First report of Ophiosphaerella narmari causing spring dead spot of hybrid bermudagrass in China

Hybrid bermudagrass (Cynodon dactylon×C. transvaalensis) is widely used as turf in transition zone of China. Spring dead spot (SDS) is one of the most damaging diseases of hybrid bermudagrass. Symptoms of SDS appear when hybrid bermudagrass starts to break dormancy with warm temperature in early spring. The symptoms show sunken, circular or irregularly shaped, straw-colored patches, with 20 to 100 cm in diameter. The patches maintain dormant as the surrounding uninfected turfgrass resumes growth and turns green. SDS pathogens are soilborne fungi that colonize roots, stolons and rhizomes, infected roots or rhizomes become black and eventually collapse. Three species of fungi are reported to cause SDS: Ophiosphaerella herpotricha (Fr) J. Walker; O. korrae (J. Walker & A.M. Smith) Shoemaker & C.E. Babcock; or O. narmari (J. Walker & A.M. Smith) Wetzel, Hubert & Tisserat (Walker and Smith 1972; Walker 1980; Shoemaker and Babcock 1989; Wetzel et al. 1999). However, distribution of the three species may vary by geographical region (Cottrill et al. 2016). In October 2020, symptoms of SDS were observed on hybrid bermudagrass fairways of Taihu golf course in Wuxi, Jiangsu province. Root samples of SDS were collected, symptomatic roots with 3-4 cm length were cut, washed 2-3 times, surface sterilized in 0.6% NaOCl for 5 min, rinsed and blotted dry for 2 min and placed on potato dextrose agar (PDA) amended with 50 mg L-1 each of ampicillin, streptomycin sulfate and tetracycline. Plates were incubated in the dark at 25℃ for 5-7 days, Hyphae growing from the roots were transferred to new PDA plates. A total of 7 fungal isolates with morphology similar to SDS pathogens were obtained (Tredway et al. 2009). The genomic DNA was extracted from 2 of them (7-41, 8-6) and amplified with universal primers ITS5 and ITS4 (White et al. 1990). PCR products were sequenced (deposited as MW536995 and MW536994 in GenBank, not available yet) and showed 99.79% similarity to O. narmari (KP690979). Pathogenicity tests were performed on ‘Tifdwarf’ hybrid bermudagrass (9-week-old in 5 × 20 cm Cone-Tainers containing a sand and nutrition substrate mixture). Eight oat seeds infested with O. narmari were inserted 5 cm below the soil surface in the root zone of hybrid bermudagrass. The inoculated turfgrass grew for five weeks in the growth chamber with a 12-h day/night cycle of 25/20°C and 90% relative humidity. A control treatment was inoculated with 8 noninfested sterile oat seeds, and each treatment was replicated 3 times. The root tissues of hybrid burmudagrass inoculated with O. narmari became black and necrotic, no symptoms were observed on the roots of noninfested plants. O. narmari was consistently reisolated from symptomatic roots, and confirmed by PCR as mentioned above. To the best of our knowledge, this is the first report of O. narmari caused spring dead spot in the transition zone of China. The identification of SDS caused by O. narmari will have important implications for the management of this root-rot species on hybrid bermudagrass.

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First Report of Summer Patch of Creeping Bentgrass Caused by Magnaporthiopsis poae in Southeastern China

Plant Disease ◽

10.1094/pdis-09-21-1892-pdn ◽

2021 ◽

Author(s):

Yuxin Zhou ◽

Min Yin ◽

Fei Liu

Keyword(s):

