TEXAS

Texas A & M University

Southwestern Great Plains Research Center, Bushland, TX 79102, USA.

Research Center, Rt. 7, Box 999, Beaumont, TX 77713, USA.

Research and Extension Center, 17360 Coit Road, Dallas, TX 75252, USA.

Soil & Crop Science Department, Texas A&M University, College Station, TX 77843, USA.

Agricultural Research Center, Drawer E., Overton, TX 75684, USA.

Research Center, P.O. Box 1658, Vernon, TX 76384, USA - W.D. Worrall and S.J. Caldwell.

Amarillo.

B.W. Bean, M.D. Lazar, G.J. Michels, C.M. Rush, C.D. Salisbury, J.D. Booker, J. Hu, G.L. Peterson, G.M. Piccinni, J.E. Simmons, and Q. Xue.

High Plains. A mild winter in 1993-94 was followed by two severe freeze events on April 3 and April 30, the latter including hail in many locations. The entire spring season was drier than normal across the region. Significant infestations of greenbug in the fall of 1993 resulted in widespread outbreak of BYDV. Both irrigated and dryland yields were below normal. The highest-ranking irrigated varieties included Quantum 588A, Ogallala, TAM-201, and Chisholm. The highest dryland yields were produced by TAM-105, TAM-200, TAM-202, and Ogallala.

Drought tolerance. Variability in response to irrigation has been observed among sister selections of pedigree `(TAM105*4/Amigo)*4 //Largo', over several years of testing at Bushland. Such distinctions have been shown not to be related to timing of developmental events or variation in disease or insect reactions. The largest distinction among these closely related lines, as measured by the Fischer-Maurer `S' statistic, is between TX86A8072 (greater stress tolerance) and TX86A5606 (lesser stress tolerance). Evaluation of conventional yield components indicates that only seed weight variation explains the differences in irrigation response between these two lines. Preliminary data from 1994 only suggest that the distinction may be explained further by a combination of higher CO₂ incorporation rate and longer green leaf duration in TX86A8072.

Greenbug resistance. Near-isogenic lines have been developed for resistance/susceptibility to biotype `E' greenbug, based upon resistance previously identified in Largo. An examination was conducted of development and fecundity of biotype `C' and `E' greenbugs, restricted to a single host, either TAM-105 (susceptible to both biotype), TAM-107 (pedigree `TAM105*4/Amigo', biotype C resistant), or one of a pair of NILs (pedigree `(TAM105*4/Amigo) *5//Largo'). Responses of biotype C to resistant hosts were not significantly different, whereas fecundity on the susceptible host (TAM-105) was nearly fourfold greater than on the resistant hosts. Significant differences in fecundity of biotype E were found, not only between resistant and susceptible hosts, but also among the three susceptible hosts,

with fecundity being lower on hosts having biotype C resistance than on the biotype C-susceptible host. In another study involving closely related lines differing in resistance genes, the response of seedling wheat to greenbug infestation was measured in terms of dry weight accumulation. In that study, a slight delay in plant dry weight reduction and death was observed in biotype C-resistant lines infested with biotype E, compared to lines lacking biotype C resistance. These results suggest that some resistance genes may be at least marginally better than no resistance genes, even after a change of biotype.

New virus-like disease. In 1993, a new virus-like disease was observed first on sweet corn and some field corn hybrids on the High Plains of Texas. The disease was found subsequently in wheat. The causal agent of this disease has not been determined, but is not a tenuivurus as initially speculated. Although disease etiology is unknown, the wheat curl mite has been identified as the vector. When young corn seedlings are infested with mites taken from diseased wheat, they will develop small chlorotic lesions within 7 to 10 days. On wheat, disease symptoms are nearly indistinguishable from those caused by wheat streak mosaic virus. However, with the new disease, stripes and streaks are more yellow than with wheat streak. Furthermore, when plants are infected early in the fall, they often turn bright yellow and then die. The impact of the disease on 1994 wheat yields could not be determined because of other diseases and insect damage.

All sweet corn cultivars evaluated to date have been highly susceptible, whereas most field corn hybrids are resistant. However, some F₂ plants from resistant hybrids were found to be susceptible to the disease. This suggests that one of the parents of the hybrid was susceptible and that disease resistance in field corn likely is due to a single dominant gene. Furthermore, in susceptible cultivars of field corn, there appears to be a relation between plant age and susceptibility. This is probably not the case with wheat, although there may be some disease tolerance may occur in some wheat lines.

In a 1994 variety trial planted by Dennis Newton, county extension agent in Deaf Smith County, definite differences in disease severity among entries were observed. All oats and triticale appeared highly resistant to the disease. Some wheat varieties such as 2157, TAM 107, TAM 202, and Quantum 589 looked fairly good, but others such as Newton, TAM 109, Garrison, and Quantum 554 looked very bad. Because plots also had extensive aphid infestations and BYDV, we cannot say for certain why plants looked the way they did. However, because we do have an antiserum specific for the new disease, we were able to determine that all the really bad looking entries were infected with the new disease. Therefore, we do know it was involved with the observed symptoms.

Control of this new disease is likely to be as complicated and difficult as that of wheat streak mosaic virus. Chemical control is unlikely in wheat, because the mite needs to feed on a plant for only a short time to transmit the pathogen. Chemicals might reduce the rate of secondary spread in wheat, but because the disease has been found in native grasses, a continual supply of inoculum will be present depending on mite populations.

