First Report of Boeremia Blight Caused by Boeremia exigua var. exigua on Pyrethrum in Australia.

Pyrethrum (Tanacetum cinerariifolium) is produced for extraction of insecticidal compounds from the flower achenes. In 2004 and 2006, isolations from necrotic lesions on stems and leaves in three fields in northern Tasmania, Australia yielded four unidentified fungal isolates. Leaf lesions were medium brown and circular (2 to 4 mm in diameter) or irregular in shape (2 to 5 mm long). Stem lesions were irregular, necrotic spots, 5 to 15 mm below the flower peduncle, medium brown, 2 to 4 mm long, and 1 to 2 mm wide. Isolations were conducted on water agar following surface sterilization. Isolates were identified by colony characteristics and the presence of metabolite 'E' (1). On oatmeal agar (OA), colonies had irregular margins, were greenish olivaceous-to-olivaceous gray with sparse, white, floccose, aerial mycelia. On malt extract agar (MEA), cultures were variable in color with olivaceous black centers with soft, dense, aerial mycelia. Conidia were hyaline, ellipsoidal to oblong, mainly aseptate, but occasionally 1-septate with dimensions ranging from 2.5 to 7.5 × 1.8 to 3.8 µm (length/width ratio = 1.7 to 2.1). All isolates had moderate reactions to the NaOH test for metabolite 'E'. DNA was extracted from all four isolates with a DNeasy Plant Mini Kit (QIAGEN Inc., Valencia, CA). For identification, the internal transcribed spacer region (ITS1, 5.8s, and ITS2) and part of the translation elongation factor (TEF) region were amplified and sequenced. Primers ITS1 and ITS4 (2) were used for the ITS region and primers EFCF1 (5'-AGTGCGGTGGTATCGACAAG) and EFCF6 (3'-CATGTCACGGACGGCGAAAC) were used for the TEF. Amplicons were sequenced in both directions and consensus sequences assembled. The ITS sequence was 100% identical to Boeremia exigua var. exigua (GenBank Accession No. GU237715). Base pairs 413 to 1,214 of the TEF sequence from the pyrethrum isolates matched base pairs 1 to 802 (799 of 802 identities) of B. exigua var. exigua (GenBank Accession No. GU349080). All isolates were confirmed as B. exigua var. exigua using morphology and sequencing. Pathogenicity tests were conducted three times in separate glasshouse trials for two of the four isolates. For each isolate, conidial suspensions in water (3 ml/plant) from MEA, adjusted to 5 × 105/ml were applied with Tween 20 (1 drop per 100 ml of water) to 8-week-old pyrethrum plants (five pots per isolate with four plants per pot) using a hand-held spray bottle. Twenty plants were sprayed with water and Tween 20 as nontreated controls. Plants were covered with plastic bags for 48 h after inoculation and examined for symptoms after 15 days at 20°C. Disease incidence (number of symptomatic leaves affected per total number of leaves) of the inoculated plants varied from 7.5 to 9.4%. Noninoculated plants did not develop symptoms. Isolations resulted in cultures morphologically identical on MEA and OA to those inoculated. To our knowledge, this is the first report of B. exigua var. exigua causing disease in pyrethrum. Cultures were deposited in the New South Wales Department of Agriculture collection (DAR79101 to 79104) and TEF and ITS sequences for DAR79101 in GenBank (Accession Nos. JF925328 and JF925329, respectively). Boeremia blight is likely to contribute to the fungal disease complex causing reductions in green leaf area in Australian pyrethrum production. References: (1) M. M. Aveskamp et al. Stud. Mycol. 65:1, 2010. (2) T. J. White et al. PCR Protocols: A Guide to Methods and Applications. Academic Press, San Diego, 1990.

The development of Trichostrongylus colubriformis larvae on a range of herbage species or on plots of differing topographical aspect.

