Thirty-four Turkish barley (Hordeum vulgare) varieties were tested for the presence of resistance genes (R-genes) to powdery mildew (Blumeria graminis f. sp. hordei) using the “leaf segment test” with nine isolates of the fungus. The most commonly found R-gene was Mla8, while a combination of R-genes Mlg and Ml(CP) was found in three varieties (Tokak 157/37, Beysehir 98, Konevei 98). The gene Mlh was found in four varieties (Obruk 86, Anadolu 86, Çıldır 02, Özdemir 05), while no R-gene was found in three varieties (Hamidiye 85, Yesevi 93, Bülbül 89). No clear inferences could be made for the partly-resistant varieties Gemici 7243, Yea 793.12 and Akhisar 98 using the test isolates selected, which suggests the presence of still unidentified R-genes. Overall, 10 previously characterized R-genes for powdery mildew (Mla8, Ml(La), Mlg, Ml(CP), Mlh, Mlat, Mla1, Mlh, Mla7, Mlra) were present in Turkish barley varieties, along with some other(s) still to be identified.
- Blumeria graminis f. sp. hordea,
- Hordeum vulgare,
- leaf segment test,
- powdery mildew,
- resistance genes
Trente-quatre variétés d’orge (Hordeum vulgare) cultivées en Turquie ont été testées pour la présence de gènes de résistance (R) a l’oïdium (blanc) (Blumeria graminis f. sp. hordei) a l’aide du « test des segments foliaires » et de neuf isolats du champignon. Le gène R le plus commun parmi les variétés testées était Mla8, alors qu’une combinaison des gènes Mlg et Ml(CP) était trouvée chez trois variétés (Tokak 157/37, Beysehir 98, Konevei 98). La présence du gène Mlh a été identifiée chez quatre variétés (Obruk 86, Anadolu 86, Çıldır 02, Özdemir 05), alors qu’aucun gène R n’a été détecté dans trois autres variétés (Hamidiye 85, Yesevi 93, Bülbül 89). Aucune inférence n’a pu être clairement établie pour les variétés Gemici 7243, Yea 793.12 et Akhisar 98 a l’aide des isolats fongiques utilisés, ce qui suggère la présence de gènes R encore non identifiés. Au total, 10 gènes de résistance à l’oïdium (Mla8, Ml(La), Mlg, Ml(CP), Mlh, Mlat, Mla1, Mlh, Mla7, Mlra) étaient présents dans les variétés d’orge cultivées en Turquie, en plus d’autre(s) gène(s) non identifié(s).
- Blumeria graminis f. sp. hordea,
- gènes de résistance,
- Hordeum vulgare,
- test des segments foliaires
Corps de l’article
Dedicated to the memory of Dr. Şahin Dere.
Barley (Hordeum vulgare L.) is the fourth most important cereal crop in the world, after wheat, maize and rice. Turkey is among the main barley producing countries, ranking ninth in the world (Anonymous 2005). Powdery mildew caused by the fungal pathogen Blumeria graminis (DC.) Golovin ex Speer f. sp. hordei Em. Marchal (synamorph Erysiphe graminis DC. f. sp. hordei Em. Marchal) is one of the most destructive leaf diseases of this crop in regions with coastal climatic conditions, including the western and southern parts of Turkey. This disease lowers product quality and causes grain yield losses of up to 25-30%. Yield losses due to powdery mildew have been estimated at ~1 M ha yr‑1 in Europe (Czembor and Czembor 2001).
In Turkey, powdery mildew epidemics usually occur in the western and southern parts of the country, especially when the spring season is cool and rainy. In recent years, epidemics have also become a problem under dry and hot climatic conditions due to the increased use of irrigation set-ups and nitrogen fertilizers. The control of powdery mildew in Turkey relies on fungicides - in some areas - and breeding for host resistance. The development of resistant cultivars, however, has not been pursued extensively as of yet, even though this control approach is generally considered cost effective and environmentally safe (Wolfe 1984; Wolfe and McDermott 1994).
