Foliar blight, Helminthosporium leaf blight (HLB), or foliar blight has been a major disease of wheat (Triticum aestivum L.) worldwide. Foliar blight disease complex consists of spot blotch and tan spot. Spot blotch is favored in warmer environments, whereas tan spot is favored in cooler environments such as United States. [3] The tan spot forms of foliar blight appears in United States causing significant yield loss. With changed climatic conditions the disease is supposed to be increasing in cooler parts of the world. Among foliar blights the tan spot, caused by Pyrenophora tritici-repentis, is the most destructive leaf spot disease found in all wheat classes throughout the growing season across North Dakota.[3]
The spot blotch form of foliar blight is severe particularly in warmer growing areas characterized by an average temperature in the coolest month above 17°C. In the past 20 years, HLB has been recognized as the major disease constraint to wheat cultivation in the warmer eastern plains of South Asia.[4][5] About 25 million hectares of nontraditional wheat growing area are under the pressure of the disease.
Early lesions are characterized by small, dark brown lesions 1 to 2mm long without chlorotic margin. In susceptible genotypes, these lesions extend very quickly in oval to elongated blotches, light brown to dark brown in colour. They may reach several centimetres before coalescing and inducing the death of the leaf. Fruiting structures develop readily under humid conditions and are generally easily observed on old lesions. If spikelets are affected, it can result in shrivelled grain and black point, a dark staining of the embryo end of the seed.[6] The small dark brown spots on the leaves contrast with the larger, light brown spots or blotches produced by tan spot and septoria avenae blotch.[2]
In recent years, Helminthosporium leaf blights (HLB), caused by both Cochliobolus sativus and Pyrenophora tritici-repentis, have emerged as serious concerns for wheat cultivation in the developing world.[6] The disease causes significant yield losses[7] overall 22% to complete failure of crop under severe epidemics.
The disease is very serious in different parts of the world. The management of this disease requires an integrative approach.
An integrated approach
The best way to control Helminthosporium diseases is through an integrated approach. It includes the use of a variety of resistance sources, such as hexaploid wheat from Brazil and China (some of which is rate-limiting), alien genes and synthetic wheats. In addition, appropriate management practices that enhance the health of the plant populations, in general, are critical. Cooperation of pathologists, breeders and agronomists will be necessary to ensure sustainable control of this group of diseases. Economic feasibility of recommended practices has to be determined as part of the research. Options for controlling tan spot and spot blotch include disease-free seed, seed treatment with fungicides, proper crop rotation and fertilization, cultural practices in order to reduce inoculum sources, the use of chemicals and the research of disease resistance. The latter offers the best long-term control at no cost for the farmer and is ecologically safe.
Seed health
In Brazil, it is recommended not to plant seed lots with more than 3% black point to limit spot blotch. Seed treatment may prove to be appropriate, although the inoculum remaining on secondary hosts or in the soil may reduce the treatment efficiency. Seed treatments with phytoalexin inducer appeared to provide good protection to wheat seedlings against B. sorokiniana infection.[9] Seed treatment with fungicide will help protect germinating seed and seedlings from fungi causing seedling blights. Fungicide seed treatments include: captan, mancozeb, maneb, thiram, pentachloronitrobenzene (PCNB) or carboxin guazatine plus, iprodione and triadimefon (Stack and McMullen, 1988; Mehta, 1993). Seed-borne inoculum of P. tritici-repentis can be controlled with seed-applied fungicides, such as guazatine and guazatine + imazalil, but other chemicals are also effective.[10]
Rotations and crop management
Clearing or ploughing in the stubble, grass weeds and volunteer cereals reduce inoculum as does crop rotation (Diehl et al., 1982). Reis et al. (1998) indicate that eradicant fungicide treatment of the seed and crop rotation with non-host crops can control spot blotch. In the rice-wheat system of South Asia, little work has been done on the epidemiology of HLB and how management of the rotation crops affects spot blotch and tan spot, except as noted earlier. More quantitative information is required on the role of alternate rotations, soil and plant nutrition, inoculum sources and climate. In the rice-wheat system, there is a need for timely planting of wheat, better stand establishment and root development, increased soil organic matter, sufficient levels of macro- and micronutrients, and water and weed management (Hobbs et al., 1996; Hobbs and Giri, 1997). Crop rotation and organic manures will play a major role in HLB. This should favour beneficial soil organisms as well as better plant nutrition. In the rice-wheat system, it will be necessary to break the rotation with other crops to make it more sustainable, and this should help reduce disease problems in general. The use of oilseed rape in South Asia is common in mixture with wheat or in rotation. Since rape is known to have some fungitoxic effects upon decay, its effects on HLB would need research (Dubin and Duveiller, 2000). In the HLB complex, rotations would need to be sufficiently long to reduce the amount of soil inoculum. Cook and Veseth (1991) note that the kind of rotation crop may not be so important to root health as the length of time out of wheat. The rotation crops and length of rotation would have to be studied in relation to HLB.
