As a result of this investigation the following conclusions were reached: 1. The application of nitrogen, in any amounts, made immediately following planting does not produce any noticeable effect on the time of fruit bud differentiation in the strawberry. 2. Nitrogen fertilizers applied to strawberry plants shortly after planting hasten the formation of runners and increase the number of runners produced. 3. The length of the runners between rooted runner plants is not materially increased by.nitrogen fertilizers. 4. Although runner production is hastened by the use of nitrogen, the actual rooting of the runner plants takes place at approximately the same time in fertilized and unfertilized plants. 5. Fruit bud differentiation is associated 1vith a decrease in the length of runners produced which probably results in an accumulation of carbohydrates. 6. Field conditions cannot be satisfactorily simulated under average greenhouse conditions and therefor results that are secured in greenhouse experiments cannot be deemed applicable to plants growing under field conditions. / Master of Science

The resistance status of Tetranychus urticae Koch and Lygus hesperus Knight sourced from California strawberry fields was evaluated in laboratory bioassay experiments. Adult female T. urticae sourced from a miticide naïve population were exposed to a range of miticide active ingredient concentrations mixed with acetone in contact bioassay experiments. LC50 concentrations for the active ingredients fenpyroximate, abamectin, bifenazate, and spiromesifen as well as LC90 concentrations for the active ingredients fenpyroximate, abamectin, and bifenazate were derived from this susceptible population. A total of ten field populations of T. urticae, five from the Santa Maria growing region and five from the Ventura/Oxnard growing region, were exposed to these concentrations and mortality response was compared with the susceptible population to determine the resistance status of T. urticae on a per-field basis. Resistance detection occurred less often in the LC50 concentration groups compared to their respective LC90 concentrations. Resistance to the LC50 concentration of spiromesifen could not be detected in any field population. Resistance to the LC90 concentrations of fenpyroximate and abamectin was detected in three field populations from Santa Maria and four populations from Ventura/Oxnard. Resistance to the LC90 concentration of bifenazate was detected in three populations from Ventura/Oxnard and in no populations from Santa Maria. Lygus hesperus were exposed to formulated products registered in California strawberries after being separated into three groups based on life stage. Instars one through three were considered small, instars four and five were considered large, and winged individuals were considered adults. The small and large groups were exposed to the maximum field labeled rate of Rimon® (a.i. = novaluron). Adults were exposed to the maximum field labeled rate of Actara®, Brigade®, and Sivanto®, the active ingredients of which are thiamethoxam, bifenthrin, and flupyradifurone respectively. A total of 14 field populations were screened for resistance, six collected from the Santa Maria growing region in 2021, and eight collected in 2022, five of which came from the Santa Maria region, and three from the Salinas/Watsonville region. Resistance was detected by comparing the mortality response of an insecticide naïve population of L. hesperus and field collected populations in residual laboratory bioassay experiments. Resistance to Rimon® in the small group was effectively detected in all populations in 2021 and 2022. Resistance to Rimon® in the large group was detected in four populations in 2021 and five populations in 2022. Resistance to Actara® and Brigade® was effectively detected in all populations in 2021 and 2022. Resistance to Sivanto® was effectively detected in four populations in 2021 and two of three populations in 2022. A full submersion assay was utilized for the second half of Sivanto® trials in 2022 since mortality response of the susceptible population was low in the residual group. Five of five populations tested with the modified assay were considered effectively resistant.

Net photosynthesis (Pn) and photosynthate partitioning were compared between fruiting and deblossomed strawberry plants. Throughout a six-week fruiting cycle, Pn (leaf area basis), specific leaf weight (SLW), and chlorophyll content were determined at 7-day intervals for an early-formed leaf (old leaf) and for the most recently expanded leaf (young leaf) of fruiting and deblossomed day-neutral plants (cv. Tribute). During the fifth week of the fruiting cycle, Pn of the young leaf was higher for fruiting plants than for deblossomed plants. Pn of the old leaf was not different between treatments during any week. During weeks 4 and 5, the young leaf of the deblossomed plants had a higher SLW than that of fruiting plants; SLW of the old leaf was higher for deblossomed plants during weeks 4-6. The young leaf of the deblossomed plants had a higher chlorophyll content than that of fruiting plants during weeks 1 and 4. Chlorophyll content of the old leaf was higher for deblossomed plants during weeks 1, 2, and 4. There were no differences between treatments for stomatal conductance for CO₂ or dark respiration during any week of the fruiting cycle. In another experiment, deblossoming day-neutral strawberry plants (cv. Tribute) increased the amount of ¹⁴C translocated to the newly-emerging leaves 48 hrs after treatment with ¹⁴CO₂. During weeks 3-6 of the fruiting cycle, leaves of deblossomed plants had a greater total area, dry weight, and total non-structural carbohydrate (TNSC) content than leaves of fruiting plants. Pn on a whole-plant basis was higher for deblossomed plants than fruiting plants. This was largely due to the greater leaf area of the deblossomed plants, since total leaf area was highly correlated with Pn (whole plant basis). Pn (whole plant basis) was highly correlated with total dry weight and TNSC of plants in both treatments. Thus, deblossoming changed Pn and dry matter partitioning of strawberry plants. The additional leaf area and greater Pn rates (whole plant basis) obtained by deblossoming strawberry plants may result in increased yields during subsequent fruiting cycles. / Ph. D.