Root Zone ◽

Soil Surface ◽

Creeping Bentgrass ◽

Golf Club ◽

Golf Courses ◽

Root Tips ◽

Southeastern China ◽

Putting Greens ◽

First Report ◽

Oat Seeds

Creeping bentgrass (Agrostis stolonifera L.) is an important cool-season perennial turfgrass that has been widely used on golf courses across China. In July 2017, an unknown disease outbreak caused damages on seven of the 18 putting greens of creeping bentgrass at Jiuqiao golf club in Hangzhou city of Zhejiang province, day-time high temperatures were consistently above 35°C during the disease development. Symptoms appeared in tan irregular patches of 5 to 20-cm diameter, exhibiting chlorosis and foliar dieback in most part. Necrotic roots were frequently observed in diseased areas and colonized with ectotrophic hyphae under a microscope. Similar symptoms and signs were reported on creeping bentgrass caused by Magnaporthiopsis poae (Landschoot & Jackson) J. Luo & N. Zhang on golf courses in Beijing (Hu et al. 2017). Fifteen disease samples were collected from seven putting greens. Dark root tips were cut, surface sterilized in 0.6% sodium hypochlorite (NaClO) for 5 min, washed twice with sterilized water, air dried for 1 min and placed on potato dextrose agar (PDA) containing each of 50 mg L-1 ampicillin, streptomycin sulfate, and tetracycline. Plates were incubated in the dark at room temperature for 4 days, and 10 fungal isolates with similar morphology as described by Clarke and Gould (1993) were consistently recovered from the diseased root tips. DNA of two representative isolates was extracted and amplified with primers ITS 5/ITS 4 (White et al. 1990). PCR products were sequenced (deposited in GenBank as MZ895215 and MZ895216), and BLAST analysis showed 99.17% similarity to M. poae (accession number: DQ528765). Six plastic pots (15 cm height × 15 cm top diameter × 10 cm bottom diameter, three replicates for each isolate) were seeded with creeping bentgrass and placed in the greenhouse for two months of plant growth before inoculation. The pathogenic inoculum was prepared by inoculating autoclaved oat seeds with M. poae isolates, followed by two weeks of incubation at 25°C. About 25 mg M. poae-infested oat seeds were placed 10 cm below the soil surface in the root zone of creeping bentgrass. Non-infested oat seeds were inoculated on healthy creeping bentgrass as controls. Pots were placed in a growth chamber with a 12-h day/night cycle at 35/28°C and watered daily to keep high soil moisture. Disease symptoms (foliar dieback and necrotic roots) were noted 3 weeks after inoculation. M. poae was consistently recovered from the roots of inoculated turf and identified molecularly as described above, fulfilling Koch’s postulates. To our knowledge, this is the first report of summer patch on creeping bentgrass caused by M. poae in southeastern China. This research demonstrates a wider distribution of M. poae and will be an important step towards the development of management strategies for summer patch control in China.

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Micro-Water Harvesting and Soil Amendment Increase Grain Yields of Barley on a Heavy-Textured Alkaline Sodic Soil in a Rainfed Mediterranean Environment

Agronomy ◽

10.3390/agronomy11040713 ◽

2021 ◽

Vol 11 (4) ◽

pp. 713

Author(s):

Edward G. Barrett-Lennard ◽

Rushna Munir ◽

Dana Mulvany ◽

Laine Williamson ◽

Glen Riethmuller ◽

...

Keyword(s):

Soil Solution ◽

Elemental Sulfur ◽

Root Zone ◽

Soil Surface ◽

Conventional Tillage ◽

Barley Grain ◽

Control Treatment ◽

Water Harvesting ◽

Hordeum Vulgare L ◽

Salt Leaching

This paper focuses on the adverse effects of soil sodicity and alkalinity on the growth of barley (Hordeum vulgare L.) in a rainfed environment in south-western Australia. These conditions cause the accumulation of salt (called ‘transient salinity’) in the root zone, which decreases the solute potential of the soil solution, particularly at the end of the growing season as the soil dries. We hypothesized that two approaches could help overcome this stress: (a) improved micro-water harvesting at the soil surface, which would help maintain soil hydration, decreasing the salinity of the soil solution, and (b) soil amelioration using small amounts of gypsum, elemental sulfur or gypsum plus elemental sulfur, which would ensure greater salt leaching. In our experiments, improved micro-water harvesting was achieved using a tillage technique consisting of exaggerated mounds between furrows and the covering of these mounds with plastic sheeting. The combination of the mounds and the application of a low rate of gypsum in the furrow (50 kg ha−1) increased yields of barley grain by 70% in 2019 and by 57% in 2020, relative to a control treatment with conventional tillage, no plastic sheeting and no amendment. These increases in yield were related to changes in ion concentrations in the soil and to changes in apparent electrical conductivity measured with the EM38.