How this new disease will impact future wheat production in the Texas Panhandle is uncertain. The disease was observed on winter wheat early in September 1994, and the mite populations were moderate. Field plots evaluated in January 1995 had relatively high populations of the wheat curl mite. The mild, dry winter we have had to date certainly favors high mite populations and gives cause for concern.

Beaumont.

J. Sij.

A soft red winter wheat variety trial was conducted in 1993-95. Several entries yielded 70 or more bu/acre. Coker 9835 and Coker 9134 (79 bu/acre), Coker 762 and FFR525W (75 bu/acre), Andy (73 bu/acre), and Coker 9024 (70 bu/acre) produced higher yields. Approximately 750 genotypes were evaluated for disease reaction using the newly established wheat disease nursery. Leaf rust developed late in the season and generated excellent selection pressure.

College Station.

G.E. Hart, M.E. McDaniel, B.A. McDonald, C. Erickson, L. Rooney, and N.A. Tuleen.

Population genetics of wheat fungal pathogens. Single locus RFLP analysis and DNA fingerprinting were used to show that populations of Stagonospora nodorum (anamorph Septoria nodorum) in Switzerland have a genetic structure similar to that found for S. nodorum populations in Texas and Oregon. No genotypes were shared between the two populations, and preliminary data analysis suggests moderate levels of gene flow between these populations. An experiment to study adaptation of S. nodorum to Swiss wheat varieties is underway.

Dallas.

D. Marshall, R.L. Sutton, M. Harrington, and W.C. Wang.

Rainfall in the north Texas Blacklands has been highly unusual over the past 5 years. The average annual rainfall from 1945 to 1989 for Dallas, TX, was 33.5 inches. The average for 1990-1994 was 48.5 inches per year, with high rainfall records being set in 1990 (52.4 inches), again in 1991 (53.4 inches), and yet again in 1994 (55.6 inches). This may help explain why soft wheats (with their better disease resistance, overall) have dominated our field trials and have gained most of the north Texas wheat acreage over the hard wheats. The hard wheats predominated from 1983 to 1989 when rainfall averaged 29.4 inches per year.

Overton.

L.R. Nelson, S. Ward, and J. Crowder.

Wheat grain yields in Northeast Texas were very good in 1994. At Overton, Coker 9134 yielded 82 bu/acre. At Mt. Pleasant, Pioneer 2580 yielded 73 bu/acre. The highest yielding hard red winter wheat at Overton was TAM W-101 (75 bu/acre). Test weight continues to be a serious problem on all wheat cultivars in Central and East Texas. An advanced experimental line, TX85-119, has proven to be very high in test weight, averaging above 60 pounds/bu. We are increasing this line for possible release as a soft red winter wheat. Neither leaf rust or powdery mildew were serious disease problems in the 1994 crop; however, leaf rust was observed in December of 1994, indicating potentially significant yield losses for 1995. A rye forage line, to be named `Bates' will be co-released with the Noble Foundation in 1995.

Publications.

Bean BW, Salisbury CD, Lazar MD, and Piccinni GM. 1995. Wheat variety tolerance to atrazine. Proc Southern Weed Sci Soc (Abstract).

Chen RS, Boeger JM, and McDonald BA. 1994. Genetic stability in a population of a plant pathogenic fungus over time. Mol Ecol 3:209-218.

Ivors KL, Guthrie PAI, McDonald BA, and Appel DN. 1994. RFLPs in nuDNA differentiate isolates of Ceratocystis fagacearum in a Texas oak wilt center. Phytopathology 84:1096 (Abstract).

Lazar MD and Salisbury CD. 1994. Variation in drought susceptibility among closely related wheat lines. Agron Abstr:113.

McDonald BA, Miles J, Nelson LR, and Pettway RE. 1994. Genetic variability in nuclear DNA in field populations of Stagonospora nodorum. Phytopathology 84:250-255.

Nelson LR, Barnett RD, Marshall D, Erickson CA, McDaniel ME, Worrall WD, Tuleen NA, and Lazar MD. 1994. Registration of TX76-40-2 Wheat Germplasm. Crop Sci 31:1137.

Nelson LR, Crowder J, and Ward S. 1994. Wheat grain variety tests at Overton for 1992-93 and two-year means. In: Overton Field Day Report - 1994. Res Cnt Tech Rept 94-1. Pp. 137-138.

Nelson LR and Fang X. 1994. Effect of heterosis on Septoria nodorum disease level and plant yield in wheat. Proc Fourth International Workshop on Septoria of Cereals. Pp. 213-218.

Piccinni GM, Lazar MD , and Salisbury CD. 1994. Analysis of yield components for drought tolerance evaluation in several wheat lines. Agron Abstr:149.

Rosewich UL and McDonald BA. 1994. DNA fingerprinting in fungi. Meth Mol Cell Biol 5:41-48.

Rosewich UL, Frederiksen RA, and McDonald BA. 1994. Development of RFLP markers to elucidate the population genetics of Colletotrichum graminicola. Phytopathology 84:1075 (Abstract).

Vaughn KM, Rush CM, and Lazar MD. 1994. Effects of common root rot on wheat cultivars and breeding lines closely related to TAM 107. Phytopathology 84:1101 (Abstract).

Ward S, Crowder J, and Nelson LR. 1994. Wheat forage yields at Overton for 1992-92 and three-year means. In: Overton Field Day Report - 1994. Res Cnt Tech Rept 94-1. Pp. 33-34.