Turner B. Sutton

NAPPFAST : An internet system for the weather-based mapping of plant pathogens

In recent years, the number of exotic pest introductions has increased rapidly as a result of increased volume of trade (22). The serious and sometimes irreparable ecological and economic damage of exotic pathogens, such as Cryphonectria parasitica, Ophiostoma novo-ulmi, and Phytophthora ramorum, the causal agents of chestnut blight, Dutch elm disease, and Sudden Oak Death, respectively, are amply documented (1,6,42). An estimate of annual losses for exotic plant pathogens is

A Simple Generic Infection Model for Foliar Fungal Plant Pathogens

21 billion dollars (32). The Plant Protection and Quarantine (PPQ) (Sidebar 1) division within the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service (USDA-APHIS) has the goal of safeguarding agriculture and natural resources from the risks associated with the entry, establishment, and spread of exotic pathogens. Two important components of the APHIS-PPQ mission are risk analysis and pest detection. A key goal of the risk analysis program is to identify exotic pest pathways and to assess the risks these exotic pests pose to plants and plant products as well as to the environment. Three types of risk assessments that evaluate the probability of the introduction and establishment of exotic plant pests are pathway analysis, organism pest risk assessment, and commodity risk assessment. The PPQ pest detection program and its state cooperators provide a continuum of pest surveillance, from offshore preclearance programs through port inspections, to surveys in rural and urban sites across the United States. The Center for Plant Health Science and Technology (CPHST) and the Cooperative Agricultural Pest Survey (CAPS) programs are instrumental in APHIS-PPQ’s pest detection programs. CAPS is responsible for supplying a means of detection, documentation, and rapid dissemination of information regarding the survey of regulated significant plant pests and weeds in the United States. The survey information gathered by CAPS is entered into a central database known as National Agricultural Pest Information System (NAPIS). CPHST, headquartered in Raleigh, NC, is a multi-program scientific support organization for PPQ. One way CPHST scientists help facilitate the APHIS-PPQ activities of risk analysis and pest detection is by mapping the potential introduction and establishment of exotic pathogens in the United States. These maps are the result of pathogen-specific information analyses, including climate, pathogen distribution, host distribution, and trade. Given its influence on pest phenology, reproduction, dispersion, and overwintering survival, climate is a critical component for the geographic assessment of potential pathogen distribution. A large number of climate-based risk mapping systems, such as CLIMEX, BIOCLIM, and GARP, have been used for pest risk analysis (3,10,38,44). Literature typically focuses on the development and/or evaluation of the best modeling techniques (10); however, often the quality of the inputs, including biological parameters, weather

Sensitivity of Mycosphaerella fijiensis, causal agent of black sigatoka of banana, to propiconazole

ABSTRACT In this study, a simple generic infection model was developed for predicting infection periods by fungal foliar pathogens. The model is designed primarily for use in forecasting pathogens that do not have extensive epidemiological data. Most existing infection models require a background epidemiological data set, usually including laboratory estimates of infection at multiple temperature and wetness combinations. The model developed in this study can use inputs based on subjective estimates of the cardinal temperatures and the wetness duration requirement. These inputs are available for many pathogens or may be estimated from related pathogens. The model uses a temperature response function which is scaled to the minimum and optimum values of the surface wetness duration requirement. The minimum wetness duration requirement (W(min)) is the number of hours required to produce 20% disease incidence or 5% disease severity on inoculated plant parts at a given temperature. The model was validated with published data from 53 controlled laboratory studies, each with at least four combinations of temperature and wetness. Validation yielded an average correlation coefficient of 0.83 and a root mean square error of 4.9 h, but there was uncertainty about the value of the input parameters for some pathogens. The value of W(min) varied from 1 to 48 h and was relatively uniform for species in the genera Cercospora, Alternaria, and Puccinia but less so for species of Phytophthora, Venturia, and Colletotrichum. Operationally, infection models may use hourly or daily weather inputs. In the case of the former, information also is required to estimate the critical dry-period interruption value, defined as the duration of a dry period at relative humidities <95% that will result in a 50% reduction in disease compared with a continuous wetness period. Pathogens were classified into three groups based on their critical dry-period interruption value. The infection model is being used to create risk maps of exotic pests for the U.S. Department of Agricultures Animal Plant Health and Inspection Service.