Five "contaminations", where faeces containing Trichostrongylus colubriformis eggs were deposited on pasture and serially recovered, were used to compare the rate of decline of faecal mass and larval development. In the first three contaminations, faeces from a common source were deposited on swards of browntop (Agrostis capillaris cv Grasslands Muster), ryegrass (Lolium perenne cv Grassland Nui), white clover (Trifolium pratense cv Grassland Tahora), or onto bare ground in the late spring, summer or autumn. The last two contaminations were done on the north facing aspect or south facing aspect of hill country pastures in summer and autumn. Number of free-living nematodes (first- and second-stage larvae (L(1) and L(2)) and soil dwelling nematodes) and third stage larvae (L(3)) recovered from faeces were counted. In spring there was a significant (P<0.01) effect of sward type on the mass of faeces remaining, with greatest mass remaining on browntop and ryegrass 28 days later, and less on bare ground and white clover. In summer there were more (P<0.05) faeces remaining on browntop than on other herbages which had little faeces remaining and which did not differ one from another. In autumn there was a rapid decline in faecal mass. All faeces were gone from white clover and ryegrass swards by day 10 and from browntop and bare ground by day 14. The number of free-living nematodes did not differ markedly between seasons, ranging from 5 to 8.5% of eggs deposited. The number of L(3) recovered was low in spring ( approximately 0.4% of eggs deposited) and did not differ between swards. In summer, more (P<0.05) L(3) were recovered from faeces deposited on swards of ryegrass and white clover than from bare ground or browntop. Most L(3) were recovered from days 7 to 14 ( approximately 1.3% of eggs deposited). In the autumn, low numbers of L(3) were recovered from browntop on day 3 and ryegrass on day 7 (0.2% of eggs deposited) with virtually no L(3) recovered from faeces placed on white clover or bare ground. There were significant (P<0.001) effects of aspect on the amount of faecal mass remaining in both summer and autumn with less faeces remaining on the south facing aspect than on the north. This was particularly evident during the summer when virtually all of the faeces were intact on the north facing aspect but only 40% was remaining on the south on day 28. In the autumn, while faeces were completely gone from both aspects by day 28 but there were less (P<0.05) faeces remaining on the south facing aspect from days 3 to 18 than from the north. There was no aspect effect in either season on the number of free-living nematodes recovered which averaged 8-11% of eggs deposited. In both seasons a greater number of L(3) were recovered from faeces on the south facing aspect than on the north, particularly 3-10 days after faecal deposition. In summer the rise in L(3) recovered in faeces was more rapid on south facing aspect than on the north but both attained a maximum level of approximately 4% of eggs deposited. In autumn on day 3 there was a rapid rise on south facing aspect to approximately 21% of eggs deposited followed by a gradual decline on day 10 while on the north facing aspect numbers of L(3) recovered only attained 10% of eggs deposited.

Spatiotemporal analysis of epiphytotics of downy mildew of oilseed poppy in tasmania, australia.

Downy mildew, caused by Peronospora arborescens, has become the major disease affecting oilseed poppy (Papaver somniferum) since its first record in Tasmania in 1996. Two field trials conducted in 2000 and 2001 studied the progression and spatial distribution of downy mildew epiphytotics. The logistic and exponential models best described the progression of disease incidence and severity, respectively. Incidence and severity increased rapidly following canopy closure. In 2001, incidence increased from 0.16%, prior to canopy closure, to 100% at late flowering (40 days). Spatial analyses of epiphytotics were conducted by fitting the beta-binomial and binomial distributions, median runs analysis, and the spatial analysis by distance indices. All analyses demonstrated that the distribution of incidence and severity was strongly spatially aggregated from canopy closure until at least late flowering. These results suggest that secondary spread from a few primary infections is the major factor in epiphytotics.

First Report of Fusarium crookwellense Causing Tip Blight on Cones of Hop.

