The effect of temperature and soil moisture on the ecology of two bacteria in the rhizosphere of downy brome. Conservation tillage practices in winter wheat management systems, although reducing erosion and surface water contamination, can affect the distribution and severity of weed infestations. Winter annual grass weeds, such as downy brome (Bromus tectorum L.), thrive in reduced tillage systems and can reduce wheat yields. Neither chemical controls nor cultural practices satisfactorily control downy brome; therefore, development of alternative management strategies, such as biological control measures, is desirable. The ability of an introduced microorganism to effectively colonize the rhizosphere is key to its ultimate influence on the growth and development of target plants (Mazzola et al. 1995). Pseudomonas putida strain FH160 and Stenotrophomonas maltophilia strain FH131 have shown potential as bioherbicides (Harris and Stahlman 1990); we have examined the effect of temperature and soil moisture on the ecology and phytopathological ability of these strains. Effect of Temperature. Rifampicin-resistant (rif R) derivatives of FH160 and FH131 were applied to soil at an initial population of 106 cfu/gdw soil. Cones were filled with bacteria-treated or untreated soil and planted to downy brome. Soil was maintained at 10 % moisture; growth chambers were maintained at 18 C or 28 C. Plant dry weight was determined at 30 days after planting (DAP). Populations of the introduced strains in soil and the brome rhizosphere were determined at 5 (soil only), 11, 15, 20, and 30 DAP. Serial dilutions of the soil suspension or brome root wash were plated onto Pseudomonas agar F containing 40 FONT SIZE=2 FACE="WP MathA"/ml rifampicin and 75 micro g/ml cycloheximide. Colonies were enumerated after 48 hours at 28 C. Rhizosphere and soil populations of the two strains showed similar trends. First, soil and rhizosphere populations of both strains tended to be higher at 18 C than at 28 C. Second, populations of both strains decreased over time in soil and the rhizosphere. In soil, populations of both strains decreased significantly by 20 DAP at 18 C; the decrease was significant by 15 DAP at 28 C. These data suggest that temperature affects strain survival in soil. Third, populations of FH160 in rhizosphere and soil typically were larger than FH131 populations at either temperature. Rhizosphere populations of FH160 declined significantly by 20 DAP at both temperatures, but rhizosphere populations of FH131 exhibited insignificant declines at both temperatures. Thus, although FH160 appears to colonize the rhizosphere earlier and at larger populations than FH131, FH131 populations appear to fluctuate less, especially at higher temperatures. At both temperatures, bacteria-treated plants were smaller than the untreated controls. In addition, at 28 C, FH131-treated plants were smaller than FH160-treated plants. Finally, plants at 28 C were larger than plants at 18 C, regardless of bacterial treatment (Table 1). Effect of Soil Moisture. Cones were filled with soil treated with rif R FH131 (108 cfu/gdw), rif R FH160 (108 cfu/gdw), or left uninoculated; cones were planted to downy brome and maintained in the greenhouse at 10 %, 15 %, 17.5 %, or 20 % moisture. Soil and rhizosphere samples were collected at 5 (soil only), 10, 15, 20, 30, and 40 DAP; the soil suspension or root wash was plated onto selective medium as described above. Plant biomass was determined for samples harvested at 40 DAP. The experiment was repeated twice. Seasonal differences in the greenhouse were apparent in the replication of this experiment; however, the trends presented here were common to both trials. Figure 1 represents the average strain survival in soil over time at the various moisture levels tested. In both experiments, soil populations of strain FH160 were significantly larger at 17.5 % and 20 % moisture than at 10 %. This difference reflects a general trend: by 15-20 DAP, soil populations of both strains were smallest at 10% moisture and highest at 15 and 17.5 % moisture. In addition, there was a trend in both experiments for FH131 populations in soil to be larger than FH160 populations at 10 % moisture. There was also a trend for FH160 populations to be larger than FH131 populations at 17.5 % and 20 % soil moisture. Taken together, these trends imply that FH160 is more drought-sensitive and more tolerant of wet conditions than FH131. FH160 soil populations declined, on average, 2.5 logs during the experiment, with final populations ranging from 4.2-6.7 log cfu/gdw soil. FH131 populations exhibited an average decline of 2-2.5 logs; populations at 40 DAP were 5.5-6.5 log cfu/gdw soil. Rhizosphere populations of the strains exhibited responses to soil moisture that were similar to, but less pronounced than, responses of soil populations. Rhizosphere populations of FH160 were significantly larger at 20 % moisture than at 15 % moisture in both experiments. There was a general tendency for populations of FH160 to be larger at higher moisture levels. Populations of strain FH160 were larger at 17.5 % moisture than at other moisture levels at most sampling times. There was a general decline in rhizosphere populations of this strain over time at all moisture levels; this decline averaged 2.5 logs. Populations at 40 DAP ranged from 1.2-4.0 log cfu/cm radicle. The population decline was earlier and more precipitous at the lower moisture levels, again suggesting that FH160 is drought-sensitive. An additional indication that FH160 may be more drought-sensitive than FH131 is that FH160 populations tended to be smaller than FH131 populations at 10 and 15 % moisture. Like FH160, rhizosphere populations of FH131 tended to be larger at higher moisture percentages. Populations of FH131 declined 1.5 logs on average; final populations ranged from 2.7-3.7 log cfu/cm radicle. There was a general trend, regardless of bacterial treatment, for higher plant biomass at higher moisture percentages. No bacterial phytotoxic effects were observed consistently in both experiments. Acknowledgments. Many thanks to Tim Todd and Anne Fischer for technical assistance.