Race-specific resistance to powdery mildew is governed by major resistance genes (or R-genes) that can be introgressed from resistant varieties into susceptible cultivars of agronomic interest. The best potential sources of new resistance genes for cultivated barley most likely are landraces from the centre of origin (Ceccarelli et al. 1987, 1995). The Fertile Crescent area, covering the southeastern part of Turkey, is considered as the centre of origin for barley and wheat (Czembor 1996; Willcox 1995; Zohary 1999), which suggests that barley varieties, landraces and wild relatives from Turkey might represent an interesting source of R-genes for powdery mildew (Jahoor and Fishbeck 1987). Until now, nearly all European barley cultivars have been assessed for the presence and identity of R-genes to powdery mildew, making it possible to conclude to the presence of one or two R-genes in most varieties. Although the interaction between powdery mildew and barley is often regarded as one of the best characterized host-pathogen systems, and although many resistance alleles have already been identified (Kolster et al. 1986), the identification of R-genes for this disease in Turkish barley varieties and landraces still remains incomplete.
As a first step towards the effective use of powdery mildew R-genes in breeding programs, it is essential to test for the presence of those genes in registered cultivars and for the virulence of the pathogen through periodical surveys (Czembor and Bladeno-poulos 2001; Czembor and Czembor 1998, 2000a; Czembor and Gacek 1990; Czembor and Johnston 1999). In practice, such surveys are conducted based on the gene-for-gene hypothesis, i.e. by inoculating plants with pathogen isolates that present a defined virulence spectrum (Flor 1942, 1955; Moseman 1959). The infection spectra observed make it possible to determine a ’reaction spectrum’ for each interaction, which then makes it possible to identify the resistance phenotype of the tested plant (Czembor and Czembor 1998, 1999, 2001; Dreiseitl and Jørgensen 2000). Although Turkish varieties probably possess a number of unidentified and/or still uncharacterized R-genes for powdery mildew, monitoring has not yet been done on a systematic basis. As an attempt to provide useful information for future breeding efforts, the objective of this study was to identify major powdery mildew R-genes in barley varieties grown in Turkey.
Seed samples from 34 barley cultivars were provided by the Aegean Agricultural Research Institute of Turkey. A list of the varieties tested and their origin is presented in Table 1. All barley cultivars in this study were of the spring type, with six- and two-row heads, covered kernels, and an intermediate heading date. These cultivars are grown in the Aegean and Mediterranean coastal regions. In this experiment, the plants were grown at 20-22°C in a growth room under a 14h:10h light/dark photoperiod, until they reached the second leaf stage. The leaves of these seedlings were used for the “leaf segment test” (Lutz et al. 1992) (see below).
Nine isolates of Blumeria graminis were used as differentiating races for resistance tests (Table 2). These isolates were obtained from collections of the Riso National Laboratory of Denmark, and chosen based on their virulence spectrum as observed on the Pallas isogenic differential line set (Kolster et al. 1986). The fungi were provided by Dr. M.S. Hovmøller (Royal Agricultural and Veterinary University, Denmark) as purified single spore isolates, maintained and propagated on young seedlings of the powdery mildew-susceptible cultivar Cartegana.
The infection type of the isolates was assessed on host leaves using 3-cm-long leaf segments cut from the middle part of the primary leaf of 12-d-old seedlings laid on benzimidazole-containing agar (35 ppm benzimidazole in 1.5% agar). Inoculations were performed using a homemade mini-settling tower. The leaf segments inoculated on agar plates were placed in a growth chamber at 17-18°C under a 12h:12h light/dark photoperiod. Infection types were scored after 10 d according to the 0-4 scale of Welz (1988) (Table 3). Leaf segments with infection types (or scores) of 0, 1 or 2 were classified as resistant to the fungus; leaf segments with scores of 3 or 4 were classified as susceptible.
Specific R-genes associated with each genotype were inferred by comparing their reaction spectrum with that of previously characterized differential lines (Brown and Jørgensen 1991; Czembor and Bladenopoulos 2001). Identifications were done based on the gene-for-gene hypothesis (Flor 1942, 1955). When a compatible reaction was observed with a given isolate (scores 3 and 4), it was inferred that the tested cultivar did not possess the resistance allele(s) for which the isolate was avirulent. Incompatible reactions (scores 0-2) with isolates possessing only one avirulence allele among the remaining possible resistance alleles then made it possible to postulate that the matching resistance allele was present (Czembor and Czembor 2001; Dreiseitl and Jørgensen 2000). Table 4 presents putative resistance alleles for the 34 barley varieties tested.
