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Phytophthora shuck and kernel rot infection usually started at the stem end of the pecan fruit and progressed distally to encompass the entire shuck within 4 to 6 days. A distinct margin developed between dark brown necrotic tissue and healthy green tissue during rotting of the shucks. Phytophthora cactorum was isolated from the rapidly rotting pecan fruit. Two to three weeks after the symptoms appeared, the diseased shucks dried and stuck tightly to the shell. The seed coat of the kernel turned dark brown and the endosperm rotted. The new disease of pecan was first observed during September 1988 on maturing pecan fruit in central Georgia in the vicinity of the town of Byron where growers estimated losses of 50% or greater in some orchards. In south Georgia near the cities of Albany and Cordele, the disease was present but less severe. The causal agent was identified as P. cactorum and deposited with ATCC as isolate B1, ATCC No. 66186. Laboratory and field inoculations of nut clusters using the B1 isolate produced typical symptoms observed in nature. Symptoms of the disease were observed in 13 orchards, and the pathogen was isolated from the soil of 10 of these orchards in south and central Georgia.

Copes, W. E., and Hendrix, F. F., Jr. 2004. Effect of temperature on sporulation of Botryosphaeria dothidea, B. obtusa, and B. rhodina. Plant Dis. 88:292-296. Three Botryosphaeria spp. were grown on autoclaved apple and peach stems in cotton-plugged tubes with constant moisture at 6, 12, 18, 24, and 30°C to determine the effect of temperature on sporulation. Number of conidia per pycnidium was determined weekly from 4 to 10 weeks after inoculation. The experiment was repeated three times. Maximum sporulation occurred at 24°C with B. dothidea and at 18 and 24°C with B. obtusa. Spore production of both fungi showed a quadratic curvilinear response to temperature. Pycnidia were erumpent, typical of their habit in nature. Maximum sporulation of B. rhodina occurred at 12, 24, and 30°C instead of at a distinctive peak. Of the three fungi, B. rhodina produced the greatest number of conidia per pycnidium at all temperatures. Mycelia and pycnidia of B. rhodina grew on top of the bark, which is atypical of their habit in nature. For spore production by B. dothidea, there was a significant interaction between temperature and time. Maximum sporulation over the 10-week period occurred in week 4 and/or 6 for B. dothidea at 12, 18, and 24°C, with a linear response at 12 and 24°C (P ≤ 0.05). Conidial maturation of B. obtusa and B. rhodina had a quadratic curvilinear response due to temperature, with a maximum maturation at 12, 18, and 24°C with B. obtusa and at 24°C with B. rhodina. Spore maturation would affect longevity of conidial viability. Maximum spore production over time and percent pigmented spores over time by B. obtusa, and spore maturation over time by B. rhodina occurred in weeks 8, 9, and 10 with a significant linear response (P ≤ 0.05). All three Botryosphaeria spp. produced conidia over the 6 to 30°C range and over the 7week period (weeks 4 to 10), with maximum sporulation or spore maturation at 18 to 24°C.

Fertility treatments were applied every 2 days in three factorial experiments : (i) N (52, 105, 158 μg of N per ml) x NO 3 /NH 4 ratio (1 :0, 3 :1, 1 :1, 1 :3) ; (ii) NO 3 /NH 4 ratio (3 :1, 1 :3) x K (113, 213, 313 μg of K per ml) ; and (iii) pH range (4.6 to 4.8 and 6.2 to 6.4) x NO 3 /NH 4 ratio (1 :0, 2 :1, 1 :3) to pansy plants grown in sand culture. Inoculum (noninoculated and inoculated with T basicola) was a factor in all three experiments. The NO 3 /NH 4 ratio was the dominant nutritional factor that reduced disease. Disease incidence, presence on root segments, was lowest with high NH 4 (1 :3 NO 3 /NH 4 ratio) and a low level of K (113 μg/ml) when the NO 3 /NH 4 ratio was 1 :3, compared with other NO 3 /NH 4 ratios. pH had no effect on disease incidence in sand medium (cation exchange capacity [CEC] = 0.225), presumably because element availability from sand surfaces into substrate solution was low. High disease incidence corresponded with reductions in plant growth. Plant growth of noninoculated plants was greatest at the 3 :1 NO 3 /NH 4 ratio. Plant growth of inoculated plants was greatest at the 3 :1, 2 :1, or 1 :1 NO 3 /NH 4 ratios with disease being moderate at the 2 :1 and 1 :1 ratios, compared with other ratios. Plant growth was not affected by pH or K at the levels tested.

