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Krishna V. Subbarao - One of the best experts on this subject based on the ideXlab platform.

  • a single recessive gene conferring short leaves in romaine latin type lettuce lactuca sativa l crosses and its effect on plant morphology and resistance to lettuce drop caused by Sclerotinia Minor jagger
    Plant Breeding, 2011
    Co-Authors: Ryan J Hayes, Krishna V. Subbarao
    Abstract:

    With 1 figure and 5 tables Abstract Understanding the relationship between plant morphology and disease resistance is crucial to successful lettuce breeding. Latin type cultivars are a potential useful source of resistance to Sclerotinia Minor for breeding resistant romaine cultivars. However, resistance in Latin cultivars may be conditioned by their relatively short stature. The objective of this research was to determine the segregation for plant height and the relationship between plant height and S. Minor resistance in romaine × Latin crosses. The frequency of short plants was conditioned by a single recessive gene in F1, F2 and F3 families from nine romaine × Latin crosses tested in 2007, 2008 and 2009 field experiments. The gene, named short leaf 1 (sl1), affects only leaf length in rosette plants and is morphologically distinct from other dwarfing genes. In two S. Minor-infested field experiments with 75 F3 romaine × ‘Eruption’ families, no difference in disease incidence was detected between short (sl1sl1), tall (Sl1Sl1) or segregating families. Therefore, development of resistant romaine cultivars from crosses with ‘Eruption’ is feasible.

  • reduced efficacy of rovral and botran to control Sclerotinia Minor in lettuce production in the salinas valley may be related to accelerated fungicide degradation in soil
    Crop Protection, 2010
    Co-Authors: Susanne Klose, S T Koike, Husein A Ajwa, Krishna V. Subbarao
    Abstract:

    Abstract Accelerated soil degradation with repeated application was suggested to be responsible for the lack of efficacy of commercial fungicides to control lettuce drop caused by Sclerotinia Minor in the Salinas Valley in California. In 2000, a study was initiated in a field artificially infested with S. Minor to evaluate the efficacy and degradation potential of four selected fungicides (i.e., Rovral, Botran, Switch, and Endura). Crisphead lettuce was direct-seeded twice a year (spring and fall season) from 2000 to 2002. Fungicides were applied at recommended label rates twice during each season. Disease incidence was evaluated in fungicide treatments and nontreated control plots weekly starting immediately after thinning until harvest, and areas under the disease progress curves (AUDPC) were compared between treatments from 2000 to 2002. Soil samples (0–15 cm) were collected at regular intervals during the spring and fall 2002 lettuce seasons, and analyzed for residual fungicide concentration. Disease progress and final disease incidence were significantly affected by the fungicide treatment, season, year and interactions among these factors (p

  • mustard and other cover crop effects vary on lettuce drop caused by Sclerotinia Minor and on weeds
    Plant Disease, 2009
    Co-Authors: Tiffany Bensen, Krishna V. Subbarao, S T Koike, Richard Smith, Steven A Fennimore, Shachar Shemtov
    Abstract:

    Mustard cover crops have been suggested as a potential biofumigant for managing soilborne agricultural pests and weeds. We conducted several experiments in commercial lettuce fields in the Salinas Valley, CA, to evaluate the effects of mustard cover crops on lettuce drop caused by Sclerotinia Minor and on weed density and seed viability. In a long-term study, we measured the effects of white and Indian mustard cover crops on the density of S. Minor sclerotia in soil, lettuce drop incidence, weed densities, weed seed viability, and crop yield in head lettuce. We also tested broccoli and rye cover crop treatments and a fallow control. Across several short-term studies, we evaluated the density of S. Minor sclerotia in soil, lettuce drop incidence, weed densities, and weed seed viability following cover cropping with a mustard species blend. Numbers of sclerotia in soil were low in most experimental locations and were not affected by cover cropping. Mustard cover crops did not reduce disease incidence in the long-term experiment but the incidence of lettuce drop was lower in mustard-cover-cropped plots across the short-term experiments. With the exception of common purslane and hairy nightshade, weed densities and weed seed viability were not significantly reduced by cover cropping with mustard. Head lettuce yield was significantly higher in mustard-cover-cropped plots compared with a fallow control. Glucosinolate content in the two mustard species was similar to those measured in other studies but, when converted to an equivalent of a commercial fumigant, the concentrations were much lower than the labeled rate for lettuce production. Although mustard cover cropping resulted in yield benefits in this study, there was little to no disease or weed suppression.

