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1.
The pathogenicity of Alternaria spp. isolated from wheat leaves collected in regions where alternaria leaf blight has been reported was compared with that of IMI reference isolates of A. triticina and A. alternata using two durum and two bread wheat genotypes. To identify isolates putatively corresponding to A. triticina , morphological and DNA sequence analyses based on ribosomal DNA from the internal transcribed spacer (ITS) region (ITS1, 5·8S rRNA gene, ITS2) and toxicity bioassays of culture filtrate were combined. Glasshouse inoculations provided reliable information to assess the pathogenicity of A. triticina isolates on wheat. Alternaria leaf blight symptoms were produced by the A. triticina isolates only on durum wheat cv. Bansi, while A. alternata , A. tenuissima and A. arborescens isolates were found to be nonpathogenic on the wheat cultivars tested. Alternaria triticina isolates were distinguished from other Alternaria species by Simmons and Roberts' sporulation pattern 6 and two to three conidia per sporulation unit associated with primary conidia bearing long (> 7 µ m) apical secondary conidiophores. Phylogenetic analysis also proved effective at discriminating wheat-pathogenic A. triticina from other nonpathogenic Alternaria species. Alternaria triticina isolates yielded longer ITS sequences than A. alternata , A. tenuissima and A. arborescens isolates, leading to clear-cut differences as visualized with agarose gel electrophoresis. Additionally, only culture filtrates of A. triticina isolates caused nonspecific necrotic lesions on leaves of 3-week-old wheat plants. 相似文献
2.
The role of potassium in sustaining yields in a long-term rice-wheat experiment in the Indo-Gangetic Plains of Nepal 总被引：2，自引：0，他引：2
A. Regmi J. Ladha E. Pasuquin H. Pathak P. Hobbs L. Shrestha D. Gharti E. Duveiller 《Biology and Fertility of Soils》2002,36(3):240-247
A long-term soil fertility experiment (1988-1999) at the Regional Agricultural Research Station, Bhairhawa, Nepal, was analysed to determine: (1) how long the yields of rice (Oryza sativa L.) and wheat (Triticum aestivum L.) can be sustained without K but with N and N+P (NP) applied with or without farmyard manure (FYM) and green manure, and (2) the impact of K application on yields. Starting from the 1995 wheat season, the experiment was modified to accommodate K at 0, 42, and 84 kg ha-1 in plots receiving NP to study the response of rice and wheat to K. Both rice and wheat responded to K application but the response of wheat was substantially higher, indicating that the availability of native K may have been lower in wheat. Rice yields were lower in treatments without P than with P, and yields declined significantly (0.11-0.20 Mg ha-1 year-1) in all the treatments except in NP and NP+FYM. Wheat yield was more adversely affected than rice yield when P and K were not applied. In addition, wheat yields were low (average 0.5-2.1 Mg ha-1 in various treatments). Wheat yields declined (0.08-0.12 Mg ha-1 year-1) in all but FYM treatments indicating the role of FYM in sustaining yields. The interaction of K deficiency with Helminthosporium leaf blight (spot blotch and tan spot) is also suggested as one of the factors limiting wheat yields. The estimated K balance in soil was highly negative. Results suggest that farmers should apply adequate amount of K for higher and sustainable rice and wheat yields. 相似文献
3.
