Abstract

Testing of common spring wheat cultivars against 15 test-pathotypes of leaf rust identified Lr resistance genes. Twelve resistance genes Lr1, Lr2a, Lr3, Lr10, Lr14b, Lr16, Lr19, Lr23, Lr25, Lr26 and Lr27+31 were revealed. Gene Lr1 was postulated in cvs. Moskovskaya 39, Ivolga, Bezenchukskaya 616 and Lutescens 661, gene Lr2a - in cv. Trizo, gene Lr3 - in cvs. Mironovskaya 808 and Zarya. The resistance gene Lr10 was discovered in cvs. Smena, Noris, Vadimovka, Nasledniza, Kurskaya 2038, Malahit and Svetoch. Lr14b was found in cvs. Zhemchuzhina Zavolzhya, Tulaykovskaya belozernaya, Tulaykovskaya stepnaya, and Lr16 - in cvs. Voronegskaya 14, Priokskaya, Krestiyanka. The resistance gene Lr19 was postulated in the cvs. Ekada 6, Aestivum 276, Ulia, Volgouralskay and Samsar. Cvs. Batiko, Pyramida and Tulaikovskaya 1 carried the resistance gene Lr23. Gene Lr25 was postulated in cvs. Amir, Milturum, Ester, MIS, Lada, gene Lr26 - in cvs. Alisa and Mironovskaya 61. The resistance gene Lr14b combined with Lr10 was determined in cv. Zhiguleovskaya, Lr27+31 - in cv. Enita. Eight Lr genes: 1, 10, 16, 27, 28, 31, 43 and 44 have been revealed in lines spring soft wheat with alien genes. Most cultivars and lines also have from one to four extra unidentified genes for resistance to leaf rust.

Introduction

Knowledge of genetic nature of the resistance to infective diseases, determining particular genes and a character of their inheritance and interaction, are essential for breeding for resistance. There are several approaches to identification of resistance genes to leaf rust in wheat cultivars: phytopathological testing, hybrid analysis, and molecular markers.

The phytopathological testing without hybrid analysis allows suggestion of the existence of resistance genes and their combinations in cultivars in question. Gene identification by this method rests on the "gene-for-gene" theory of Flor. Data for infection-type of the host: pathogen interaction have been used to postulate or verify the genes present in wheat cultivars for leaf rust and stem rust resistance (Chekowski et al., 2003; Kolomiets et al., 2003; Kovalenko et al., 2003; Lapochkina et al., 2003; McVey, 1989, 1992; McVey & Long, 1993; Modawi et al., 1985; Odintsova et al., 1986; Singh, 1983; Singh et al., 1999; Statler, 1984; Zhemchuzhina & Kryazheva, 2002).

Use of pathogen clones with different numbers and combinations of virulence genes is the important step of the investigation. Postulation of resistance genes in wheat cultivars will be effective providing that sets of test-cultures are available with virulence genes overcoming the resistance.

Materials and Methods

Resistance genes to leaf rust were determined in twelve common wheat cultivars and eighteen standard lines of wheat (2n=42), obtained by means of wide hybridization of the spring cv. Rodina with Aegilops speltoides. Wheat cultivars chosen for genetic study exhibited immunity the artificial disease nursery in the field or in the controlled climatic chamber.

As the test-cultures fifteen isolates collected in natural uredopopulations of the pathogen in Central, Low-Volga, Middle-Volga, North-Caucasian, and West-Siberian regions of Russian Federation were used. Pathotypes of P. triticina carried from 15 to 25 virulence genes. All pathotypes used belonged to ten races (FBK, FHT, PCT, PGT, PHK, PHT, TBT, TCK, TCT, and THT) according to the North American system of nomenclature (Long & Kolmer, 1989) (Table 1).

Experiments were carried out under strictly controlled conditions of the climatic chamber: average daily temperature +20°C, relative air humidity 60-70%, light intensity 10k lux, photoperiod 16 h. Plant were grown in the hydroponic culture and inoculated using the conventional technique.

The spore material P. triticina was reproduced on universally susceptible cultivar Khakasskaya in the climatic chamber. Infected plants were segregated in separately glass isolators.