Publications. Harris PA and Stahlman PW. 1990. Selective control of winter annual grass weeds in winter wheat with soil bacteria. Agron Abstr 54:250. Mazzola M, Stahlman PW, and Leach JE. 1995. Application method affects the distribution and efficacy rhizobacteria suppressive of downy brome (Bromus tectorum L.). Soil Biol Biochem (In press). Table 1. Response of downy brome grown at two temperatures to two biocontrol bacteria. Plants were harvested, dried, and weighed individually. Different superscripted letters in the per plant biomass column imply statistically significant differences at the P = 0.05 level. Lowercase letters pertain to differences between treatments within a temperature; uppercase letters indicate differences between temperatures within a treatment. ___________________________________________________________________ per plant biomass, 18 C /28 C Temperature Treatment % of control % per plant biomass ___________________________________________________________________ 18 C untreated 100 aA 46 FH131 77 bA 64 FH160 76 bA 47 28 C untreated 100 aB FH131 56 bB FH160 75 cB ___________________________________________________________________ Figure 1. Response of soil populations of two bacterial strains to four moisture regimes over time. Bacterial populations were plotted over time, generating a line for each strain at each moisture percentage. The slope of each line represents strain survival over time. These slopes, when plotted as a function of moisture, result in lines representing the average strain survival over time at a given moisture level. A more negative slope implies poorer strain survival or steeper decline.
The Wheat Genetics Resource Center
Departments of Plant Pathology and Agronomy, Throckmorton Hall, Manhattan, KS
66506, USA. T.S. Cox, B.S. Gill, R.G. Sears, T.L. Harvey, J.H. Hatchett, S.H. Hulbert, E.V. Boyko, G.L. Brown-Guidera, D.E. Delaney, B. Friebe, K.S. Gill, J. Jiang, M.A. Knackstedt, W.J. Raupp, and N.D. Van Mettern.
Notice of release of KS94WGRC32 leaf rust-resistant hard red winter wheat germplasm. The Agricultural Research Service, U.S. Department of Agriculture, and the Kansas Agricultural Experiment Station announce the release of KS94WGRC32 hard red winter wheat (Triticum aestivum L.) germplasm for breeding and experimental purposes. Scientists participating in this development were T. S. Cox, USDA-ARS and Department of Agronomy; B.S. Gill, Dept. of Plant Pathology; and R.G. Sears, Dept. of Agronomy. Seedlings of KS94WGRC32 are resistant to culture PRTUS25 and other isolates of Puccinia recondita Rob. ex Desm. Adult plants were resistant under moderate to severe leaf rust epidemics at Manhattan and Hutchinson, Kansas in 1992, 1993, and 1994. KS94WGRC32 (TAM 107*2//KS8010-1-4-1/TA 359) is an F3-derived line. The leaf rust-resistant donor parent, TA 359, is an accession of T. boeoticum Bioss., a wild, diploid wheat species. KS94WGRC32 heads 3 days later than TAM 107 and is slightly taller; its reactions to diseases other than leaf rust are similar to those of TAM 107. It carries neither the T1BL-1RS nor the T1ABL-1RS translocation. In 1994 yield trials at Manhattan and Hutchinson, KS, KS94WGRC32 had mean grain yields 12 and 20 % higher than TAM 107 and Karl 92, respectively. The infection type of KS94WGRC32 was mesothetic (23X) under heavy field infection in 1992-93, low (01C) under moderate field infection in 1994, and consistently low (01C) under seedling inoculation with PRTUS25. Resistance is governed by a single, dominant gene that segregates independently of genes transferred previously from T. monococcum L., a cultivated relative of T. boeoticum. Transfer of resistance to leaf rust from T. boeoticum has not been reported previously. Small quantities (3 grams) of seed of KS94WGRC32 are available upon written request. It is requested that appropriate recognition of source be given when this germplasm contributes to research or development of new cultivars. Seed stocks are maintained by T.S. Cox (USDA-ARS), Wheat Genetics Resource Center, Dept. of Agronomy, Throckmorton Hall, Kansas State University, Manhattan, KS 66506. (Cox, BS Gill, Sears)