Identification and characterization of international Fusarium head blight screening nurseries of wheat at CIMMYT, Mexico 总被引：1，自引：0，他引：1
Xinyao He Pawan K. Singh Etienne Duveiller Norbert Schlang Susanne Dreisigacker Ravi P. Singh 《European journal of plant pathology / European Foundation for Plant Pathology》2013,136(1):123-134
Fusarium head blight (FHB) is a major threat to wheat production globally, causing not only yield losses but also food and feed contamination. FHB research began at the International Maize and Wheat Improvement Center (CIMMYT) in the early 1980’s, and since then, large-scale FHB screening has been conducted to identify and incorporate new resistance genes into elite CIMMYT germplasm. Promising lines with good FHB resistance were regularly compiled as a Fusarium Head Blight Screening Nursery (FHBSN) and distributed worldwide. The first FHBSN was assembled in 1985, and the most recent two were the 13th and 14th FHBSN that were released in 2011 and 2012, respectively. Candidate lines for a FHBSN came mainly from different CIMMYT wheat breeding programs and were tested for three consecutive years before being included in an FHBSN. FHBSN screening was conducted under strictly standardized field conditions at El Batán, where CIMMYT headquarters is located, using artificial inoculation of F. graminearum strains, whose aggressiveness and DON chemotypes had been previously identified. FHB index was scored at 31 days after inoculation for all lines and DON concentration was measured only for elite lines in their 2nd and 3rd year of evaluation. Haplotyping is a new tool for genetic characterization of FHBSN entries and helps to identify new resistance sources with novel resistance genes and to better target crosses toward diversifying and/or pyramiding resistance. The 13th FHBSN was taken as an example in this paper to show the procedure and strategy for the development of new FHB resistant lines. 相似文献
4.
Spot blotch, caused by Cochliobolus sativus, is a serious constraint to wheat production (Triticum aestivum L.) in the warmer plains of South Asia. Fourteen genotypes were tested in Bangladesh, India and Nepal during 6 years (2000–2005) to determine disease severity and resistance stability over these years. We analyzed the area under the disease progress curve per day (AUDPC/day) to assess spot blotch severity, and examined grain yield, 1000-kernel weight (TKW), days to heading, and plant height. Disease severity differed in the 6 years and several genotypes showed low disease severity in all years. A few genotypes had high grain yield and low disease severity in all years. Genotype Altar-84/Ae. Sq. (224)//Yaco, with the lowest disease severity and highest 1000-kernel weight (TKW) and grain yield was also the most stable for spot blotch resistance, TKW and grain yield. Results demonstrated that wheat genotypes with improved spot blotch resistance, high grain yield, acceptable TKW, and plant height are available as a result of the regional and international collaboration in South Asia. Despite this progress, the challenge lies ahead because of an apparent tendency of increasing spot blotch overall severity in the region and decreasing TKW over 6 years (2000–2005). Higher, average night time temperature during the month of March is an indicator showing that wheat crop performance is challenged in two ways—increasing spot blotch severity and decreasing TKW causing lower yield. The results underline the possible effect of changing climatic factors on disease pressure and the continuous need to identify new resistance sources to develop more spot blotch resistant wheat for the warmer Eastern Gangetic Plains of South Asia. 相似文献
5.
Pathogenicity of Bipolaris sorokiniana isolates from wheat roots, leaves and grains in Mexico 总被引：1，自引：0，他引：1
Pathogenicity of 27 Bipolaris sorokiniana isolates from roots, leaves and grains of spring wheat, collected at a site in Mexico, showed no clear differences between groups of isolates, based on lesion density after seedling inoculation of the susceptible cultivar Ciano T-79 under controlled conditions. Results were variable when tests were repeated over time or in experiments using a smaller number of isolates. The lesion number per leaf was significantly different depending on the isolate used for inoculation, irrespective of the plant part group. No difference was found between individual isolates when pathogenicity was assessed using a disease severity scale. No cultivar–isolate interaction was observed for lesion density when 12 isolates were tested on six cultivars, but there were some significant differences between cultivars and between isolates. Results obtained confirmed that infection by B. sorokiniana is highly variable, and very sensitive to environmental conditions. In this study no physiological specialization was observed. The fungus appeared as a continuum of isolates differing in aggressiveness. This work was conducted with isolates from a single site, and highlights the need to assess carefully the biological significance of any differences observed among B. sorokiniana isolates. 相似文献
6.