  • comparative survival of sclerotia of Sclerotinia Minor and s sclerotiorum
    Phytopathology, 2008
    Co-Authors: Krishna V. Subbarao, Y B Liu
    Abstract:

    Wu, B. M., Subbarao, K. V., and Liu, Y.-B. 2008. Comparative survival of sclerotia of Sclerotinia Minor and S. sclerotiorum. Phytopathology 98:659-665. Survival of sclerotia of Sclerotinia Minor and S. sclerotiorum was compared in irrigated fields during the summer in two major lettuce production areas in California. More than 50% sclerotia of S. sclerotiorum compared with 4 and 35% of S. Minor remained viable after 24 weeks of burial at 15 and 5 cm depths, respectively, in the San Joaquin Valley while >80% of sclerotia survived in the Salinas Valley for both species. The results explain in part the lower infections from S. Minor in the San Joaquin Valley. To identify factors that contribute to the rapid decline in the viability of sclerotia, the effects of soil moisture, temperature, and oxygen levels were studied in laboratory. More than 90% of sclerotia of both species survived for at least 3 months in sterilized dry soils at temperatures between 15 and 40°C. Soil moisture did not affect survival at 15 and 25°C. At 35°C, however, survival rates were significantly lower at high (–0.3 to –0.01 MPa) water potential than at low (<–1.0 MPa) water potential. Incubation under ultralow oxygen concentration (0.01%) significantly reduced survival of sclerotia in nonautoclaved moist soils at 25°C, with less than 2% sclerotia surviving over 4 weeks compared with about 45% sclerotia surviving at the ambient oxygen level (21%). The combination of high temperature, high soil moisture, and reduced oxygen in irrigated fields contribute to the lower survival of both Sclerotinia species and the responses of the two species to these conditions shape their relative geographical distribution.

  • dynamics of lettuce drop incidence and Sclerotinia Minor inoculum under varied crop rotations
    Plant Disease, 2006
    Co-Authors: Jianjun Hao, Krishna V. Subbarao
    Abstract:

    Field experiments were conducted to determine the population dynamics of Sclerotinia Minor and incidence of lettuce drop at two sites during 1995 to 1998. Rotation treatments at the Spence site, which had a low density of inoculum ( 7 sclerotia per 100 cm3 of soil) that was distributed uniformly, included: continuous lettuce (LLLL), alternate crops of broccoli and lettuce (BLBL), continuous broccoli or lettuce (BBLL), and fallow-lettuce-fallow-lettuce (FLFL). Under continuous lettuce cropping (LLLL) at the Hartnell site, a progressively aggregated spatial pattern of inoculum distribution developed, despite the initial uniform distribution of high inoculum density. In the fallow treatment (FLFL), the spatial pattern tended to be aggregated following a lettuce crop and less aggregated or random when left fallow. In contrast to these two treatments, treatments involving rotations with broccoli (BLBL and BBLL) exhibited consistently random spatial patterns of inoculum regardless of the crop in the field. The marginal increases in the number of sclerotia contributed by the few diseased lettuce plants were offset by the significant reductions in the number of sclerotia by the broccoli residue. Spatial patterns of disease incidence reflected the pattern of inoculum distribution in the soil at the Hartnell site. Higher inoculum density coupled with an aggregated distribution was associated with an aggregation in disease incidence. At Spence, this correlation was poor in most seasons because of progressive decline in the lettuce drop incidence and lack of treatment differences. In greenhouse experiments, the competence volume for S. Minor sclerotia was quantified, which was calculated to be 25 3 for 100% infection and 200 cm3 for 50% infection. Thus, in 100 cm3 of soil, a minimum of four to five sclerotia are needed for 100% of infection, explaining the high correlation between inoculum density and disease incidence.

S T Koike - One of the best experts on this subject based on the ideXlab platform.