Evaluation of a Triticum araraticum collection for resistance to disease and insect pests of wheat. The collection of Triticum timopheevii var. araraticum held at the Wheat Genetics Resource Center was screened for reaction to fungal pathogens and insect and mite pests of wheat. All accessions tested for reaction to Septoria tritici were resistant. Ninety percent of the tested accessions were resistant to the necrosis causing tan spot toxin. The frequencies of accessions having intermediate and low reaction types to leaf rust were 68 % and 36 %, respectively. Although intermediate levels of resistance to stripe rust and powdery mildew were also common in the collection, the frequencies of low infection types were 7 % for powdery mildew and 0 % and 2 % for strip rust isolates CDL-43 and CDL-45, respectively. Resistance to stem rust was less frequent than resistance to the other rust pathogens, with 15 % of the tested accessions having intermediate reaction types and 6 % having low infection types. Ninety-one percent of the accessions tested were scored as resistant or segregating for resistance to Hessian fly biotype D, and 27 % of the accessions tested had some level of resistance to the wheat curl mite. Thirty-one accessions were identified with intermediate to high levels of resistance to at least five pests. Resistance was not related strictly to geographic origin; however, our results support the conclusion of others that Iraq is a center of diversity of T. araraticum. The leaf rust, stem rust, and powdery mildew isolates used for screening allowed us to determine that the resistance gene(s) present are different from the resistance genes that previously were transferred to wheat from T. timopheevii (Lr18, Pm6, and Sr36). Attempts are underway to transfer resistance genes from T. araraticum to common wheat. Backcross derivatives from hybrids between wheat cultivars and 15 accessions have been developed. Some are resistant to powdery mildew in seedling tests and resistant to leaf rust pathogen in the field, indicating that these genes are expressed in a wheat background. We are assessing the genetic diversity of resistance genes in T. araraticum. (Brown-Guedira, Cox, BS Gill, Bockus, Hatchett, and Harvey)
Triticum tauschii-derived lines and their effect on bread making quality. Triticum tauschii is increasingly used as a source for disease and insect resistance genes in common wheat. Detrimental genes, which may be introduced inadvertently, need to be monitored. Some previous introductions of resistance genes have resulted in a marked declined in bread making quality. Our research estimates the effect of the use of T. tauschii-derived lines on bread making quality. Additionally, we identified BC2F2:5 lines carrying novel gliadin protein bands and found, in at least one case, that mixing time was shortened, whereas mixing tolerance and other bread making quality parameters were not affected adversely. (Knackstedt; Sears; Cox; R.K. Baguette, Department of Agronomy, Kansas State University; and O.K. Chung, USDA Grain Marketing Research Laboratory, Manhattan, KS)
Hybrid and pureline response to high temperature stress under two environments in hard red winter wheat. High temperature stress of winter wheat in the Great Plains is a frequent occurrence, especially during the grain filling period. Field observations have suggested that hybrid wheat may be more tolerant to high temperature stress than their parents or other pureline varieties. The purpose of this research was to compare the effects of high temperature stress on F1 hybrids, their parents, and pureline varieties grown in both greenhouse and growth chamber environments. In 1994, seven hybrids, their parents, and four varieties were grown in the greenhouse in a randomized complete block design. Four days after anthesis (Feekes 10.52), plants were transferred to either growth chambers or greenhouses set at control (25/20 C) 16-h day length. Data were collected on yield/plant, primary tiller grain weight, seeds/spike, fertile spikelets/spike, tiller number/plant, and total