Most books on epidemiology have treated the subject from a statistical, mathematical or computer applicational point of view However, experiments must be performed first to provide the data for models which in turn can then be proven by further experimentation This mutual interplay of theory and empirics gives epidemiology its scientific thrust and charm This book provides a choice of methods for varying applications and objectives, covering all important aspects for the designing of experiments Furthermore, the reader is supplied with solutions to his experimental problems and many "tricks of the trade" The newcomer to the field will also profit by this methodology guide

Experimental Techniques in Plant Disease Epidemiology

The abundance and diversity of vesicular-arbuscular mycorrhizal (VAM) fungi in pioneer dune populations of Uniola paniculata were determined. Samples were obtained in November, 1983, and May, August, and November, 1984, from two locations in northeastern Florida. Roots of sea oats were well colonized by a diverse populaton of VAM fungi. Three species of Glomus and two species each of Acaulospora and Gigaspora were collected. Total spore densities ranged from 0 to 677 per 100 g of sand. The frequency distributions of spore counts were best described by the negative binomial model, suggesting spores were aggregated in the dunes. There was no trend in spore populations through the 1984 season; highest spore numbers were found in May for one species, August for three species, and November for two species. Spore densities in non-vegetated areas adjacent to vegetated dunes averaged less than 6% of the spore densities found in the root zone of sea oats. The length of all fungal hyphae in the dunes was estimated at 12 m g-l sand or 592 m cm-1 of colonized root length. Seventy-eight percent of the hyphae observed were non-septate.

Spatial and Temporal Distribution of Vesicular-Arbuscular Mycorrhizal Fungi Associated with Uniola Paniculata in Florida Foredunes

A collection of 241 isolates of Rhizoctonia solani obtained from potato plants grown in different areas in France was characterized for anastomosis grouping, symptomatology on tubers of different cultivars and sensitivity to three fungicides. Most isolates collected belonged to (anastomosis groups (AGs)) AG 3, but 2% and 4% of the isolates were AG 5 and AG 2-1. AG 3 and AG 2-1 isolates were mostly obtained from sclerotia on tubers, but all AG 5, some AG 3 and some AG 2-1 isolates were recovered from superficial tuber alterations, like deformations, corky or scabby lesions. Sclerotia were formed on tubers produced by healthy stem cuttings grown in soil artificially infested with AG 3, but not on tubers grown in soil infested with either AG 5 or AG 2-1. No variation in susceptibility to sclerotial formation was observed among five potato cultivars. In all cases, a large proportion of tubers showed superficial corky lesions, often associated with deformations. The proportion of tubers with lesions and deformations was highest in soil infested with AG 2-1 and significantly lower on cv. Samba in all treatments. All isolates were highly sensitive to flutolanil, iprodione and pencycuron, except the AG 5 isolates, moderately sensitive to pencycuron. These results show that, although AG 3 is the most common R. solani group on potato in France, AG 5 and AG 2-1 may be present. Isolates differed for pathogenicity. In vitro sensitivity to fungicides varied among AGs.

Anastomosis Groups, Pathogenicity and Sensitivity to Fungicides of Rhizoctonia solani Isolates Collected on Potato Crops in France

Disease prevention is a current practice used to minimize fungal diseases of turfgrasses in lawns and golf greens. Prevention is accomplished through fungicide applications, and by periodic thatch removal. During the development of a microbial biodethatch product utilizing the lignocellulose-degrading Streptomyces hygroscopicus strains YCED9 and WYE53, we demonstrated using in vitro plate antagonism bioassays that both strains are antagonists of various turfgrass fungal pathogens. These activities were present when the cultures were growing on thatch, as demonstrated by antifungal antagonism bioassays with culture filtrates. Experiments conducted using a growth chamber demonstrated that a bio-dethatch formulation containing spores of strains YCED9 and WYE53 in a zeolite carrier, provided protection for Kentucky bluegrass seedlings against turfgrass pathogens, including Pythium ultimum, Fusarium oxysporum, Rhizoctonia solani, Sclerotinia homeocarpa, Gaeumannomyces graminis and Microdochium nivale. Results showed that by integrating the use of the S. hygroscopicus YCED9/WYE53 bio-dethatch formulation into routine turf management practices, it should be possible to both minimize thatch build-up while also controlling fungal turfgrass diseases by way of the antifungal biocontrol activity of these strains. This in turn would help control fungal pathogens in turfgrass while minimizing the need for routine chemical fungicide applications.

In vitro and in vivo antagonism of pathogenic turfgrass fungi by Streptomyces hygroscopicus strains YCED9 and WYE53.

The effects of temperature and soil moisture on infection and disease development by Rhizoctonia solani on soybean were studied individually. In addition, the anastomosis group of R. solani isolates recovered from soybean from 35 fields in 15 counties was determined. All of the 44 isolates recovered in this study were AG-2-2 IIIB. Five isolates of R. solani were able to infect and colonize soybean roots and hypocotyls at 20, 24, 28, and 32°C in growth chamber studies. The temperatures evaluated in this study were not limiting to the isolates tested. In greenhouse studies, nine R. solani isolates and a noninoculated control were evaluated at 25, 50, 75, and 100% soil moisture holding capacity (MHC). Root weights were greater and percent stand averages higher at 50 and 75% than at 25 or 100% MHC; however, as percentage of control, the main effect on percent moisture for percent stand, plant height, or root weight was not significant. There were significant differences among the isolates for the percent stand, root rot rating, and root fresh weight of soybean in each study. In both temperature and moisture studies, the R. solani isolates could be separated as predominantly causing (i) seed rot, as detected by greatly reduced plant stand; (ii) root rot generally having no effect on plant stand but a high root rot rating and low root weight; or (iii) hypocotyl lesions, having no effect on plant stand, a low root rot score, and a high number of red lesions on the hypocotyl. In the greenhouse seed treatment evaluations of five fungicides, there was no fungicide by isolate interaction using these pathogenic types of R. solani. None of the seed treatments evaluated in this study provided 100% control of the four isolates tested. Due to the wide range of environmental factors that permit R. solani infection and disease on soybeans, other control measures that last all season, such as host resistance, should be emphasized.

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Temperature, Moisture, and Seed Treatment Effects on Rhizoctonia solani Root Rot of Soybean.

Comparative Sensitivity ofRhizoctonia solaniand Rhizoctonia-like Fungi to Selected Fungicides In Vitro

Repartition des propagules de R. spp dans les debris organiques d'un sol de gazon a Festuca arundinacea. Identification des especes, proportion relative de chaque espece ou type

C. L. Campbell

Papers

Comparative Sensitivity ofRhizoctonia solaniand Rhizoctonia-like Fungi to Selected Fungicides In Vitro

Horizontal distribution and characterization of Rhizoctonia spp. in tall fescue turf

Response of Rhizoctonia Blights of Tall Fescue to Selected Fungicides in the Greenhouse