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Aggregate stability of Alfisols root zone upon turfgrass treatment

Sains Tanah - Journal of Soil Science and Agroclimatology ◽

10.20961/stjssa.v17i1.40455 ◽

2020 ◽

Vol 17 (1) ◽

pp. 50

Author(s):

Rahayu Rahayu ◽

Jauhari Syamsiyah ◽

Laila Nikmatus Sa'diyah

Keyword(s):

Cynodon Dactylon ◽

Root Zone ◽

Aggregate Stability ◽

Soil Surface ◽

Soil Aggregate ◽

Soil Aggregate Stability ◽

Carbon Particles ◽

Zoysia Matrella ◽

Aggregate Index ◽

Middle Leaf

Soil degradation mostly occurs on land where a lack of surface coverage results in soil-aggregate destruction due to heavy rainfall. Turfgrass is an ornamental plant and covers the soil surface and, thus, potentially improves soil-aggregate stability. This study determined the potential of some summer grasses to improve soil-aggregate stability and was a pilot experiment using six turfgrass species: Paspalum vaginatum; middle-leaf Zoysia sp.; Cynodon dactylon; coarse-leaf Zoysia sp.; Axonopus compressus; Zoysia matrella. Turfgrasses were planted using stolons in a 0.6 m2 plot unit with 5 cm x 5 cm space. Lawn maintenance included irrigation, fertilizing, and weeding. Soil characteristics were observed six months after planting and showed that turfgrass increased the soil-aggregate index from 42.3% to 83.0% in control, and carbon particles measuring 6.4 μm from 28.3% to 63.0%.

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Establishment of Seeded Bermudagrass Using Subsurface Drip Irrigation

HortScience ◽

10.21273/hortsci.39.4.764d ◽

2004 ◽

Vol 39 (4) ◽

pp. 764D-764 ◽

Cited By ~ 2

Author(s):

Michael Maurer* ◽

Justin Weeaks

Keyword(s):

Drip Irrigation ◽

Cynodon Dactylon ◽

Soil Surface ◽

Poor Quality ◽

Subsurface Drip Irrigation ◽

Control Treatment ◽

Annual Rainfall ◽

Surface Salinity ◽

Salinity Levels ◽

Subsurface Drip

Throughout much of the Southwestern United States, poor quality water and limited water resources require innovative methods to conserve water. No research to date has indicated whether seeded bermudagrass Cynodon dactylon can be established by using subsurface drip irrigation (SDI). In 2001 (Expt. I) and 2002 (Expt. II), seeded bermudagrass was evaluated for establishment using SDI. Treatments consisted of emitters and tubing spaced at 30, 46, and 61 cm. The control treatment consisted of pop-up sprinklers. Salinity accumulation is a concern when irrigating turfgrass in areas of poor water quality and low annual rainfall. Salinity accumulation was visible at the soil surface during establishment in 2001, but turfgrass showed no visible signs of stress due to salinity. In 2002, substantial rainfall reduced salinity accumulation during establishment as salinity was not present on the soil surface. Salinity accumulation was greater in most months at the 0-15 cm depth in both years compared to the 15-30 cm depth. Full turfgrass coverage (≥90%) for the control plots in 2001 was about 8.5 weeks and the SDI treatments had complete coverage in 10 weeks. Turfgrass coverage for all treatments in 2002 was 9 weeks. Expt. II had a slightly faster establishment rate due to greater rainfall and different soil characteristics than that of Expt. I. Root count and depth of roots for both years showed roots to 61 cm depth in all treatments. A general trend of higher salinity accumulation at the midpoint between tubing was seen in Expts. I and II. However, after significant rainfall salinity levels returned to concentrations comparable to initial soil salinity concentrations in both years. This research documents the ability to successfully establish seeded bermudagrass using SDI.

