Oat Resistance to Pyrenophora avenae Ito et Kurib.

O. S. Petrova¹, O. S. Afanasenko¹, I. G. Loskutov²

¹ - All Russian Reserch Institute for Plant Protection, Saint Petersburg, Pushkin,

² – N.I.Vavilov Institute of Plant Industry Institute, Saint Petersburg

e-mail: i.loskutov@vir.nw.ru

 

Introduction

Pyrenophora leaf blotch of oat is the most harmful and widely distributed disease in Europe and Russia (Northwest, Central and the Volgo-Vjatsky regions of the Nonchernozem zone, the Far East) (Amelung, 1990; Šebesta et al., 1995; Šebesta et al., 2000; Ishkova et al., 2002; Petrova, 2004). The causal agent is an ascomycete fungus Pyrenophora avenae Ito et Kurib.; anamorpha Drechslera avenae (Eidam) Scharif.

The breeding of resistance cultivars is the most effective and ecologically safe method of plant protection which realization is possible at presence of a collection of genetically various donors of resistance. The literature data shows the insignificant number of resistance accessions among the investigated oat collections. In conditions of artificial infection in a greenhouse and at an estimation in a field a number of resistance accessions were revealed: B 1-47-67 and Wisconsin hybrid X 279-1, (Earhard, Shands, 1952), Flamingsweiss II, Omeko Clinton, Bontram, 2411 (Müller, 1963), 7930-6, 8172-2, 8174-20, 8184-5, 8184-14, 8184-18 (Frank, Christ, 1988).

Resistance to crown rust and Pyrenophora leaf blotch appeared to be in Canadian and American oats (for example accessions: Garry, Abegweit, Rodney, Iowa 2052) (Grachev, 1961). By results of 5 years studying in the field conditions in North West region of Russia several resistance oat cultivars and accessions were determined (Eshibaev, 1993).

J. Šebesta et al. (1995, 2001) studied resistance of 68 oat cultivars and accessions to Pyrenophora leaf blotch in 12 countries of Europe (including Russia). In result the high level of resistance in majority Illinois lines (IL 86-1158, IL 86-6467, IL 86-4189, IL 85-2069, IL 86-6404 and IL 86-5698) and at other 24 cultivars (Maldwyn, Manod, Cc 3678, Рс 61, Рс 60, Cc 4761, Рс 67, Рс 58, Orlando, Pg 15, Рс 59, Рс 50, Rodney A, Pg 16, Cc 6490, Jostrain, Garland, Рс 50-2, Рс 55, Roxton, KR 3813/73, Рс 39, Рс 56 and Рс 50-4) has been revealed.

The resistance accessions were concerned to following oat cultivated species: A. strigosa Schreb., A. strigosa subsp. brevis, A. sativa L. and A. byzantina C. Koch. (Grachev, 1961; Kunovski, Breshkov, 1981; Frank et al., 1988; Lyzlov, 1992; Šebesta et al., 1999) and some wild species (Loskutov, 2003).

The given data testify that the world oat collection of Vavilov Institute of Plant Industry (VIR) was studied only in field conditions at the natural infections (Grachev, 1961; Eshibaev, 1993; Loskutov, 2002). The data on heterogeneity of P. avenae populations on virulence, a genetic variability of resistance and its nature are absence in literature. There are assumptions, that steady accessions have a high level of horizontal resistance (Frank, Christ, 1988).

The purpose of our research was to find the sources of oat resistance to P. avenae among commercial cultivars and VIR world collection of oat genetic resources.

 

Materials and methods

In 2002 - 2003 resistance of 450 oat cultivars and accessions from VIR gene stocks collection (Loskutov et al., 1997), and also 78 release commercial cultivars were investigated. From this amount in laboratory conditions 220 cultivars and accessions were studied, and 170 from them on an artificial infection.

