GrainGenes

OKLAHOMA

Oklahoma State University

Plant Pathology Department, 110 Noble Research Center, Stillwater, OK 74078-9947 USA.

R.M. Hunger, J.L. Sherwood, C.K. Evans, and J.R. Montana.

Foliar diseases of wheat.

The 1993 Southern Regional Performance Nursery (SRPN) was tested for reaction to wheat leaf rust (Puccinia recondita f. sp. tritici) and tan spot [Pyrenophora tritici-repentis (PTR)]. Two single-pustule isolates (SPI) of P. recondita f. sp. tritici were used to test the SRPN. One SPI (87 CTY) had an avirulence virulence formula of 2a 9 19 26 / 1 2c 3 3ka 11 16 17 24 30. The second SPI (87 SXL) had an avirulence/virulence formula of 2a 9 19 / 1 2c 3 3ka 11 16 17 24 26 30. Seedling tests in the greenhouse indicated that entries 05 (OK88767-02), 06 (OK88767-15), 14 (TX90V7911), 15 (TX91V5739), 29 (N87V106), 31 (NE90479), and 33 (NE90574) were resistant to both SPIs. Entries 04 (OK88767-11), 07 (OK88767-24), 16 (TX91V3308), and 22 (KS831374-142) were resistant to 87 CTY, and entries 26 (KS92P0363-134) and 27 (KS92P0425-155) were resistant to 87 SXL. The complete results of this screening were published in Biological and Cultural Tests for Control of Plant Disease 9:118, APS Press, 1994.

The 1993 SRPN and 1993 Northern Regional Performance Nursery (NRPN) were tested for reaction to tan spot (P. tritici-repentis) by measuring lesion lengths produced on inoculated seedlings following inoculation with conidia of P. tritici-repentis. Results indicated that entries 22 (KS831374-142), 24 (KS92P059E), 43 (T70), and 36 (XH1520) from the SRPN expressed levels of resistance comparable to that of the resistant winter wheat check `Red Chief'. Entry 32 (MT8719) from the NRPN was as resistant as Red Chief, and entries 14 (ND89142), 18 (NE89526), 30 (WI88-083), 31 (MT8713), and 35 (W-235) from the NRPN were as resistant as the resistant check 'Agrotricum'. The complete results of this screening were published in Biological and Cultural Tests for Control of Plant Disease 9:123-124, APS Press, 1994.

For his Ph.D. thesis, Mr. C.K. Evans compared screening wheat genotypes for reaction to tan spot as seedlings in the greenhouse with screening adult plants in the field. The reaction to tan spot of seedlings in the greenhouse was determined by measuring lesion lengths on seedling leaves. Reaction in the field was determined by measuring tan spot severity following inoculation with conidia. To facilitate infection following conidial inoculations in the field, a mist system was constructed to maintain free moisture on foliage. Results indicated that reactions determined on seedlings in the greenhouse correlated with reaction to tan spot in the field trials, but factors other than tan spot were the primary determinants of agronomic traits such as yield and thousand kernel weight.

Wheat soilborne mosaic virus (WSBMV).

Reaction of entries in the 1993 SRPN to WSBMV was determined in the field by symptomatology and the enzyme-linked immunosorbent assay (ELISA). Sixteen entries [05 (OK88767-02), 06 (OK88767-15), 16 (TX91V3308), 22 (KS831374-142), 23 (KS84063-9-7), 24 (KS92P059E), 25 (KS92P0263-137), 27 (KS92P0425-155), 28 (KS89H48-1, 34 (XH1455), 35 (XH1485), 36 (XH1520), 39 (W87-017-44), 42 (T4731), 43 (T70), and 45 (TH905)] were considered resistant to WSBMV. One entry [31 (NE90479)] may be resistant, because no positive values from ELISA were obtained, but two of the three reps exhibited symptoms indicative of WSBMV. The reactions of three entries [26 (KS92P0363-134), 37 (XH1529), and 38 (XH1610)] were puzzling because no symptoms indicative of WSBMV were

seen, but values from ELISA were positive in the three reps of these entries. The complete results of this screening are available in, Biological and Cultural Tests for Control of Plant Disease 9:123-124, APS Press, 1994.