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First Report of Cercospora carotae, Causal Agent of Cercospora Leaf Spot of Carrot, in Serbia

Plant Disease ◽

10.1094/pdis-08-13-0858-pdn ◽

2014 ◽

Vol 98 (8) ◽

pp. 1153-1153 ◽

Cited By ~ 1

Author(s):

A. Milosavljević ◽

E. Pfaf-Dolovac ◽

M. Mitrović ◽

J. Jović ◽

I. Toševski ◽

...

Keyword(s):

Leaf Spot ◽

28S Rdna ◽

Control Treatment ◽

Universal Primers ◽

Its Sequence ◽

Pathogenicity Test ◽

Cercospora Leaf Spot ◽

First Report ◽

Morphological Studies ◽

Cercospora Carotae

Carrot (Daucus carota L. subsp. sativus [Hoffm.] Arcang.) is an important vegetable in Serbia, where it is grown on nearly 8,000 ha. In August 2012, ~1,500 ha of carrot fields were inspected in southern Bačka in North Serbia. In nearly 40% of the fields, severe foliar and stem symptoms characteristic of cercospora leaf spot of carrot, caused by Cercospora carotae (Pass.) Solheim (3), were observed. Lesions on stems were oblong, elliptical, and more or less sunken, while those on the leaves were amphigenous, subcircular, light brown in the center, and surrounded by a dark brown margin. Conidiophores emerging from the lesions formed very loose tufts but sometimes were solitary. Conidiophores were simple and straight to subflexuous with a bulbous base (17 to 37 × 3 to 5 μm). Conidia were 58 to 102 × 2 to 4 μm, solitary, cylindrical to narrowly-obclavate, and hyaline to subhyaline with 2 to 6 septa. To obtain monosporial isolates, the conidia from one lesion were placed on water agar plates at 25°C in the dark for 24 h, after which single germinated conidia were selected and each placed on a petri dish containing potato dextrose agar (PDA). To confirm pathogenicity of three of the isolates, Koch's postulates were tested on carrot seedlings (3-true-leaf stage of growth) of a Nantes cultivar, SP-80, with 12 plants tested/isolate and 12 non-inoculated plants used as a control treatment. The leaves were atomized until runoff with the appropriate C. carotae spore suspension (104 conidia/ml sterilized water), while control plants were atomized with sterile water. All plants were then incubated in a dew chamber for 72 h, then transferred to a greenhouse at 25 ± 2°C. After 2 weeks, characteristic symptoms resembling those observed in the field developed on all inoculated plants; control plants were asymptomatic. The pathogen was re-isolated from all inoculated plants, and identity of the re-isolated fungi confirmed morphologically as described above, and molecularly as described below. The pathogenicity test was repeated with no significant differences in shape and size of lesions, or dimensions of conidiophores and conidia among isolates. To verify the pathogen identity molecularly, the 28S rDNA was amplified and sequenced using the V9G/LR5 primer set (2,4) as well as internal primers OR-A (5′-ATACCCGCTGAACTTAAGC-3′) and 2R-C (5′-AAGTACTTTGGAAAGAG-3′); the ITS region of rDNA using the ITS1/ITS4 universal primers (5); and histone H3 gene (H3) using the CylH3F/CylH3R primers (1). The sequences for the three isolates were deposited in GenBank as Accession Numbers KF468808 to KF468810, KF941306 to KF941308, and KF941303 to KF941305 for the 28S rDNA, ITS and H3 regions, respectively. BLAST results for the ITS sequences indicated 94% similarity to the ITS sequence of an isolate of Pseudocercosporella capsellae (GU214662) and 92% similarity to the ITS sequence of an isolate of C. capsici (HQ700354). The H3 sequences shared 91% similarity with that of several Cercospora spp., e.g., C. apii (JX142548), C. beticola (AY752258), and C. capsici (JX142584), all of which shared the same amino acid sequence of the encoded H3 protein. Also, the 28S rDNA sequences had 99% similarity (identity of 318/319, with 0 gaps) with the single sequence of C. carotae available in GenBank (AY152628), which originated from Norway. This is, to our knowledge, the first report of C. carotae on carrot crops in Serbia as well as southeastern Europe. References: (1) P. W. Crous et al. Stud. Mycol. 50:415, 2004. (2) G. S. de Hoog and A. H. G. Gerrits van den Ende. Mycoses 41:183, 1998. (3) W. G. Solheim. Morphological studies of the genus Cercospora. University of Illinois, 1929. (4) R. Vilgalys and M. Hester. J. Bacteriol. 172:238, 1990. (5) T. J. White et al. PCR Protocols: A Guide to Methods and Applications. Academic Press, Inc., San Diego, CA, 1990.

