Euphytica 96: 327–330, 1997. 327c 1997 Kluwer Academic Publishers. Printed in the Netherlands.

Resistance to Karnal bunt in Hordeum chilense and its amphiploids withTriticum species

R.S. Chauhan & B.M. SinghBiotechnology Centre, HPKV, Palampur-176 062, India

Received 10 August 1996; accepted 7 April 1997

Key words: amphiploids, Karnal bunt, resistance, Tilletia indica, tritordeum, Hordeum chilense

Summary

Reactions of Hordeum chilense accessions H1 and H7 and their amphiploids, HT8, HT9 and HT28 (named astritordeum) alongwith wheat lines, T22, T24 and T59 used in their synthesis, were studied for resistance to theKarnal bunt pathogen (Tilletia indica) of wheat. Both the accessions of H. chilense and one tritordeum line, HT8,were rated as highly resistant with zero co-efficient of infection, whereas the other two tritordeum lines HT28 andHT9 were rated as moderately susceptible and susceptible with 5.2 and 10.5 co-efficients of infection, respectively,compared to reaction of the wheat lines involved in their synthesis. Karnal bunt infection was maximum on thesusceptible wheat cultivar WL-711 with 24.3 co-efficient of infection. All the wheat lines involved in the synthesisof amphiploids were susceptible to Karnal bunt except, T59 (Triticum sphaerococcum) (6X), which showed amoderate level of resistance.

Introduction

Karnal bunt of wheat caused by Tilletia indica Mitrais a serious floral infecting disease of wheat in themajor wheat growing areas of India (Gill et al., 1981)and some other wheat growing countries of the world(Nath et al., 1981). The pathogen is known to infectbread wheat, durum wheat and triticale (Agarwal etal., 1977). The disease causes direct losses to yieldand also affects the market value of wheat, becauseKarnal bunt infected grains are not accepted anywherein the world due to the threat of Karnal bunt intro-duction in disease free countries. Chemical controlof the disease is not economical and therefore hostresistance is the only sustainable disease managementstrategy. A high degree of resistance is highly desir-able in developing disease resistant wheat cultivars. Atpresent no wheat genotype is known to possess highdegree of resistance to Karnal bunt (Hoffman, 1983),which has been found only in barley (Warham, 1988)and in wheat-barley addition lines (Chauhan & Singh,1994). However, transfer of resistance from barley orwheat-barley addition lines to wheat appears to be dif-ficult at present because of the difficulties in inducing

homeologous pairing in spite of the report of Islam& Shephard (1992), who were successful in produc-ing wheat-barley recombinant chromosomes throughinduced homeologous pairing.

In recent years Hordeum chilense and itsamphiploids with Triticum species named as tri-tordeum have been found to be potential sourcesof resistance to septoria leaf blotch and powderymildew of wheat (Rubiales et al, 1992, 1993). TheH. chilense � Triticum spp. amphiploids also havepotential as a new crop (Martin, 1988; Alvarez et al.,1992). Our study reports the presence of Karnal buntresistance in H. chilense as well as in tritordeum lines.

Materials and methods

Seed stocks

The accessions of H. chilense and tritordeum lines wereprocured from Dr. A. Martin, Institute of SustainableAgriculture, Spain. Seed of individual lines/accessionsalong with parental wheat lines were multiplied in thescreenhouse. Spikes were bagged at anthesis to avoid

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Table 1. Reaction of Hordeum chilense accessions (H-numbers), wheat lines (T-numbers) and tritordeums (HT-numbers) to Karnal bunt infection

Line Ploidy Percent bunt infection Co-efficient of infection Disease reaction

level 1993–94 1994–95 Mean 1993–94 1994–95 Mean

H1* 2X 0 0 0 0 0 0 1 R

H7* 2X 0 0 0 0 0 0 1 R

HT8* 6X 0 0 0 0 0 0 1 R

T22 4X 14.7 7.7 11.2 5.9 4.3 5.1 1 S

T24 4X 11.0 6.7 8.3 5.5 4.9 5.2 1 S

HT9 – 23.3 13.0 18.1 12.4 8.6 10.5 2 S

T59 6X 11.0 4.3 7.6 3.1 1.7 2.4 2 R

HT28 8X 14.3 8.0 11.1 5.6 4.8 5.2 1 S

WL-711 6X 46.7 21.7 34.2 31.7 16.9 24.3 3 S

LSD (5%) 2.58 2.04 0.9

* = Highly resistant; – Not known to authors.

cross pollination. The wheat lines T22 = cocorit (4X),T24 = MA (Mexicalli � Andalucia) (4X), T59 = T.sphaerococcum (6X) and two H. chilense accessions,H1 and H7, are the parents from which the tritordeumlines, HT8 = (H1� T22)� (H1� T24); HT9 = (H7�T59)� (H1�T22) and HT28 = HT9�HT8 have beendeveloped (Martin, 1988). These amphiploids wereselections from different cross combinations. WL-711,a highly susceptible cultivar of bread wheat, served asa check for Karnal bunt infection conditions.