Disease symptoms were estimated according to the 5-point scale of Mains and Jackson (1926). Infection types 0, 0; 1, 2, X- mean that a cultivar possesses resistance genes whereas types 3, 4, ?+ indicate the absence of such genes.
Resistance genes were identified by phytopathological testing that point to Lr-genes and their combinations in the test cultivars.

The resistance genes were postulated from comparison of infection types on tested lines with near isogenic Lr-lines of wheat cv. Thatcher infected with standard pathotypes of leaf rust.

Results and Discussion

The assessment of cultivars of common spring wheat against test-pathotypes of leaf rust fungus, P. triticina, identified different genes for resistance to this pathogen (Table 2). The comparison of test cultivars with isogenic lines of cv. Thatcher in their reaction to the infection allowed postulation of the presence of Lr-genes and their combinations in the test cultivars.

The cultivars Moskovskaya 39, Ivolga, Bezenchukskaya 616 and Lutescens 661 had susceptible type of reaction to most tests-pathotypes of P.triticina. The same reaction was shown on the isogenic line Lr1 of cv. Thatcher, postulating the presence the Lr1-gene in tested cultivars. However, the cultivar Bezenchukskaya 616 was resistance to only one isolate and Lutescens 661 to two, suggesting that the cultivar Bezenchukskaya 616 has got one and Lutescens 661 two extra non-identified genes of resistance.

Lr2a was revealed in the spring soft wheat cv. Trizo. Resistance to leaf rust gene Lr3 was postulated in the cvs. Mironovskaya 808 and Zaria.

The cvs. Smena, Noris, Vadimovka, Nasledniza, Malachit, Svetoch, Kurskaya and Zhiguleovskaya were infected with virulence pathotype pp.10, which matched the resistance gene Lr10 postulated in these cultivars. The same cvs. Vadimovka, Nasledniza, Malachit, Svetoch, Kurskaya were resistance to two isolates with virulence gene ??.10. This implies the Lr10 and two non-identified genes for resistance are presence in these cultivars. The cultivars Smena and Noris besides gene Lr10 carried out one extra gene and some unidentified genes.

The cv. Zhiguleovskaya was susceptible to the rust pathotypes containing both virulence genes ??. 10 and pp. 14b. This cultivar was resistant to test-cultures containing the virulence gene ?? 14b only. Hence, this means that cv. Zhiguleovskaya may contain both resistance genes Lr10 and Lr14b.

The cultivars Zhemchuzhina Zavolzhya, Tulaikovskaya stepnay and Tulaikovskaya belozernaya manifested susceptibility to all analyzed pathotypes of the fungus. The isogenic line Lr14b of cv. Thatcher had a similar reaction to the pathogen suggesting the presence of resistance gene Lr14b in the cv. Tulaikovskaya steppe.
Lr16 was identified in cultivars Voronezhskaya 14, Priokskaya, Krest'yanka. In addition cultivars Priokskaya, Krest'yanka carried one additional unidentified resistance gene.

The susceptibility of cvs. Samsar and Volgouralskay to test-pathotypes 138-15, 158-13, and 170-7 with virulence gene pp19, as well as the symptoms on this cultivar and on isogenic line Lr19 of cv. Thatcher, suggest the presence of Lr19 gene in cv. Samsar and Volgouralskay. Cultivars Ecada 6 and Aestivum 276 showed a susceptible reaction type to two pathotypes with virulence gene pp 19 while cv. Ulia was susceptible to one pathotype. Presumably cvs. Ulia, Ecada 6 and Aestivum 276 carry some unidentified resistance genes in addition to the gene Lr19.

Cultivars Pyramida and Tulaikovskaya 1 exhibited a susceptible reaction to test-pathotypes 142-14, 145-21, 158-13, 162-6, and 170-7 with virulence gene pp 23. Complementary interactions of these cultivars with isolates indicate the presence of Lr23 in the cultivars. The fact that these cultivars express the same reaction as the isogenic line Lr23 of cv. Thatcher confirms this conclusion. Gene Lr23 with one additional gene was postulated in winter wheat cv. Batko. Gene Lr25 in combination with other non-identified resistance genes was postulated in the cvs. Amir, Milturum, Ester, Lada, MIS. There was one extra gene for resistance in cv. Amir, which was resistant to 158-13 (with the supplementary gene pp.25), and cv. Milturum - to 191-7 (also with gene pp.25). The cv. Lada was resistance to two 191-7 and 161-7, cv. Ester to three - 191-7, 142-14, 158-13, cv. MIS to four - 191-7, 142-14, 149-6, 158-13 rust pathotypes with gene of virulence ??.25, implying the presence in these cvs. two, three and four extra non-identified genes for resistance, respectively.