Hop (Humulus lupulus L.) is grown primarily for the alpha and beta acids produced in the strobile (cone) and used for bittering beer. In late summer (March) 2001, necrotic lesions covering the tips of cones of cvs. Agate, Nugget, and Willamette at hop farms in Tasmania, Australia, were observed. The necrotic lesions encompassed the proximal tips and affected between 5 and 60% of the cone; however, all bracts in the whorl were always affected. Diseased cones were observed in all seven gardens included in the survey. The incidence of plants with cone tip blight in 'Nugget' ranged from 5 to 30% in three gardens, in 'Agate' ranged from 3 to 10% in three gardens, and in the only 'Willamette' garden 30% of cones were affected. Pieces of infected hop cones (N = 55) were surface-treated for 1 min in 2% sodium hypochlorite, placed on 2% water agar, and incubated at 22 ± 2°C. Fusarium crookwellense Burgess, Nelson, & Toussoun was isolated from 95% of the cones (1). F. crookwellense was identified on carnation leaf agar by L. Burgess, University of Sydney, Australia. Koch's postulates were fulfilled by inoculating detached mature hop cones of cvs. Nugget and Willamette (N = 20 for each cultivar) with an atomized conidial suspension (3.5 × 105 spores of a single F. crookwellense isolate per milliliter) until runoff and incubated at 20 ± 2°C in a sealed container on plastic mesh over tissue wetted with sterile distilled water. Symptoms first appeared 5 days after inoculation and were identical to those found in the field. No disease symptoms were observed on cones subjected only to sterile distilled water. The pathogen was reisolated from diseased tissue on inoculated cones, completing Koch's postulates. Similar disease symptoms on hop cones have been described in Oregon and were associated with infection by F. sambucinum and F. avenaceum (C. Ocamb, personal communication). To our knowledge, this is the first report of the infection of hop cones by F. crookwellense. Reference: (1) L. W. Burgess et al. Laboratory Manual for Fusarium Research, 3rd ed. University of Sydney, Australia, 1994.

First Report of Infection of Hop Cones by Alternaria alternata in Australia.

The hop (Humulus lupulus L.) is a dioecious climbing plant, cultivated for its resins, which are produced in the cone, used primarily for the bittering of beer. In Australia, hops are grown in the states of Victoria and Tasmania. In late summer 2001, necrotic lesions were observed on the tips of bracts and bracteoles of developing cones at three hop farms in Tasmania. The necrotic area varied between 1 and 25% of the bracts and bracteoles, and in some cases progressed throughout the entire hop cone. Pieces of infected hop cones were surface sterilized for one minute in 2% sodium hypochlorite, plated on 2% water agar, and incubated at 22 ± 2°C. The most frequently isolated fungi (total number of isolations = 60) were transferred to 2% water agar and potato dextrose agar. In 90% of cases, the isolated fungus was Alternaria alternata (Fr.:Fr.) Keissl, as identified by M. Priest, NSW Agriculture, Australia. The pathogenicity of A. alternata was determined on detached, freshly picked cones of hop cultivar "Nugget." Cones (n = 25) were inoculated with a conidial suspension of the fungus (1,000 spores per ml) and incubated at room temperature in a sealed container on plastic mesh over tissue wetted with sterile distilled water. Symptoms first appeared three days after inoculation as necrotic tips of bracts and bracteoles, and within 10 days the entire cone had become necrotic. Symptoms were more severe in vitro compared to in the field. This was probably due to the maintenance of detached cones under constant high relative humidity. Disease symptoms did not appear on cones inoculated with sterile distilled water. The pathogen was reisolated from inoculated cones, completing Koch's postulates. The pathogenicity of A. alternata to hop cones was reported in the United Kingdom in 1988. To our knowledge, this is the first report of A. alternata on hop cones in Australia. References: (1) P. Darby. Trans. Br. Mycol. Soc. 90:650-653, 1988.

Infestation of sheep dung by nematophagous fungi and implications for the control of free-living stages of gastro-intestinal nematodes.

A field trial was conducted to assess the rate at which dung becomes infested by fungi which parasitise nematodes (nematophagous fungi) after deposition. Sheep dung was placed on field plots of bare ground, ryegrass (Lolium perenne), browntop (Agrostis capillaris) and white clover (Trifolium repens) in summer (February) and autumn (April), and subsamples were examined at intervals for the presence of nematophagous fungi. Nematophagous fungi occurred in 71% of 129 samples recovered in February and 57% of 58 samples recovered in April. Arthrobotrys oligospora, Monacrosporium candidum and Nematoctonus spp. were the most frequently isolated nematode-trapping fungi in both seasons. The endoparasitic nematophagous fungus Harposporium leptospira also occurred frequently in dung deposited in February, but not April. Fungi entered dung quickly, with 83% and 58% of dung samples containing nematophagous fungi at 3 days after deposition in February and April, respectively. The percentage of dung infested by nematophagous fungi on plots of bare ground, ryegrass, white clover and browntop was 76%, 75%, 61% and 55%, respectively. Results suggest that a number of species of nematophagous fungi are able to enter dung soon after deposition on a variety of types of ground cover.