Diversity and Biogeography of Sooty Blotch and Flyspeck Fungi on Apple in the Eastern and Midwestern United States

ABSTRACT One hundred monoascosporic isolates of Mycosphaerella fijiensis were collected in February and November 1994 from each of two banana (Musa spp.) plantations in Costa Rica. Locations at San Pablo and Coopecariari had been sprayed with propiconazole for the past 7 years to control black Sigatoka. One hundred monoascosporic isolates from a third location, San Carlos, with no history of fungicide use, also were tested for sensitivity to propiconazole. Fifty percent effective concentration (EC(50)) values were calculated for individual isolates by regressing the relative inhibition of colony growth against the natural logarithm of the fungicide concentration. In the February sample, the mean EC(50) values for San Pablo and Coopecariari populations were 0.06 and 0.05 mug a.i. ml(-1), respectively, which were not statistically different (P = 0.05). The mean EC(50) value of the population at San Carlos was 0.008 mug a.i. ml(-1), which was significantly lower (P = 0.001) than the mean EC(50) values obtained at San Pablo and Coopecariari. Frequency distributions of EC(50) values of isolates from the three populations collected in February showed that 80% of isolates from San Pablo and Coopecariari had EC(50) values greater than the highest EC(50) value from San Carlos, indicating a significant shift in reduced sensitivity to propiconazole. Isolates collected in November 1994, after eight treatments of propiconazole at San Pablo and Coopecariari, showed a significant increase in mean EC(50) values compared with the means observed in February. The high proportion of isolates with reduced sensitivity to propiconazole may account for the unsatisfactory control of black Sigatoka between 1992 and 1993 in the two banana plantations at San Pablo and Coopecariari.

Relationship between apple fruit epicuticular wax and growth of Peltaster fructicola and Leptodontidium elatius, two fungi that cause sooty blotch disease.

Sooty blotch and flyspeck (SBFS) fungi on apple fruit were sampled from nine orchards in four midwestern U.S. states during 2000 and 30 orchards in 10 eastern U.S. states during 2005 in order to estimate taxonomic diversity and discern patterns of geographic distribution. Forty apple fruit per orchard were arbitrarily sampled and colonies of each mycelial phenotype were counted on each apple. Representative colonies were isolated, cultures were purified, and DNA was extracted. For representative isolates, the internal transcribed spacer (ITS) and large subunit (LSU) regions of ribosomal DNA were amplified and sequenced. In total, 60 SBFS putative species were identified based on ITS sequences and morphological characteristics; 30 of these were discovered in the 2005 survey. Modified Kochs postulates were fulfilled for all 60 species in an Iowa orchard; colonies resulting from inoculation of apple fruit were matched to the original isolates on the basis of mycelial type and ITS sequence. Parsimony analysis for LSU sequences from both surveys revealed that 58 putative SBFS species were members of the Dothideomycetes, 52 were members of the Capnodiales, and 36 were members of the Mycosphaerellaceae. The number of SBFS species per orchard varied from 2 to 15. Number of SBFS species and values of the Margalef and Shannon indexes were significantly (P < 0.05) lower in 21 orchards that had received conventional fungicide sprays during the fruit maturation period than in 14 unsprayed orchards. Several SBFS species, including Schizothyrium pomi, Peltaster fructicola, and Pseudocercosporella sp. RH1, were nearly ubiquitous, whereas other species, such as Stomiopeltis sp. RS5.2, Phialophora sessilis, and Geastrumia polystigmatis, were found only within restricted geographic regions. The results document that the SBFS complex is far more taxonomically diverse than previously recognized and provide strong evidence that SBFS species differ in geographic distribution. To achieve more efficient management of SBFS, it may be necessary to understand the environmental biology of key SBFS species in each geographic region.

A New View of Sooty Blotch and Flyspeck

Sooty blotch severity varied among apple cultivars or selections surveyed in 1989 and 1992. No mycelial growth was observed on russetted areas of the cuticle that are considered impermeable. Ursolic acid and n-alkanes were the most prominent components of the epicuticular waxes of the cultivars or selections evaluated. Although there were differences in the relative proportions of these compounds among the cultivars, the differences were not related to the severity of sooty blotch. Peltaster fructicola and Leptodontidium elatius were grown on compounds that comprise the epicuticular wax of the fruit to determine if one or more of these were needed for growth. The fungi did not grow on any of the five major components of the epicuticular wax unless dilute apple juice was included. Scanning electron microscopy studies showed that mycelia of P. fructicola grew on the surface of the wax and did not appear to degrade it. Our studies support the hypothesis that P. fructicola and L. elatius fungi are epiphytes and obtain their nutrients not from components of the cuticle, but more likely from fruit leachates.

Clarification of the Etiology of Glomerella Leaf Spot and Bitter Rot of Apple Caused by Colletotrichum spp. Based on Morphology and Genetic, Molecular, and Pathogenicity Tests

Sooty blotch and flyspeck (SBFS) fungi colonize the surface wax layer of the fruit of apple, pear, persimmon, banana, orange, papaya, and several other cultivated tree and vine crops. In addition to colonizing cultivated fruit crops, SBFS fungi also grow on the surfaces of stems, twigs, leaves, and fruit of a wide range of wild plants. The disease occurs worldwide in regions with moist growing seasons. SBFS is regarded as a serious disease by fruit growers and plant pathologists because it can cause substantial economic damage. The smudges and stipples of SBFS often result in downgrading of fruit from premium fresh-market grade to processing use. This review describes the major shifts that have occurred during the past decade in understanding the genetic diversity of the SBFS complex, clarifying its biogeography and environmental biology, and developing improved management strategies.