Wheat streak mosaic virus (WSMV).

In 1993, a mixed infection of Agropyron mosaic virus (AgMV) and WSMV was identified by ELISA in hard red winter wheat in northwestern Oklahoma. The estimated yield loss in grain was 80-85 % in this field. Potential alternative gramineous hosts were collected from the periphery of this field and tested by ELISA for the presence of AgMV and WSMV. Four [Elymus smithii, Bothriochloa laguroides DC., Aristida sp., and Sorghastrum nutans (L.) Nash] of 14 grasses were positive for AgMV, and one grass (Setaria virdis L.) tested positive for WSMV. This is the first report of AgMV and the first report of a mixed infection of AgMV and WSMV in wheat in Oklahoma.

Serotypes of WSMV were reported in 1993. Research since then has confirmed the existence of serotypes, and investigations into the importance of serotypes in screening for resistance to WSMV are underway. In addition, variation in serological reactivity of WSMV isolates and variation in sequence of the coat protein region of these isolates is being determined.

Breeding for disease resistance.

A collection of emmers (Triticum dicoccoides) from Israel and Turkey was tested for reaction to leaf rust, tan spot, powdery mildew, and wheat soilborne mosaic virus. Plants resistant to these diseases have been identified and currently are being increased, retested, and crossed with cultivars of hard red winter wheat (T. aestivum).

A second year of trials is in progress to evaluate 26 germplasm lines for disease reaction and other agronomic traits. These lines combine leaf rust resistance from Eastern European wheats with resistance to WSBMV in hard red winter wheats. Results from the past two seasons will be used to identify possible germplasm releases from these lines.

Publications.

Farih AF, Hunger RM, Gough FJ, and Claypool PL. 1994. Components of resistance to Septoria tritici blotch in four Moroccan bread wheat genotypes. Cereal Res Comm 22:83-90.

Montana JR, Jacobs JL, Hunger RM, and Sherwood JL. 1994. First reports of Agropyron mosaic virus in wheat and mixed infection with wheat streak mosaic virus in Oklahoma. Plant Dis 78:432.

Evans CK, Hunger RM, and Siegerist WC. 1994. Reaction of the Northern Regional Performance Nursery to tan spot, 1993. Biol and Cul Tests for Control of Plant Dis 9:123.

Evans CK, Hunger RM, and Siegerist WC. 1994. Reaction of the Southern Regional Performance Nursery to tan spot, 1993. Biol and Cul Tests for Control of Plant Dis 9:124.

Hunger RM and Siegerist WC. 1994. Reaction of the Southern Regional Wheat Performance Nursery to leaf rust, 1993. Biol and Cul Tests for Control of Plant Dis 9:118.

Hunger RM, Siegerist WC, Myers LD, and Sherwood JL. 1994. Reaction of the Southern Regional Wheat Performance Nursery to wheat soilborne mosaic, 1993. Biol and Cul Tests for Control of Plant Dis 9:127.

Evans CK, Hunger RM, and Siegerist WC. 1994. Infection efficiency of conidia and conidiophores of Pyrenophora tritici-repentis. Phytopathology 84:1070 (Abstract).

USDA Plant Science Research Laboratory

Agricultural Research Service, 3101 N. Western St., Stillwater, OK 74074, USA.

C.A. Baker, D.R. Porter, J.A. Webster, J.D. Burd, N.C. Elliott, J.H. Lee, and K.A. Shufran.

Host plant resistance/germplasm enhancement.

The missions of the host-plant resistance program are to identify sources of Russian wheat aphid (RWA)-resistance in cereal crops, determine the nature of resistance, and assist in the development and release of RWA-resistant small grain germplasm. This year, approximately 7,500 wheat accessions were screened; 76 of the accessions were identified as having some level of resistance.

