John E. Kaminski

Water deficit effects on potato leaf growth and transpiration: Utilizing fraction extractable soil water for comparison with other crops

Numerous studies have demonstrated that physiological responses of many crops to the fraction of extractable soil water conforms to a generalizable pattern. This suggests that differences among crops in their drought tolerance are largely due to differences in the total amount of transpirable water the crop can extract. Potato is frequently assumed to be more drought sensitive than other agronomic crops due, at least in part, to a shallow root system. In the research reported here, potato leaf growth and transpiration response to water deficits were determined as a function of fraction transpirable soil water (FTSW). Transpiration was unaffected by water stress until a critical FTSW was achieved when 64% to 80% of the extractable soil water was depleted depending on the cultivar. This was similar to the response reported for 8 other agronomic crops. In terms of transpiration, potato hypersensitivity to drought stress appears to be due to less effective soil water extraction. Leaf growth, however, showed a unique response to soil water deficits. Leaf growth began to decline when 40% of the extractable soil water was depleted. The associated critical FTSW was higher than any previously reported for all other crops. These data indicate that in addition to extracting less soil water, an additional physiological process related to leaf expansion must be contributing to the potato’s hypersensitivity to drought.CompendioNumerosos estudios han demostrado que las respuestas fisiológicas de muchos cultivos a la fracción extraíble de agua del suelo se comporta de una manera posible de generalizarse. Esto sugiere que las diferencias entre sus tolerancias a la sequía son debidas considerablemente a las diferencias en la cantidad total de agua de transpiración que el cultivo puede extraer. Se considera frecuentemente que la papa es más sensible a la sequía que otros cultivos debido, al menos en parte, a un sistema radicular superficial. En la investigación sobre la que aquí se informa, se determinaron las respuestas del crecimiento de las hojas y de la transpiración a los déficits de agua, como una función de la fracción transpirable del agua del suelo (FTSW). La transpiración no fue afectada por el estrés al agua hasta que era alcanzada una FTSW crítica, cuando se consumía del 64% al 80% del agua extraíble del suelo, dependiendo del cultivar. Esto fue similar a la respuesta reportada para otros ocho cultivos. En términos de transpiración, la hipersensibilidad de la papa al estrés a la sequía parece deberse a una extracción menos efectiva del agua del suelo. El crecimiento de las hojas, sin embargo, mostró una respuesta poco común a los déficits de agua en el suelo. El crecimiento de las hojas empezó a declinar cuando se consumió el 40% del agua extraíble del suelo. La FTSW crítica asociada fue mayor que en cualquier otro informe anterior sobre todos los otros cultivos. Esta información indica que además de extraer menos agua del suelo, un proceso fisiológico adicional relacionado a la expansión foliar debe estar contribuyendo a la hipersensibilidad de la papa a la sequía.

Geographic Distribution of Fungicide-Insensitive Sclerotinia homoeocarpa Isolates from Golf Courses in the Northeastern United States

Chemical management of dollar spot in turf may lead to the development of Sclerotinia homoeocarpa populations with reduced fungicide sensitivity. The objective of this study was to determine the scope of S. homoeocarpa insensitivity to fungicides commonly used to control dollar spot on golf courses in the northeastern United States. A total of 965 and 387 isolates of S. homoeocarpa from intensively or individually sampled sites, respectively, were evaluated for in vitro sensitivity to iprodione, propiconazole, and thiophanate-methyl. Mean baseline sensitivities to iprodione and propiconazole were 0.2763 and 0.0016 μg a.i. ml-1, respectively, and all baseline isolates were sensitive to thiophanate-methyl at 1,000 μg a.i. ml-1. When compared with the baseline population, 14 and 18 of 20 total populations were less sensitive to iprodione and propiconazole, respectively. Individually sampled isolates obtained from fairways, putting greens, or tees were less sensitive to iprodione and propiconazole when compared with the baseline. For thiophanate-methyl, five populations were sensitive, six were resistant, and the remaining nine populations contained various proportions (2 to 92%) of resistant isolates. Individually sampled isolates obtained from fairways and putting greens were evaluated for associations in sensitivity among the three fungicides. A weak but positive correlation in sensitivity to iprodione and propiconazole was observed for isolates resistant to thiophanate-methyl but correlations for sensitive isolates were not significant. Furthermore, isolates with highly reduced sensitivity to iprodione clustered in a narrow range of propiconazole sensitivity. These data suggest the possible existence of resistance mechanisms common to diverse fungicide classes. Overall, results indicate that insensitivity of S. homoeocarpa to iprodione, propiconazole, and thiophanate-methyl exists in varying degrees on golf courses in the northeastern United States.