Helminthosporium leaf blight resistance and agronomic performance of wheat genotypes across warm regions of South Asia 总被引：5，自引：0，他引：5
R. C. Sharma E. Duveiller F. Ahmed B. Arun D. Bhandari M. R. Bhatta R. Chand P. C. P. Chaurasiya D. B. Gharti M. H. Hossain A. K. Joshi B. N. Mahto P. K. Malaker M. A. Reza M. Rahman M. A. Samad M. A. Shaheed A. B. Siddique A. K. Singh K. P. Singh R. N. Singh S. P. Singh 《Plant Breeding》2004,123(6):520-524
Helminthosporium leaf blight (HLB) is the most important disease constraint to wheat (Triticum aestivum L.) cultivation in the eastern Gangetic Plains of South Asia. A Helminthosporium Monitoring Nursery (HMN) including potential adapted and exotic sources of HLB resistance was developed in Bangladesh, India and Nepal to assess the stability of genetic resistance across locations. The 8th, 9th and 10th HMN assessed the HLB resistance and agronomic traits of 17 wheat genotypes across 20 environments of Bangladesh, India and Nepal in the 1999‐2000, 2000‐2001 and 2001‐2002 cropping seasons, respectively. The area under the disease progress curve (AUDPC) for HLB, grain yield, thousand‐kernel weight (TKW), days to heading, days to maturity, and plant height were examined. The 17 genotypes showed a range of variability for disease and agronomic characters. Disease severity (AUDPC) differed in the 3 years and showed the highest values in 2002. The increase in AUDPC in 2002 caused the lowest grain yield, with an average 18% reduction due to HLB. A few genotypes (SW 89‐5422, Yangmai‐6 and Ning 8201) appeared to have stable HLB resistance across environments. However, most of the higher‐yielding genotypes, except BL 1883, were unstable. The results suggest that careful selection of HLB resistance with acceptable grain yield, TKW and plant height may be possible using the wheat genotypes included in the HMN. 相似文献
7.
Knowing pests and diseases that may cause injuries and are likely to affect plant health and quality is critical to minimizing
the gap between attainable yield and actual yield. In this paper, we highlight concepts and strategies aimed at controlling
major biotic constraints affecting wheat in intensive production systems and present emerging challenges, with a special attention
to the developing world. Disease epidemics result from the combination of inoculum, favorable environment, and host susceptibility.
Changes in cropping systems as a result of adoption of conservation agriculture may have serious implications. Necrotrophic
pathogens such as those responsible for tan spot or septorias are likely to emerge, and Fusarium head blight may increase. However, resistance breeding combined with rotations, timely sowing, and irrigation or even fungicide
utilization, if affordable, are part of integrated crop management practices that can minimize losses. In South Asia, the
effect of spot blotch, a devastating foliar disease caused by Cochliobolus sativus, can be minimized by reducing physiological stress through timely sowing and adequate use of fertilizers, which demonstrates
the complex relationships among crop physiology, disease resistance, and yield. Although some root rots that induce premature
death of tillers in cooler high-yielding humid environments can be important, the dryland crown rot (Fusarium spp.), common root rot (C. sativus), and the cereal nematode (Heterodera spp. and Pratylenchus spp.) should not be ignored. These are all known to be much more damaging under suboptimal moisture (rainfed or supplementary
irrigation), particularly where plant growth is stressed. Climate change is likely to modify the wheat disease spectrum in
some regions, and pathogens or pests considered unimportant today may turn out to be potential new threats in future. 相似文献
8.
Summary Spot blotch caused by Cochliobolus sativusis considered a major disease problem of wheat(Triticum aestivumL.) in the warm areas of South Asia. This study estimated heritability (h
2) of resistance to spot blotch and its correlation with days to heading DH) and maturity (DM), one-hundred-kernel weight (HKW),
and plant height (PHT) in 14 crosses involving four resistant (‘Attila’, ‘Chirya 7’, ‘G 162’, and ‘SW89.5422’) and two susceptible
(‘Sonalika’ and ‘HD2329’) wheat genotypes. Data were recorded on F5and F6lines in fields under natural epidemics of spot blotch in 2003 and 2004, respectively. Heritability was estimated for area
under disease progress curve (AUDPC), AUDPC/day, and the highest disease score (HDS) using offspring-parent regression (h
op
2) and realized heritability (h
2
R) procedures. Heritability estimates were low to high in terms of AUDPC (0.21 < h
op
2< 0.64; 0.32 < h
R
2< 0.70), AUDPC/day (0.40 < h
op
2< 0.96; 0.42 < h
R
2< 0.99), and HDS (0.29 < h
op
2< 0.92; 0.32 < h
R
2< 0.95). The h
2estimates for AUDPC/day were higher than for AUDPC and HDS. Estimates of h
R
2were by and large higher than h
op
2in the same cross. A weak negative or nonsignificant correlation of spot blotch score with HKW, DH, DM, and PHT indicated
that independent selection for resistance and these agronomic traits is possible. 相似文献
9.