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First Report of Ophiosphaerella herpotricha Causing Spring Dead Spot of Bermudagrass in Mississippi

Plant Disease ◽

10.1094/pdis-92-3-0482a ◽

2008 ◽

Vol 92 (3) ◽

pp. 482-482 ◽

Cited By ~ 2

Author(s):

D. H. Perry ◽

M. Tomaso-Peterson ◽

R. Baird

Keyword(s):

Genomic Dna ◽

Cynodon Dactylon ◽

Root Zone ◽

Specific Primers ◽

Causal Organism ◽

Spring Dead Spot ◽

Putting Green ◽

Ophiosphaerella Herpotricha ◽

Species Specific ◽

High Level

Spring dead spot (SDS) is the most destructive disease of bermudagrass (Cynodon dactylon (L.) Pers.). Symptoms of SDS appear in the spring when bermudagrass transitions out of winter dormancy. These symptoms include depressed, straw-colored patches that range from several centimeters to a meter in diameter. Infected roots and rhizomes are black, brittle, and necrotic. The disease is caused by three species of fungi: Ophiosphaerella herpotricha (Fr:Fr) J. Walker; O. korrae (J. Walker & A.M. Smith) Shoemaker & C.E. Babcock; or O. narmari (J. Walker & A.M. Smith) Wetzel, Hubert & Tisserat. However, O. korrae is the most prevalent causal organism of SDS in the southeastern United States and was the only species reported in Mississippi (1). In April of 2006, root samples were collected from a bermudagrass putting green in Booneville, MS with a high level of SDS incidence and severity. Symptomatic roots were collected and surface disinfested in 0.6% NaOCl and plated on one-quarter-strength potato dextrose agar (PDA) amended with streptomycin sulfate and chloramphenicol. Hyphae growing from the roots were transferred to full-strength PDA after 5 to 7 days. Mycelium from five pure-culture colonies plus an O. herpotricha control was harvested after 4 weeks of growth and the genomic DNA was extracted. The genomic DNA of the Booneville isolates and the O. herpotricha control were amplified by PCR using species-specific primers OHITS1 and OHITS2 for O. herpotricha (2). Amplification of a 454-bp fragment of DNA confirmed one of the five unknown isolates as O. herpotricha. The other four isolates were not identified. ‘Sahara’ bermudagrass (4 weeks old in 3.8 × 20 cm Cone-tainers containing a sand and soil mixture) was inoculated with the Booneville-O. herpotricha isolate and the O. herpotricha control. One gram of oat seed infested with O. herpotricha isolates was inserted 2 cm below the crowns in the root zone of bermudagrass plugs. The inoculated bermudagrass plants were incubated for 4 weeks in the greenhouse. A control consisting of noninfested sterile oats was included. Following incubation, black, necrotic roots were observed on the plants inoculated with both O. herpotricha isolates. No symptoms were observed on roots of noninfested plants. Symptomatic roots were disinfested and plated on one-quarter-strength PDA. Koch's postulates were completed after O. herpotricha was reisolated from roots of plants inoculated with both O. herpotricha isolates and confirmed by PCR as mentioned above. The identification of O. herpotricha as a causal organism of SDS in Mississippi clarifies the involvement of multiple causal agents in this state and broadens the geographic distribution of this root-rot species. References: (1) F. B. Iriarte et al. Plant Dis. 88:1341, 2004. (2) N. A. Tisserat et al. Phytopathology 84:478, 1994.