Etiology of apple sooty blotch disease in North Carolina

ABSTRACT Morphological characteristics and vegetative compatibility groups (VCGs) of 486 isolates of Glomerella cingulata, Colletotrichum gloeosporioides, and C. acutatum collected from apple leaves with Glomerella leaf spot (GLS) symptoms and fruit with bitter rot symptoms in the United States and Brazil were studied. From this collection, 155 isolates of G. cingulata (93 from fruit, 61 from leaves, and 1 from buds), 42 isolates of C. gloeosporioides from fruit, and 14 isolates of C. acutatum (10 from fruit and 4 from leaves) were studied using mitochondrial (mt)DNA restriction fragment length polymorphism (RFLP) haplotypes. A subset of 24 isolates was studied by examining the sequence of a 200-bp intron of the glyceraldehyde 3-phosphate dehydrogenase (GDPH) nuclear gene. In addition, 98 isolates were tested for pathogenicity on leaves of cvs. Gala and Golden Delicious in the greenhouse, and 24 isolates were tested for pathogenicity on fruit of cv. Gala in growth chambers. In total, 238 and 225 isolates of G. cingulata were separated into four distinct morphological types and six VCGs, respectively. Five morphological types and six VCGs were identified among 74 and 36 isolates of C. gloeosporioides, respectively. Three morphological types and four VCGs were identified among 74 and 23 isolates of C. acutatum, respectively. Seven different mtDNA RFLP haplotypes were observed within isolates of G. cingulata, two within isolates of C. gloeosporioides, and two within isolates of C. acutatum. Phylogenetic trees, inferred based on maximum likelihood and maximum parsimony methods using the intron sequence, produced similar topologies. Each species was separated into distinct groups. All isolates tested were pathogenic on fruit, though only isolates with specific VCGs and haplotypes were pathogenic to leaves. Vegetative compatibility was a better tool than molecular characters for distinguishing isolates of G. cingulata pathogenic on both leaves and fruit from the ones pathogenic only on fruit. Isolates of G. cingulata capable of causing both GLS and bitter rot were included in haplotypes and groups based on the sequence analysis of the 200-bp intron that also included isolates capable of causing bitter rot only. Additionally, isolates of G. cingulata from the United States and Brazil which cause GLS were included in different haplotypes and sequence analysis groups. Therefore, one hypothesis is that isolates of G. cingulata from the United States capable of causing both GLS on foliage and bitter rot on fruit may have arisen independently of Brazilian isolates of G. cingulata capable of causing both GLS and bitter rot, and the two groups of isolates may represent distinct populations.

Management of Sclerotinia Blight of Peanut with the Biological Control Agent Coniothyrium minitans

ABSTRACT Sooty blotch disease of apples (Malus x domestica), previously attributed to the fungus Gloeodes pomigena, was shown to be a disease complex caused by fungi previously considered mycelial types of G. pomigena. Peltaster fructicola and Geastrumia polystigmatis were associated with the ramose mycelial type. A fungus similar to P. fructicola, but with smaller pycnothyria and conidia, was associated with the punctate mycelial type. The diffuse fuliginous mycelial type was caused by Leptodontium elatius. Fungi that fit the classical morphological description of G. pomigena were not observed. Pycnothyria of P. fructicola developed on overwintered colonies on blackberries, and conidia were a source for primary infection during the entire growing season. Secondary spread was through conidia produced in colonies on fruit. L. elatius was observed infrequently producing conidia on fruit during periods of extended high moisture. Histological examination did not reveal penetration of the cuticle of apple fruit for any of the fungi of the apple sooty blotch complex.

Characterization of benomyl resistance in Mycosphaerella fijiensis, cause of black Sigatoka of banana, in Costa Rica

Sclerotinia blight, caused by Sclerotinia minor, is an important disease of peanut in North Carolina. The effectiveness of Coniothyrium minitans, a mycoparasite of sclerotia of Sclerotinia spp., was studied in a 5-year field experiment and in eight short-term experiments in northeastern North Carolina. The 5-year experiment was initiated in November 1999 to evaluate the effectiveness of repeated soil applications of C. minitans (commercial formulation, Contans WG) at 2 and 4 kg ha-1 in reducing Sclerotinia blight. In addition, individual commercial peanut fields were selected in 2001 and 2002 to evaluate a single application of C. minitans at 4 kg ha-1. No differences were found between the 2 and 4 kg ha-1 rates of C. minitans in reducing Sclerotinia blight. In 2002, there was less disease in plots receiving applications of C. minitans for either 1 or 3 years compared with the nontreated control; whereas, in 2003, C. minitans applications for 1, 2, or 3 years reduced disease and the number of sclerotia isolated from soil. A single application of C. minitans reduced sclerotia in only two of the eight short-term experiments. The integration of consecutive years of soil applications of C. minitans at 2 kg ha-1 with moderately resistant cultivars and fungicide applications may aid in the management of Sclerotinia blight in peanut.