Sodium hypochlorite and captan significantly reduced propagule viability of Thielaviopsis basicola on polypropylene fabric, pressure-treated wood, and galvanized metal hardwarecloth surfaces that had been thoroughly wetted with a solution of endoconidia and aleuriospores of T basicola. Viability of other unidentified fungal propagules was also reduced with captan sprays. Bromine and quaternary ammonium compounds did not reduce propagule viability of Thielaviopsis basicola and their effects were not significantly different from that of water.

Dogwood fruit were collected from trees with symptoms of dogwood anthracnose in 11 locations in western North Carolina in September 1989-1991. Fruit from each location were divided into four groups based on symptoms: completely necrotic, discrete necrotic lesions, shriveled without necrosis, and symptomless. Fruit and extracted seeds were surface-disinfested and placed on acidified potato-dextrose agar. Discula destructiva was isolated more often from seeds than from whole fruit, particularly from seeds extracted from completely necrotic fruit. The mean isolation frequency from extracted seeds was 0.12 in 1989, following a wet summer. D. destructiva was isolated from only 0.008 and 0.05 of extracted seeds in 1990 and 1991, respectively, when spring and early-summer rains were followed by midsummer dry periods

Boron deposition, soil B, and foliage B were sampled in a field study around two geothermal generating units with different operating histories; the study also determined relative sensitivities of several native tree species to B in soil and foliage. Boron emissions from the older cooling tower, operational for 11 yr, were nearly 5 times greater than emissions from the newer cooling tower, operational for 2.5 yr. This difference was due to substantially greater B concentrations in circulating water at the older unit. Boron deposition was as great as 129.6 kg ha⁻¹ yr⁻¹ at the older unit and 4.2 kg ha⁻¹ yr⁻¹ at the newer unit. Soil B (saturation extract) was as great as 44.0 mg L⁻¹ at the older unit and 0.6 mg L⁻¹ at the newer unit. At a given rate of B deposition, soil B was more than 4 times greater at the older unit due to its longer operating history. At a given soil B level, the deciduous bigleaf maple (Acer macrophyllum Pursh) contained double the foliage B of the broadleaf evergreen, interior live oak (Quercus wislizeni A. DC.), and about 5 times greater foliage B than the conifer, Digger pine (Pinus sabiniana Dougl.). Foliage B thresholds for detectable levels of visible injury due to B toxicity were about 500 mg kg⁻¹ for both bigleaf maple and interior live oak. These relationships suggest that more rapid B accumulation is responsible for higher levels of visible injury due to B in bigleaf maples than in other native tree species.

Helleri holly were grown in 100% sand, 50% bark-50% sand, and 100% bark media and inoculated with Pythium irregulaye Buis. Pythium populations were determined at 4, 10 and 17 cm depths at planting date and every two weeks thereafter. After 7 weeks fresh weight of plants and populations of bacteria, actinomycetes, and total fungi were determined. P. irregulare was highest at the 4 and 10 cm depths, with bark media reaching their highest Pythium levels 4 weeks after inoculation. Pythium peaked in 100% sand 6 weeks after inoculation and declined thereafter.

Eight plant species were subjected to artifical acid rains of pH 2.5, 2.0, 1.5, 1.0 and 0.5 in order to determine the threshold for and symptoms of damage. The plants were Erechtites, Robinia, Pinus, Quercus, Carya, Liriodendron, Acer and Corpus from the Coweeta Hydrologic Laboratory near Franklin, North Carolina Droplets of pH 2.0 produced brown necrotic spots on all species except Pinus while droplets of pH 1.0 produced necroses on leaves of all species examined. The size of necrotic spots increased with increasing acidity. Comparison of these results with the literature suggests that developing leaves are more easily damaged than are the mature leaves used in this study. The volume weighted average rainfall pH for Coweeta is 4.6 with observations ranging from 3.2 to 5.9. Results of this study suggest that a 10-fold increase in acidity from pH 3.2 to 2.2 in a single spring or summer storm could bring damage or death to mature leaves of dominant flowering plants in the Southern Appalachians.