Call number: LD2668 .T4 1986 H534 / Master of Science / Horticulture, Forestry, and Recreation Resources

Graduation date: 1953

Graduation date: 2004

Knowledge of disease epidemiology and the impact of plant nutrient status on development of disease is fundamental in establishing effective management strategies for crop pathogens such as Podosphaera aphanis Br. (Braun et al., 2002), the causal agent of powdery mildew on strawberries. The following study investigated the conditions conducive for powdery mildew in strawberry crops in South Australia, the effect of foliar concentration of potassium and calcium on yield and pathogen development on the strawberry cultivars Aromas (resistant to powdery mildew) and Selva (susceptible), the potential for use of foliar-applied potassium silicate to control disease and identification of genes differentially expressed during disease. Meteorological conditions associated with establishment of powdery mildew were observed over three consecutive seasons in commercial strawberry crops grown in Woodside, South Australia. Conducive conditions appear to be >28 oC, <55 % relative humidity (RH) with no rain during the day (for conidiation), followed by a night with >10 oC, >90 % RH and no rain (for germination). Colony development was then promoted by days of >15 oC and <70 % RH, with nights of >8 oC, >80 % RH and less than 2 mm rain in every 24 hour period. These are consistent with epidemiological studies of this pathogen (Peries, 1962a; Jhooty and McKeen, 1964; Mukerji, 1968; Perera and Wheeler, 1975; Byrne et al, 2000; Miller et al, 2003; Blanco et al, 2004; Davik and Honne, 2005; Amsalem et al, 2006). This knowledge may facilitate prediction of times considered high risk for establishment of powdery mildew in strawberry crops. Subsequently, this may allow optimisation of fungicide application and improved management of this disease and reduced yield loss and management expenses. P. aphanis developed at an increased rate on leaves of Selva with low calcium content compared with development on normally fertilised leaves. Increased numbers of conidia germinated successfully on leaves of Aromas with low calcium content compared with development on normally fertilised Aromas leaves, however, the germinated conidia still failed to develop into sporulating colonies. Potassium nutrition had no obvious effect on P. aphanis development. Foliar concentration found to be adequate for growth of cultivars, Selva and Aromas were 6.0 mg/g and 4.5 mg/g Calcium, dry weight and 11.0 mg/g and 12.5 mg/g potassium, dry weight (respectively). Potassium silicate, buffered to pH 7.0 and applied as a foliar fertiliser, reduced the severity of powdery mildew below the economic threshold, though not below the disease severity on plants treated with the fungicide, Systhane® (Bayer CropScience). As potassium silicate can be produced organically this compound may provide a useful management tool for both organic and conventional strawberry growers. Although the cultivar Aromas was not immune to disease under conducive conditions and high inoculum load in the field, inoculation of healthy Aromas plants with P. aphanis in the laboratory failed to produce disease. Conidia were seldom found attached to the leaf surface of healthy Aromas leaves. Germination and subsequent colony development were also not observed in inoculated samples. This suggests there is some mechanism of Aromas that inhibits development of this fungus. Preliminary investigation of differential expression in Aromas inoculated with P. aphanis, identified sequences with homology to a putative antimicrobial protein and photosynthesis-related genes. The results of these studies should enable growers to increase both crop yields and control of powdery mildew, one of the major economic diseases in South Australia. The epidemiological knowledge attained will be valuable, and may provide the basis for future forecast modelling for P. aphanis in strawberry crops in South Australia. Recommendations for calcium and potassium leaf content will allow growers to monitor their fertiliser regime for increased yield of these cultivars. Aromas was identified as a powdery mildew resistant cultivar potentially suitable for production in South Australia, and the genes associated with this resistance response may be used in studies of Fragaria species and breeding for powdery mildew resistant cultivars. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1297684 / Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food and Wine, 2007