Germplasm enhancement for RWA continued. Selected resistant lines have been backcrossed and/or topcrossed to cultivars for the development of elite RWA-resistant germplasm. Several germplasm releases with different resistance genes are forthcoming. Studies on an RWA-resistant selection from PI225217 indicated that tolerance is the most important mechanism of resistance and is inherited as a single, dominant gene. Genetic analysis of three additional lines has been completed. In all cases, inheritance of resistance was controlled by two genes. Genetic analysis of additional lines is continuing. In order to identify and enhance genetic diversity, allelism tests of identified sources of resistance are ongoing. Transfer of RWA resistance genes from triticale to wheat continued. Several populations resulting from x-ray irradiation therapy were advanced. RWA-resistant wheat plants were recovered and will be examined cytologically to determine chromosomal complement. RWA resistance evaluation of various wheat accessions from around the world continued. (Baker, Porter, and Webster)

Biocontrol.

The exotic hymenopterous parasitoids Aphelinus asychis Walker, Aphelinus albipodus Hayat and Fatima, Aphelinus varipes (Forester), Diaeretiella rapae McIntosh, Aphidius colemani Viereck, Aphidius matricariae Haliday, and Ephedrus plagiator (Nees) were released at several sites in eastern Colorado from 1991 through 1994 in an attempt to establish the species in wheat agroecosystems for biological control of the Russian wheat aphid (RWA). Approximately 1.8 million exotic parasitoids were released during the 4 years. Recovery of A. asychis and A. albipodus near Akron, Colorado, in 1994, and A. asychis near Pritchett, Colorado, in 1994, 1 year after releases were made at the locations indicates that exotic species had established populations. Recovery of D. rapae, an endemic species, in relatively high numbers in 1994 near Akron, Colorado, where previous surveys had shown rare incidence of parasitism of RWA by this species suggests that an exotic strain of D. rapae also may have established. However, the increase in parasitism of RWA by D. rapae may reflect annual variation in parasitism rates by native D. rapae or adaptation by native D. rapae to the recently introduced host. (Burd, Elliott, and Lee)

Aphid biology/genetics.

Russian wheat aphid. Studies of genotypic and phenotypic variation of Russian wheat aphid populations in the US are in progress. The importance of noncultivated grass hosts (e.g., crested wheat grass, Canada wild rye, volunteer wheat, and barley), which serve as oversummering `bridges' and `reservoirs', is being evaluated with regard to their effect on RWA metapopulation dynamics and population genetics. Genotypic diversity of Russian wheat aphids on cultivated and noncultivated hosts is being determined using DNA fingerprinting techniques. Phenotypic variation (i.e., biotypes) on resistant wheat and barely sources also is being determined for Russian wheat aphids collected from noncultivated hosts.

A complex of Diuraphis species aphids, including the Russian wheat aphid, exists in North America and utilizes wheat and barley as hosts. The polymerase chain reaction (PCR) is being utilized as an aid in separating these species,

as well as determining their phylogenetic relationships. Field studies on the effects of host plant resistance in a hard red winter wheat (`Halt') on RWA overwintering biology and natural enemies are in progress. (Burd, Elliott, Shufran, and Webster)

Greenbug. Using DNA fingerprinting techniques, specific greenbug genotypes (i.e., clones) were found infesting both grain sorghum and weedy grasses in the same field. This indicated that these genotypes moved freely to sorghum from johnsongrass and crabgrass, or vice-versa, and that they are not limited to a single host species.

Previous studies have shown a great deal of clonal diversity among greenbugs collected in wheat and sorghum. It is believed that holocycly (intermittent sexual reproduction) plays a key role in generating this diversity. Studies are in progress to determine the effect of sexual reproduction on clonal diversity. (Burd, Elliott, Shufran, and Webster)

Personnel changes.