This study is, to our knowldege, the first to identify R-genes for powdery mildew in commonly grown barley cultivars bred in the National Agricultural Research Institutes of Turkey. The presence of several R-genes was inferred among the varieties tested, including Mla8, MlLa, Mlg, Ml(CP), Mlh, Mlat, Mla1, Mlh, Mla7, Mlra, and a few uncharacterized genes. The most common R-gene was Mla8; it was found in nine cultivars out of 34 (Zafer-160, Yesilköy 387, Efes-2, Sahin-91, Basgöl, Yesevi-93, Ince-04, Kalaycı-97, and Erginel 90). Several cultivars contained a single (known) R-gene for powdery mildew [namely Orza-96 (Mlra), Serife hanım (Mla7), Bornova-92 (Mla1), Kaya-7794 (Mla(La)), Bilgi 91 (Mlg), Vamık hoca-98 (Ml(Ab)), Sülayman bey-98 (Ml(Ab)), Obruk-86 (Mlh), Özdemir 05 (Mlh), Çıldır 02 (Mlh), and Anodulu-86 (Mlh)], while three cultivars (Tokak-157/37, Beysehir-98, and Konevi-98) contained both Mlg and Ml(CP). Interestingly, the varieties Gemici-7243, Yea-793.12, and Akhisar-98 were partly resistant to the fungus, but no R-gene could be inferred because their reaction spectra with the test isolates were not conclusive. By contrast, the cultivars Hamidiye-85, Yesevi-93, and Bülbül-89 showed no resistance to any of the isolates tested, as also observed by Lower et al. (1997).
Compared with other studies on R-genes in barley cultivars or landraces, the number of distinct R-genes postulated here is relatively large considering the limited number of cultivars tested (10 different genes in 34 cultivars). Of these genes, none had previously been detected in barley landraces from Morocco (Czembor and Czembor 2000a, b), and the previously described R-genes detected in landraces from Greece, such as Mla6, Mla14 or Mlat, were not found in the varieties tested in the present study (Czembor 2001). By contrast, the genes Mlg, Mlak, Mla7, and Mla(Ab) have also been detected in North American cultivars (Dreiseitl and Steffenson 2000). Likewise, the genes Mlg, Mlk, Mla7, MI(CP), and Mla1 were previously detected in a population of 108 Baltic spring barley cultivars and breeding lines (Tueryapina et al. 1996), the genes Mla1, Mla7, and Mlk were detected in Tunisian landraces (Czembor and Johnston 1999), and the genes Mlg and Mla7 were detected in a population of 20 cultivars from Greece (Czembor and Bladenopoulos 2001). Based on these previous reports and on the present study, the most commonly found R-genes for powdery mildew in barley appear to be Mlg, which has been introduced into many European cultivars a long time ago, and Mla7, which has also been introduced into common barley varieties over the years.
The identification of R-genes based on tests performed using leaf segments and fungal isolates with different virulence spectra is an effective and useful tool for plant breeders (Russel 1978). Based on our data, it can be concluded that Turkish barley cultivars possess several genes for resistance to powdery mildew that can be used as parental plant materials in different gene deployment strategies aimed at efficiently controlling powdery mildew through gene pyramiding. None of the cultivars assessed in the study showed resistance based on the gene Mlo, which is known to provide efficient monogenic, non-race-specific and durable resistance (Hovmøller et al. 2000; Jørgensen 1992, 1994). Future work for barley breeders in Turkey should now focus on pyramiding this gene with the newly described Ml genes.
We gratefully acknowledge Dr. Mogens S. Hovmøller for providing the Blumeria graminis f. sp. hordei races, and the Aegean Agricultural Research Institute, Menemen, Izmir, for providing seeds of Turkish barley cultivars. We also thank the administrators of Mugla University and Ordu University for allowing Dr. Zeybek and Dr. Dere to participate in this study. This work was funded by the DOSAP program, the METU and the DPT (Project No. DPT2004K120750).
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