Effects of the tall fescue endophyte on seed germination and resistance to preemergence damping-off

Tall fescue (Festuca arundinaceae) infected with the endophyte Neotyphodium coenophialum is correlated with increased resistance to damping-off. The objective of this research was to determine the mechanism for endophyte-mediated resistance (EMR) to Pythium aphanidermatum. In experiments using Kentucky 31 seed differing only in endophyte infestation levels (endophyte-infected (95%) was defined as 95E+ and endophyte-free was defined as 95E-), 95E+ seed were more resistant to damping-off than 95E- seed. However, when seed were presoaked in sterile deionized water (SDW) for 24 h before planting, no resistance was observed. Embryo infection and seed colonization of 95E-t- and 95E- seed were compared in P. aphanidermatum-infested soilless medium. Seed were incubated in infested medium for 20 h, rinsed, placed on selective medium, and observed at 20 and 30 h. Embryos of 95E- seed developed necrosis at twice the rate of 95E-I- seed. However seed coat colonization was not different and did not affect embryo viability. Radicle emergence was assessed fi-om seed incubated in rotating flasks of SDW for 24, 48, 72, or 96 h. At 24 h the germination rate of 95E-^ seed was 13% and 95E- seed was 34%; at 96 h germination rates of 95E+ and 95E- seed were equivalent (ca. 80%). To determine the effect of presoaking on germination three seed treatments were compared: 1) nonscarified, 2) scarified, presoaked for 3 h, 3) scarified, presoaked for 24 h. Seeds were planted in soilless mix and incubated for 7 d. No differences in germination were observed between 95E-I- and 95E- seed when presoaked for 24 h, but 95E-I- shoot lengths were 15% less than those of 95E-. Germination of 95E-I- seed was reduced by 30% and 40% when nonscarified or presoaked for 3 h, respectively, but 95E seed was not affected by seed treatment. Similar germination rates for all seed treatments were observed when incubated for 3 weeks. Antifungal activity of 95E+ seed against P. aphanidermatum mycelium was not observed. The influence of endophyte on the spermosphere was measured using pH, conductivity, carbohydrate content, and a Pythium bioassay. Seeds were placed in 24-well plates with 1 ml SDW. Using iodine tests of 24 h steep water, it was determined that wells with 95E- seed contained more carbohydrate. Conductivity and pH were measured at 3 and 24 h. Rates of pH decline and conductivity increase were greater in 95E- wells than 95E+ wells. In wells containing 2 seeds/ ml SDW the pH decreased to 4.0 at 3 h. The effects of pH, molarity, and endophyte status on sporangia of P. aphanidermatum were tested in sterile sodium citrate buffer with 95E+ and 95E- seed. Buffers tested ranged from pH 4.0 to pH 6.5, and concentrations ranged from 0.05 to 0.00IM. Seeds were placed in tissue culture dishes with buffer then a Py/Zz/M/n-infested grass piece was placed in each well. Controls with no seeds were included. Cultures were incubated at 28 C with continuous fluorescent light for 24 h and observed for presence of zoospores. Zoospore production was evident in wells with high pH and low molarity. No zoospores were observed in wells with 0.05M buffers; no zoospores were observed in wells with pH of 4.0. At low buffer concentration (0.00IM and 0.005 M) and medium pH levels (5.5 and 6.0) zoospore production was less in wells with 95E+ seed than 95E- seed or controls. Thus differences in pH and conductivity in the spermosphere as a result of delayed germination may partially explain EMR. These results were inconsistent with the response of P. aphanidermatum propagules to 95E+ and 95E- seed in SDW, where 95F+ seed differentially inhibited zoospore production. Based on these data, factors other than a reduction in 95E+ seed exudation may be involved in EMR. However, it was concluded that a primary factor of reduced infection of 95E+ seed by P. aphanidermtum is believed to be escape through germination delay

Final Year of Decade-long National Elm Trial

Although many Dutch elm disease-resistant elm cultivars are available in the nursery trade, much of the public is hesitant to purchase and plant any elm trees. In order to promote interest in planting these trees, scientific data on growth, form, and pest resistance for existing Dutch elm disease resistant elm cultivars are essential

National Elm Trial

Although many Dutch elm disease-resistant elm cultivars are available in the nursery trade, much of the public is hesitant to purchase and plant any elm tree. In order to promote interest in planting these trees, scientific data on growth, form, and pest resistance for existing Dutch elm disease resistant elm cultivars are essential

Testing a Warning System for Anthracnose Fruit Rot on Day-neutral Strawberry–Year 4

Anthracnose fruit rot (AFR) of strawberry is considered to be caused by three Colletotrichum spp. In the Midwest, however, only Colletotrichum acutatum is found. This pathogen can attach itself to healthy plants and spread throughout the field without causing symptoms on the foliage. When fruit begins to ripen and weather conditions are rainy and warm, AFR can suddenly cause large sunken lesions on the fruit. To protect against AFR where it has occurred in the past, growers need to spray every 7 to 10 days beginning at the start of bloom until harvest

Controlling Bacterial Wilt in Muskmelon with Perimeter Trap Cropping

Perimeter trap cropping (PTC) involves planting one or more rows of a cucurbit crop that is highly attractive to cucumber beetles around the border of a main cucurbit cash crop that is less attractive to the beetles. Cucumber beetles attempting to migrate into the field are concentrated in the relatively more attractive border crop, where they can be controlled by insecticides

On-farm Cooperator Trials: Effect of Extended-duration Row Covers on Muskmelon and Winter Squash on Bacterial Wilt and Yield

Susceptible cucurbit crops are difficult to grow in Iowa because of bacterial wilt, caused by Erwinia tracheiphila. Striped and spotted cucumber beetles transmit bacterial wilt. Other insect pests such assquash vine borer and squash bugs may also have an economic impact on yield, particularly in squash

Controlling Bacterial Wilt in Muskmelon with Perimeter Trap Cropping

Perimeter trap cropping (PTC) involves planting one or more rows of a cucurbit crop that is highly attractive to cucumber beetles around the border of a main cucurbit cash crop that is less attractive to the beetles. Cucumber beetles attempting to migrate into the field are concentrated in the relatively more attractive border crop, where they can be controlled by insecticides

National Elm Trial Update for Iowa, 2007

The graceful American elm that once dominated urban forests across the United States has essentially disappeared from urban landscapes after the introduction of Dutch elm disease. This tragedy illustrates why it is essential to maximize genetic diversity within the nation’s urban forests. Exotic pathogens and insects continue to threaten the health of our shade trees. Dutch elm disease-resistant elm cultivars could enhance the diversity as well as the beauty of urban forests. Although many Dutch elm disease-resistant elm cultivars are available in the nursery trade, much of the public is hesitant to purchase and plant any elm tree. In order to promote interest in planting these trees, scientific data on growth, form, and pest resistance for existing Dutch elm disease resistant elm cultivars are essential

Organic Practices for the Production of Muskmelon

Cucurbit crops, especially muskmelon, are difficult to grow due to bacterial wilt (Erwinia tracheiphila). This disease is vectored by the cucumber beetle, both spotted and striped. The highest risk period for disease infection is early in the season when adult beetles emerge from overwintering in the ground and begin feeding on young cucurbit plants