above ground biomass. Direct statistical comparisons of the two environments (growth chambers and greenhouse) was not possible because of heterogeneous variances. However, in the greenhouse experiments, the hybrids overall were less affected by high temperature than their parents. Yield, biomass, and heterosis values were generally lower in the growth chambers. The reduction of yield from high temperature in the greenhouse was 53.2 % for hybrids (41.7-65.9 %). The parents had an average reduction of 57.2 % (39.1-66.9 %). In the growth chambers, the hybrids had a 50.5 % reduction in yield, with a range of 39.5 % to 60.3 %. The parents had a 50.1 % reduction in yield, with a range of 38.6 % to 52.4 %. Hybrids had a significant advantage over their parents in the greenhouse for yield, primary tiller grain yield, seeds/spike, and fertile spikelets/spike. Significant differences occurred between hybrids and their parents in primary grain tiller yield and harvest index in the growth chamber. Correlations between main tiller grain yield and total grain yield in the greenhouse were 0.92 and 0.76 for hybrids and parents, respectively. Correlations in the growth chamber were 0.54 and 0.79 for hybrids and parents, respectively. The actual average high parent heterosis for yield in the greenhouse was 1.69 %, with a high at 13.39 %. In the growth chambers, the average high parent heterosis was -5.58 %, with a high of 17.57 %. The hybrids with heat-tolerant parents generally had high parent heterosis. (Van Mettern, Sears, Cox)
Molecular analysis of wheat-alien translocation lines. The wild relatives and related species are important sources for improving disease and pest resistance of cultivated bread wheat. C-banding and genomic in situ hybridization analyses are sensitive cytological techniques that allow the detection of alien chromatin in wheat. We used these methods to identify the chromosomes involved and to determine the breakpoints and sizes of the transferred alien segments in spontaneous and induced wheat alien translocations. The table below summarizes the results on wheat-alien translocations carrying the resistance genes: Lr9, Lr19, Lr24, Lr25, Lr28, Lr38, Lr, Sr24, Sr25, Sr26, Sr27, Sr32, Sr34, Wsm1, Pm7, Pm17, Pm20, Gb2, Gb5, H21, and H25. (Friebe, Jiang, Raupp, BS Gill) _____________________________________________________________________________________________ Chromosome Telosomic Chromosome Telosomic Trans- Species addition addition substitution substitution location Source _____________________________________________________________________________________________ T. searsii 7 14 21 31 2 Tuleen T. longissimum 15 15 24 - 27 Tuleen, Feldman T. sharonense 1 - 3 - - Tuleen T. speltoides - - - - 2 Sears, Miller T. tauschii 7 - - - 3 WGRC T. umbellulatum 6 9 - - 6 Sears, Kimber, Tuleen T. dichasians 6 1 - - - BlFONT SIZE=2 FACE="WP MultinationalA Roman"hthner, Schubert, T. comosum 1 - - - 3 Riley, Miller T. peregrinum 14 22 - - - Tuleen T. araraticum - 1 7 - 4 WGRC T. dicoccoides - 2 - - - Sears T. ovatum 4 - - - 1 Mettin A. intermedium 10 3 4 - 7 Cauderon, Wells, Wienhues, Tuleen A. elongatum 3 2 - 2 20 Knott, Sears, Wells, Sebesta, Marais E. ciliaris 3 1 - 2 - WGRC E. trachycaulus 9 7 2 - 11 WGRC H. chilense 7 - - - - Miller, Cabrera D. villosum 7 - - - - Sears S. cereale 12 17 8 1 24 Sears, Sebesta, Marais, WGRC TOTAL 112 95 69 36 110 _____________________________________________________________________________________________
A diploid genetic map of wheat based on Triticum tauschii (2n = 14), the D genome progenitor of bread wheat. Among the three ancestral A, B, and D genomes of bread wheat, the D genome is the least modified and almost completely homologous to the genome of the diploid donor T. tauschii. The D genome is a readily available source of resistance and other useful genes that can be transferred rapidly to wheat by direct hexaploid x diploid crosses. Genetic analysis and tagging of useful genes can be carried out in T. tauschii to enhance efficiency and precision of their transfer to bread wheat. Moreover, T. tauschii is ideal for RFLP mapping because of simple diploid inheritance and a high degree of polymorphism, even among different accessions. Because of these favorable attributes, we are constructing a high density, diploid, genetic linkage map of wheat based on T. tauschii. So far, we have mapped 318 probes from wheat, barley, and oats that detect 440 loci. We have selected 260 loci that segregate 1:2:1 to make an anchor map. The remaining probes will be mapped in reference to these markers. The basic wheat linkage map can be compared to maps of barley and oats for each chromosomes. (Boyko, KS Gill, Cox, Sears, BS Gill)