  • first report of white mold caused by Sclerotinia Minor on mexican sunflower in california
    Plant Disease, 2013
    Co-Authors: S T Koike
    Abstract:

    Mexican sunflower (Tithonia rotundifolia) is a plant in the Asteraceae that is grown commercially as a cutflower commodity and also as a beneficial insectary plant. In June 2012 in coastal California (Santa Cruz County), several fields of organic lettuce (Lactuca sativa) were interplanted with direct-seeded rows of Mexican sunflower (cv. Torch) in order to attract beneficial insects. When approximately 2 to 3 weeks from harvest, lettuce plants began to wilt and collapse. Lettuce crowns were decayed and covered with white mycelium and small (0.5 to 3 mm diameter), irregularly shaped, black sclerotia. These plants were confirmed to have lettuce drop disease caused by Sclerotinia Minor (2). In addition, Mexican sunflower plants began to wilt and eventually died. Initial symptoms on crowns and bases of the main stems in contact with soil consisted of a light tan discoloration. These discolored areas turned darker brown, became necrotic, and later were covered with white mycelium and sclerotia that were identical to those found on lettuce. Symptomatic sunflower stems were surface disinfested and small pieces from the margins of necrotic areas were placed into petri plates containing acidified potato dextrose agar. Resulting fungal colonies were white, produced profuse numbers (approx. 39 sclerotia/cm2) of small black sclerotia, and were identified as S. Minor. Six-week-old Mexican sunflower plants grown in a peat moss-based rooting medium in 5-cm square pots were used to test the pathogenicity of four isolates. Isolates were grown on cubed and autoclaved potato pieces and resulting sclerotia were recovered and dried (1). For each isolate, 12 plants for each of three cultivars (cvs. Fiesta del Sol, Torch, and Yellow Torch) were inoculated by placing 3 to 5 sclerotia 1 cm below the soil level and adjacent to the plant crowns/stem bases. Sterile sand was placed next to crowns of the control plants. Plants were maintained in a greenhouse at 22 to 24°C. Symptom development was rapid and after 6 to 7 days, inoculated Tithonia plants exhibited brown necrosis at inoculated areas. After 10 days, Tithonia crowns were decayed and plants wilted. S. Minor was reisolated from selected necrotic crown and stem tissues. Diseased plants that were not used for reisolations later supported the growth of the characteristic white mycelium and black sclerotia. There were no significant differences between the Tithonia cultivars, and overall disease incidence ranged from 74 to 100%. Non-inoculated plants were asymptomatic. The experiment was repeated and results were similar. In addition, the sclerotia of the four Tithonia isolates were similarly inoculated onto sets of 12 romaine lettuce plants (cv. Green Towers). After 5 to 6 days, all plants developed lettuce drop disease and the pathogen was reisolated. To my knowledge, this is the first report of Mexican sunflower as a host of S. Minor. These findings indicate that Mexican sunflower and lettuce are susceptible to the same lettuce drop pathogen, and that this beneficial insectary plant could increase soilborne inoculum of S. Minor. Growers should therefore be aware of the host status of beneficial insectary and other plants interplanted with crops. References: (1) P. Chitrampalam et al. Phytopathology 101:358, 2011. (2) K. V. Subbarao. Plant Dis. 82:1068, 1998.

  • reduced efficacy of rovral and botran to control Sclerotinia Minor in lettuce production in the salinas valley may be related to accelerated fungicide degradation in soil
    Crop Protection, 2010
    Co-Authors: Susanne Klose, S T Koike, Husein A Ajwa, Krishna V. Subbarao
    Abstract:

    Abstract Accelerated soil degradation with repeated application was suggested to be responsible for the lack of efficacy of commercial fungicides to control lettuce drop caused by Sclerotinia Minor in the Salinas Valley in California. In 2000, a study was initiated in a field artificially infested with S. Minor to evaluate the efficacy and degradation potential of four selected fungicides (i.e., Rovral, Botran, Switch, and Endura). Crisphead lettuce was direct-seeded twice a year (spring and fall season) from 2000 to 2002. Fungicides were applied at recommended label rates twice during each season. Disease incidence was evaluated in fungicide treatments and nontreated control plots weekly starting immediately after thinning until harvest, and areas under the disease progress curves (AUDPC) were compared between treatments from 2000 to 2002. Soil samples (0–15 cm) were collected at regular intervals during the spring and fall 2002 lettuce seasons, and analyzed for residual fungicide concentration. Disease progress and final disease incidence were significantly affected by the fungicide treatment, season, year and interactions among these factors (p