Low pathotype diversity in a recombinant Puccinia striiformis population through convergent selection at the eastern Himalayan centre of diversity (Nepal) 
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下载免费PDF全文 S. Ali S. Sharma M. Leconte S. J. A. Shah E. Duveiller J. Enjalbert C. de Vallavieille‐Pope 《Plant pathology》2018,67(4):810-820
Worldwide Puccinia striiformis f. sp. tritici (Pst) epidemics have been reported to be driven by few genetic lineages, while a high diversity is evident at the Pst Himalayan centre of diversity. This study investigated the relationship between pathotype diversity and genetic structure in Nepal, the eastern Himalayan region, which has been largely unexplored. Despite the high genetic diversity and recombinant structure detected through microsatellite genotyping, characterization of virulence phenotypes for 62 isolates identified only eight pathotypes, with two pathotypes predominant over all the populations. This is in contrast to the Pakistani and Chinese recombinant populations, where high pathotype diversity is associated with genetic diversity. The most prevalent Nepali pathotype was not a unique clonal lineage, but was represented by seven multilocus genotypes from four distinct genetic subgroups, suggesting strong directional selection on virulence genes, resulting in convergent pathotypes in distinct genetic groups. This convergent selection is discussed in comparison with clonal French and recombinant Pakistani populations. Additionally, the Nepali Pst population carried virulence to 17 out of 24 tested yellow rust resistance genes (Yr), with the absence of virulence to Victo and Early Premium and resistance genes Yr5, Yr10, Yr15, Yr24 and Yr26. Virulence to Yr2, Yr7, Yr27 and YrSu were fixed in all isolates, in line with the deployment of these resistance genes in Nepal. The results reflect the influence of resistance gene deployment on selection of virulence and pathotypes in a recombinant pathogen population, which must be considered in the context of durable resistance gene deployment. 相似文献
10.
Spot blotch, caused by Cochliobolus sativus (Ito and Kurib.) Drechsler ex Dastur, and heat stress are two important stresses of bread wheat (Triticum aestivum L.) causing substantial yield reduction in the warm areas of South Asia. These two stresses put pressure on at least 25 million
hectares of wheat areas worldwide. This study was conducted to examine variation in physiological traits and its association
with heat and spot blotch. Eleven diverse bread wheat genotypes were evaluated in replicated field trials under spot blotch
epidemics and heat stress conditions in 2006 and 2007 at Rampur, Nepal. Canopy temperature depression (CTD), chlorophyll fluorescence
(CF), chlorophyll content, percent disease leaf area, yield and yield components were recorded. Heat and spot blotch individually
reduced CTD, CF, chlorophyll content, grain yield (GRY), and thousand kernel weight (TKW), with greater reductions recorded
under combined stress. Genotypes showing lower GRY or TKW loss due to spot blotch also exhibited lower yield loss due to heat
stress or combined heat and disease stress, suggesting an association between tolerance mechanisms to the stresses. The physiological
traits chlorophyll content, CF and CTD showed higher correlations with GRY and TKW than with area under disease progress curve
(AUDPC) suggesting their potential application in screening for heat and spot blotch tolerant genotypes. Genotypes with lower
disease showed the highest values for chlorophyll content, CF and CTD. Our findings provide new information on the relationship
of these physiological traits with spot blotch resistance and heat tolerance when examined in the same study. The physiological
traits studied have potential application in integrative indirect selection criteria for improving spot botch and heat tolerance
in wheat. 相似文献