Excessive growth by red clover, Trifolium pratense L., grown for seed interferes with maximum seed production and harvest in Oregon's Willamette Valley. This study was conducted during 1986 and 1987 on red clover cv. Kenland to determine if plant height and dry matter production could be inhibited and seed yields improved with the plant growth regulators (PGRs) uniconazol (XE-1019) and paclobutrazol (Parlay). The effects of different soil-applied and foliar-applied PGRs and application rates on plant height, crop biomass, and yield components of red clover were measured at Corvallis, OR on Woodburn silt-loam (fine-silty mixed mesic Aquultic Argixerolls) soil. Soil-applied PGRs were also managed under single and multiple irrigation regimes in 1986. Under a single irrigation regime in 1986, canopy height was reduced by 32% when XE-1019 was applied at 1.12 kg ai/ha and was reduced by 13% when Parlay was applied at 1.68 kg ai/ha. Averaged over the two-year period, straw yield was reduced 40% with XE-1019 (1.12 kg ai/ha) and by 12% with Parlay (1.68 kg ai/ha). Seed yield was increased by 11% with the lower XE-1019 rate (0.14 kg ai/ha) and was increased by 14% with the higher Parlay rate (1.68 kg ai/ha). Soil-applied PGR treatments reduced canopy height by 25% with XE-1019 (1.12 kg ai/ha) and was reduced by 11% with Parlay (1.68 kg ai/ha) under multiple irrigation in 1986. Straw yield was reduced by 30% with XE-1019 (0.84 kg ai/ha), but Parlay had no effect on straw yield. In addition, seed yield was increased by 8% with XE-1019 (0.56 kg ai/ha) and by 18% with Parlay (1.68 kg ai/ha). Foliar-applied XE-1019 (1.12 kg ai/ha) reduced canopy height by 13% in 1986 and by 25% in 1987, whereas foliar-applied Parlay (1.12 kg ai/ha) reduced canopy height by 9% in 1986 and by 19% in 1987. In 1986, seed yield increases averaged 16% across all 3CE-1019 treatments (0.07 to 1.12 kg ai/ha) and was increased an average of 21% across all Parlay treatments (0.28 to 1.68 kg ai/ha). However, 1987 was drier and warmer than 1986, consequently, foliar-applied XE-1019 reduced seed yields by an average of 23% and Parlay reduced seed yields by an average of 21%. Total dry weight and straw weight were unaffected by foliar-applied PGR treatment in both years. Use of XE-1019 and Parlay in field crop production has the potential to reduce dry matter production and improve seed recovery, but results vary from year to year. These PGRs have the potential to improve seed yields and may be effective in improving harvest conditions by reducing vegetative biomass. / Graduation date: 1995

Bacteria that provide benefit to plants are considered to be plant growth-promoting bacteria (PGPB) and can facilitate plant growth by a number of different mechanisms. Plant growth-promoting bacteria that are able to utilize the plant compound 1-aminocyclopropane-1-carboxylate (ACC) as a sole source of nitrogen, as a consequence of possessing the enzyme ACC deaminase, can protect host plants from a number of environmental stresses. In addition to ACC deaminase, PGPB may utilize other mechanisms to facilitate plant growth including IAA synthesis, siderophore production, phosphate solubilization activity, ammonia production, and antibiotic production. Plant growth-promoting bacterial endophytes employ similar plant growth promotion mechanisms to those used by rhizospheric PGPB. In fact, bacterial endophytes are PGPB that go one step further and colonize the inside of the plant tissues and provide more efficient and prompted protection to their hosts compared to those that bind exclusively to the plant’s rhizosphere. Therefore, it is likely that endophytic plant growth-promoting bacteria will be superior to similar non-endophytic bacterial strains in promoting plant growth under a wide range of environmental conditions. In the work reported here, new bacterial endophytes were isolated and characterized. Among twenty-five ACC deaminase positive strains, two best strains were selected and ACC deaminase deficient mutants were constructed. The ability of two newly isolated 1-aminocyclopropane-1-carboxylate (ACC) deaminase-containing plant growth-promoting bacterial endophytes Pseudomonas fluorescens YsS6, Pseudomonas migulae 8R6 and their ACC deaminase deficient mutants was shown to 1) delay the senescence of mini carnation cut flowers and 2) to facilitate tomato plant growth under salinity stress. In the mini carnation flower senescence evaluation, the only difference between wild-type and mutant bacterial endophytes was ACC deaminase activity, our results demonstrate that this enzyme is directly responsible for a significant delay in flower senescence. Despite containing ACC deaminase activity, the rhizosphere-binding PGPB Pseudomonas putida UW4 was not taken up by the cut flowers and therefore had no effect on prolonging flower shelf life. In evaluating the effect of bacterial endophytes under salt stress, tomato plants treated with either of the wild-type strains of the two selected bacterial endophytes demonstrated early flowering and fruiting and had significantly greater numbers of flowers, buds, and fruits than either the corresponding ACC deaminase mutant strain-treated plants or the control plants. Although both bacterial endophytes P. fluorescens YsS6 and P. migulae 8R6 showed significant plant growth-promotion capabilities, P. migulae 8R6 demonstrated better plant growth facilitation under salt stress than did P. fluorescens YsS6. P. migulae 8R6 treated tomato plants demonstrated the least sodium uptake, the highest chlorophyll content, and highest fresh and dry biomass. The results of the work presented here suggest that ACC deaminase containing selected bacterial endophytes could be employed as environmentally friendly adjuncts to agricultural and horticultural practice.

