshouse. These wheat germplasm could be used as a source of resistance in CDRP-NARC for the further development of resistant wheat varieties against BYDV / CYDV .
The objective of the present study was to investigate what extent the leaf rust disease severity affects the photosynthesis and grain yield in wheat. This was done by estimating disease severity, photosynthetic rate, chlorophyll contents and grain yield loss in six wheat varieties under the natural and fungicide treated conditions. Among six wheat varieties/lines (Galaxy-13, Millat-11, Lasani-08, Faisalabad-08 and two wheat lines NW-1-8183-8 and NW-3-3341-7), the mean severity level of leaf rust was the highest on Galaxy-13 and Faisalabad-08, however, grain yields were also higher in Galaxy-13, Millat-11 and FSD-08. Wheat lines NW-1-8183-8, NW-3-3341-7 and wheat variety Millat-11 showed less severity with high yield. One application of fungicide, propiconazole reduced the rust infections significantly and enhance the photosynthetic rate and chlorophyll contents, resulting in significantly higher yield in fungicide treated plots. On the basis of leaf rust severity and grain yield assessment, wheat varieties Galaxy-13 and FSD-08 were found highly tolerant against rust diseases. Maximum cost-benefit ratio was found in NW-3-3341-7 (1:12.2) when treated against rust fungicide. The study concluded that rust disease significantly reduced the grain yield when not protected by fungicide. Integration of host resistance with minimum fungicide application can reduce the deleterious effect of leaf rust and gives maximum net returns.
Bacterial leaf blight (BLB) is one of the most damaging diseases of rice in Asia and annually incurring significant yield loss to rice production in Pakistan. Management of disease required the information of BLB incidence and severity in basmati and non-basmati rice areas. The current study presented the observation of BLB disease incidence and severity in 19 major rice growing districts of Punjab. In this study, 9 Basmati growing and 10 non-basmati rice growing districts were surveyed from September to October in 2009, 2010, 2012, and 2013. Rice fields near to roadside, research stations and adjoining farmer fields were preferred for the survey. Each halt was after 10 km on the route depending upon the crop intensity. The general appearance of the field was observed for the absence or presence of BLB disease symptoms. The incidence of BLB was recorded as a percentage of plants infected in a field on a visual basis. For each field, 4 plants were observed at 5 points/hill along the diagonal transect for disease symptoms. The data of severity was recorded as the percentage of leaf area infected out of the total leaf area. Among the districts with basmati rice, the mean incidence of BLB was maximum in Gujranwala, Sheikhupura and Hafizabad followed by Mandi Bahauddin and Gujrat. A similar pattern of disease severity was observed in the basmati rice belt with maximum BLB mean severity in Gujranwala, Sheikhupura and Hafizabad having most of the field with a severity scale of 9. Overall, the disease trend showed that both the incidence and the severity were higher in 2010, 2012 and 2013 in the basmati rice belt. The ten districts, comprising of mostly non-basmati rice varieties showed relatively less BLB incidence and severity compared to basmati rice districts. The maximum mean incidence of 20-25% was observed in Faisalabad, Chiniot and Sahiwal in at least one year of the rice season. None of the field with BLB disease symptoms was observed in districts Okara, Khanewal and Bahawalpur during the 2012 and 2013 rice season. Maximum disease severity of mean value 3 was observed in Sahiwal during 2009 while the rest of the districts showed less than 2 mean severity during all rice growing season. Overall, in non-basmati rice districts, no specific trend of disease incidence and severity was apparent, however, the disease was present in very low magnitude or absent during the surveyed years. The information from this study is helpful in the selection of variety for basmati and non-basmati districts of Punjab and the adoption of appropriate disease management strategies.
Barley yellow dwarf disease is globally the most important viral disease of wheat. The full-length nucleotide sequence of coat protein (CP) gene of 12 isolates revealed the presence of three distinct clusters. Pakistani isolate of MAV (MAV-PK) has maximum similarity of 99.23% with MAV isolate of Morocco and PAV-Australia following 99.22 and 99.22% with PAV-France. Similar degree of similarity was found in comparison of amino acid sequence. The finding of this study is that MAV-PK has similarity with both MAV-France and PAV-Australia, which is due to the reason that both MAV and PAV belong to the same group and both share maximum nucleotide homology. Low genetic diversity was found not only between MAV isolates but also between MAV and PAV isolates because phylogenetic analysis was done on the CP gene which is highly conserved region in genome of Barley yellow dwarf viruses (BYDVs). Divergence in MAV-PK was due to this recombination which is now most prevalent in Pakistan. MAV-PK has maximum similarity with MAV-Morocco followed by MAV-Sweden and MAV-Cz, which seems to indicate that Pakistani isolate of MAV evolved as the result of recombination between MAV isolates of the USA and PAV isolates of Australia and France. At the same time, recombination of MAV-CZ and MAV-Sweden also occur. This work can be successfully utilised in epidemiological studies of MAV isolate in Pakistan. Further analysis of variation level in these isolates will help scientists to formulate appropriate management strategies like incorporation of BdV 2 gene in wheat against BYDVs.
We characterized yellow rust (YR) resistance in sixteen winter wheat breeding lines using three different pathogen races and macroscopic and microscopic phenotyping in lab and greenhouse. Three rust races were used on seedlings and two races on fifth and flag leaf growth stages. The wheat lines were previously characterized to possess none or different quantitative trait loci for YR resistance in field trials. At the seedling stage, twelve lines showed race-specific seedling resistance whereas four lines gave strong seedling resistance to all three races. Seven of eight lines with QTL.1B showed strong seedling resistance against the two races also used at fifth and flag leaves. Microscopic phenotyping of line NOS50906215 (QTL.1B) showed small fungal colonies stopped within 3 dpi associated with extensive hypersensitive response (HR). The lines NOS51014910 and NOS51014911 (QTL.3D alone) showed strong adult plant resistance (APR) from the fifth leaf stage. The lines NOS70140801 and NOS70140808 (QTL.3D + 7B) showed strong APR to one race but partial resistance to the other race at all growth stages. Microscopic phenotyping of line NOS70140801 (QTL.3D + 7B) showed more fungal growth and less HR against the race revealing strong APR compared to the one revealing partial resistance. Line NOS51010312 (QTL.7B alone) showed strong APR response against both races whereas line NOS51010313 (QTL.7B) was susceptible. A partial APR response was observed on line NOS51005019 (no QTLs reported). In conclusion, the approach of combining macroscopic and microscopic phenotyping and diverse pathogen races facilitates the identification of multiple and diverse seedling and adult plant resistance responses to yellow rust in wheat.
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