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- Author or Editor: Rhoda Burrows x
Growing a plant host in association with other plant species (i.e., increasing diversity) changes the composition of the associated arbuscular–mycorrhizal (AM) fungal community. We tested whether this alteration in the fungal community causes significant differences in the growth of Schizachyrium scoparium L. (Little Bluestem, a C4 grass) or Lespedeza capitata L. (Bush clover, a legume). Seedlings were transplanted into pasteurized soil inoculated with soil from monoculture plots of Schizachyrium or Lespedeza, respectively, vs. plots containing one, seven, or 15 additional plant species. Soil washes from a composite of the plots were added to all pots, including non-inoculated controls, to reduce differences in the non-AM microbial communities. Spore counts of the inoculum from Lespedeza plots showed increasing numbers of AM fungal spores and species richness with increasing plant diversity; this was not true with the Schizachyrium plots, possibly because Schizachyrium may be a better host to more species of AM fungi than Lespedeza. Both Schizachyrium and Lespedeza responded to inoculation with increased growth compared to non-inoculated controls. Tissue analyses of both species showed that inoculation increased the percentage of Cu, and lowered the percentage of Mn compared to control plants. Schizachyrium showed no significant differences in growth due to inoculum source (1-, 2-, 8-, or 16-species plots); while Lespedeza showed increases in root and shoot weights with increasing source-plot diversity.
Grape growers are interested in production systems that are ecologically sustainable. The positive effect of colonization by arbuscular-mycorrhizal (AM) fungi on water and nutrient uptake, and thereby plant growth, is well-documented, at least in greenhouse studies. However, we have only limited data on how this complex association between grapes and these fungi might affect entry into winter dormancy, a factor crucial to vine survival in the northern great plains. To test this relationship, we rooted cuttings of grape genotypes Vitis riparia and an F1 selection of `Seyval' × V. riparia in a soil mix containing either inoculum of the AM Glomus intraradices, or a control. These cuttings were then used in growth chamber, greenhouse, and field experiments. The inoculated rooted cuttings were successfully colonized; no significant differences were observed among treatments in initial cutting vigor, budbreak, or leaf number. In the field and greenhouse, periderm development (an indicator of entry into dormancy) occurred earlier in AM-inoculated plants, regardless of genotype. Growth chamber-grown plants did not display differences in the first year, but, after a dormancy cycle, buds from inoculated plants survived lower temperatures in freezing tests compared to controls.
Fungicides applied as soil drenches affect arbuscular-mycorrhizal (AM) fungal colonization of plant roots to different degrees, depending on the chemical used. However, the effect of fungicides applied as seed treatments has been less studied, and is of particular interest to growers who want to encourage beneficial mutualisms while protecting seedlings against pathogens. We tested the effects of four common seed treatments, Apron (mefenoxam), Thiram, Raxil (tebuconzaole), and Captan on colonization of `Superstar' muskmelon roots by the AM fungus Glomus intraradices in the greenhouse. By 30 days after planting, colonization was very high (>90% root length) for all treatments, with relatively minor (<10%) differences in percent length root with AM hyphae. The Apron seed treatment had the highest percent root length with hyphae, but the lowest amount of vesicles, while roots from Raxil and Captan-treated seeds had the lowest hyphal colonization and highest vesicle formation. Myconate ®, a commercial formulation of formononetin, an isoflavone previously shown to increase AM colonization, significantly increased the percent colonization of roots from the Raxil treatment, but not other treatments. Myconate also increased vesicle numbers in all but the Captan treatments, but not significantly.
Nitrification-induced subsoil acidification is a major problem encountered with the use of ammonium- or urea-containing fertilizer solutions for drip fertigation of tree fruit crops. We conducted a laboratory experiment to evaluate the soil acidification potential of the four fertilizer N solutions most frequently used for fertigation within the Washington tree fruit industry. Treatments were five orchard soils x four commercial N solutions (calcium nitrate, calcium-ammonium nitrate, ammonium nitrate, urea-ammoniun nitrate) x four N rates (0, 100, 200, 500 mg N/kg). Air-dry subsamples of each soil were inoculated with fresh soil known to exhibit nitrifying behavior amended with treatment solutions. Subsamples were maintained at simulated field capacity of –15 kPa. Soil pH was measured after 5 weeks incubation. The treatment solutions were reapplied and pH measured after another 5 weeks. The soil were then leached with distilled water and further incubated to determine if pH would increase as has been observed in the field. The fertilizer solutions acidified the soils in direct relation to their ammonium plus urea content. The calcium nitrate solution was acidifying because it contains ammonium nitrate as an impurity. We will present the pH “rebound” data.