Creeping Bentgrass Tolerance and Annual Bluegrass Control With Bispyribac-Sodium Tank- Mixed With Iron and Nitrogen

Annual bluegrass (Poa annua L.) (ABG) is considered by many turfgrass managers to be an intractable weed problem, particularly in creeping bentgrass (Agrostis stolonifera L.) (CBG) fairways. Bispyribac-sodium (BPS) is labeled for the control of ABG, but it can elicit objectionable levels of chlorosis in CBG. Little information exists regarding the longevity of chlorosis, other potential phytotoxic effects or the ability of BPS to control ABG in CBG. The primary objectives of this field study were to determine if the chlorosis elicited by BPS could be masked by tank-mixing the herbicide with a chelated iron plus nitrogen product and to determine an effective BPS rate for controlling ABG. Bispyribac-sodium was applied to mature fairway height CBG three times at 49 and 111 g ai/ha and two or three times at 74 g ai/ha on a two-week interval. Chlorosis appeared within one week and generally persisted for 14 to 21 days, but there was no BPS rate effect on the level or longevity of the CBG chlorosis. Tank-mixing BPS with Fe + N effectively masked the chlorosis, regardless of herbicide rate. All BPS rates and timing provided similar levels (≥ 82%) of ABG control.

Reactivation of Bentgrass Dead Spot and Growth, Pseudothecia Production, and Ascospore Germination of Ophiosphaerella agrostis

Ophiosphaerella agrostis incites bentgrass dead spot (BDS) of creeping bentgrass. Little is known about the biology of O. agrostis; hence the primary goal of this study was to determine some basic biological properties of the pathogen and epidemiological components of the disease. Winter-dormant creeping bentgrass field samples showing symptoms of BDS were incubated at temperatures ranging from 15 to 30°C. Between 12 and 28 days of incubation, reactivation of BDS symptoms occurred at temperatures ≥20°C, but the greatest expansion in BDS patch diameter occurred at 25 and 30°C. The optimum temperatures for growth of hyphae among 10 O. agrostis isolates ranged from 25 to 30°C, and growth was suppressed at 35°C. Pseudothecia of O. agrostis were produced in vitro on a mixture of tall fescue seed and wheat bran. Pseudothecia developed under constant fluorescent light at 13 to 28°C, but no pseudothecia developed in darkness at any temperature. Pseudothecia developed in as few as 4 days, but the highest numbers appeared about 30 days after incubation began. Ascospores incubated at 25°C germinated in as little as 2 h, with germ tubes generally emerging from the terminal rather than interior cells of ascospores. Germination during the first 4 h of incubation was enhanced by both light and the presence of bentgrass leaves or roots. After 18 h of incubation, however, there were few differences in the percentage of ascospores germinated regardless of light treatment or presence of plant tissue.

Geographic Distribution, Cultivar Susceptibility, and Field Observations on Bentgrass Dead Spot