Apparently, sound management recommendations may antagonize specific diseases as in the case of tan spot. Tan spot has been controlled largely by cultural practices, such as rotation with non-host crops and removal or burial of stubble (Rees and Platz, 1992). Bockus and Claassen (1992) observed that rotation to sorghum was as effective as ploughing for control of tan spot, and under certain conditions, crop rotations as short as one year controlled tan spot. In South Asia, recent work by Hobbs and Giri (1997) indicates that minimum tillage may be the best way to reduce turnaround time from rice to wheat and thus permit the planting of wheat more timely. Since this probably increases inoculum of tan spot, it highlights the need for integration of disciplines to determine how best to achieve attainable yields.
Fungicides
Although pesticide use should be minimized, fungicides have proven useful and economical in the control of tan spot (Loughman et al., 1998) and spot blotch (Viedma and Kohli, 1998). The triazole group (e.g. tebuconazole and propiconazole) especially has proven to be very effective for both HLBs, and their judicious use should not be overlooked. However, it may provide acceptable control but not always economic return in commercial grain production. This is dependent on the price received for the wheat, the price of the fungicide and the percent yield increase from using the fungicide. Situations will differ significantly according to geographical areas and cropping conditions. Spot blotch in particular is a very aggressive disease, and under a favourable environment, spraying at one- to two-week intervals for as long as necessary may be needed to maintain the disease under control.
For general information on management of the disease visit Ohio State University Link and FAO link
Breeding for resistance
The wheat cultivars of South Asia have only low to moderate levels of resistance to spot blotch. However, genetic variation for resistance has been reported in a few wheat cultivars. The best sources of resistance, to date, were identified in the Brazilian and Zambian wheat lines. Recently, a few Chinese wheat genotypes from the Yangtze River valley were identified with acceptable levels of resistance to spot blotch. The following genotypes has been reported to have satisfactory level of resistance, although complete resistance or immunity is lacking: [11][12]
1 SW 89-5193
2 SW 89-3060
3 SW 89-5422
4 Chirya 7
5 Ning 8319
6 NL 781
7 Croc 1/A. sq.// Borl
8 Chirya 3
9 G162
10 Chirya 1
11 Yangmai-6
12 NL 785
The field resistance governed by Chirya-3 and Milan / Shanghai 7 was found under monogenic control [13]
Similarly resistant genotypes Acc. No. 8226, Mon/Ald, Suzhoe#8 from India are found to possess three genes for resistance.
CIMMYT wheat pathologist Dr. Duveiller and Rosyara at a spot blotch screening nursery at Rampur
A study was conducted to determine microsatellite markers associated with resistance in the F7 progeny from a cross between the spot blotch-susceptible Sonalika and resistant G162 wheat genotypes. 15 polymorphic markers showed association with two bulks, one each of progeny with low and with high spot blotch severity.
One of the interesting phenomena associated with foliar blight in some of susceptible cultivars is tolerance (low yield loss even at very high level of disease severity). In addition, the resistance seems to be associated with late maturity (which is an undesirable characteristic as late maturing genotypes need to face more heat stress than early ones), complete understanding of physiological association may aid to complete understanding of the host-pathogen system.