  • mustard and other cover crop effects vary on lettuce drop caused by Sclerotinia Minor and on weeds
    Plant Disease, 2009
    Co-Authors: Tiffany Bensen, Krishna V. Subbarao, S T Koike, Richard Smith, Steven A Fennimore, Shachar Shemtov
    Abstract:

    Mustard cover crops have been suggested as a potential biofumigant for managing soilborne agricultural pests and weeds. We conducted several experiments in commercial lettuce fields in the Salinas Valley, CA, to evaluate the effects of mustard cover crops on lettuce drop caused by Sclerotinia Minor and on weed density and seed viability. In a long-term study, we measured the effects of white and Indian mustard cover crops on the density of S. Minor sclerotia in soil, lettuce drop incidence, weed densities, weed seed viability, and crop yield in head lettuce. We also tested broccoli and rye cover crop treatments and a fallow control. Across several short-term studies, we evaluated the density of S. Minor sclerotia in soil, lettuce drop incidence, weed densities, and weed seed viability following cover cropping with a mustard species blend. Numbers of sclerotia in soil were low in most experimental locations and were not affected by cover cropping. Mustard cover crops did not reduce disease incidence in the long-term experiment but the incidence of lettuce drop was lower in mustard-cover-cropped plots across the short-term experiments. With the exception of common purslane and hairy nightshade, weed densities and weed seed viability were not significantly reduced by cover cropping with mustard. Head lettuce yield was significantly higher in mustard-cover-cropped plots compared with a fallow control. Glucosinolate content in the two mustard species was similar to those measured in other studies but, when converted to an equivalent of a commercial fumigant, the concentrations were much lower than the labeled rate for lettuce production. Although mustard cover cropping resulted in yield benefits in this study, there was little to no disease or weed suppression.

  • Sclerotinia petiole and crown rot of celery caused by Sclerotinia Minor in california
    Plant Disease, 2006
    Co-Authors: S T Koike, Oleg Daugovish, J A Downer
    Abstract:

    Celery (Apium graveolens) is grown extensively in the coastal counties (Ventura, Santa Barbara, San Luis Obispo, Monterey, and Santa Cruz) of California. In 2004 and 2005, field plantings of celery in Ventura and Monterey counties showed symptoms of a petiole and crown rot. Initial symptoms consisted of a light tan discoloration at the crowns and on outer petioles that were in contact with soil. These discolored areas developed a soft, brown, watery rot. Affected petioles wilted and later collapsed. White mycelium and small (0.5 to 3.0 mm in diameter), irregularly shaped, black sclerotia formed on diseased tissues. Isolations from symptomatic petioles, crowns, mycelium, and sclerotia produced colonies of Sclerotinia Minor. Eight-week-old celery transplants (cv. Conquistador) grown in a peat-moss based rooting medium in 10-cm2 pots were used to test pathogenicity. Colonized agar plugs (one plug per plant) from eight celery isolates were inserted into slots made in the potting mix adjacent to the crowns and lower petioles of the transplants. Noncolonized plugs were placed in slots for control celery plants. Twenty plants were used for each isolate and control, and all test plants were incubated in a greenhouse at 21 to 23°C. Disease development was rapid, and after 4 days, inoculated celery plants exhibited brown necrosis at inoculation points. After 9 days, celery crowns were decayed and petioles collapsed. S. Minor was reisolated from necrotic crown and petiole tissues. Noninoculated plants were asymptomatic. The experiment was repeated and results were similar. To our knowledge, this is the first report of celery as a host of S. Minor in California (2). In the United States, S. Minor has been reported on celery in Florida (1). Celery in California is only occasionally infected by S. Minor and is more often infected by S. sclerotiorum. Reference: (1) D. F. Farr et al. Fungi on Plants and Plant Products in the United States. The American Phytopathological Society. St. Paul, MN, 1989. (2) M. S. Melzer et al. Can. J. Plant Pathol. 19:272, 1997.