Bentgrass dead spot (BDS) is a disease of creeping bentgrass incited by Ophiosphaerella agrostis. This project was designed to determine the susceptibility of field-grown bentgrass cultivars to BDS and to gather information regarding the geographic distribution and field conditions favoring the disease. In a field cultivar evaluation trial, all major Agrostis spp. used on golf courses, including colonial, creeping, and velvet bentgrasses, were shown to be susceptible to an isolate of O. agrostis. Velvet bentgrass cvs. SR7200 and Bavaria were among the most and least susceptible cultivars, respectively. Among creeping bentgrass cultivars, L-93 generally was the most susceptible and Pennlinks, Penncross, and Crenshaw were among the least susceptible. Although recovery of BDS patches in the autumn was slow, Bardot colonial bentgrass and Crenshaw, Imperial, L-93, and Penn G-6 creeping bentgrasses showed the most rapid recovery prior to winter. Variation in the virulence of isolates and the potential for races of the pathogen, however, may affect cultivar susceptibility. The disease was most commonly found on 1- to 4-year-old golf greens and disease severity declined 1 to 3 years after it first appeared. BDS only was found on sand-based greens, collars, and tees and has not been observed in bentgrass grown on native soil. Between 1998 and 2001, O. agrostis was isolated from diseased leaves, roots, crowns, and stolons of creeping bentgrass and hybrid bermudagrass turf samples received from 13 states. The disease was most severe in sunny and exposed locations, especially on ridges, mounds, and slopes. In the mid-Atlantic region, BDS appeared as early as May and remained active as late as December. The disease was most active in July and August, and usually became inactive with the advent of frost in October.

Geographic Distribution and rDNA-ITS Region Sequence Diversity of Waitea circinata var. circinata Isolated from Annual Bluegrass in the United States

Waitea circinata var. circinata is the causal agent of brown ring patch, an emergent disease of turfgrass in the United States. Forty-two isolates from annual bluegrass were obtained from California, Connecticut, Idaho, Illinois, Massachusetts, New York, Ohio, Oregon, and Rhode Island. Almost all isolates produced white to orange sclerotia (bulbils), 2 to 5 mm in size, that turned dark brown after 21 days on ¼-strength potato dextrose agar. The ribosomal DNA internal transcribed spacer regions and 5.8S region (ITS) were analyzed by restriction fragment length polymorphism (RFLP) analysis using MspI and sequencing to attempt identification of the isolates. Some isolates were heterozygous at the MspI restriction site, results not found in previous reports using the RFLP technique for identification. Four additional nucleotide positions were found to be variable within ITS based on sequence analysis, including two indels and two additional heterozygous positions. A total of 17 ITS haplotypes were found, and there was no obvious relationship between ITS haplotype and the geographic distribution of the isolates. Results of this work indicate that W. circinata var. circinata is present in multiple states and provide an initial understanding of the diversity of the pathogen in the United States.

A PCR-Based Method for the Detection of Ophiosphaerella agrostis in Creeping Bentgrass

Dead spot is a relatively new disease of creeping bentgrass and hybrid bermudagrass that is incited by Ophiosphaerella agrostis. Initial symptoms are difficult to diagnose and clinicians generally rely on the presence of pseudothecia within infected tissue or isolation of O. agrostis on an artificial medium. The main goal of this study was to develop a polymerase chain reaction-based technique capable of quickly identifying O. agrostis within infected creeping bentgrass tissues. Oligonucleotide primers specific for O. agrostis were developed based on the internal transcribed spacer (ITS) rDNA regions (ITS1 and ITS2) of three previously sequenced isolates of O. agrostis. The 22-bp primers amplified a 445- or 446-bp region of 80 O. agrostis isolates collected from creeping bentgrass and bermudagrass in 11 states. Primers did not amplify DNA from other common turfgrass pathogens, including three closely related species of Ophiosphaerella. Selective amplification of O. agrostis was successful from field-infected creeping bent-grass samples and primers did not amplify the DNA of noninfected, field-grown creeping bent-grass or hybrid bermudagrass plants. Amplification of purified O. agrostis DNA was successful at quantities between 50 ng and 5 pg. The entire process, including DNA isolation, amplification, and amplicon visualization, may be completed within 4 h. These results indicate the specificity of these primers for assisting in the accurate and timely identification of O. agrostis and the diagnosis of dead spot in both bentgrass and bermudagrass hosts.

Environmental Influences on the Release of Ophiosphaerella agrostis Ascospores Under Controlled and Field Conditions.

