African Journal of Plant Science Vol. 4 (2), pp. 026-031, February 2010 Available online at http://www.academicjournals.org/ajps ISSN 1996-0824 © 2010 Academic Journals Full Length Research Paper Virulence of Puccinia triticina on wheat in Iran S. Elyasi-Gomari Azad Islamic University, Shoushtar Branch, Faculty of Agriculture, Shoushtar, Iran. E-mail: [email protected]. Accepted 12 January, 2010 Wheat leaf rust is controlled mainly by race-specific resistance. To be effective, breeding wheat for resistance to leaf rust requires knowledge of virulence diversity in local populations of the pathogen. Collections of Puccinia triticina were made from rust-infected wheat leaves on the territory of Khuzestan province (south-west) in Iran during 2008 - 2009. In 2009, up to 20 isolates each of the seven most common leaf rust races plus 8 -10 isolates of unnamed races were tested for virulence to 35 near- isogenic wheat lines with different single Lr genes for leaf rust resistance. The lines with Lr9, Lr25, Lr28 and Lr29 gene were resistant to all of the isolates. Few isolates of known races but most isolates of the new, unnamed races were virulent on Lr19. The 35 Lr gene lines were also exposed to mixed race inoculum in field plots to tests effectiveness of their resistance. No leaf rust damage occurred on Lr9, Lr25, Lr28 and Lr29 in the field, and lines with Lr19, Lr16, Lr18, Lr35, Lr36, Lr37 and the combination Lr27 + Lr31 showed less than 15% severity. A total of 500 isolates of P. triticina obtained from five commercial varieties of wheat at two locations in the eastern and northern parts of the Khuzestan region were identified to race using the eight standard leaf rust differential varieties of Johnson and Browder. Thirteen known wheat leaf rust races and several new, unnamed races were identified. The most common races in each year were races 57, 64, 84, 143 and 167. Key words: Puccinia triticina, wheat leaf rust, specific resistance. INTRODUCTION Leaf rust, caused by Puccinia triticina Eriks., is the most virulence of the regional populations of P. triticina. Each common rust disease and regularly occurring disease of 1% increase in leaf rust severity decreases yield 40.07 kg wheat (Triticum estivum L.) in Iran and worldwide. The ha-1 and 1000 kernel weight 0.13 g (Leonard KJ et al., fungus is heteroecious, and therefore requires a telial/ 2005). In Iran and worldwide all three rusts are present uredinial host (usually wheat) and an alternative (pycnial/ but stripe rust and leaf rust are more important. Yield aecial) host (Thalictrum speciosissimum or Isopyrum losses in wheat from P. triticina infections are usually the fumaroides) to complete the full life cycle. result of decreased numbers of kernels per head and It is important to understand the genetic diversity in lower kernel weights (Elyasi-Gomari and Lesovaya, populations of P. triticina, because major genes for leaf 2009). P. triticina is now recognized as an important pa- rust resistance in wheat are race-specific. P. triticina has thogen in wheat production worldwide, causing significant a relatively long history of population studies, with nation- yield losses over large geographical areas (Elyasi- wide race surveys for this rust beginning in the US in Gomari and Panteleev, 2006; Kolmer et al., 2007; 1926 (Johnston et al., 1968), in Iran in 1968 (Bamdadian, Beyhan et al., 2008; Gilla et al,. 2008). Brennan and 1973), in Canada in 1931 (Johnson, 1956) and in Murray (1988) undertook an economic analysis of losses Australia in 1920 (Waterhouse, 1952). The wheat due to wheat rust diseases in Australia and estimated the cultivars Malakof (Lr1), Webster (Lr2a), Carina (Lr2b, annual value of control strategies for leaf rust at $A26 LrB), Loros (Lr2c), Brevit (Lr2c, LrB), Hussar (Lr11), million. An epidemic of leaf rust in Western Australia in Democrat (Lr3) and Mediterranean (Lr3) were designated 1992 affected more than 100,000 ha of wheat and as the International Standard set of leaf rust differentials, caused yield losses of up to 37% (McIntosh et al., 1995). and used in the early race identification studies. Abdel Hak et al., (1980) estimated crop losses of up to The use of wheat cultivars with genetic resistance to 50% due to leaf rust infection in Egypt. In 2007, Yield leaf rust is the most practical method of controlling this losses in wheat due to leaf rust were estimated to be 14% disease (Elyasi-Gomari and Lesovaya, 2009). Effective in Kansas (Kolmer et al., 2009). In Iran, leaf rust is an leaf rust resistance in wheat cultivars is dependent on the endemic disease of wheat in north, west and south Elyasi-Gomari 027 which appears each year. In 1993, yield losses due to determination, or a total of 500 isolates over all varieties. Leaf rust in some parts of Iran were estimated at about The single uredinial isolates were tested for virulence on the 1.5 million