P. avenae was isolated on CLM media (g/l: KH₂PO₄ – 0.5; KCl – 0.5; MgSO₄ – 0.5; urea – 1.2; lactose – 20 and an agar – 20 (Benken et al., 1969) from the leaves with symptoms of disease. Conidia were formed after 12-14 days at constant illumination by fluorescent lamps (3000 lux). Single conidia isolates were obtained by transferring conidia with needle to the same media.

Virulence test was conducted in laboratory conditions by inoculation of detached first leaves of oat seedlings, putting on the filter paper, soaked with 0.004% benzimidazol solution. Conidia suspension with concentration 30000-35000 conidia per ml was used (Petrova, 2004).

Types of reaction of oat accessions were determined for 6-7 days after inoculation on five score scale:

1 – dot necrosis without chlorosis (high resistance);

2 – fine (0.5-1.0 mm) necrotic spots without chlorosis or with weak chlorosis (resistance);

3 – necrotic spots more than 3 mm with chlorotic adjoining tissues, the leaves may have reddish colouring (susceptibility);

4 – necrosis and chlorosis occupied all leaf surface, mycelium tufts and conidia sporulation can be visible (high susceptibility);

2-3 – the size of spots are the same as at a score 3, but chlorosis is absent (intermediate type of reaction).

At a laboratory estimation of oat resistance to Pyrenophora leaf blotch a mix from different isolates from one population was used. For determination rare virulence to resistant oat genotypes 20 – 30 isolates from each of 3 populations from Saint Petersburg region were used for inoculation.

Resistance of the selected accessions was checked on an artificial infection which was created by applying of a grain inoculum (100 g of artificially infected autoclaving oat grains per 1 m²).

The first score of types of reactions was carried out in 15-20 days in a tillering stage on following scale:

1 – highly resistant. A spots are absent, or a spots fine (up to 3 mm at length and 1.5 mm at width), without clorosis;

2 – moderate resistant. A spots fine (5-10 х 1.5-3.0 mm), with chlorosis or without it;

3 – susceptible. A spots 20-75 х 5-12 mm, with large yellow halos;

4 – highly susceptible. Lesions is continue to enlarge and coalesce to form blotches that cover large areas of leaves.

The second score was carried out in a flowering stage. Types of reactions and disease severity (%) were determined.

Field estimation of resistance of oat cultivars on a natural infection was carried out also in flowering stage: 30 plants on the plot of 1 m² were studied and the type of reaction and a degree of disease severity on all leaves, including a flag – leaf was determined.

 

Results and discussion

Studies the virulence of 40 P. avenae isolates to 209 oat cultivars and accessions allowed to postulate the specificity of host-pathogen interaction in pathosystem oat – P. avenae. Differential interaction of isolate – oat genotype was proved with high significance (Р=0,999). High heterogeneity of P. avenae populations on virulence to selected oat differentials, and on DNA structure was shown. These data was the basis for searches of sources of specific and nonspecific oat resistance to Pyrenophora leaf blotch.

 

Resistance of commercial oat cultivars

Laboratory studies of 78 oat release commercial cultivars form Russian Federation allowed to determine 7 resistant cultivars to Pyrenophora leaf blotch (number of virulent isolates up to 10 %). These cultivars belong to one cultivated species A. sativa L. (table 1). On an artificial infection they also have been recorded as moderate resistant. On cultivars Selma, Kubanskii, Belozernyi and Boog has been marked type of reaction 1 and both of disease severity and disease frequency – 10 %; on cultivars Taezhnik, Pisarevskii and Metis observed type of reaction 2, and both of disease severity and disease frequency (number of plant with symptoms of disease) – 20 %.