Targeted mapping of a Hessian fly resistance gene from rye by representational difference analysis. Genomic subtraction techniques are particularly useful for obtaining markers closely linked to genes of interest. Representational difference analysis (RDA, Lisitsyn et al. 1993, Science 259:946-951) is a new PCR-based cyclic genomic subtraction technique that is well suited to organisms with large, complex genomes. We have used this technique to obtain probes for the long arm of chromosome 6 in rye (6RL), which carries a gene for resistance to Hessian fly larvae (H25), as well as other resistance genes. Our tester (or target) DNA was a ditelosomic addition line with 42 Chinese Spring wheat chromosomes and ditelosomic for 6RL. The driver DNA was another Chinese Spring addition line with two complete rye chromosome 4s. Both driver and tester DNAs were digested to completion with BamHI, and were carried through three cycles of RDA. From two separate experiments, we isolated five unique new RFLP probes for the distal half of 6RL. Linkage relationships among these probes, as well as five additional wheat probes, were determined using two mapping populations that were both derived from a cross between two wheat-rye 6RL translocation lines. We did three experiments with BamHI amplicons (using different primer set orders), two of which were successful in yielding useful low copy clones. All low copy clones were confirmed by Southern analysis to be fragments of 6RL. A total of 108 clones was analyzed from the two successful experiments, of which 70 % mapped to 6RL. However, many of the clones were multiples of the same fragments. Five clones were confirmed to be unique. Although some of the same fragments were cloned in both experiments, each did yield some unique RFLP probes. Experiments with HindIII amplicons and primer sets yielded only repetitive clones that could not be used for mapping. Future studies will focus on using RDA and other genomic subtraction techniques with new genetic stocks containing (or lacking) only the distal region of 6RL. In this way, we hope to obtain more probes closer to our gene of interest. In molecular terms, we have localized the Hessian fly resistance gene to within an approximately 7.5 Mbp segment of the telomeric region of 6RL. Physical mapping studies of all the wheat chromosomes have revealed a consistent clustering of marker loci and probably genes in the distal regions of the chromosomes. If the same is true for rye, it would indicate that this is probably the most promising region of the chromosome for successful map-based cloning, once we have localized the gene within a smaller region. (Delaney, Friebe, Hatchett, Gill, Hulbert)
Publications. Brown GL, Cox TS, Gill BS, Bockus WW, Hatchett JH, Harvey TL, Leath S, Peterson J, Thomas JB, and Zwer PJ. 1994. Evaluation of a Triticum araraticum collection for resistance to disease and insect pests of wheat. Agron Abstr:221. Chen PD, Tsujimoto T, and Gill BS. 1994. Transfer of Ph1 genes promoting homoeologous pairing from Triticum speltoides to common wheat. Theor Appl Genet 88:97-101. Cox TS, Raupp WJ, and Gill BS. 1994. Leaf rust-resistance genes Lr41, Lr42, and Lr43 transferred from diploid goatgrass to common wheat. Crop Sci 34:339-343. Cox TS, Sears RG, Gill BS, and Jellen RN. 1994. Registration of KS91WGRC11, KS92WGRC15, and KS92WGRC23 leaf rust-resistant hard red winter wheat germplasms. Crop Sci 34:546. Cox TS, Sorrells ME, Bergstrom GC, Sears RG, Gill BS, Walsh EJ, Leath S, and Murphy JP. 