IACR – Rothamsted, Harpenden, AL5 2JQ, United Kingdom.

 *Present Address: Department of Crop Science & Production

Sokoine University of Agriculture,

P.O. Box 3005

Morogoro - Tanzania

The survival activity of the grain aphid Sitobion avenae, an important vector of barley yellow dwarf virus (BYDV) was studied in six varieties of spring barley (Hordeum vulgare L.) in an attempt to explain the mechanisms in some varieties apparently conferring apparently resistance/tolerance to BYDV. There was no significant difference between the apparently resistant and susceptible varieties as they affect aphid survival. The mechanisms underlying BYDV resistance do not seem to involve factors that invoke alterations in the aphid survival and feeding behaviour. The results show that aphids do not survive less on the resistant varieties and that BYDV transmission among the varieties does not clearly differ.

Barley yellow dwarf virus (BYDV), a luteovirus confined to the phloem was first recognised and named as such in 1951 (Oswald and Houston, 1951), although it is believed to be a problem much earlier (Bremer, 1965).

The virus is found worldwide, having been identified in at least one country in every continent. It is the most widely distributed of all the cereal viruses (Rochow, 1970; Lister and Ranieri, 1995). Over 100 monocotyledonous species are known to be susceptible to BYDV including most grasses and all commercially available cereal cultivars (Plumb, 1977; Irwin and Thresh, 1990). Economic losses have been associated with BYDV in the U.K. (A'Brook, 1974), U.S.A. (Oswald and Houston, 1951) and New Zealand (Smith, 1963).

At least 25 aphid species have been reported as vectors of BYDV (Halbert and Voetglin, 1995). The grain aphid (Sitobion avenae), the rose grain aphid (Metopolophium dirhodum) and the bird cherry aphid (Rhopalosiphum padi) are the most important vectors in the U.K. (A'Brook and Dewar, 1980).

BYDV can be a serious problem in the U.K. in spring-sown cereals (Mann et al., 1992). It could be a problem one year in three (Tasker, 1995) and the use of tolerant/resistant varieties for pest and/or pathogen control is often perceived by the grower as an effective and cheap method of control. Resistance in cereals is thought to be related to aphid activity (Ogecha et al., 1992; Called et al., 1995). Hence, the fortuitous discovery of some varieties apparently resistant to BYDV by New Farm Crops (a subsidiary of Ciba-Geigy), Lincolnshire, United Kingdom made this study necessary.

Test plants used in this study were three BYDV 'resistant' (Cooper, R1; Optic, R2 and Amber, R3) and three 'susceptible' (Alexis, S1; Derkado, S2; and Triumph, S3) varieties of spring barley. Oat (cv. Dula) was used as the control since it is thought to be the most susceptible cereal to BYDV. Ten seeds of each variety were planted. One set was used for the four inoculation access feeding periods. One-week-old test plants were used and one winged viruliferous S. avenae per plant for the required length of time. Aphids were contained in a 2.5cm diameter cellulose acetate tube with a netting top. After each feeding/survival period, aphids were recorded as dead or alive. Any aphid which did not respond when touched with a camel hairbrush was regarded as being dead. Aphids were then removed and any nymphs killed. The feeding/survival period used were 6,12, 24 and 48 hours (Lowles et al., 1996; Banwo and Harrington, 1998). The experiment was replicated six times. The glasshouse mean temperature was 21^oC during this study. The indirect double sandwich ELISA (Lister and Rochow, 1979) was used in testing the plants for BYDV presence three weeks after inoculation.

ELISA test results showing the proportion of plants infected is presented in Table 1 and there was no host effect on BYDV transmission in all the varieties used. The result on aphid survival is summarised in Table 2 and there was a highly statistically significant difference in aphid survival between the different times (6hr, 12hr, 24hr and 48hr) studied. However, there was no significant difference in aphid survival in the groupings below;

a) Oats, all the "susceptible" (Alexis, S1; Derkado, S2; and Triumph, S3) combined together as a single entry and all the "resistant" varieties (Cooper, R1; Optic, R2; and Amber, R3) also combined together as a single entry. b) Oats, all "susceptible" varieties (Alexis, S1; Derkado, S2; and Triumph, S3) as individual entries and all the "resistant" varieties (Cooper, R1; Optic, R2; and Amber, R3) combined together as a single entry. c) Oats, all the "susceptible" (Alexis, S1; Derkado, S2; and Triumph,S3) and "resistant" (Cooper,R1;Optic,R2; and Amber,R3) varieties as individual entries.

Also, no significant relationship was also observed between;

a) Survival period, Oats, all the "susceptible" (Alexis, S1; Derkado, S2; and Triumph, S3) combined together as a single entry and all the "resistant" varieties (Cooper, R1; Optic, R2; and Amber, R3) also combined together as a single entry. b) Survival period, Oats, all "susceptible" varieties (Alexis, S1; Derkado, S2; and Triumph, S3) as individual entries and all the "resistant" varieties (Cooper, R1; Optic, R2; and Amber, R3) combined together as a single entry. c) Survival period, Oats, all the "susceptible" (Alexis, S1; Derkado, S2; and Triumph, S3) and "resistant" (Cooper, R1; Optic, R2; and Amber, R3) varieties as individual entries. There was a decreasing number of surviving aphids with an increase in time.

