A two year study was conducted to investigate the effect of intercropping corn with alfalfa or red clover with or without an initial application of the herbicide EPTC$ sp+$ (S-ethyl dipropylthiocarbamate + R-25788 antidote) on the weed yellow nutsedge (Cyperus esculentus L.). EPTC$ sp+$ applied prior to crop seeding in 1984 significantly reduced yellow nutsedge shoot growth in the first year but did not significantly reduce tuber populations. EPTC$ sp+$ significantly improved corn silage and grain yield and alfalfa establishment in the first year but did not significantly improve red clover establishment. In the second year, a trend of superior forage legume establishment and lower yellow nutsedge shoot production was observed in those treatments established the previous year with EPTC$ sp+$. Over the two year period, yellow nutsedge tuber populations in treatments established with EPTC$ sp+$ were significantly greater in the monocropped corn treatment than in any other treatment. In treatments established without a herbicide, yellow nutsedge tuber populations were also greatest in the monocropped corn treatment.

Potato leafhopper causes considerable damage in red clover. The main objectives of this study were to clarify the inheritance of pubescence and to evaluate the relationship between pubescence and potato leafhopper (Empoasca fabae (Harris) resistance. Thirteen red clover clones of diverse origin, including both pubescent and non-pubescent types were used as parents. A series of crosses were made in all possible combinations among the 13 parental clones. Seedlings of F$ sb1$ progeny and stem cuttings from parents were planted in the field in the summer of 1993 in a randomized complete block design. Based on the results, the inheritance of pubescence type on red clover stems, petioles and abaxial leaf surfaces was best explained individually by two-locus models showing dominant and recessive interaction. A two locus model with recessive epistasis was proposed for pubescence on stipules and basal internodes, but there were a number of crosses that deviated from expected ratios. There was quantitative variation for trichome density on red clover and it appeared to be inherited as a quantitative trait. Based on mid-parent offspring regression, the heritability estimates of trichome density on petioles, stems, abaxial leaf surfaces, and adaxial leaf surfaces were 0.16, 0.77, 0.50 and 0.48, respectively. Pubescence was apparently associated with potato leafhopper resistance. Visual ratings of feeding injury, the numbers of leafhopper nymphs per plant and the numbers of nymphs per gram of dry plant material were higher on glabrous plants than on pubescent plants. (Abstract shortened by UMI.)

The objectives of the study were to determine whether intercropped alfalfa (Medicago sativa L.), red clover (Trifolium pratense L.) or rye grass (Lolium multiflorum Lmk.) could simultaneously contribute to the nitrogen regime of grain-corn (ie: increased yield), improve edaphic quality, and decrease the level of inorganic nitrogen present in the soil after corn harvest. To achieve these objectives the seeding of the intercrops was delayed, the corn population was increased, and the red clover was spring-ploughed. / Fall-ploughed red clover maintained the mean weight diameter (MWD) of aggregates on the Ste-Rosalie clay. Spring-ploughed red clover on the other hand caused a decrease in bulk density in the top 10 cm of the Chicot loam. / The nitrogen-response of corn indicated that the intercrops did not contribute to the nitrogen regime of grain-corn. There were also indications that intercrops competed with corn for available inorganic nitrogen and water. The intercrops, however, did reduce the levels of soil inorganic nitrogen in the fall allowing for a possible decrease in the nitrogen load of soil percolates. / Despite the beneficial effect of nitrogen fertilisation on the organic nitrogen content of the soil, the presence of leguminous intercrops did not prevent the increase of the soil CN ratio.

Thesis (M.Sc.). / Written for the Dept. of Plant Science. Title from title page of PDF (viewed 2008/12/09). Includes bibliographical references.

