Strawberry (Fragaria ×ananasa Duch. `Chandler') tips containing only root initials were inoculated with mycorrhizal fungus Glomus intraradices and were fertilized with rockphosphate levels of 1, 2, 4 and, 6 mg·cm–3 to study root growth and mycorrhizal infection. The addition of rockphosphate at >2 mg·cm–3 decreased mycorrhizal infection. Root dry weight of mycorrhizal strawberry plants increased significantly over the controls with addition of rockphosphate, and mycorrhizal infection significantly decreased the shoot: root ratio. Foliar P levels decreased in mycorrhizal plants fertilized with up to 4 mg·cm–3 of rockphosphate and a quadratic relationship was seen between rockphosphate levels and foliar P. In nonmycorrhizal plants, the highest foliar P level was with rockphosphate at 1 mg·cm–3. The study revealed rockphosphate at 1 to 2 mg·cm–3 is beneficial for greater root growth with mycorrhizal inoculation.
Phytophthora root rot is a severe disease on blueberry (Vaccinium corymbosum L.) in poorly drained soils. The objective of the study was to determine the frequency of water-logged conditions on disease severity of blueberry. Phytophthora cinnamomi was grown on rice hulls and incorporated into the soil at the rate of 10% v/v. Water logging conditions were inflicted for 48 hr on mulched and non–mulched blueberry plants at 1-, 2-, and 4-week intervals. Non-water logging conditions were used on both mulched and non-mulched control plants. There was a significant linear relationship between disease severity of shoots and roots and the frequency of water-logging conditions. Disease symptoms were low in control plants, but disease ratings were high in mulched and non-mulched plants that were treated with water-logging conditions every week. There was also a linear trend between shoot dry weight and root dry weight of plants with frequency of water logging. Higher dry weights were seen on control plants. There was a significantly higher shoot, root dry weight and number of leaves of mulched plants than non-mulched plants. The percentage of infection on roots were high with frequent water logging. The study revealed high disease incidence with frequent water loggings. However, growth of mulched blueberry plants were comparable in control plants and plants that were subjected to water logging at 4-week intervals.