The genus Pythium includes a number of readily recognized species with wide distributions and host ranges. The taxonomic position of the genus and its relationship to other Phycomycetes were well established during the latter part of the 19th century. In the early 1900s pathologists found Pythium spp. consistently associated with root diseases and it soon became apparent that these fungi were important plant pathogens. Certainly, while 1),ot all isolates of Pythium species are capable of causing diseases of plants, many are soil­ borne pathogens that cause serious economic loss on a wide variety of hosts, while others are more limited in host and geographic range or affect plants only under special environmental conditions. New species are being discov­ ered as pathologists investigate soil organisms associated with plant growth problems. Rands & Dopp (123) in their classic investigation of sugarcane root dis­ eases established the symptoms and determined the conditions needed for these fungi to become destructive. This work, and others of a similar nature, are part of the extensive literature on diseases caused by species of Pythium. This review will concentrate on examples of the readily available literature of the past 50 years and will emphasize the pathology of the genus, with only brief treatment of other aspects such as taxonomy and control. It will be con­ fined to Pythium spp. as they affect economic plants and will not deal with those affecting algae, other marine plants, fungi, and unusual hosts.

Pairings of 5 heterothallic isolates of Pythium sylvaticum in all possible combinations revealed the existence of 2 sexually compatible groups of isolates.Tracings of gametangial hyphae leading to ...

By the use of selective media and techniques which favor the isolation of Phycomycetes, 85 soil samples from four old growth forest sites in Kentucky, North Carolina and Tennessee were assayed for ...

In studies of Pythium species common to forest and agricultural soils of the Southeast, numerous assays for these fungi have been made on Hendrix and Kuhlman's modification of Kerr's Pythium medium (Hendrix and Kuhlman, 1965; Kerr, 1963). A frequently isolated Pythium produced only globose, terminal or intercalary sporangia or chlamydospores on corn meal and hempseed agar plates. These bodies failed to form zoospores when agar blocks bearing mycelium were flooded or continuously irrigated with distilled water or with soil leachate. A few isolates from several soil samples produced well-developed oogonia and oospores. The globose sporangia which were also present failed to produce zoospores on flooding or irrigation. Apparently the oospore-producing isolates were closely related to those producing only sporangia or chlamydospores. Extensive pairings of the sporangial isolates on hempseed agar2 plates demonstrated that well-formed oospores were produced when the mycelium of certain isolates made contact. The oospores so formed were similar to those produced by the homothallic isolates. The existence of a Pythium species normally heterothallic is of mycological interest, and because this fungus is morphologically different from other named species it is described here as a new species. The nature of the heterothallic reaction will be discussed in a separate paper.

Pythium heterothallicum is described as a new species. The species designation “heterothallicum” was chosen to emphasize the absence of homothallic isolates, in contrast to P. sylvaticum in which i...

(1974). Taxonomy of Pythium Sylvaticum and Related Fungi. Mycologia: Vol. 66, No. 6, pp. 1049-1053.

Oospores and oogonia of P. dissotocum, P. myriotylum, P. irregulare, and one isolate of P. ultimum increased in diameter after being subcultured for 30 mo. Oospores and oogonia of P. aphanidermatum and one isolate of P. ultimum decreased in diameter during this period. Sporangia of P. irregulare increased in diameter and of two isolates of P. ultimum decreased in diameter during this period. The taxonomic value of reproductive cell diameter in the genus Pythium is discussed.

Pythium dimorphum, a new species, is characterized by oogonia partially to completely covered with blunt irregularly spaced projections averaging 3 / in length and aplerotic to nearly plerotic oospores averaging 30 / diam. Antheridia may be hypogynous or monoclinous but are frequently absent. Prominent ovoid to elongate thin-walled, spherical chlamydospores averaging 64 L in diam with dark contents are a distinguishing feature of this fungus. Ovoid or club-shaped sporangia, averaging 28 X 54 1A, are present.