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An advisory program to determine the timing of fungicide application for control of early leafspot of peanut, caused by Cercospora arachidicola, was developed based on growth responses of the pathogen to specific environmental conditions. The advisory program (89-ADV) assigned time-duration values to conditions conducive for infection (TDVi). Cumulative TDVi levels were used to determine when fungicide applications were needed. Various spray thresholds (TDVi=48, 72, 96, 120) of the 89-ADV program were compared to a 14-day spray schedule and an advisory program that was released to growers in 1981 (81-ADV). Leafspot incidence, area under the disease progress curve (AUDPC), spray number, yield and value were used to evaluate the performance of spray programs. Preliminary trials used Florigiant peanut and the fungicide chlorothalonil (1.26 kg/ha). The 89-ADV program with TDVi=48 performed exceptionally well for three consecutive years in field tests and in simulated disease environments reconstructed from historical weather data. Benefits of this program compared to the 81-ADV program included significant improvement of leafspot control, and improved crop yield and value. Based on performance, the 89-ADV program was delivered to growers as the on-line peanut leafspot advisory in 1989. Subsequent evaluations of the 89-ADV program included cultivars and fungicides in large multi-factorial experiments. Three classes of cultivars were identified: class I or highly susceptible, Florigiant and NC 9; class II or moderately susceptible, NC 7 and NC-V11; and class III or moderately resistant, NC 6. The efficiency of fungicide sprays was improved through effective leafspot control with about three fewer sprays per season than the 14-day spray schedule when chlorothalonil at 1.26 kg/ha, diniconazole at 140 g/ha or terbutrazole at 126 g/ha was applied on class I cultivars according to the TDVi=48 threshold of the 89-ADV program. The same efficiency was achieved when chlorothalonil or terbutrazole was applied on class II cultivars according to the TDVi=96. Cupric hydroxide at 1.79 kg/ha plus sulfur at 1.04 kg/ha or terbutrazole at 126 kg/ha with TDVi=96 as well as chlorothalonil at 1.26 kg/ha with TDVi=120 resulted in efficient control of disease on the class III cultivar. The spray adjuvant SoyOil 937® at 0.5% of spray volume consistently improved the performance of chlorothalonil, and allowed a reduction of application rate from 1.26 to 0.95 kg/ha without sacrificing disease control. The integrated use of cultivar resistance, fungicide, spray adjuvant, and TDVi thresholds of the 89-ADV program contributed to a reduction of fungicide input and improved disease control. / Ph. D.

Thirty-two resistant varieties of winter type barley from the United States Department of Agriculture's World Collection were chosen for a study of the inheritance of scald resistance. They were crossed with Wong (0.1. 6728), a highly susceptible variety and with Hudson (0.I. 8067), a highly resistant variety. The crosses with Wong were made for the purpose of determining the number of pairs of genes for resistance in each of the resistant varieties. The crosses with Hudson were made for the purpose of determining whether any of the resistant varieties has genes for scald resistance at loci other than in Hudson. The F2 seedling populations from these crosses were studied in the greenhouse at Blacksburg in the early spring of 1960 and the winter of 1961. / Master of Science

Research and development of Bt rice in Southeast Asia has been overshadowed by the contentious debate over the potential release of transgenic food crops into the region. The study provides empirical evidence on the potential size and distribution of economic benefits of adopting Bt Indica rice in the Philippines and Vietnam through the years 2000 to 2020. Total welfare gains from Bt rice are projected at 618.8 million USD (discounted at 5 percent) and aggregate benefits by region are projected at 269.6 million USD for the Philippines, 329.1 million USD for Vietnam, and 20.1 million USD for the rest of the world. Simulation results indicate that producers in both countries will capture 66.5 percent of the total welfare effect from Bt rice adoption, 25.9 percent will accrue to consumers, 3 percent to the rest of the world, and the loss in Philippine government revenue accounts for 4.6 percent of the total welfare effect. The study also reports how other factors will determine the size and distribution of economic benefits of Bt rice. <i>Vita removed, Sept. 13, 2012, Gmc</i> / Master of Science

Field experiments with the green peach aphid on tobacco were conducted at Blackstone, Virginia in 1983 and 1984. The objectives were to: 1) confirm and identify source materials resistant to the green peach aphid; 2) study the inheritance of aphid resistance; 3) verify heritability of resistant genotypes through F2 and advanced generation testing and 4) investigate the nature of the resistance. Results showed green peach aphid resistance in Tobacco Introductions 1462, 1118, 1112, 1024, breeding line 1-35 and cultivar NC 745. Inheritance studies showed that the resistance is a recessive trait controlled by three separate, non-linked loci; such that a homozygous recessive at any one locus will condition for the resistance reaction. Among the source materials, one locus conditioned the resistance shown by TI 1118, TI 1112 and breeding line I-35. A second independent locus conditioned the found in TI 1024 and a third independent locus conditioned the resistance observed in NC 745. Tobacco Introduction 1462 possessed alleles for resistance at both the second and third loci. Small aphid cages were of questionable value for studying the resistance reaction. Higher leaf temperatures were noted for the caged leaf surfaces and may be responsible for the unreliable results. Evaluation of F2, F3, F5, F5 populations developed from resistant x susceptible crosses indicated that aphid resistance is a heritable trait and is not closely linked to adverse agronomic quality characteristics. / Master of Science

The state of leaf health of intact Penneagle creeping bentgrass leaves into which Curvularia lunata was able to ingress was determined by reducing cuticle/wax formation with trichloroacetic acid (TCA) and stressing plants with high air temperatures. Plants were grown until the third leaf had fully expanded and the fourth leaf had not yet emerged from the whorl. Plants were then treated with TCA for 6 times on alternate days. Half of the plants were high air temperature stressed at 38°C for 18 hr before plants were inoculated. Leaf health was estimated throughout the growing period of the plants by extracting chlorophylls and then regressing the values with respect to time. In this manner, leaves at each nodal position could be classified as either juvenile, mature or senescent. Also, selected leaves were examined by scanning electron microscopy. The addition of TCA to plants decreased leaf and plant life, increased tillering and reduced the deposition of leaf surface waxes. High air temperature stressing the plants caused a rapid entry of the leaf into senescence and higher levels of TCA accelerated this process. Plants were inoculated with either C. lunata, C. lunata var. aerea or Drechslera sorokiniana. Histochemical techniques were used to determine if penetration of the fungus into plant tissue had occurred. Inoculation with D. sorokiniana resulted in lesion formation within 2 days. Symptoms commonly attributed to Curvularia blight were present on plants treated with 0.047 or 0.14 mM TCA and then high air temperature stressed and inoculated with C. lunata. Histochemical procedures failed to show the presence bf mycelium Qf C. lunata· within the cells of Curvularia blight symptom areas. In a separate study, plants were grown, clipped and maintained at 2.0 cm and grown until 30 or 120 days of age. Plants were high air temperature stressed or not and clipped 128, 64, 32, 16, 8, 2, 1 or 0 hr before inoculation with C. lunata. Results again showed that C. lunata had the ability to colonize heat stressed and/or old leaves but did not have the ability to infect and colonize juvenile or mature tissues. The amount of the turf foliage that is susceptible to thinning by C. lunata depends on the physiologic age of the leaf tissue. As stresses of high air temperatures are placed on the leaf tissue, a greater percentage of the leaf blades are forced into advanced senescence, thereby increasing their susceptibility to infection and colonization by C. lunata. / Ph. D.