Late dormant copper (Cu) sprays and mid-summer foliar Cu sprays are being promoted within the Washington apple industry as a means to enhance fruit typiness and red skin color, respectively. While there appears to be theoretical bases for these practices, they have not been tested for horticultural significance. Differential late dormant spray treatments of Cu hydroxide (the Cu source most commonly recommended by agricultural consultants) were imposed in two `Delicious' orchards. Flower cluster Cu was positively related to Cu rate, but the sprays had no effect on leaf Cu or on six fruit typiness variables. Differential mid-summer spray treatments of water, Cu sulfate, and Cu oxysulfate solutions were imposed in three `Delicious' orchards and one `Fuji' orchard. The Cu sprays increased leaf Cu, but had no effect on market color grade measured using a commercial color sorter. The results appear to reflect Cu physicochemistry and timing of application. These preliminary results call into question the utility of the Cu sprays for improving apple fruit quality characteristics when trees show no visual signs of Cu deficiency. They do suggest some alternative ways to manage Cu nutrition in deciduous tree fruit orchards.
After the first full growing season, 9- and 11-week-old asparagus (Asparagus officinalis L.) seedlings transplanted in fall exhibited superior crown and fern characteristics relative to seedlings of the same ages transplanted in spring. Seedlings overwintered in coldframes and planted in the spring matched or exceeded growth of those transplanted the previous fall. The hybrid ‘Jersey Giant’ was superior to an improved selection of ‘Mary Washington’ for all planting dates. Correlations between seedling size at transplanting and after one season’s growth were significant for crown weight (r = 0.82), fern weight (r = 0.65), and fern number (r = 0.60). The importance of seedling size is further confirmed by the superior growth of 11-week-old over 9-week-old seedlings up to 18 months after planting.
Asparagus offcinalis L. `Mary Washington' seedlings inoculated with Glomus fasciculatum (Thaxter) Gerd. and Trappe emend. Walker and Koske showed increased growth after 9 weeks, compared with noninoculated plants. Phosphorus supplementation (25 g·m-3) increased seedling growth of inoculated and noninoculated plants throughout the 26 weeks of the experiment. However, after 9 weeks, there were no differences in growth of inoculated, non-P-supplemented plants and noninoculated, P-supplemented plants. Fern height, fern and crown weight, and bud numbers correlated positively to the percentage of G. fasciculatum root infection.
Two year old sugar maples grown in 25 gallon containers were subjected to different levels of stress by withholding water. Drought levels were measured using irrometers. Irrometer readings of 40, 60, and 80 centibars were used to determine when to add water. The media used were a primary nursery mix of 50:50 sand and pine bark by volume. The maples were evaluated for differences in stomatal responsiveness with the porometer and growth parameters of number of nodes, internode length, and leaf number were taken. Some of the trees were treated with ROOTS as a drench to determine if it would enhance resistance to water stress of containerized nursery plants. Despite the use of ROOTS there was no significant difference between the stressed and the non-stressed plants of stomatal responsiveness or the growth parameters.
Three- to 4-month-old seedlings of an improved selection of Asparagus officinalis L. cv. Mary Washington were artificially hardened and crowns subjected to controlled freezing tests. Two low-temperature acclimation regimes were used. The first was 3C for 0, 1, or 2 weeks before freezing at 0, −5, or − 10C; the second, 3C for 0, 1.5, or 3 weeks, followed by freezing at 0, −2.5, −4.5, −6.5, or −8.5C. Regrowth tests showed that hardiness increased with 2 and 3 weeks of acclimation, with tolerance to −5 and −6.5C, respectively. Water-stressed seedlings (relative water content at 57%) withstood exposure to −5C, but not to −6.5C; rehydrated crowns and well-watered controls were hardy to −3.5C.