  • effects of broccoli rotation on lettuce drop caused by Sclerotinia Minor and on the population density of sclerotia in soil
    Plant Disease, 2003
    Co-Authors: Jianjun Hao, Krishna V. Subbarao, S T Koike
    Abstract:

    Field experiments were conducted at Spence Road site and at the Hartnell College East Campus site in Salinas, CA, to determine the effects of crop rotation with broccoli or a fallow period on lettuce drop caused by Sclerotinia Minor and the density of pathogen sclerotia in the soil. Treatments at the Spence Road site with low inoculum density ( 7 sclerotia per 100 cm3 of soil) distributed uniformly included: continuous lettuce (LLLL), broccoli-lettuce-broccoli-lettuce (BLBL), broccoli-broccoli-lettuce-lettuce (BBLL), and fallow-lettuce-fallow-lettuce (FLFL). At the Spence Road site, continuous lettuce did not increase lettuce drop incidence for at least 2 years, although an increase in soilborne sclerotia was observed annually but was below the threshold at which a correlation between inoculum density and disease incidence is observed. Rotation with broccoli resulted in small reductions in disease incidence only in the first year. The density of sclerotia was lowest in the LFL treatment, and the highest in the LLL. At the Hartnell site, rotation with broccoli significantly reduced both sclerotia and lettuce drop incidence. The number of broccoli crops rather than the sequence of lettuce rotations with broccoli was critical for reducing the numbers of S. Minor sclerotia in soil. Fallowing after a lettuce crop resulted in marginal reductions in sclerotia and lettuce drop incidence. Viability of recovered sclerotia was not significantly different between treatments, although differences between seasons were detected. Results suggest that rotations with broccoli can be a practical lettuce drop management strategy.

B B Shew - One of the best experts on this subject based on the ideXlab platform.

  • analysis of factors that influence the epidemiology of Sclerotinia Minor on peanut
    Plant Disease, 2006
    Co-Authors: Damon L Smith, J. E. Hollowell, Thomas G. Isleib, B B Shew
    Abstract:

    ABSTRACT In North Carolina, sclerotia of Sclerotinia Minor germinate myceliogenically to initiate infections on peanut. The effects of soil temperature and soil matric potential (ψM on germination and growth of S. Minor have not been well characterized, and little is known about relative physiological resistance in different parts of the peanut plant. Laboratory tests examined the ability of the fungus to germinate, grow, and infect detached peanut leaflets at soil temperatures ranging from 18 to 30°C at ψM of -100, -10, and -7.2 kPa. In addition, detached pegs, leaves, main stems, and lateral branches from three peanut lines varying in field resistance were examined for resistance to infection by S. Minor. Sclerotial germination was greatest at 30°C and ψM of -7.2 kPa. Final mycelial diameters decreased with decreasing ψM, whereas soil matric potential did not affect lesion development. Mycelial growth and leaflet lesion expansion were maximal at 18 or 22°C. Soil ψM did not affect leaflet infection and l...

  • first report of Sclerotinia Minor on sida spinosa in north carolina
    Plant Disease, 2005
    Co-Authors: J. E. Hollowell, B B Shew
    Abstract:

