A SURVEY TO ASSESS WHEAT RUST INCIDENCE IN BANGLADESH DURING 2010-2011 WHEAT GROWING SEASON
Mustarin, P. K. Malaker, M. M. A. Reza, M. S. Hossain, M. A. Hakim, N. C. D. Barma, M. Mokhlesur Rahman, R. Islam and M. Mahbubur Rahman. 2014. A survey to assess wheat rust incidence in Bangladesh during 2010-2011 wheat growing season. Bangladesh J. Plant Pathol. 30 (1&2): 1- 5.
A field survey was conducted in the major wheat growing areas of Bangladesh during 2010-2011 wheat growing season to assess the incidence of wheat rusts. Altogether 162 farmers’ fields and trial sites covering 26 districts and experimental farms of Wheat Research Centre, Dinajpur, Bangladesh were visited several times during the survey. Among three rust diseases of wheat, incidence of stem or yellow rust was not found but occurrence of leaf rust was found with varying degrees of severity depending on wheat variety and locations of survey. About 37% of the visited fields were infected with leaf rust where the majority of infected fields showed low (<20%) to moderate (20-40%) levels of disease severity. The highest percentage of infected fields was observed in Rajshahi region followed by Rangpur and Mymensingh, while none of the fields was infected in Tangail district under Dhaka region. The variety Kanchan showed moderate levels of disease incidence and severity with MSS type reaction, whereas low to moderate incidence and severity with MSS type response were observed in variety Prodip. The variety Shatabdi showed low disease levels with MR type reaction in Rajshahi region but it was free from the disease in other regions. The variety BARI Gom-26 showed low disease levels with MRMS type reaction. Three advanced lines BAW-1051, BAW-1120 and BAW-1141, and varieties Bijoy and BARI Gom-25 were completely free from rust.
Wheat (Triticum aestivum L.) is the second most important cereal crop after rice in Bangladesh. It covers about 400,000 ha annually with an average production of one million tons (Anon. 2012). The current annual requirement of wheat is about 4 million tons. One-third of the requirement is met through local production. The shortfall of about 3 million tons per year is met through import from foreign countries. The rate of increase in wheat consumption is about 3% per year and by 2020 the annual wheat requirement of the country will be more than 5 million tons. Wheat Research Centre of BARI has so far released 28 wheat varieties of which Shatabdi, Bijoy, Prodip and BARI Gom-26 are important producing about 4.0-4.5 t/ha in the farmers’ field (Uddin et al. 2012, 2013).
The major constraints of wheat production in Bangladesh are attributed to competition with other winter crops, inadequate crop management; late planting due to late harvest of transplanted Aman paddy and attack of various pests and diseases. Among the diseases Bipolaris leaf blight or spot blotch (Bipolaris sorokiniana) and leaf rust (Puccinia triticina Eriks.) are the major problems
(Malaker et al. 2007). Yield losses due to leaf rust are usually limited but can be significant if a susceptible variety is grown and infection occurs early in the crop season. The disease appears almost every year in all wheat growing areas of Bangladesh with varying degrees of severity depending on varieties grown. The disease usually appears in mid February and its severity increases between mid and late March. Wheat planted in optimum times (15-30 November), either escapes the disease to a large extent or suffers less compared to those planted in late season. Stem rust of wheat caused by P. graminis Pers. f. sp. tritici Eriks. & E. Henn. was a common disease during the early years of wheat research and development in the country. However, the disease has not been observed since mid 1980s, possibly due to introduction of several resistant varieties. Yellow rust of wheat caused by P. striformis West. f. sp. tritici Eriks. & E. Henn. appears occasionally in north-western parts of the country, where relatively cooler climate prevails during the winter months of wheat growing season.
Rust pathogens explicitly possess two major characteristics. Firstly, they are highly mobile trans-boundary fungi capable of rapid and long distance movements even over continents, either by wind-assisted or inadvertent human-mediated dissemi-nation. Secondly, rust pathogens have an inordinate ability to change and evolve through mutation or sexual recombination (Waston 1981, Knott 1989, Park 2007). A virulent race of stem rust fungus called Ug99 was detected in Uganda in 1998 (Pretorius et al. 2000) and subsequently found in epidemic proportions in Kenya and Ethiopia. The race has knocked down many useful resistance genes including Sr31 that were deployed in 90% of the wheat varieties grown worldwide (Singh et al. 2008). Seven variants of the Ug99 lineage are now known and have spread to various countries in the eastern African highlands as well as Zimbabwe, South Africa, Sudan, Yemen, and Iran (Singh et al. 2011). The experts of Borlaug Global Rust Initiative (BGRI) have predicted further movement of Ug99 and other virulent strains to the important wheat production areas of the Indian subcontinent and beyond (McIntosh and Pretorius 2011). Appearance of new virulence in leaf and yellow rust pathogens of wheat is also likely in future, particularly under the changing crop climate. Although none of the rusts has so far reached an epidemic level in Bangladesh, but there is no guarantee that damaging epidemics will not occur in future, particularly if a virulent race develops or is introduced. Therefore, regular survey and monitoring becomes inevitable in order to identify signs of emergence of virulent races of wheat rusts for mitigating their future threats.
In view of the above facts, a survey was conducted to assess the incidence of rust diseases in major wheat growing areas of Bangladesh.