Knowledge of disease epidemiology and the impact of plant nutrient status on development of disease is fundamental in establishing effective management strategies for crop pathogens such as Podosphaera aphanis Br. (Braun et al., 2002), the causal agent of powdery mildew on strawberries. The following study investigated the conditions conducive for powdery mildew in strawberry crops in South Australia, the effect of foliar concentration of potassium and calcium on yield and pathogen development on the strawberry cultivars Aromas (resistant to powdery mildew) and Selva (susceptible), the potential for use of foliar-applied potassium silicate to control disease and identification of genes differentially expressed during disease. Meteorological conditions associated with establishment of powdery mildew were observed over three consecutive seasons in commercial strawberry crops grown in Woodside, South Australia. Conducive conditions appear to be >28 oC, <55 % relative humidity (RH) with no rain during the day (for conidiation), followed by a night with >10 oC, >90 % RH and no rain (for germination). Colony development was then promoted by days of >15 oC and <70 % RH, with nights of >8 oC, >80 % RH and less than 2 mm rain in every 24 hour period. These are consistent with epidemiological studies of this pathogen (Peries, 1962a; Jhooty and McKeen, 1964; Mukerji, 1968; Perera and Wheeler, 1975; Byrne et al, 2000; Miller et al, 2003; Blanco et al, 2004; Davik and Honne, 2005; Amsalem et al, 2006). This knowledge may facilitate prediction of times considered high risk for establishment of powdery mildew in strawberry crops. Subsequently, this may allow optimisation of fungicide application and improved management of this disease and reduced yield loss and management expenses. P. aphanis developed at an increased rate on leaves of Selva with low calcium content compared with development on normally fertilised leaves. Increased numbers of conidia germinated successfully on leaves of Aromas with low calcium content compared with development on normally fertilised Aromas leaves, however, the germinated conidia still failed to develop into sporulating colonies. Potassium nutrition had no obvious effect on P. aphanis development. Foliar concentration found to be adequate for growth of cultivars, Selva and Aromas were 6.0 mg/g and 4.5 mg/g Calcium, dry weight and 11.0 mg/g and 12.5 mg/g potassium, dry weight (respectively). Potassium silicate, buffered to pH 7.0 and applied as a foliar fertiliser, reduced the severity of powdery mildew below the economic threshold, though not below the disease severity on plants treated with the fungicide, Systhane® (Bayer CropScience). As potassium silicate can be produced organically this compound may provide a useful management tool for both organic and conventional strawberry growers. Although the cultivar Aromas was not immune to disease under conducive conditions and high inoculum load in the field, inoculation of healthy Aromas plants with P. aphanis in the laboratory failed to produce disease. Conidia were seldom found attached to the leaf surface of healthy Aromas leaves. Germination and subsequent colony development were also not observed in inoculated samples. This suggests there is some mechanism of Aromas that inhibits development of this fungus. Preliminary investigation of differential expression in Aromas inoculated with P. aphanis, identified sequences with homology to a putative antimicrobial protein and photosynthesis-related genes. The results of these studies should enable growers to increase both crop yields and control of powdery mildew, one of the major economic diseases in South Australia. The epidemiological knowledge attained will be valuable, and may provide the basis for future forecast modelling for P. aphanis in strawberry crops in South Australia. Recommendations for calcium and potassium leaf content will allow growers to monitor their fertiliser regime for increased yield of these cultivars. Aromas was identified as a powdery mildew resistant cultivar potentially suitable for production in South Australia, and the genes associated with this resistance response may be used in studies of Fragaria species and breeding for powdery mildew resistant cultivars. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1297684 / Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food and Wine, 2007