 

Table 1. Resistant to P. avenae commercial oat cultivars (estimation in field in a flowering stage and in laboratory in a seedling stage, 2002-2003)

 

32 oat cultivars from 78 commercial to which less than 30 % virulent isolates were found in laboratory conditions, were studied on the artificial infection. Among these cultivars only 9 (Weikus, Mirnyi, Argamak etc.) appeared to be resistant and moderate resistant (types of reactions 1 and 2). Disease severity and disease frequency on them were 10-15 % and 10-20 %, accordingly. Other cultivars (for example Skorospelyi and Krasnodarskii – 73) had type of reaction 4 on infection and in some cases disease severity and disease frequency reached 40 and 50 %, accordingly.

 

The characteristic of resistance to P. avenae of oat accessions on an artificial infection.

170 oat cultivars and accessions were studied on an artificial infection: 90 from them were susceptible, 42 – moderate resistant, 22 – resistant and 16 – high resistant.

Among accessions before studied in the European oat disease nursery (EODN), 4 were characterized as high resistant (type of reaction 1: IL 85-6467, IL 86-6404, Melys and SG-K-961010. In the laboratory test there were not more than 7.5 % virulent isolates to these accessions (table 2).

Among accessions from the gene stock collection of VIR on an artificial infection 12 were highly resistant: Gopher Oats, Saia, Dupree, Minhafer, ТAM 0-312, Pc 49, Riel, Pc 61, Coker 227, IA H 677 and Bondvic which also had been infected with not more than 10 % isolates in laboratory conditions (table 2).

 

Table 2. Oat accessions with high resistance to P. avenae from the gene stocks collection of VIR

№ catalogue VIR	Cultivar	Origin	Number of virulent isolates in population from Rozhdestveno, %	On an artificial infection
				Disease severity, %	Disease frequency, %
7684	Gopher Oats	USA	10.0	10	10
11008	Saia	Brazil	5.0	5	10
11010	Bondvic	USA	5.0	5	10
11192	Dupree	USA	10.0	10	10
11206	Minhafer	USA	5.0	10	10
13280	ТAM 0-312	USA	7.5	5	10
13666	Pc 49	Canada	7.5	5	10
14022	Riel	Canada	5.0	5	10
14315	IL 85-6467	USA	7.5	5	10
14320	IL 86-6404	USA	7.5	5	10
14432	Pc 61	Canada	7.5	10	10
14444	Coker 227	USA	10.0	10	10
14446	Местный	Poland	5.0	5	10
14526	Melys	Great Britain	5.0	10	10
14769	IA H 677	USA	10.0	10	10
14807	SG-K-961010	Czech Republic	5.0	5	10
The susceptible control
11840	Borrus	Germany	50.0	75	75

 

The data received in result of seven years studying of oat accessions in EODN (Šebesta et al., 1995; 2000) and our data in most cases are coincide. However such accessions as: Cc 4146, Cc 6490, Manod, POB-W 14391/93 and Rodney ABDH, characterized as susceptible in West Europe, in our experiments showed resistance. On the contrary the accession Pc 55, was evaluated as resistant (Šebesta et al., 2000) in our experiments has been characterized as high susceptible. It may testify the differences in P. avenae population structure in Northwest of Russian Federation and in the Western Europe.

In some accessions the high level of horizontal resistance is present. For example, cultivars Chernigovskii – 27, Krasnoobskii and Orlando had a high number of virulent isolates in the laboratory tests – 42.5, 70.0 and 35.0 %, accordingly. Since on the artificial infection they showed a high degree of resistance (the type of reaction 1), disease severity 5 % and disease frequency – 10 %; also cultivars Rodney M, Zlatak and accessions IL 86-1158, Pc 50-4, Pc 67 and Рс 47 on an artificial infection showed moderate resistance, since in laboratory conditions were found 40.0 – 57.5 % virulent isolates. In these cases different level of horizontal resistance or adult plant resistance can be postulated.

Thus, release commercial oat cultivars and accessions from gene stocks collection of VIR were characterized on resistance to Pyrenophora leaf blotch. All selected accessions with high rate of resistance can be used as sources in oat breeding.

 

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