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First Report of Powdery Mildew Caused by Erysiphe heraclei on Carrot in Central China

Plant Disease ◽

10.1094/pdis-04-13-0439-pdn ◽

2014 ◽

Vol 98 (2) ◽

pp. 277-277 ◽

Cited By ~ 1

Author(s):

Y. Wang ◽

K.-D. Xu ◽

Y. Zhang ◽

K. Liu ◽

F.-L. Zhang ◽

...

Keyword(s):

Powdery Mildew ◽

Its Region ◽

The United States ◽

Henan Province ◽

Central China ◽

Control Treatment ◽

Universal Primers ◽

Post Inoculation ◽

First Report ◽

Major Region

Carrot (Daucus carota) is an important root vegetable crop in China, which accounted for 46% of global production in 2011. Carrot was grown in Henan Province on >20,000 ha/year, which ranks first in China for area of carrots harvested. In October 2012, a powdery mildew outbreak was observed in 16 investigated carrot production fields in Zhoukou, Henan Province, in central China. White colonies typical of powdery mildew were seen on leaves of affected plants. The colonies enlarged and finally coalesced. Small, scattered fruiting bodies found on the adaxial and abaxial leaf surfaces were determined microscopically to be chasmothecia. Examining the pathogen morphologically revealed that appressoria were lobed, conidiophores were straight and bore single conidia, and cylindrical foot cells were followed by one to three shorter cells in the conidiophores. Conidiophores were subhyaline and 54.1 to 66.1 × 6.1 to 8.1 μm. Conidia were barrel-cylindrical and 28.8 to 38.6 × 11.4 to 14.8 μm. Chasmothecia were subspherical, dark brown to black, formed hyphoid appendages, and 110 to 122 μm in diameter. Appendages typically had one to five branches, which were nearly dichotomous or irregular, flexuous or almost straight, and 30 to 165 μm long. Each chasmothecium contained multiple asci that were saccate, multiguttulate, short-stipitate or not, 62.5 to 63.8 × 43.2 to 45.9 μm, and each contained two to six ascospores. Ascospores were subhyaline, ovoid to ellipsoid, and 16.5 to 17.7 × 11.2 to 12.7 μm. Based on characteristics of the anamorphic and teleomorphic stages, the fungus was identified as Erysiphe heraclei (2,4). To verify the identity, the internal transcribed spacer (ITS) region of ribosomal DNA was amplified with universal primers ITS1 and ITS4, and sequenced. The ITS sequence was assigned GenBank Accession No. KC480605, and showed 100% similarity to ITS sequences of E. heraclei on carrot in GenBank (EU371725 and GU252368). Koch's postulates were completed by using detached infected leaves from 10-week-old carrot plants growing in a field to inoculate 10 healthy, 5-week-old plants of the carrot cultivar Dinghong, growing in a growth chamber under 22/16°C (day/night) cycle at 50% relative humidity with 120 μmol/m2/s light and a 14-h photoperiod. Ten non-inoculated plants served as replicates of a control treatment. Symptoms consistent with those in the field were observed on inoculated plants 20 days post-inoculation. No symptoms were observed on the control plants. Microscopic observation of the pathogen growing on the inoculated plants revealed that it was the same as the original fungus. Powdery mildew on carrot has been observed in many countries including Australia (1), Mexico (3), and the United States (2). To our knowledge, this is the first report of E. heraclei infection on carrot in central China, a major region of carrot production, although the disease has previously been observed in northwestern China (4). Further research should help to reduce losses in carrot crops caused by E. heraclei in central China. References: (1) J. H. Cunnington et al. Australas. Plant Dis. Notes 3:38, 2008. (2) D. A. Glawe et al. Plant Health Progress doi: 10.1094/PHP-2005-0114-01-HN, 2005. (3) G. Rodríguez-Alvarado et al. Plant Dis. 94:483, 2010. (4) R. Zheng and G. Chen. Pp. 97-99 in: Flora Fungorum Sinicorum Vol. 1. Erysiphales. R. Zheng et al., eds. Science Press, Beijing, 1987.