1994. Registration of KS92WGRC21 and KS92WGRC22 hard red winter wheat germplasms resistant to wheat streak mosaic virus and powdery mildew. Crop Sci 34:546. Delaney DE, Friebe BR, Hatchett JH, Gill BS, and Hulbert SH. 1995. Targeted mapping of rye chromatin in wheat by representational difference analysis. Genome 38:In press. Friebe B, Heun M, Tuleen N, Zeller FJ, and Gill BS. 1994. Cytogenetically monitored transfer of powdery mildew resistance from rye into wheat. Crop Sci 34:621-625. Friebe B and Gill BS. 1994. C-band polymorphism and structural rearrangements detected in common wheat (Triticum aestivum). Euphytica 78:1-5. Friebe B, Gill BS, Tuleen NA, and Cox TS. 1995. Registration of KS93WGRC28 powdery mildew resistant T6BS-6RL hard red winter wheat germplasm. Crop Sci (In press). Friebe B, Jiang J, Knott DR, and Gill BS. 1994. Compensation indices of radiation-induced wheat-Agropyron elongatum translocations conferring resistance to leaf rust and stem rust. Crop Sci 34:400-404. Friebe B, Jiang J, Raupp WJ, and Gill BS. 1994. Molecular cytogenetic analysis of wheat-alien germplasms. Agron Abstr:116. Friebe B, Jiang J, Tuleen NA, and Gill BS. 1995. Standard karyotype of Triticum umbellulatum and the characterization of derived chromosome addition and translocation lines in common wheat. Theor Appl Genet (In press). Gill BS, Cox TS, Sears RG, Raupp WJ, Friebe B, Brown GL, Jellen EN, Jiang J, Gill KS, Singh S, Miller DE, Nasuda S, Wilson DL, Young LM, and Zhang J. 1994. Research summary. Ann Wheat Newslet 40:251-260. Gill BS, Friebe B, Wilson DL, Martin TJ, and Cox TS. 1995. Registration of KS93WGRC27 wheat streak mosaic virus-resistant hard red winter wheat germplasm. Crop Sci (In press). Gill KS and Gill BS. 1994. Mapping in the realm of polyploidy: The wheat model. BioEssays 16(11):841-846 with cover photo. Jellen RN, Gill BS, and Cox TS. 1994. Genomic in situ hybridization differentiates between A/D- and C-genome chromatin and detects intergenomic translocations in polyploid oat species (genus Avena). Genome 37:613-618. Jiang J and Gill BS. 1994. Different species-specific chromosome translocations in Triticum timopheevii and T. turgidum support the diphyletic origin of polyploid wheats. Chromosome Res 2(1):59-64. Jiang J and Gill BS. 1994. New 18S-26S ribosomal RNA gene loci: Chromosomal landmarks for the evolution of polyploid wheats. Chromosoma 103:179-185. Jiang J and Gill BS. 1994. Non-isotopic in situ hybridization and plant genome mapping: the first 10 years. Genome 37(5):717-725. Jiang J, Friebe B, and Gill BS. 1994. Recent advances in alien gene transfer in wheat. Euphytica 73:199-212. Jiang J, Friebe B, and Gill BS. 1994. Chromosome painting of Amigo wheat. Chromosoma (In press). Jiang J, Morris KLD, and Gill BS. 1994. Introgression of Elymus trachycaulus chromatin into common wheat. Chromosome Res 2(1):3-13. Knackstedt MA, Sears RG, Rogers DE, and Lookhart GL. 1994. Effects of a T2BS-2RL wheat-rye translocation on breadmaking quality in wheat. Crop Sci 34:1066-1070. Kota RS, Gill BS, and Hulbert SH. 1994. Presence of various rye-specific repeated DNA sequences on the midget chromosome of rye. Genome 37:619-624. McIntosh RA, Friebe B, Jiang J, and Gill BS. 1994. Collaborative studies in wheat and Triticale cytogenetics. Wheat Breeding Soc Australia p. 295 (Abstract). Porter DR, Webster JA, and Friebe B. 1994. Inheritance of greenbug biotype G resistance in wheat. Crop Sci 34:625-628. Woo SS, Jiang J, Gill BS, Paterson AH, and Wing RA. 1995. Construction and characterization of a bacterial artificial chromosome library of Sorghum bicolor. Nuc Acids Res (accepted).
U.S. Grain Marketing Research Laboratory
USDA, Agricultural Research Service, Manhattan, KS 66502, USA. O.K. Chung, G.L. Lookhart, J.L. Steele, L.M. Seitz, I.Y. Zayas, C.R. Martin, V.W. Smail, D.B. Bechtel, J.B. Ohm, C.S. Chang, J.D. Wilson, S.R. Bean, B.W. Seabourn, H.S. Park, A.K. Dowdy, D.W. Hagstrum, K.J. Kramer, W.H. McGaughey, S.K. Akkina, H.H. Converse, R.E. Dempster, P.W. Flinn, W.J. Jun, B. Oppert, D.B. Sauer, D.E. Johnson, J.E. Throne, D.E. Walker, T.J. Morgan, and Y.S. Kim.