Precipitation Impacts Dissemination of Three Sooty Blotch and Flyspeck Taxa on Apple Fruit

The spatial dissemination of three prevalent taxa of sooty blotch and flyspeck (SBFS) fungi under several levels of precipitation was compared during 2015 and 2016 in an Iowa apple orchard. Overhead irrigation was used to supplement ambient precipitation in order to insure SBFS spore dissemination and colony development. There were five irrigation levels, involving 1-min-long periods of irrigation that were imposed either once or twice per hour at intervals of 3, 6, or 12 h, as well as a nonirrigated control. Preselected apple fruit were inoculated with one of the three SBFS taxa to serve as sources of inoculum. Dissemination from these inoculated apple fruit was assessed at harvest by counting SBFS colonies on water-sprayed and nontreated fruit. As a further control, additional fruit were enclosed in fruit bags throughout the fruit development period. In both 2015 and 2016, the number of colonies of the SBFS fungus Peltaster gemmifer per apple increased sharply as the duration of irrigation increased, whereas the number of colonies of Microcyclosporella mali increased to a lesser extent and Stomiopeltis sp. RS1 showed no increase. In 2015, the linear relationship between the duration of irrigation-imposed precipitation levels and the number of colonies on the water-sprayed apple fruit was similar for P. gemmifer (slope = 0.09), Stomiopeltis sp. RS1 (slope = 0.07), and Microcyclosporella mali (slope = 0.13); whereas, in 2016, the slope was higher for P. gemmifer (0.28) than for Stomiopeltis sp. RS1 (−0.09) or M. mali (0.06). The results indicated that dissemination of P. gemmifer increased sharply in response to increased irrigation-imposed precipitation, and that dissemination patterns differed considerably among the three SBFS taxa. The apparent advantage of P. gemmifer in precipitation-triggered dissemination may stem from its ability to produce spores rapidly by budding. To our knowledge, this is the first article to assess splash dispersal by SBFS fungi in the field and the first to document taxon-specific patterns of dissemination in this pathogen complex.

Manure contamination with Clostridium botulinum after avian botulism outbreaks: management and potential risk of dissemination

BackgroundPersistence of Clostridium botulinum in the environment is well known. Getting rid of it after animal botulism outbreaks is so tricky, especially as far as manure concerns. This study aimed at 1. describing manure management on 10 poultry farms affected by botulism and 2. assessing the persistence of C botulinum in poultry manure after the outbreak.MethodsEach farm was visited twice at two different manure storage times (two weeks after manure removal and two months later). Fifteen samples of manure were collected on each visit and C botulinum was detected using real-time PCR.ResultsManagement of manure varied among poultry farms (classical storage, addition of quicklime, bacterial flora or incineration). C botulinum was detected in the manure of all 10 farms, 56.5per cent of samples being positive. C botulinum was detected significantly more frequently at the second visit (65.8per cent vs 49.7per cent, P<0.01) and on the surface of the pile (63.1per cent vs 50per cent, P=0.025).ConclusionThis study shows the persistence of C botulinum in poultry manure over time after a botulism outbreak and highlights manure management as a key health issue in preventing spore dissemination in the environment and recurrence of the disease.

Histological Aspects of a Hypersensitive Response in Poplar to Melampsora larici-populina

The course of the infection and development of the biotrophic fungus Melampsora larici-populina on leaf tissue from the hybrid poplar Populus deltoides × P. nigra ‘Ogy’ was monitored at the histological level. Leaf disks were inoculated with one of two rust physiological races (E1 and E2), resulting in interactions that were either incompatible (race E1) or compatible (race E2). In the compatible interaction, the fungus rapidly colonized the leaf without inducing any apparent host response. Symptoms appeared on the leaf several days after inoculation just prior to spore dissemination. The incompatible interaction was characterized by the early collapse and disorganization of cytoplasm of infected cells 17 h after inoculation and within 2 h after the appearance of the first haustoria. Resistance to M. larici-populina was mediated through a hypersensitive response, since it was extremely localized and involved only the few cells that were in the immediate vicinity of each infected cell.

The phenology and spore dissemination patterns of Uredinopsismirabilis on Abiesbalsamea and Onocleasensibilis

Phenology and spore dissemination patterns of Uredinopsismirabilis (Peck) Magnus were monitored from 1982 to 1984 in the Champlain Valley and north central Vermont. Teliospore germination began as early as May 5 and basidiospore dissemination continued as late as the week of June 17. Maximum basidiospore dissemination occurred after measurable precipitation. Infection of Abiesbalsamea (L.) Mill, occurred between May 19 and 30. Pycnia were apparent on current-year needles of A. balsamea by the week of June 17. Aeciospore development was observed by the week of June 24 and dissemination of aeciospores was completed about July 29. Aeciospores were trapped at highest concentrations during precipitation events. During dry periods, aeciospore dissemination showed a diurnal periodicity, with most spores trapped in the late morning hours. Uredia were formed on Onocleasensibilis L. as early as July 28 and urediniospores were trapped as late as October 4. Teliospores were formed in host tissues as early as July 7.

Observations on Wallrothiella arceuthobii, a fungus parasite of dwarf mistletoes

Certain aspects of the life cycle of Wallrothiella arceuthobii are detailed from field and microscopical observations. Infected fruits of the host often continue to develop for several weeks after spore dissemination. Sectioned material shows that the fungus tends to avoid the young embryo and endosperm, yet attacks other adjacent mistletoe tissues. Perithecial shape varies considerably between eastern and western North America. Some western specimens show periostiolar locules of unknown function. The genus may be related to Coryneliaceae.

Puccinia asparagi. [Descriptions of Fungi and Bacteria].

A description is provided for Puccinia asparagi. Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: On Asparagus officinalis (cult.), also on a few other species, including A. maritimus, A. plumosus and A. scaber; slight infections can be obtained on Allium cepa (see CMI Descript. 52). DISEASE: Asparagus rust. Causing lesions on asparagus stems, either oval yellowish spots (aecia and pycnia) or blister-like pustules (uredia and telia), and producing premature desiccation with subsequent weakening of roots and crowns which reduces the yield of edible shoots in the following season. May also attack onion, shallot and chives. GEOGRAPHICAL DISTRIBUTION: Occurs in Africa, Asia, Australasia, Europe and North America wherever asparagus is grown (CMI Map 216, Ed. 2, 1950). TRANSMISSION: Spore dissemination mainly by wind with rain contributing to spread on individual plants (33: 333). Also believed to be transmitted in shipments of contaminated plants or packing material and soil accompanying roots (Arthur 1929). Volunteer and wild plants may serve as sources of infection (32: 58).

Environment and sporulation in phytopathogenic fungi. III. Peronospora tabacina Adam: Field environment, sporulation, and forecasting

An account is given of measurements of temperature and humidity at a number of positions and heights within a tobacco crop during a 4 day period. Measurements of the intensity of sporulation of Peronospora tabacina Adam were made at the same time. It is shown that the capacity of P. tabacina to sporulate is controlled not only by nocturnal humidity but also by day temperature. The observations confirm that Cruickshank's laboratory findings hold in the field. The implications of the observations reported here, together with those of other workers on such factors as the spore dissemination and germination characteristics of P. tabacina, are discussed. It is concluded that the basic information necessary to initiate, on a trial basis, a blue mould forecasting and spray warning service is now available.