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Effect of irrigation on soil oxygen status and root and shoot growth of wheat in a clay soil

Australian Journal of Agricultural Research ◽

10.1071/ar9850171 ◽

1985 ◽

Vol 36 (2) ◽

pp. 171 ◽

Cited By ~ 21

Author(s):

WS Meyer ◽

HD Barrs ◽

RCG Smith ◽

NS White ◽

AD Heritage ◽

...

Keyword(s):

Root Growth ◽

Root Zone ◽

Pore Space ◽

Soil Surface ◽

Control Treatment ◽

Water Control ◽

Undisturbed Soil ◽

Soil Oxygen ◽

Maximum Root ◽

And Control

Two watering treatments (flood and control) were applied to undisturbed (bulk density �? 1.6 mg mm-3 ) and repacked �? 1.2 mg mm-3 ) cylinders of Marah clay loam. The cylinders (0.75 m o.d. by 1.4 m deep) were housed in a lysimeter facility. Wheat (cv. Egret) was grown in the cylinders and the soil was either kept well watered with frequent small amounts of water (control treatment) or subjected to three separate periods, ranging from 4 to 72 h, of surface inundation (flood treatment). The greater pore space and better drainage of the repacked soil ensured that its average level of soil oxygen (O2) was about three times that of the undisturbed soil. Nevertheless, inundation of the soil surface for either 48 or 72 h rapidly decreased soil O2 levels in both soils. Root growth in these soils appeared to be slowed when soil O2 levels became less than 15% of the maximum that would occur in dry, aerated soil. Root growth ceased in both repacked and undisturbed soil cores after a 48-h flooding, when the soil O2 status was probably < 10% of the maximum. Root growth was greatest in the repacked soil with controlled water additions. The ranking of treatments, by either root intercept counts or O2 status, were the same. Leaf and stem growth were not very sensitive to the root zone conditions, but this may have been due to the advanced stage of plant growth when the treatments were applied and to the generally low nitrogen status of all treatment plants. There was a 44% reduction in yield from the best to the worst aerated soil treatment. The data show that if soil O2 levels become low as the result of flooding, root growth of wheat will stop and grain yield will be substantially decreased. Greatly improved aeration of these fine-textured soils is only possible if both the internal drainage properties of the soil are improved and prolonged periods of surface inundation are avoided.

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First Report of Damping-off Caused by Alternaria japonica on Chinese Cabbage Seedlings in China

Plant Disease ◽

10.1094/pdis-04-12-0328-pdn ◽

2012 ◽

Vol 96 (9) ◽

pp. 1378-1378 ◽

Cited By ~ 4

Author(s):

X. X. Ren ◽

G. Z. Zhang ◽

W. A. Dai

Keyword(s):