Dr. Kevin A. Shufran has joined us, in a postdoctoral position, working on aphid genetics. Dr. Jang-Hoon Lee is a visiting scientist from South Korea working on biological control and ecology of the Russian wheat aphid

Publications.

Baker CA, Porter DR, and Webster JA. 1994. Registration of STARS-9302W and STARS-9393W Russian wheat aphid-resistant wheat germplasm. Crop Sci 34:1135-1136.

Baker CA, Webster JA, and Porter DR. 1994. Inheritance and mechanisms of Russian wheat aphid resistance in PI 225217. Agron Abstr:110.

Belefant-Miller H, Porter DR, Pierce ML, and Mort AJ. 1994. An early indictor of resistance in barley to Russian wheat aphid. Plant Physiol 105:1289-1294.

Burd JD, Webster JA, and Porter DR. 1994. Russian wheat aphid injury and plant damage. In: Proc 6th Russian Wheat Aphid Workshop (Peairs FB, Kroenig ML, and Simmons CL comps), Colo. State Univ. Ft. Collins, CO. Pp. 21-36.

Elliott NC, Reed DK, French BW, and Kindler SD. 1994. Aphid host effects on the biology of Diaeretiella rapae. Southwestern Ent 19:279-284.

Elliott NC, French BW, Reed DK, Burd JD, and Kindler SD. 1995. Effects of temperature and aphid host species on the biology of Syrian Diaeretiella rapae McIntosh (Hymenoptera: Aphidiidae). Can Ent 126:1515-1517.

Elliott NC, Kindler SD, Reed DK, and French BW. 1994. Parasitism, adult emergence, sex ratio, and size of Aphidius colemani (Hymenoptera: Aphidiidae) on several aphid species. Great Lakes Ent 27:137-142.

Grossl RA and Porter DR. 1994. Differential protein production in RWA- resistant and susceptible barley. Agron Abstr:211.

Lee JH, Graybosch R, Peterson CJ, and Porter DR. 1994. Identification of wheat-rye 1AL/1RS chromosomal translocations of diverse origin. Agron Abstr:210.

Merkle OG, Hatchett JH, Porter DR, and Webster JA. 1995. Registration of wheat germplasm (PI 510693) resistant to Hessian fly. Crop Sci 35:294.

Miller HL, Porter DR, Burd JD, Mornhinweg DW, and Burton RL. 1994. Physiological effects of Russian wheat aphid (Homoptera: Aphididae) on resistant and susceptible barley. J Econ Ent 87:493-499.

Mornhinweg DW, Brewer MJ, Struttman J, and Porter DR. 1994. Field evaluation of RWA resistant barley germplasm lines under RWA infestation. Agron Abstr:210.

Porter DR, Friebe B, and Webster JA. 1994. Inheritance of greenbug biotype G resistance in wheat. Crop Sci 34:625-628.

Porter DR, Nguyen HT, and Burke JJ. 1994. Quantifying acquired thermal tolerance in winter wheat. Agron Abstr:211.

Reed HC, Tan S, Reed DK, Elliott NC, Burd JD, and Walker C. 1994. Evidence for a sex attractant in Aphidius colemani Viereck with potential use in field studies. Southwest Ent 19:273-278.

Sebesta EE, Smith EL, Young HC Jr, Porter,DR and Webster JA. 1995. Registration of Teewon wheat germplasm. Crop Sci 35:294.

Sebesta EE, Wood EA Jr, Porter DR, Webster JA, and Smith EL. 1995. Registration of Amigo greenbug-resistant wheat germplasm. Crop Sci 35:293.

Sebesta EE, Wood EA Jr, Porter DR, Webster JA, and Smith EL. 1994. Registration of Gaucho greenbug-resistant triticale germplasm. Crop Sci 34:1428.

Webster JA and Treat RK comps. 1994. The Russian Wheat Aphid, Sixth Annual Report. USDA-ARS, PSWCRL Prog Rep. Pp. 94-001.