Rosyara et al.[14] reported that the AUDPC showed a significant negative correlation with the width of large vascular bundles, percentage of small vascular bundles with two girders and the number of large veins. Also the AUDPC was positively correlated with the distance between adjacent vascular bundles and leaf thickness. The chlorophyll or general health indicators, SPAD and AUSDC values were higher in spot blotch resistant and tolerant genotypes. The findings the study underlined the importance of mesophyll structure and chlorophyllcontent in spot blotch resistance in wheat. Also tolerant genotypes responded in the same way as artificial defoliation showing mechanisms of nutrient balance playing role.[15] Similarly, canopy temperature depression was found associated with foliar blight resistance. Leaf tip necrosis was found to be associated with foliar blight resistance and is suggested as phenotypic marker. Different studies are done to estimate heritability[12] and increase selection efficiency. Heritability estimates were low to high in terms of AUDPC. To increase efficiency of selection use of selection index has been suggested.[7] The index includes days to heading (maturity related trait), thousand kernel weight, and area under foliar blight disease progress curve.
Related Research Articles
Phytophthora infestans is an oomycete or water mold, a fungus-like microorganism that causes the serious potato and tomato disease known as late blight or potato blight. Early blight, caused by Alternaria solani, is also often called "potato blight". Late blight was a major culprit in the 1840s European, the 1845–1852 Irish, and the 1846 Highland potato famines. The organism can also infect some other members of the Solanaceae. The pathogen is favored by moist, cool environments: sporulation is optimal at 12–18 °C (54–64 °F) in water-saturated or nearly saturated environments, and zoospore production is favored at temperatures below 15 °C (59 °F). Lesion growth rates are typically optimal at a slightly warmer temperature range of 20 to 24 °C.
Magnaporthe grisea, also known as rice blast fungus, rice rotten neck, rice seedling blight, blast of rice, oval leaf spot of graminea, pitting disease, ryegrass blast, Johnson spot, neck blast, wheat blast and Imochi (稲熱), is a plant-pathogenic fungus and model organism that causes a serious disease affecting rice. It is now known that M. grisea consists of a cryptic species complex containing at least two biological species that have clear genetic differences and do not interbreed. Complex members isolated from Digitaria have been more narrowly defined as M. grisea. The remaining members of the complex isolated from rice and a variety of other hosts have been renamed Magnaporthe oryzae, within the same M. grisea complex. Confusion on which of these two names to use for the rice blast pathogen remains, as both are now used by different authors.
Pyrenophora teres is a necrotrophic fungal pathogen of some plant species, the most significant of which are economically important agricultural crops such as barley. Toxins include aspergillomarasmine A and related compounds.
The cereal grain wheat is subject to numerous wheat diseases, including bacterial, viral and fungal diseases, as well as parasitic infestations.
Stem rust, also known as cereal rust, black rust, red rust or red dust, is caused by the fungus Puccinia graminis, which causes significant disease in cereal crops. Crop species that are affected by the disease include bread wheat, durum wheat, barley and triticale. These diseases have affected cereal farming throughout history. The annual recurrence of stem rust of wheat in North Indian plains was discovered by K.C. Mehta. Since the 1950s, wheat strains bred to be resistant to stem rust have become available. Fungicides effective against stem rust are available as well.
Wheat leaf rust is a fungal disease that affects wheat, barley, rye stems, leaves and grains. In temperate zones it is destructive on winter wheat because the pathogen overwinters. Infections can lead up to 20% yield loss. The pathogen is a Puccinia rust fungus. It is the most prevalent of all the wheat rust diseases, occurring in most wheat-growing regions. It causes serious epidemics in North America, Mexico and South America and is a devastating seasonal disease in India. P. triticina is heteroecious, requiring two distinct hosts.
The fungus Cochliobolus sativus is the teleomorph of Bipolaris sorokiniana (anamorph) which is the causal agent of a wide variety of cereal diseases. The pathogen can infect and cause disease on roots, leaf and stem, and head tissue. C. sativus is extremely rare in nature and thus it is the asexual or anamorphic stage which causes infections. The two most common diseases caused by B. sorokiniana are spot blotch and common root rot, mainly on wheat and barley crops.
