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  • Author or Editor: B.L. Goulart x
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Current literature reports that commercially produced and cultivated highbush blueberry (Vaccinium corymbosum) are virtually non-mycorrhizal, while native populations of Vaccinium are highly infected with the ericoid fungal symbiont. To confirm this information, a nursery and grower survey was initiated in PA, MI, and NC. Percent infection was determined by presence/absence counts using a grid-line intersect method. Results from 5-plant samples of cultivars `Jersey', `Northland'. `Bluecrop', `Blueray', and/or `Berkeley' (all obtained from nursery sources) from which three root subsamples per plant were cleared and stained revealed that all plants were mycorrhizal. Infection rates ranged from an average of 9.4% for two year old plants to 55.5% on one year old plants. An inverse relationship occurred between rate of ammonium-N and infection rate. Data also indicated a significant difference in infection rate among cultivars with `Northland' most highly infected and `Berkeley' least. Plants propagated in woodchip/sand or peat/sand media developed ericoid mycorrhizas. Data from a current greenhouse experiment supports this observation. We are currently identifying the fungi involved in this symbiosis.

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Previous experiments in the laboratory and the field have suggested that location of mycorrhizal infection within the rhizosphere of blueberry plants may depend on cultural practices that are being used. Furthermore, we have observed that rapidly growing roots, whether in solution culture or within petri dishes, appear to be less likely to become infected when inoculated. A preliminary experiment found higher levels of mycorrhizal infection in roots growing at a 5-cm depth of soil compared to roots growing just under the mulch layer. To further test this hypothesis, an experiment was designed to evaluate the infection intensity of highbush blueberry plants (Vaccinium corymbosum L.) at different locations within the rhizosphere on plants growing under varying cultural practices. Cultural practices included mulching (mulch vs. no mulch) and nitrogen level (0 and 120 g ammonium sulfate/plant). Four-year-old `Bluecrop' highbush blueberry plants subjected to these treatments were arranged in a complete factorial design with six replications at the Russell E. Larson Agricultural Research Center at Rock Springs, Pa. Mycorrhizal infection intensity was evaluated from roots sampled nondestructively using a 2.5 cm soil corer at the interface of the mulch and soil, and at soil depths of 3 and 15 cm from two locations 15 cm from the crown of each plant. Results will be discussed.

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Since air temperature measurements in agricultural applications are subject to radiation errors, aspirated radiation shields are used. Typically researchers employ a double-walled shield, but a simplified design has been developed that gives comparable results and was implemented in strawberry and raspberry trellis research. Components used to build one radiation shield were: one 7.6-cm fan, one 11.4-cm to 8.9-cm PVC reducer, one 8.9-cm to 3.8-cm reducer, two 25-cm sections of 3.8-cm PVC pipe, a ring of PVC (11.4-cm outside diameter, 7.6-cm inside diameter), one hose clamp, clear silicone sealant, and wire to connect the fan to an electricity supply. A reflective suface may be applied to enhance accuracy. The shield can be located at any height within a canopy and can be easily relocated by inserting the holder on which it is mounted into a 5.1-cm PVC pipe that has been imbedded in the ground. Experimental evidence revealed that either a DC or an AC power supply could be used, as long as noise distortion from the AC supply was integrated to 0 by choosing 60 Hz noise rejection as an option with the Campbell datalogger. With an AC fan, air flow over the sensor exceeds 6 m/s.

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Abstract

Carbofuran (2,3-dihydro-2,2-dimethyl-7 benzofuranyl methylcarbamate) at 5.7 and 11.1 kg/ha reduced soil populations of lesion (Paratylenchus penetrans, Filipjev & Shuurmans Stekhoven), pin (Paratylenchus sp. Cobb), and lance (Hoplolaimus galeatus, Cobb, Filipjeu & Schuurmans Stekhoven) nematodes. The highest rates of granular and flowable carbofuran were phytotoxic on peach [Prunus persica (L.) Batsch] planted just prior to treatment. In a subsequent experiment in soil previously planted to peach (old soil) or not previously planted to peach (new soil), trickle irrigation alone reduced dagger (Xiphinema americanum, Cobb) and lesion nematode populations. Carbofuran plus trickle irrigation reduced the dagger and lesion nematode populations and had the highest rate of tree growth in the old soil. Granular phenamiphos (ethyl-3-methyl-4-(methylthio) phenyl (1-methylethyl) phosphoridate) either alone or in combination with trickle irrigation reduced the stunt (Tylenchorhynchus claytoni, Steiner) nematode population. However, when phenamiphos was applied alone, tree growth was equal to the control in old soil but less than the control in new soil.