MATERIALS AND METHODS
The survey of wheat rusts was conducted in the major wheat growing districts representing six regions of Bangladesh during 2010-2011 seasons. One hundred and sixty two farmers’ fields and trial sites were selected from 26 districts under six wheat growing regions of the country. The work was carried out throughout Wheat Research Centre of Dinajpur, Joydebpur, Jessore, Jamalpur, Rajshahi and Ishurdi. Rust incidence at field level was recorded and severity of infection was estimated following the modified Cobb scale (Stubbs et al. 1986). The BGRI protocols for wheat rust assessment (Anon. 2008) were used.
RESULTS AND DISCUSSION
Among 162 farmers’ fields and trial sites surveyed, incidence of stem and yellow rusts were not found in any location but leaf rust was observed in 60 fields that accounts for 37% of all visited fields. The highest percentage of infected field (64%) was recorded in Rajshahi region, which was followed by Rangpur, Mymensingh and Jessore region with 52%, 48% and 19% infected fields, respectively. The lowest percentage of 3% leaf rust incidence was observed in Barisal region. All of the fields visited in Tangail district under Dhaka region were free from rust incidence. However, the frequency and percentage of field infection in different regions were largely influenced by number of fields surveyed, time of planting and varieties grown. Wheat planted in November largely escaped or had less disease incidence compared to late-sown crops. Fields planted with varieties Prodip and Kanchan showed higher percentages of leaf rust infection than those planted with other varieties or advanced lines. Infection of fields planted with Prodip and Kanchan was as high as 100% in Mymensingh and Rangpur regions. When planted with BARI Gom-26 in Rangpur and Rajshahi regions, 50% of the fields showed leaf rust infection, while only 20% of the fields planted with Shatabdi was infected in Rajshahi region and found disease free in other regions. Fields planted with other varieties and advanced lines were completely free from leaf rust infection in all the regions. Severity of leaf rust infection was found higher in north-western parts compared to other wheat growing areas of the country (Table 1).
Rust resistance genes present in Bangladeshi wheat varieties observed during the present survey were reported by Malaker and Reza (2011). Genes detected in six varieties are presented in Table 2. A total of six leaf rust resistance genes viz. Lr1, Lr10, Lr13, Lr23, Lr26 and Lr34; five stem rust resistance genes viz. Sr5, Sr8b, Sr9b, Sr11 and Sr31; and two yellow rust resistance genes Yr2KS and Yr9, either singly or in combination were identified in those varieties. The gene Lr34, conferring adult plant slow rusting resistance to leaf rust was identified on the basis of conspicuous leaf tip necrosis developed under field condition. In addition to the named genes, some unidentified factors for resistance (+) were also inferred in most of the varieties (Table 2).
Altogether six wheat varieties and three advanced lines observed during the survey showed different levels of leaf rust incidence and severity with different types of disease reactions (Table 3). Among the varieties, Kanchan released in 1983 and having the genes Lr13+Lr23 showed moderate levels of incidence and severity (20-40%) with MSS type reaction, while Shatabdi released in 2000 and carrying the genes Lr1+Lr13+ displayed low levels of disease (<20%) with MR type reaction in Rajshahi region but it was disease free in other regions. The variety Prodip showed low to moderate disease levels with MSS reaction, while only low disease severity with MRMS response was recorded in variety BARI Gom-26. Advanced lines BAW-1051, BAW-1120 and BAW-1141, and variety Bijoy released in 2005 and BARI Gom-25 released in 2010 and having the gene Lr13+ were completely free from leaf rust in all the regions surveyed.
In the late 1980s and early to mid 1990s, the variety ‘Columbus’ having the genes Lr13 and Lr16 was highly resistant to leaf rust in Canada. As the frequency of isolates with virulence to Lr13 and Lr16 increased, the resistance conditioned by these genes has been eroded (Kolmer and Liu 2002). The pathotypes having matching virulence for genes Lr1, Lr2a, Lr2c, Lr3, Lr10, Lr13, Lr14a, Lr15, Lr17 and Lr23 were quite common in Bangladesh (Malaker et al. 2005). This also correlates with leaf rust infection on the old cultivar Kanchan that showed moderate levels of disease severity with MSS type reaction during the present survey. The variety Prodip released in 2005 and having genes Lr1+Lr26+ showed low to moderate levels of disease with MSS type reaction in all the regions except Dhaka. The alien gene Lr26 (1BL/1RS translocation) has been the most widely exploited source of rust resistance in the world for developing high yielding wheat cultivars (Malaker and Reza 2011). Nayar et al. (2001) reported that at least 10 pathotypes with matching virulence for Lr26 have been identified in India between 1984 and 2001. Leaf rust reaction and severity on Prodip in different wheat growing areas indicates the presence of this type of Lr26-virulent pathotypes in Bangladesh. The variety BARI Gom-26 released in 2010 and having genes Lr10+Lr13+Lr34+ exhibited low levels of disease incidence and severity with MRMS type of reaction. The resistance conferred by Lr34 is non-specific in nature, since isolates that are fully virulent to this gene have not yet been detected (Kolmer 1999, 2001). Adult plant gene Lr34 along with some minor resistance genes has provided durable resistance to leaf rust in wheat throughout the world (Kolmer 1996). Wheat materials of Bangladesh have a narrow genetic base for resistance to rust diseases. Cultivars with narrow genetic base are unlikely to provide durable resistance and may lead to vulnerability to new races of the rust pathogens. This underlines the needs for field monitoring on a wider scale and development of increased genetic diversity with durable type of resistance in order to mitigate the future threat of wheat rusts in Bangladesh.
Technical and financial supports provided by BGRI, DRRW Project, CIMMYT, FAO Wheat Rust Disease Global Program, DWR-India and Sathguru Management Consultants are gratefully acknowledged.
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