Pyrenophora tritici-repentis (teleomorph) and Drechslera tritici-repentis (anamorph) is a necrotrophic plant pathogen of fungal origin, phylum Ascomycota. The pathogen causes a disease originally named yellow spot but now commonly called tan spot, yellow leaf spot, yellow leaf blotch or helminthosporiosis. At least eight races of the pathogen are known to occur based on their virulence on a wheat differential set.
Zymoseptoria tritici, synonyms Septoria tritici, Mycosphaerella graminicola, is a species of filamentous fungus, an ascomycete in the family Mycosphaerellaceae. It is a wheat plant pathogen causing septoria leaf blotch that is difficult to control due to resistance to multiple fungicides. The pathogen today causes one of the most important diseases of wheat.
Ascochyta is a genus of ascomycete fungi, containing several species that are pathogenic to plants, particularly cereal crops. The taxonomy of this genus is still incomplete. The genus was first described in 1830 by Marie-Anne Libert, who regarded the spores as minute asci and the cell contents as spherical spores. Numerous revisions to the members of the genus and its description were made for the next several years. Species that are plant pathogenic on cereals include, A. hordei, A. graminea, A. sorghi, A. tritici. Symptoms are usually elliptical spots that are initially chlorotic and later become a necrotic brown. Management includes fungicide applications and sanitation of diseased plant tissue debris.
Bipolaris sacchari is a fungal plant pathogen in the family Pleosporaceae.
Urocystis is a genus of smut fungi containing plant pathogens, which infect grass species and other plants.
Wheat yellow rust, also known as wheat stripe rust, is one of the three major wheat rust diseases, along with stem rust of wheat and leaf rust.
Epoxiconazole is a fungicide active ingredient from the class of azoles developed to protect crops. In particular, the substance inhibits the metabolism of fungi cells infesting useful plants, and thereby prevents the growth of the mycelia. Epoxiconazole also limits the production of conidia (mitospores). Epoxiconazole was introduced to the market by BASF SE in 1993 and can be found in many products and product mixtures targeting a large number of pathogens in various crops. Crops are, for example, cereals, soybeans, banana, rice, coffee, turnips, and red as well as sugar beets.
Southern corn leaf blight (SCLB) is a fungal disease of maize caused by the plant pathogen Bipolaris maydis.
Aspergillomarasmine A is an polyamino acid naturally produced by the mold Aspergillus versicolor. The substance has been reported to inhibit two antibiotic resistance carbapenemase proteins in bacteria, New Delhi metallo-beta-lactamase 1 (NDM-1) and Verona integron-encoded metallo-beta-lactamase (VIM-2), and make those antibiotic-resistant bacteria susceptible to antibiotics. Aspergillomarasmine A is toxic to leaves of barley and other plants, being termed as "Toxin C" when produced by Pyrenophora teres.
Dr. Sanjaya Rajaram was an Indian-born Mexican scientist and winner of the 2014 World Food Prize. He was awarded this prize for his scientific research in developing 480 wheat varieties that have been released in 51 countries. This innovation has led to an increase in world wheat production – by more than 200 million tons – building upon the successes of the Green Revolution. The Government of India awarded him India's fourth- and third-highest civilian awards Padma Shri (2001) and Padma Bhushan (2022).
Northern corn leaf blight (NCLB) or Turcicum leaf blight (TLB) is a foliar disease of corn (maize) caused by Exserohilum turcicum, the anamorph of the ascomycete Setosphaeria turcica. With its characteristic cigar-shaped lesions, this disease can cause significant yield loss in susceptible corn hybrids.
2Blades is an agricultural phytopathology non-profit which performs research to improve durable genetic resistance in crops, and funds other researchers to do the same. 2Blades was co-founded by Dr. Roger Freedman and Dr. Diana Horvath in 2004.
Helminthosporiosis may refer to two diseases of wheat:
References
↑ Wiese, M.V. (1987). Compendium of wheat diseases. American Phytopathological Society. pp.124 pp.
1 2 Martens, J.W.; W.L. Seaman; T.G. Atkinson (1984). Diseases of field crops in Canada. Canadian Phytopathological Society. pp.160 pp.