The gene Lr26 was postulated in cvs. Aliza and Mironovskaya 61; Lr27+31 with one additional unidentified gene was found in cv. Enita.

Thus, the identification of resistance genes in wheat cultivars by means of phytopathological testing revealed (12) resistance genes: Lr1, Lr2a, Lr3, Lr10, Lr14b, Lr16, Lr19, Lr23, Lr25, 26, Lr27, Lr31. Gene Lr1 was postulated in cvs. Moskovskaya 39, Ivolga, Bezenchukskaya 616 and Lutescens 661, gene Lr2a - in cv. Trizo, gene Lr3 - cvs. Mirinovskaya 808 and Zaria, Lr10 - in cvs. Smena, Noris, Vadimovka, Nasledniza, Malachit, Svetoch and Kurskaya 2039. Cvs. Volgouralskaya, Ekada 6, Aestivum 276 and Ulia carried Lr19, cvs. Voronezhskaya 14, Priokskaya, Krestianka - Lr16. Lr23 was postulated in cvs. Batko, Pyramida, Tulaikovskaya 1, Lr25 - in cvs. Amir, Milturum, Ester, MIS, Lada, Lr26 - in cvs. Alisa and Mirinovskaya 61. The gene Lr10 combined with Lr14b was determined in cv. Zhiguleovskaya, Lr27+31 combined with one unidentified gene was postulated in cv. Enita. Most cultivars therefore have from one to four extra unidentified genes for resistance to leaf rust in there besides identified genes.

In immunologic tests of ten wheat-Aegilops lines to test pathotypes of leaf rust it has been established that most of the tested lines carry juvenile genes of resistance transferred from cv. Rodina: Lr1, Lr10, Lr16, Lr27, Lr28, Lr31, Lr43 and Lr44 (Table 3).

In a line 126/02i the gene for resistance Lr1 in a combination with one not identified gene is postulated. Lines 127/02i and 136/02i carry a gene for resistance Lr10 in combination with four unidentified genes for resistance. Line 148/02i has Lr16 in a combination to one additional gene. Lines 121/02i (1) and 132/01i has Lr28, line 132/01i has one more resistance gene, and line 121/02i (1) contains Lr44 in combination with another unknown gene. Line 98/02i has Lr27+31 with two additional genes are identified. Lines 106/02i and 121/02i (2) carry Lr43, and in a second sample 121/02i (2) there is another gene and in 106/02i are two unidentified resistance genes. Lines 129/02i (1), 129/02i (4) and 149/00i have Lr44. However, in lines 129/02i (1), 129/02i (4) there is another resistance gene, and in line 149/00i there are two additional resistance genes to P. triticina.

In lines of winter soft wheat with alien genes (32/98w = 28/01w, 84/98w= 30/01w) the Lr10 in combination with one unidentified gene to P.triticina is postulated.

The genes for resistance to leaf rust are not postulated because the lines with alien genes L-501, 85/01i, 97/01i, 79/02i, 96/02i, 152/02i (1), 155/03i had resistance reaction to all isolates in the infection test. We can therefore assume introgression new genes of resistance from Ae.speltoides, working as at the seedling and adult plant stage.

Discussion

Twelve genes for resistance to P. triticina were postulated as a result of testing 37 native cultivars to 15 test pathotypes. Most of them were inneffective for almost all regions of the world except for the cultivars with Lr19 gene are only (Volgogradskaya, Samsar, Aestivum, Ujlia). Account must be taken that in recent years this gene lost effectiveness in Russia.

The cultivars of wheat with additional unidentified genes are the greatest interest. It is necessary to use a wide spectrum of test pathotypes of leaf rust for postulation resistance genes. For full characterisation of test cultivars it is necessary to determine in them the presence the adult-plant resistance genes. Eight resistance genes were identified in the standard lines by crossing cv. Rodina and Ae. speltoides. The most of them have some unidentified resistance genes, among them 127/02i, 136/02i. These lines will be investigated further..

Acknowledgemets

Research had been done by project #1721, the International Science and Technology Center (ISTC)

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