Red clover (Trifolium pratense L.) cvs 'Altaswede' (2n=2X=14) and 'Norseman' (2n=4X=28) were used in the present study to investigate tissue culture initiation, plant regeneration and the occurrence of somaclonal variation. Hypocotyl explants of aseptic seedlings were inoculated into L2 medium containing 0.06 mg/1 Picloram and 0.1 mg/1 benzyladenine for callus induction. Calli were usually induced after two weeks of culture. Callus induction frequency was 60% to 85% of the explants cultured with 'Altaswede' showing a slightly higher frequency than 'Norseman'. Satisfactory results were obtained under dark or light conditions using either test tubes or petri plates, as culture vessels. After callus induction, an experiment was conducted to regulate shoot induction by subculturing the calli on L2 medium containing 0.01 mg/1 2,4-dichlorophenoxy acetic acid and 2 mg/1 adenine (LSE) and on B₅ medium containing 2 mg/1 naphthalene acetic acid and 2 mg/1 adenine, media which have been reported to be shoot-supportive. However, both media failed to initiate shoots under the present experimental conditions. Further tests confirmed that LSE medium did not induce shoots from these calli and that callus growth on LSE medium steadily deteriorated over several subcultures. Subsequently, various media were tested with an emphasis on different combinations of growth regulators. Root differentiation from these calli was frequently observed. Shoots were initiated from some calli when they were transferred from SCP medium to media containing naphthalene acetic acid and kinetin. Embryogenic callus of one genotype was selected and maintained on LSP medium, leading to the regeneration of numerous plants. Supplementation with arginine, glutamic acid and casein hydrolysate did not show a significant effect on callus growth and differentiation. The source of callus influenced rates of growth and the occurrence of differentiation. Usually 'Norseman' calli grew faster and produced more roots than 'Altaswede' calli, while shoots were induced only from 'Altaswede' calli. Although 'Norseman' had more shoot tips induced to produce multiple shoots, the multiple shoot number per culture of 'Altaswede' was higher than that of 'Norseman'. Shoot tip cultures were also established to induce multiple shoots and to regenerate plants via root organogenesis. Regenerants from initial multiple shoots (RG1), multiple shoots after two subcultures (RG2), three-month calli (RG3) and one-year calli (RG4) were evaluated for chromosome number stability, morphology and several biochemical traits. When 'Altaswede' plants were analysed for chromosome number, RG1 and RG3 plants were normal, while one RG2 plant and 23% of 119 RG4 plants had tetraploid chromosome numbers. Regenerated plants were quite stable regarding their isozyme patterns of malate dehydrogenase, 6-phosphogluconate dehydrogenase, phosphoglucose isomerase, phosphoglucomutase and shikimate dehydrogenase and their nodule leghaemoglobin profiles. Morphologically, the leaflet length to width ratio of RG1, RG2 and RG3 plants of 'Altaswede' showed significantly more variation than control plants (P≤0.01), while RG4 plants of 'Altaswede' and RG1 and RG2 plants of 'Norseman' were not different from control plants. It is suggested that the absence of detectable differences in the RG4 'Altaswede' plants was a consequence of their origin from one original genotype. Variability and stability of regenerated plants are discussed. / Land and Food Systems, Faculty of / Graduate

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Both red (Trifolium pratense L.) and white (Trifolium repens L.) clover seed yields can be highly variable and low in western Oregon. The objectives of this study were to: i) determine crop water requirements and supplemental irrigation timing, and ii) quantify the effects of soil and water status on inflorescence production, seed yield and seed yield components for red and white clover seed crops. In each species, five supplemental irrigation treatments were applied in 1990 and 1991 to first and second year seed crops grown on a Woodburn silt loam (fine-silty, mixed, mesic Aquultic Argixeroll) near Corvallis, OR. Non-irrigated controls were also maintained. In red clover, increased plant water stress reduced the duration of the season-long bud and flower production, stem length, potential floral capacity (PFC), and seed yield (SY). Root rot index (RRI) increased with increasing levels of plant water stress, indicating that supplemental water applications reduced second-year root rot severity. The reduction in SY from increasing plant water stress was primarily caused by a decrease in floral fertility, and less conclusively by reductions in inflorescence number per unit area. One irrigation to fill the soil active profile during peak flowering provided adequate water to maintain efficient seed production. In white clover, SY was maximum in 1990 when water application was delayed until 68% of the available soil-water was used by the crop which maintained an even flush of flowers and restricted vegetative growth. In 1991, all irrigation treatments yielded the same or less than the non-watered control. This was due to the excessive vegetative growth from stolons that had grown between the planted rows the previous and present crop year. In both years excessive amounts of irrigation water favored profuse vegetative growth and reduced SY. Inflorescence density was increased by constraining soil-water in 1990 and was the yield component that most affected SY both years. Crop water stress index (CWSI) was a useful indicator of plant stress status and can be used to schedule irrigations in red and white clovers grown for seed under typical climatic conditions of western Oregon. / Graduation date: 1993