Open Access

The current state of knowledge regarding the role of mycorrhizae in Vaccinium spp. will be summarized. Survey data from Pennsylvania, New Jersey and Michigan indicate higher levels of mycorrhizae in both native and commercial plantings than have been previously reported for other locations in the U.S. However, level of infection was not correlated with soil ammonium, nitrate or organic matter. In a separate experiment, nitrogen supplied either as urea (67 kg actual N/Ha) or in a slow release formulation suppressed mycorrhizal development. Mycorrhizae infection level was highest in the fine feeder roots close to the crown, as compared to medial or apical portions of the root

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Past experiments have proven that meristem tip-cultured blueberry plantlets are extremely difficult to inoculate using laboratory-grown cultures of existing known isolates of Hymenoscyphus ericae, Scytalidium vaccinii, and Oidiodendron griseum; fungi that have been previously established as ericoid mycorrhizal symbionts. An experiment using both seedling and meristem tip-cultured plantlets was conducted using these proven fungal symbionts from the Canadian Fungal Culture Collection (DAOM), as well as fungi isolated from local blueberry populations at Little Flat, Pa. Treatments included inoculation using soil from the Little Flat population, the same soil (autoclaved), autoclaved soil that was reinoculated with fungi, as well as axenic treatments using H. ericae, S. vaccinii, O. griseum, Little Flat Hymenoscyphus sp., Little Flat Scytalidium sp., and Little Flat Oidiodendron sp. Sampling after 21 days revealed that only the nontreated soil plantlets were infected (≈4%). Results from later sampling dates will be presented, and the mechanism of infection discussed.

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The effects of preharvest applications of pyrrolnitrin (a biologically derived fungicide) on postharvest longevity of `Bristol' black raspberry (Rubus occidentals L.) and `Heritage' red raspberry [R. idaeus L. var. strigosus (Michx.) Maxim] were evaluated at two storage temperatures. Preharvest fungicide treatments were 200 mg pyrrolnitrin/liter, a standard fungicide treatment (captan + benomyl or iprodione) or a distilled water control applied 1 day before first harvest. Black raspberries were stored at 18 or 0 ± lC in air or 20% CO2. Red raspberries were stored at the same temperatures in air only. Pyrrolnitrin-treated berries often had less gray mold (Botrytis cinerea Pers. ex Fr.) in storage than the control but more than berries treated with the standard fungicides. Storage in a modified atmosphere of 20% CO2 greatly improved postharvest quality of black raspberries at both storage temperatures by reducing gray mold development. The combination of standard fungicide or pyrrolnitrin, high CO2, and low temperature resulted in more than 2 weeks of storage with less than 5% disease on black raspberries; however, discoloration limited marketability after≈ 8 days under these conditions. Chemical names used: 3-chloro-4-(2'-nitro-3'-chlorophenyl) -pyrrole (pyrrolnitrin); N-trichloromethylthio-4-cyclohexene-l12-dicarboximide (captan); methyl 1-(butylcarbamoyl) -2-benzimidazolecarbamate) (benomyl); 3-(3,5 -dichlorophenyl) -N-(l-methylethyl -2,4-dioxo-l-imi-dazolidinecarboxamide (Rovral, iprodione).

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An elite group of 38 strawberry accessions representing all subspecies of the beach strawberry [Fragaria chiloensis (L.) Miller] and the scarlet strawberry (F. virginiana Miller) was planted in a replicated design at five locations across the United States, and evaluated for plant vigor, flowering date, runner density, fruit set, fruit appearance, and foliar disease resistance. Considerable genotyp× location interaction was observed for many of these traits. However, a few genotypes were impressive at all locations including PI 551735 (FRA 368) with its unusually large, early fruit, and PIs 612486 (NC 95-19-1), 612493 (Frederick 9), and 612499 (RH 30), which were very vigorous and had unusually good fruit color. Genotypes that were superior at individual locations included PIs 551527 (FRA 110) and 551728 (Pigeon Pt.) in Maryland for their large fruit, and PI 612490 (Scotts Creek) in Oregon which had extremely large fruit, superior color, firmness, and flavor. The PIs 612495 (LH 50-4), 612498 (RH 23), and 612499 (RH 30) performed well as day neutrals at multiple sites.

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