S1=Alexis; S2= Derkado; S3 = Triumph

R1= Cooper; R2=Optic; R3=Amber

** = Highly statistically significant (1%)

NS = Not statistically significant

TIME = Survival periods (6hr, 12hr, 24 hr and 48 hr)

F1 = Oats vs S1+S2+S3 vs R1+R2+R3

F2 = Oats vs S1 vs S2 vs S3 vs R1+R2+R3

F3 = Oats vs S1 vs S2 vs S3 vs R1 vs R2 vs R3

The results in Table 2 also show that aphid survival decreased with time in all the plant groupings. This corroborates reports by Hodgson (1977), Way (1968), Way and Cammell (1970) and Lowles et al. (1996). Deaths might be due to intrinsic causes since the acetate tubes used can also prevent aphids from being fed on by parasitoids or predators. Since there was no significant difference in aphid survival between the plants, there was no suggestion of any toxic substance in the plants that could negatively influence aphid survival. This agrees with McMurtry and Standford (1960), Walkey et al. (1985) and Cole et al. (1993).

Since no host effect on aphid survival and feeding was observed it seems unlikely that aphid survival would affect BYDV transmission in all the plants studied. This result and the one obtained earlier (Banwo and Harrington, 1998) may further validate the view that to date there is no commercial use of aphid resistance (at least in the United Kingdom) to control aphid activity or BYDV in spring barley.

A'Brook, J. (1974). Barley yellow dwarf virus: what sort of a problem? Ann. Appl. Biology. 77: 92 - 96.

A'Brook, J. and Dewar, A.M. (1980). Barley yellow dwarf virus infectivity of alate aphid vectors in West Wales. Ann. Appl. Biol. 96: 51 - 58.

Banwo, O.O. and Harrington, R. (1998). 'Is resistance to barley yellow dwarf virus in spring barley related to aphid feeding behaviour?' Barley Newsletter. Vol. 42. (In Press)

Bremer, K. (1965). Characteristics of barley yellow dwarf virus in Finland. Ann. Agr. Finland. 4: 105 - 120.

Caillaud, C.M., Di Pietro, J.P., Chamber, B. and Pierre, J.S. (1995). Application of discriminant analysis to electrical penetration graphs of the aphid S. avenae feeding on resistant and susceptible wheat. Jour. Appl. Entom. 119: 103-106

Cole, R.A., Rigall, W. and Morgan, A. (1993). Electronically monitored feeding behaviour of the lettuce root aphid on resistant and susceptible lettuce varieties. Entom. Exp. Appl. 68: 179 - 185.

Halbert, S. and Voetglin, D. (1995). Biology and Taxonomy of vectors of barley yellow dwarf. In Barley Yellow Dwarf. 40 years of Progress. (Ed. D'Arcy, C. and P.Burnett). A.P.S. Press Minnesota pp217-258.

Hodgson, C.J. (1977). The Biology of Myzus persicae and Brevicoryne brassica on healthy and cabbage black ringspot virus infected turnips. Ph.D Thesis. Wye College, University of London.

Irwin, M.E. and Thresh, J.M. (1990). Epidemiology of barley yellow dwarf: a study in ecological complexity. Ann. Rev. Phytopath. 28: 393 - 424.

Lister, R.M. and Ranieri, R. (1995). Distribution and economic importance of Barley Yellow Dwarf. 40 years of progress. Eds. D'Arcy, C. and P. Burnnett. A.P.S. Press, Minessota. pp. 29 - 54.

Lister, R.M. and Rochow, F. (1979). Detection of barley yellow dwarf virus by enzyme linked immunosorbent assay. Phytopath. 69: 649 - 654.

Lowles, A.J., Harrington, R., Tatchell, G.M. and Clarke, S.J. (1996). The effect of temperature and inoculation access period on the transmission of barley yellow dwarf virus by R. padi and S. avenae Ann. Appl. Biol.128: 45-53

Mann, J.A., Carter, N., and Plumb, R.T. (1992). The epidemiology of barley yellow dwarf virus in spring sown cereals and potential for its control. In Virus, Vectors and the Environ. 5th Int. Symp. Bary, Italy. P. 205.

McMutry, J.A. and Stanford, E.H. (1960). Observations of feeding habits of the spotted alfalfa aphid in resistant and susceptible alfafa plants. Jour. Entom. 53: 5, 714 - 716.

Ogecha, J., Webster, J.A and Peters, D.C. (1992). Feeding behaviour and development of biotypes E, G and H of Schizaphis graminum on winter malt. Journ Econ. Entom. 85: 1522- 1526

Oswald, J.W. and Houston, B.R. (1951). A new virus disease of cereals transmissible by aphids. Plant Disease Rep. 35: 471 - 475.

Plumb, R.T. (1977). Grass as a reservoir of cereal viruses. Ann. Phytopath. 9: 361 - 364.

Rochow, W.F. (1970). Barley yellow dwarf virus. Desc. of Plant Viruses CMI/AAB 32.

Smith, H.C. (1963). Control of barley yellow dwarf virus in cereals. New Zealand Jour. Agr. Res. 6: 229 - 234.

Tasker, C. (1995). "Spring barley to rise again". Farmers Weekly 14 July 1995. pp. 56 - 57.

Walkey, D.G.A., Ward, C.M. and Phelps, K. (1985). Studies on lettuce mosaic virus in commercial lettuce cultivars. Plant Path. 34: 545 - 551.

Way, M.J. (1968). Intra-specific mechanisms with special reference to aphid populations. Pp. 18 - 36. In Southwood, T.R.E. (Ed.). Insect Abundance. Oxford, Blackwell Sc. Publ. (Symposium R.E.S.N., London).

Way, M.J. and Cammell, M.E. (1970). Self-regulation in aphid populations. Proc. Adv. Study Inst. on Dynamics of Numbers in populations. Oostbeeke, The Netherlands. 1970: 232 - 239.