Search Results
Abstract
Seedlings of highbush blueberry (Vaccinium corymbosum L.) subjected to 3 fungal treatments and 2 soil pH levels (4.2 and limed to 6.0) displayed no significant treatment interaction in respect to growth, mycorrhizal infection intensity, or nutrient uptake. Among the fungal treatments, there were differences in nutrient uptake and infection intensity, but no difference in total linear stem growth or number of shoots. Lower soil pH resulted in significantly greater stem growth and number of shoots; however, intensity of infection was not significantly different compared to the high pH soil.
Abstract
‘Jersey’ blueberry plants were greenhouse-grown through 1 season with treatments consisting of a factorial combination of 4 soil factors: inoculation with a mycorrhiza-forming fungus; high or low nutrient regime; with or without leachate from a native blueberry soil; and soil porosities corresponding to a clayey, silty, or sandy, and a native blueberry soil, Berryland, as a standard comparison. Although very low in nutrient elements, Berryland soil or its leachate significantly increased plant growth. There was no significant effect on growth from mycorrhizal inoculation at either high or low nutrient levels and only a slight effect from varying the soil free-pore space.
Abstract
Citrus blight is a vascular wilt disease of unknown etiology. Blight-affected ‘Pineapple’ sweet orange [Citrus sinensis (L.) Osb.] trees on rough lemon (C. jambhiri Lush.) rootstock in early stages of decline were treated with benzimidazole fungicides or with oxytetracycline (OTC) by trunk injection, soil drench, or injection plus drench. The distribution and persistence of the materials were monitored by bioassay using Bacillus cereus var. mycoides for OTC and Penicillium expansum L. for benzimidazoles. Both materials were well-distributed in the canopy following trunk injections, in the root systems following soil drenches, and though most of the tree after injection plus drench treatments. Benzimidazoles and OTC persisted within the trees for several months and relatively high levels of activity were maintained for over a year by 3 applications. OTC persisted in soil for more than 6 months; whereas, benomyl disappeared from the soil in 3 months or less. Although high levels of bactericidal or fungicidal activity were maintained in the treated trees, most treated trees declined as rapidly as the untreated control trees. The injection plus drench group treated with OTC showed a slight improvement after 2 years. None of the treatments increased tree growth or resulted in increased water uptake. High levels of zinc in trunk wood, an internal symptom of blight, were unaffected by the benzimidazole treatments, but injection plus drench treatment with OTC significantly reduced zinc levels in trunk wood. Since neither OTC nor benzimidazoles completely reversed symptoms of blight, we were unable to conclusively confirm or refute proposed bacterial or fungal etiologies for citrus blight.
Abstract
Blight-affected sweet orange [Citrus sinensis (L.) Osb.] trees on rough lemon (C. jambhiri Lush.) rootstock were injected with high concentrations of oxytetracycline (OTC) (10–30 g a.i./tree) under high pressure (1300–1700 kPa) in an attempt to induce remission of blight symptoms. OTC activity, determined by bioassay with Bacillus cereus var. mycoides, was distributed in 70–95% of the twigs sampled 3 weeks after injection. Activity persisted in the twigs and mature leaves for 3 to 5 months and in a few twigs as long as 7 to 8 months after a single injection. No activity was detected in small roots and downward movement appeared to be limited. Distribution and persistence of OTC in healthy trees was similar to that in blight trees. Trees with mild blight symptoms injected once with OTC continued to decline and had moderate to severe blight 2 years later. Of 16 healthy trees injected with OTC 4 times over 2 years, 1 became severely blighted and several others developed mild symptoms. Our trunk injection work with OTC does not support the hypothesis that blight is caused by a tetracycline-sensitive organism, but does not eliminate that possibility.
A study was conducted to evaluate the effects of salinity on growth and nutrient uptake in basil (Ocimum basilicum L. ‘Siam Queen’). Plants were fertilized with a complete nutrient solution and exposed to no, low, or moderate levels of salinity using NaCl or CaCl2. The plants in control and moderate salinity treatments were also inoculated or not with the arbuscular mycorrhizal fungus (AMF), Rhizophagus irregularis (Blaszk., Wubet, Renker, & Buscot) C. Walker & A. Schler., to determine whether AMF mitigate the effects of salinity stress. Electrical conductivity (EC) of leachate collected from salinity treatments reached levels ≥8 dS·m−1 but had no effect on plant growth in the first 41 days of treatment. However, by 75 days, plants exposed to low and moderate levels of NaCl and CaCl2 had 20% to 38% less dry weight (DW) than controls. Reductions in DW were similar between NaCl and CaCl2 and was greater in roots than in shoots. Both NaCl and CaCl2 salinity reduced stomatal conductance (g S) within 25 days, but hastened flowering by 2–3 days, and nearly doubled the DW of flowers at 75 days. Salinity from NaCl increased uptake of Na and reduced uptake of Ca, whereas CaCl2 salinity increased uptake of Ca and reduced uptake of Mg and Mn. Both salts also increased relative uptake of N, Cu, and Zn, and reduced relative uptake of S and Fe. In general, Na was concentrated in roots and excluded from shoots, whereas Cl was concentrated primarily in leaves. Both salts reduced root colonization by AMF. However, AMF increased g S by 10% with NaCl and 22% with CaCl2, and increased shoot DW by 22% and 43%, respectively. Other than Ca and Cl, AMF did not enhance nutrient uptake under NaCl or CaCl2 salinity. ‘Siam Queen’ basil was moderately tolerant to salinity, due at least in part to exclusion of Na from the shoots, and inoculation with AMF increased tolerance to both NaCl and CaCl2 salinity. Differences in basil tolerance to NaCl and CaCl2 indicate plants may have different mechanisms for dealing with salinity and sensitivity is not solely a function of EC. This highlights the importance of understanding the source of salinity in irrigation waters and soil for predicting damage.