ABSTRACT Ophiosphaerella agrostis, the causal agent of dead spot of creeping bentgrass (Agrostis stolonifera), can produce prodigious numbers of pseudothecia and ascospores throughout the summer. The environmental conditions and seasonal timings associated with O. agrostis ascospore release are unknown. The objectives of this research were to (i) determine the influence of light and relative humidity on ascospore release in a controlled environment, (ii) document the seasonal and daily discharge patterns of ascospores in the field, and (iii) elucidate environmental conditions that promote ascospore release under field conditions. In a growth chamber, a sharp decrease (100 to approximately 50%; 25 degrees C) in relative humidity resulted in a rapid (1- to 3-h) discharge of ascospores, regardless of whether pseudothecia were incubated in constant light or dark. In the field, daily ascospore release increased between 1900 and 2300 h and again between 0700 and 1000 h local time. The release of ascospores occurred primarily during the early morning hours when relative humidity was decreasing and the canopy began to dry, or during evening hours when relative humidity was low and dew began to form. Few ascospores were released between 1100 and 1800 h when the bentgrass canopy was dry. The release of ascospores also was triggered by precipitation. Of the ascospores collected during precipitation events, 87% occurred within 10 h of the beginning of each event.

Effects of Dew Removal and Mowing Frequency on Fungicide Performance for Dollar Spot Control

Dollar spot (Sclerotinia homoeocarpa) is a severe disease problem on creeping bentgrass (Agrostis stolonifera) fairways. The objective of this study was to evaluate the effects of dew removal and mowing frequency on fungicide performance for dollar spot control. In 2009 and 2010, an experiment involving daily dew removal or no dew removal, mowing frequency (2, 4, and 6 days week-1), and fungicides (chlorothalonil, propiconazole, and iprodione) was conducted on creeping bentgrass maintained as a fairway. Daily dew removal resulted in fewer dollar spot infection centers (IC) compared with not removing dew during late summer 2009 and 2010 for all mowing-frequency and fungicide treatments. As mowing frequency increased from 2 to 6 days week-1, dollar spot IC decreased when averaged across all fungicide treatments. For all fungicides, daily dew removal increased the number of days needed to reach a 15-IC plot-1 point of reference when compared with fungicide treatments in which dew was not removed. The number of days required to reach 15 IC varied with fungicide, mowing frequency, and year the test was conducted. Results demonstrate that dollar spot control with fungicides can be extended when daily dew removal is employed and, in some cases, when mowing frequency is increased on dew-covered turf. Benefits of dew-removal practices on dollar spot and fungicide performance can vary with weather conditions, fungicide, threshold level, and possibly other factors.

Environmental Monitoring and Exploratory Development of a Predictive Model for Dead Spot of Creeping Bentgrass

Dead spot of creeping bentgrass is incited by Ophiosphaerella agrostis. The objectives of this 3-year field study were to: (i) elucidate environmental conditions associated with the expression of dead spot symptoms, (ii) develop a model to assist in predicting the appearance of dead spot symptoms and epidemics in creeping bentgrass, and (iii) elucidate the association between ascospore release and the appearance of new dead spot symptoms. Environmental parameters measured included relative humidity (RH), air (AT) and soil (ST) temperatures, solar irradiance (SOL), precipitation and irrigation (RAIN), and leaf wetness duration (LWD). Dead spot symptoms generally did not occur at temperatures (air or soil) below 15°C. Two descriptive models were developed that predicted the appearance of dead spot symptoms with an accuracy of 74 to 80%. Between 1 May and 31 October 2000 to 2002, the appearance of new dead spot infection centers was most accurately predicted (80%) by the single parameter of STMean ≥ 20°C. In years with severe levels of dead spot, the occurrence of major infection events was predicted on 37 of 40 days (93%). A combination of elevated air (ATMax ≥ 27°C) and soil (STMean ≥ 18°C) temperatures, low relative humidity (RHMean ≤ 80%), shortened periods of leaf wetness (LWD ≤ 14 h), and high levels of solar radiation (SOLMean ≥ 230 W m-2) were associated with the development of major dead spot epidemics. Ascospore discharge and the appearance of new infection centers occurred in a cyclic pattern that peaked about every 12 days. New infection centers appeared 3 to 10 days after the release of a large number of ascospores.