Pathogen cultures and inoculation procedure

For isolating and culturing T. indica, the methods ofDhiman & Bedi (1983) and Warham & Burnett (1990)were followed. Teliospores of T. indica from buntedgrains were dusted over petriplates containing 20 mlsterile distilled water and incubated at 15 � 1 �C.After 20 days of incubation the floating teliosporeswere streaked on the surface of potato dextrose yeastextract agar slants and again incubated. The whitishfungal colonies which developed after 2–3 days weretransferred on to potato dextrose yeast extract agarplates and incubated at 20 � 1 �C. After 15–20 days,10–20 ml of distilled water was added to each plate, thefungal mass was scraped and the resultant suspensionwas filtered through four layers of muslin cloth. Con-centration of allantoid sporidia was adjusted to about10,000 per ml with the help of a haemocytometer. Tentillers of each accession/line were selected for inocu-lation and each spike was injected with 1 ml of sus-pension into the boot at growth stage GS44 (Zadoks etal., 1974) using a hypodermic syringe. The experiment

was conducted in a screenhouse and repeated for twocrop seasons (1993–4, 1994–5).

Scoring for reaction

The intensity of Karnal bunt infection on individuallines was recorded according to the scale of Aujla et al.(1989) taking severity (total bunted grains in a spike)and response (extent of bunt infection on individualgrains) into consideration. Response was categorisedinto five grades of infection depending on the intensityof bunt infection in individual grains. Numerical val-ues of 0, 0.25, 0.5, 0.75 and 1.0 were assigned to 0, 1,2, 3 and 4 grades of infection respectively. Number ofgrains in each grade of infection was multiplied withthe numerical value to obtain gross total. Co-efficientof infection was calculated by dividing the gross totalwith total number of grains in the inoculated ear andmultiplied with 100 to get the value in per cent. Inten-sity of Karnal bunt was categorised into co-efficientsof infection for each line as follows: 0: highly resistant(1 R); 0.1–5.0: resistant (2 R); 5.1–10.0: moderatelysusceptible (1 S); 10.1–20.0: susceptible (2 S); 20.1and above: highly susceptible (3 S)

Results and discussion

Two accessions of H. chilense, H1 and H7, and one tri-tordeum line, HT8, were found completely free fromKarnal bunt infection with zero co-efficient of infec-tion during both crop seasons and therefore, rated ashighly resistant. Two durum wheat lines, T22 (4X) and

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T24 (4X) showed 5.1 and 5.2 as mean co-efficientsof infection respectively, and were rated as moderate-ly susceptible. Per cent mean bunt infection was sig-nificantly different among three tritordeum lines withmaximum in HT9 (18.1) and zero in HT8. Per centbunt infection was higher in wheat line T22 (11.2)compared to lines T24 (8.3) and T59 (7.6). Thus thetrend of Karnal bunt infection on tritordeum lines aswell as on their wheat parents for both years of testingclearly indicates that Karnal bunt resistance in HT8 iscontributed by H. chilense accession H1 because percent bunt infection and co-efficient of infection wereof susceptile type on T22 and T24 involved in the syn-thesis of HT8. Tritordeum line HT9 was rated as sus-ceptible with 10.5 co-efficient of infection, despite oneof its wheat components T59 showing moderate resis-tance to Karnal bunt infection during both seasons oftesting. Similarly, tritordeum line HT28 was also rat-ed as moderately susceptible with a mean co-efficientof infection of 5.2. Karnal bunt infection was max-imum in 1993–94 with 31.7 co-efficient of infectioncompared to 16.9 in 1994–95 on the susceptible wheatcultivar WL-711. Mean per cent bunt infection and co-efficient on infection were 34.2 and 24.3 respectivelyon susceptible wheat cultivar WL-711.

Absence of Karnal bunt resistance in two tri-tordeum lines, HT9 and HT28, can be attributed tothe fact that during the development of these syntheticamphiploids, there was no selection for Karnal buntresistance although in the development of HT9 whichshowed maximum susceptibility not only the highlyresistant H. chilense accessions H1 and H7, but also amoderately resistant hexaploid wheat species T. sphae-rococcum, were involved. Per cent bunt infection wasalso significantly higher on HT9 compared to HT28in spite of the fact that the ploidy level of the latteramphiploid is higher. Therefore, the observations ofRubiales et al. (1991, 1993) that resistance to wheatrusts in tritordeums is either predominantlycontributedby the wheat parents or the expression of H. chilenseresistance is inhibited by the wheat genome, do notappear to be applicable in case of Karnal bunt. Howev-er, possibilities of such conclusions are not yet exclud-ed until either additional plant material of tritordeumsis evaluated for Karnal bunt resistance or the expres-sion of Karnal bunt resistance genes is studied in genet-ic backgrounds of different ploidy levels. Reports onthe genetic basis of Karnal bunt resistance till nowhave indicated that degree of resistance in wheat ispositively correlated with the number of genes con-trolling resistance (Fuentesdavilla et al., 1995; Singh

et al., 1995). In another study on evaluation of Karnalbunt resistance in advanced breeding lines derived fromcrosses between synthetic hexaploids (T. turgidum �T. tauschii) and T. aestivum cultivars, Villareal et al.(1995) were successful in identifying one line free fromKarnal bunt infection out of 800 tested under artificialinoculations. These reports as well as those publishedon identification of Karnal bunt resistance in wheat andalien/wild species indicate that dilution of Karnal buntresistance can occur at higher ploidy levels, because ahigh degree of Karnal bunt resistance has been reportedonly in diploid species, Secale cereale, Hordeum vul-gare and Aegilops species followed by less resistancein tetraploid, T. turgidum and the least in hexaploid,T. aestivum (Chauhan & Singh, 1994, 1995; Warham,1988; Warham et al., 1986).

Acknowledgement

The authors are thankful to Dr. A. Martin, Institute ofSustainable Agriculture, Cordoba, Spain for sendingseed material used in the study.

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