tones (Torabi et al., 1995). In particular, losses eight standard differential varieties of Johnston and Browder (Johnston and Browder, 1964; Lesovoj, and Panteleev, 2000): to leaf rust in spring wheat in the Khuzestan province of Malakof, Carina, Brevit, Webster, Loros, Mediterranean, Hussar, Iran were greater than at any time in the last 10 years and Democrat (Tables 1, 2). Detached leaves of each differential (Mahdian and Dehghani, 2004). Over the last 10 years variety were incubated under artificial light on water agar with the effectiveness of many known leaf rust resistance benzimidazole as described for establishment of single uredinial genes (Lr genes) have been tested on single-gene lines isolates. In previous tests we found that infection types on detached leaf pieces under these conditions were comparable to those on in field plot tests at various locations in central and intact seedlings in the greenhouse. Leaves of each differential western, southern and eastern regions of Iran (Torabi et variety were placed in a separate Petri dish. The detached leaves al., 1995; Torabi et al., 2001). Results showed that were inoculated by spraying them with a suspension of uredinio- effectiveness of some Lr genes against regional spores of a single uredinial isolate in water with Tween 80 and incu- populations of P. triticina in field tests varied among bated one day with the Petri dishes covered with moist filter paper regions. On the other hand, some Lr genes showed a as described above. The worksite and equipment were sterilized with 96% ethanol between inoculations with different isolates to general tendency to lose effectiveness over time in all prevent cross contamination. After one day the moist filter paper regions, while some others generally increased in was removed from the Petri dishes and replaced with glass covers. effectiveness over time. Hence, we have analyzed the After 10 days under artificial light at 24°C, the leaf rust reaction frequencies races and virulence of P. triticina populations types on each differential variety were determined according to in Iran. The objectives of this study were to characterize Mains and Jackson’s (Mains and Jackson, 1926) scale, with infec- the current virulence of P. triticina populations the tion types 0, 1 and 2 considered resistant and infection types 3 and 4 considered susceptible. Khuzestan province (south-west) in Iran. Selected isolates of seven races as well as isolates of unnamed races collected in 2009 were tested for virulence on 35 near- isogenic wheat lines. With the exception of one line with both Lr27 MATERIALS AND METHODS and Lr31, each line had a different single Lr gene for leaf rust resistance (Table 3). The isolates tested included 20 each from Collections of P. triticina were made from rust-infected wheat leaves races 57, 64, 84, 143, and 167, and 8 - 10 isolates each of races on the territory of Khuzestan province (south-west) in Iran during 12, 45, and the unnamed races (Table 2). The 35 near-isogenic 2008 - 2009. In 2008, 100 isolates were obtained from each of five wheat lines were tested both as seedlings in the greenhouse and wheat varieties, ‘Mahdavi’, ’Zarin’, ’Darab2’, ’Atila5’ and ’Niknezhad’ as adult plants in field plots. In the greenhouse the lines were in one location. In 2009, 100 isolates were obtained from each of grown in soil in boxes and were inoculated 10 days after planting five wheat varieties, ‘Mahdavi’, ’Zarin’, ’Darab2’, ’Atila5’ and when the second leaves were beginning to form. Seedlings were ’Niknezhad’ in the same one location as in 2008. Thus, a total of sprayed with a suspension of urediniospores in water with Tween- 500 isolates were collected from this site each in each year. 80 and the inoculated plants were incubated on day at 100% RH Leaves with leaf rust uredinia were collected at 50 sites before being returned to the greenhouse. Infection types were according to standard procedures (Peterson et al., 1948), one leaf scored according to Mains and Jackson’s (Mains, and Jackson, per site, in each of the five varieties in each year. The collections 1926) scale. were taken at equidistant sites during the time of maximum rust In field tests, the near-isogenic lines were planted in 1 m rows in development (milk-dough stage). Each rusted leaf was placed in a blocks surrounded with spreader rows of a susceptible wheat filter paper package and the package was labeled. Packages of variety. At 17 - 20 days prior to heading, the plots were inoculated rusted leaves were held at 4°C in a refrigerator until urediniospores by spraying them with a suspension of urediniospores (75 - 100 mg were collected for inoculation in the greenhouse. Urediniospores spores per L) in water with Tween-80. The inoculums consisted of a were collected by placing a piece of the rusted leaf sample in a mixture of races collected from the field in Iran.