Chickpea production in the short growing season of the Canadian Prairies is still a challenging task due to excessive and continuous vegetative growth which often results in severe yield and quality reduction. This study examined the effects of three plant growth retardants (PGR), Chlormequat Chloride (CCC), Prohexadione Calcium and Trinexapac Ethyl applied during flowering stage on vegetative growth, seed quality, yield and crop maturity of the Kabuli chickpea cultivar CDC Frontier. Field experiments were conducted at Brooks and Bow Island in southern Alberta in the 2010 and 2011 growing seasons. Four concentrations of each PGR were applied at 10, 20 and 30 days after flowering (DAF) stages. During the 2010 growing season the crop experienced above average moist and cooler temperature conditions. In contrast, later half of the 2011 growing season was above average dry and hot. None of the three PGR tested in this study had a significant effect on plant height at 30 days after treatments or on above ground biomass plant-1 at harvest. Application of PGR had no significant effects on the number of seeds m-2, except at the Brooks rain-fed site in 2011 where the PGR treatment applied at 10 and 20 DAF increased the number of seeds m-2 at harvest. An increase of 1000-seed weight of marketable seeds was obtained with Prohexadione Calcium and Trinexapac Ethyl applications at Bow Island, but the effects were not consistent across sites and years. Results suggested that the effect of PGR on 1000-seed weight of marketable seeds mainly depended upon the growing environment and the type of PGR. In general, PGR applications reduced the total and marketable seed yields. Application of Prohexadione Calcium and Trinexapac Ethyl at the Bow Island site delayed crop maturity in 2011. In contrast, the application of CCC at 6000 mg L-1 at 20 DAF accelerated crop maturity at the Brooks irrigated site in 2011. In addition to this main study, the potential effects of Pyraclostrobin and Prothioconazole fungicides on the activities of the three PGR were compared by a separate experiment conducted at the Brooks irrigated site in 2011. The results of that study revealed that there were no significant differences in the effects of PGR on chickpea vegetative growth, seed yield parameters and maturity when they were applied as a mixture with either Pyraclostrobin or Prothioconazole fungicide. In summary, results revealed that PGR applied during flowering stage were not effective on controlling vegetative growth of chickpea and did not improve seed yield and crop maturity. Their effects on yield-related traits were highly inconsistent. Thus, it can be concluded that the application of PGR is not a reliable agronomic option to handle the production issues associated with continues vegetative growth at the late reproductive stage of the chickpea cultivar CDC Frontier under the western Canadian growing conditions.

Although plant growth-promoting rhizobacteria (PGPR) have shown tremendous potential to be used as inoculants for many agricultural crops, they may not survive severe environmental conditions in the field which could limit their large scale applications. Endophytic bacteria, which can be recovered from inside plant tissues such as roots, stems and leaves, might overcome this limitation due to their unique ecological niche inside plant roots where they are sheltered from external environmental disturbances. Some of these bacterial endophytes have beneficial effects on their host plants and stimulate plant growth or reduce disease symptoms, apparently through mechanisms that are similar to those proposed for PGPR. The objective of this study was to assess a collection of endophytic bacteria for PGPR traits and potential use to enhance the rhizobial-legume symbiosis. Forty isolates obtained from the roots of various plants were identified by fatty acid methyl ester (FAME) analysis, and 16S RNA gene sequencing analysis. The majority (i.e., 75%) were identified as Pseudomonas species. Many of these isolates were able to solubilize phosphate, produce indole-3-acetic acid (IAA), produce aminocyclopropane-1-carboxylic acid (ACC) deaminase, synthesize siderophores and show antagonistic activities against several soil-borne plant pathogenic fungi under in vitro conditions. Selected isolates were further evaluated for the ability to enhance plant growth and nodulation of alfalfa when co-inoculated with Sinorhizobium meliloti under growth chamber conditions using growth pouch and potted soil assays. Results revealed that P. putida strain EB EE 4-25, P. syringae strain EB XDE 4-48, and P. fluorescens strain EB EE 2-23 significantly increased shoot length, root length, enhanced nodulation and increased lateral root formation of alfalfa plants in growth pouch and potted soil assays when co-inoculated with S. meliloti strain P102 compared to plants inoculated with S. meliloti strain P102 alone. Results also suggested that expression of one or more of the mechanisms, such as solubilization of phosphate, production of IAA, production of siderophores, and ACC deaminase production might have played a role in the enhancement of the alfalfa- Sinorhizobium symbiosis. These results suggest that some endophytic bacterial strains may be useful as biofertilizers and/or biocontrol agents in sustainable agricultural practices.

Coastal communities will be most affected by global climate change and are important to study to understand current and future ecological processes. The current model for global climate change predicts a change in rainfall, which will alter the salinity of coastal systems. Given the presence of eutrophication in many coastal waters, it is important to understand the effects that this increase in nutrients, coupled with changes in salinity, will have on these communities. This study was conducted to understand the effect of salinity increase on the growth and herbivory of the black mangrove, Avicennia germinans, in the presence of increased nutrients. Explicitly, the effects of changing salinity (high, medium, and low) were coupled with fertilizer additions of nitrogen, phosphorus, both, or no fertilizer. Nutrient enrichment differentially affected the growth and herbivory of the plants between salinity zones. The medium salinity zone consistently produced the greatest increases in growth and herbivory. Added nutrients did not have an effect on growth in the low salinity zone. However, added nitrogen increased some growth variables in the medium salinity zone and added phosphorus increased some growth variables in the high salinity zone. Phosphorus also increased herbivory. The results point to diverse processes acting along the salinity gradient. There appears to be differential N- and P-limitation along the gradient. Additionally, the growth differences indicate abiotic and biotic limitations across the salinity gradient, with debilitating salinity acting in the high salinity zone and competition acting in the low salinity zone.

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