↑ Rosyara, U. R.; E. Duveiller, K. Pant and R. C. Sharma. 2007. Variation in chlorophyll content, anatomical traits and agronomic performance of wheat genotypes differing in spot blotch resistance under natural epiphytotic conditionsAustralasian Plant Pathology 36: 245–251.
1 2 Sharma, R.C. and E. Duveiller. 2003. Selection Index for Improving Helminthosporium Leaf Blight Resistance, Maturity, and Kernel Weight in Spring Wheat. Crop Sci. 43:2031–2036.
↑ Sharma, R.C.; E. Duveiller, S. Gyawali, S.M. Shrestha, N.K. Chaudhary, and M.R. 2004. Resistance to Helminthosporium leaf blight and agronomic performance of spring wheat genotypes of diverse origins. Euphytica 139: 33–44.
1 2 Sharma R. C., Pandey-Chhetri, B. and Duveiller E. 2006. Heritability estimates of spot blotch resistance and its association with other traits in spring wheat crosses. Euphytica 147: 317–327.
↑ Neupane R. B., R. C. Sharma, E. Duveiller, G. Ortiz-Ferrara, B. R. Ojha, U. R. Rosyara, D. Bhandari, M. R. Bhatta. (2007) Major Gene Controls of Field Resistance to Spot Blotch in Wheat Genotypes Milan/Shanghai #7 and Chirya.3. Plant Disease 91:6, 692.
↑ Rosyara, U. R.; E. Duveiller, K. Pant and R. C. Sharma. 2007. Variation in chlorophyll content, anatomical traits and agronomic performance of wheat genotypes differing in spot blotch resistance under natural epiphytotic conditions. Australasian Plant Pathology 36: 245–251.
↑ Rosyara, U.R.;R.C. Sharma, S.M. Shrestha, and E. Duveiller. 2005.YIELD AND YIELD COMPONENTS RESPONSE TO DEFOLIATION OF SPRING WHEAT GENOTYPES WITH DIFFERENT LEVEL OF RESISTANCE TO HELMINTHOSPORIUM LEAF BLIGHT.J. Inst. Agric. Anim. Sci. 26:43–50.available online or click here
Further reading
Joshi, A. K.; R. Chand, S. Kumar, and R. P. Singh. 2004. Leaf Tip Necrosis: A Phenotypic Marker Associated with Resistance to Spot Blotch Disease in Wheat. Crop Sci. 44:792–796.
Joshi A. K., S. Kumar, R. Chand and G. Ortiz-Ferrara 2004. Inheritance of resistance to spot blotch caused by Bipolaris sorokiniana in spring wheat. Plant Breeding 123, 213—219
Rosyara, U.R., R.C. Sharma, S.M. Shrestha, and E. Duveiller. 2006. Yield and yield components response to defoliation of spring wheat genotypes with different level of resistance to Helminthosporium leaf blight. Journal of Institute of Agriculture and Animal Science 27. 42–48. or
Adlakha, K.L., Wilcoxson, R.D. & Ray-chauduri, S.P. 1984. Resistance of wheat to spot blotch caused by Bipolaris sorokiniana. Plant Dis., 68: 320–321.
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Annone, J. 1998. Tan spot of wheat in Argentina: Importance and prevailing disease management strategies. In E. Duveiller, H.J. Dubin, J. Reeves & A. McNab, eds. Proc. Int. Workshop Helminthosporium Diseases of Wheat: Spot Blotch and Tan Spot, CIMMYT, El Batan, Mexico, 9–14 Feb 1997, p.339–345. Mexico, DF, CIMMYT.
Bhatta, M.R., Pokharel, D.R., Devkota, R.N., Dubin, H.J., Mudwari, A., Bimb, H.P., Thapa, B.R., Sah, B.P. & Bhandari, D. 1998. Breeding for Helminthosporium blights resistance in Nepal: strategy followed by the national wheat research program and genetic gains. In E. Duveiller, H.J. Dubin, J. Reeves & A. McNab, eds. Proc. Int. Workshop Helminthosporium Diseases of Wheat: Spot Blotch and Tan Spot, CIMMYT, El Batan, Mexico, 9–14 Feb 1997, p.188–195. Mexico, DF, CIMMYT.
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