Knowledge of disease epidemiology and the impact of plant nutrient status on development of disease is fundamental in establishing effective management strategies for crop pathogens such as Podosphaera aphanis Br. (Braun et al., 2002), the causal agent of powdery mildew on strawberries. The following study investigated the conditions conducive for powdery mildew in strawberry crops in South Australia, the effect of foliar concentration of potassium and calcium on yield and pathogen development on the strawberry cultivars Aromas (resistant to powdery mildew) and Selva (susceptible), the potential for use of foliar-applied potassium silicate to control disease and identification of genes differentially expressed during disease. Meteorological conditions associated with establishment of powdery mildew were observed over three consecutive seasons in commercial strawberry crops grown in Woodside, South Australia. Conducive conditions appear to be >28 oC, <55 % relative humidity (RH) with no rain during the day (for conidiation), followed by a night with >10 oC, >90 % RH and no rain (for germination). Colony development was then promoted by days of >15 oC and <70 % RH, with nights of >8 oC, >80 % RH and less than 2 mm rain in every 24 hour period. These are consistent with epidemiological studies of this pathogen (Peries, 1962a; Jhooty and McKeen, 1964; Mukerji, 1968; Perera and Wheeler, 1975; Byrne et al, 2000; Miller et al, 2003; Blanco et al, 2004; Davik and Honne, 2005; Amsalem et al, 2006). This knowledge may facilitate prediction of times considered high risk for establishment of powdery mildew in strawberry crops. Subsequently, this may allow optimisation of fungicide application and improved management of this disease and reduced yield loss and management expenses. P. aphanis developed at an increased rate on leaves of Selva with low calcium content compared with development on normally fertilised leaves. Increased numbers of conidia germinated successfully on leaves of Aromas with low calcium content compared with development on normally fertilised Aromas leaves, however, the germinated conidia still failed to develop into sporulating colonies. Potassium nutrition had no obvious effect on P. aphanis development. Foliar concentration found to be adequate for growth of cultivars, Selva and Aromas were 6.0 mg/g and 4.5 mg/g Calcium, dry weight and 11.0 mg/g and 12.5 mg/g potassium, dry weight (respectively). Potassium silicate, buffered to pH 7.0 and applied as a foliar fertiliser, reduced the severity of powdery mildew below the economic threshold, though not below the disease severity on plants treated with the fungicide, Systhane® (Bayer CropScience). As potassium silicate can be produced organically this compound may provide a useful management tool for both organic and conventional strawberry growers. Although the cultivar Aromas was not immune to disease under conducive conditions and high inoculum load in the field, inoculation of healthy Aromas plants with P. aphanis in the laboratory failed to produce disease. Conidia were seldom found attached to the leaf surface of healthy Aromas leaves. Germination and subsequent colony development were also not observed in inoculated samples. This suggests there is some mechanism of Aromas that inhibits development of this fungus. Preliminary investigation of differential expression in Aromas inoculated with P. aphanis, identified sequences with homology to a putative antimicrobial protein and photosynthesis-related genes. The results of these studies should enable growers to increase both crop yields and control of powdery mildew, one of the major economic diseases in South Australia. The epidemiological knowledge attained will be valuable, and may provide the basis for future forecast modelling for P. aphanis in strawberry crops in South Australia. Recommendations for calcium and potassium leaf content will allow growers to monitor their fertiliser regime for increased yield of these cultivars. Aromas was identified as a powdery mildew resistant cultivar potentially suitable for production in South Australia, and the genes associated with this resistance response may be used in studies of Fragaria species and breeding for powdery mildew resistant cultivars. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1297684 / Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food and Wine, 2007

Indiana University-Purdue University Indianapolis (IUPUI) / Winter survival is variable among commercially grown strawberry (Fragaria x ananassa) cultivars. The main objectives of this study were to evaluate the molecular basis that contribute to this difference in strawberry cultivars and to identify potential biomarkers that can be used to facilitate the development of new strawberry cultivars with improved overwintering hardiness. With these goals in mind, the freezing tolerance was examined for four cultivars, ‘Jonsok’, ‘Senga Sengana’, ‘Elsanta’, and ‘Frida’ (listed from most to least freezing tolerant based on survival from physiological freezing experiments) and the protein expression was investigated in the overwintering relevant crown structure of strawberry. Biomarker selection was based on comparing the protein profiles from the most cold-tolerant cultivar, ‘Jonsok’ with the least cold-tolerant cultivar ‘Frida’ in a comprehensive investigation using two label-free global proteomic methods, shotgun and two dimensional electrophoresis, with support from univariate and multivariate analysis. A total of 143 proteins from shotgun and 64 proteins from 2DE analysis were identified as significantly differentially expressed between ‘Jonsok’ and ‘Frida’ at one or more time points during the cold treatment (0, 2, and 42 days at 2 ºC). These proteins included molecular chaperones, antioxidants/detoxifying enzymes, metabolic enzymes, pathogenesis related proteins and flavonoid pathway proteins. The proteins that contributed to the greatest differences between ‘Jonsok’ and ‘Frida’ are candidates for biomarker development. The novel and significant aspects of this work include the first crown proteome 2DE map with general characteristics of the strawberry crown proteome, a list of potential biomarkers to facilitate the development of new strawberry cultivars with improved cold stress tolerance.