Chinese Cabbage ◽

Brassica Campestris ◽

Morphological Characteristics ◽

Soil Surface ◽

Potato Dextrose Agar ◽

Universal Primers ◽

Damping Off ◽

First Report ◽

Tibet Autonomous Region ◽

The Tibet Autonomous Region

In May 2011, samples of Chinese cabbage (Brassica campestris L. subsp. chinensis Markino) seedlings at the two-to four-leaf stage with damping-off symptoms were collected from greenhouses in the Tibet Autonomous Region of China. Infected stems of the seedlings were constricted at or near the soil surface. On diseased stems, a light to dark brown coloration was demarcated from healthy tissue. Damping-off and death of seedlings occurred as the lesions enlarged, resulting in a significant reduction of seedlings. Diseased stems were cut into 3-mm-long segments, surface-sterilized with 3.5% sodium hypochlorite for 1 min, and rinsed in sterilized water three times before being placed on water agar. A fungus frequently isolated from diseased plants was hyphal tipped under a dissecting microscope and transferred onto potato dextrose agar (PDA) to obtain a pure culture. The isolate grew slowly on PDA at 25°C with a 12-h photoperiod. The colony was white at first and gradually turned gray or grayish-green. No conidia or chlamydospores developed. However, conidia were produced on potato-carrot agar. Conidia were yellow-brown, obpyriform or obpyriform with beaks, had two to eight transverse septa, one to three vertical or oblique septa, and were produced solitarily or often in chains of two or three and measured 43.5 to 85.2 × 21.5 to 28.0 μm. A few conidia without beaks were also present and were nearly round and slightly smaller than the conidia with beaks. Several adjacent chlamydospores with thickened walls were often intercalary. The isolate was tentatively identified as Alternaria japonica based on its morphological characteristics (1,2). For molecular analyses, the internal transcribed spacer (ITS) regions of ribosomal DNA from the isolate were amplified with universal primers ITS1 and ITS4. The resulting sequence (Accession No. JN654465) submitted to GenBank had a 99% identity to that of A. japonica (Accession No. AY154703.1) isolated from leaves of Raphanus sativus. To confirm the pathogenicity of A. japonica, nine healthy 10-day-old Chinese cabbage seedlings were inoculated at the stem base with one PDA plug from a 6-day-old culture, with nine noninoculated (PDA plus only) seedlings serving as controls. Two days after inoculation, symptoms similar to those on the naturally infected plants developed on the inoculated seedlings. No symptoms developed on the controls. The pathogen was reisolated from the stems of inoculated and diseased seedlings. To our knowledge, this is the first report of A. japonica leading to damping off on Chinese cabbage seedlings in China. References: (1) M. P. Corlett and M. E. Corlett. Can. J. Plant Pathol. 21:298, 1999. (2) T. Y. Zhang. Flora Fungorum Sinicorum: Alternaria (in Chinese) Vol. 16. Science Press, Beijing, 2003.

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Seasonal activity and estivation of lumbricid earthworms in the midlands of Tasmania

Soil Research ◽

10.1071/sr9941355 ◽

1994 ◽

Vol 32 (6) ◽

pp. 1355 ◽

Cited By ~ 12

Author(s):

RB Garnsey

Keyword(s):

Soil Moisture ◽

Adult Development ◽

Survival Rates ◽

Soil Surface ◽

Early Spring ◽

Lumbricus Rubellus ◽

Late Winter ◽

Cocoon Production ◽

Density And Biomass ◽

Earthworm Activity

Earthworms have the ability to alleviate many soil degradational problems in Australia. An attempt to optimize this resource requires fundamental understanding of earthworm ecology. This study reports the seasonal changes in earthworm populations in the Midlands of Tasmania (<600 mm rainfall p.a.), and examines, for the first time in Australia, the behaviour and survival rates of aestivating earthworms. Earthworms were sampled from 14 permanent pastures in the Midlands from May 1992 to February 1994. Earthworm activity was significantly correlated with soil moisture; maximum earthworm activity in the surface soil was evident during the wetter months of winter and early spring, followed by aestivation in the surface and subsoils during the drier summer months. The two most abundant earthworm species found in the Midlands were Aporrectodea caliginosa (maximum of 174.8 m-2 or 55.06 g m-2) and A. trapezoides (86 m-2 or 52.03 g m-2), with low numbers of Octolasion cyaneum, Lumbricus rubellus and A. rosea. The phenology of A. caliginosa relating to rainfall contrasted with that of A. trapezoides in this study. A caliginosa was particularly dependent upon rainfall in the Midlands: population density, cocoon production and adult development of A. caliginosa were reduced as rainfall reduced from 600 to 425 mm p.a. In contrast, the density and biomass of A. trapezoides were unaffected by rainfall over the same range: cocoon production and adult development continued regardless of rainfall. The depth of earthworm aestivation during the summers of 1992-94 was similar in each year. Most individuals were in aestivation at a depth of 150-200 mm, regardless of species, soil moisture or texture. Smaller aestivating individuals were located nearer the soil surface, as was shown by an increase in mean mass of aestivating individuals with depth. There was a high mortality associated with summer aestivation of up to 60% for juvenile, and 63% for adult earthworms in 1993 in the Midlands. Cocoons did not survive during the summers of 1992 or 1994, but were recovered in 1993, possibly due to the influence of rainfall during late winter and early spring.

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