    The soilborne fungus Sclerotinia Minor Jagger is a major pathogen of peanut (Arachis hypogaea L.) in North Carolina, Virginia, Oklahoma, and Texas. The pathogen attacks several winter annual weed species (1). Economic crops that are hosts to S. Minor are seldom grown in rotation with peanut; therefore, its pathogenicity on weed species is of importance in understanding how inoculum densities are maintained between peanut crops. During September 2004, signs of fluffy, white mycelium, small, black sclerotia, and symptoms of bleached leaves and stems were observed on prickly sida (Sida spinosa L.) in a peanut field in Bertie County, NC. Plants of prickly sida with similar signs and symptoms were observed previously in a Chowan County, NC peanut field. Prickly sida is one of several weed species commonly found in peanut fields and rotational crops in agricultural areas of northeastern North Carolina. Cultivation and herbicides usually keep prickly sida under control in the early part of the growing season, but as the summer progresses into early fall, it can become prevalent, as was true in the two fields reported here. Symptomatic tissues were excised into 1- to 2-cm sections, rinsed in tap water, blotted dry, and placed on potato dextrose agar (PDA). The pure cultures with small, black irregular-shaped sclerotia (<2 mm) scattered abundantly over the culture surface were distinctive of S. Minor. Pathogenicity was determined by inoculating stems of two symptom-free prickly sida plants with 2-day-old fungal mycelium. Mycelial agar plugs, 4 mm in diameter, were held in place with self-sticking bandaging gauze. Plants were misted, enclosed in plastic bags, and incubated at ambient temperature (24°C) on the laboratory countertop. Fluffy mycelium developed on the stems in 2 days and water-soaked leaves and bleached lesions formed within 6 days after inoculation. Following the incubation period, S. Minor was reisolated from the inoculated plants. Two plants treated similarly with plugs of pure PDA remained healthy over the incubation period. The performance of Koch's postulates confirmed that prickly sida is a host of S. Minor. To our knowledge, this report of S. Minor on prickly sida is also the first report of a plant in the family Malvaceae as a host of S. Minor (2). Reference: (1) J. E. Hollowell et al. Plant Dis. 87:197, 2003. (2) M. S. Melzer et al. Can. J. Plant Pathol. 19:272, 1997.

  • first report of Sclerotinia Minor on allium vineale in north carolina
    Plant Disease, 2005
    Co-Authors: J. E. Hollowell, B B Shew
    Abstract:

    Allium vineale L. (wild garlic) is a bulbous perennial that emerges in early spring in many agricultural fields. The soilborne fungus Sclerotinia Minor Jagger is a major pathogen found in many peanut (Arachis hypogaea L.) production areas of northeastern North Carolina. During September 2002, symptoms of bleached, water-soaked foliage and wilting were observed on several wild garlic plants growing in a 0.8-ha (2-acre) peanut research plot in Perquimans County, NC. We had previously observed similar symptoms on wild garlic at another location. Two symptomatic wild garlic plants were collected from the field. In the laboratory, symptomatic tissues were excised into 1- to 2-cm sections, rinsed in tap water, towel dried, and placed on potato dextrose agar (PDA) for fungal isolation and identification. Pure cultures with small, black, irregular-shaped sclerotia (<2 mm) scattered abundantly over the culture surface were distinctive of S. Minor. Pathogenicity of isolates was tested by inoculating leaf blades nea...

  • first report of stem and leaf blight caused by Sclerotinia Minor on geranium carolinianum in north carolina
    Plant Disease, 2004
    Co-Authors: J. E. Hollowell, B B Shew
    Abstract:

    The soilborne fungus Sclerotinia Minor Jagger is a major pathogen of peanut (Arachis hypogaea L.) in North Carolina and overwinters in soil, on crop debris, or on winter annual weed species (1). Bleached stems and small, black sclerotia are typically seen on peanut plants infected by S. Minor. Carolina geranium (Geranium carolinianum L.) is one of several winter annual weed species found during winter fallow in peanut production areas of northeastern North Carolina. During a March 2002 survey of previously harvested peanut fields, plants of Carolina geranium were observed with typical signs and symptoms of infection caused by S. Minor. Symptomatic plants with bleached stems and signs of small, black sclerotia were collected in the field and returned to the laboratory. Pathogen isolation and fungal identification were performed from the symptomatic tissues by placing 1- to 2-cm sections of stems on potato dextrose agar after rinsing with tap water and towel drying. Pure cultures of S. Minor were obtained and observed to have white, fluffy mycelium and small, black irregular-shaped sclerotia (<2 mm) produced abundantly and scattered over the culture surface. Pathogenicity was tested by inoculating stems of three symptom-free Carolina geranium plants with 2-day-old fungal mycelium from pure isolation. Mycelial agar plugs, 4 mm in diameter, were held in place with self-sticking bandaging gauze. Plants were misted, enclosed in plastic bags, and incubated at ambient temperature (24°C) on the laboratory counter top. Bleached water-soaked lesions developed on the stems, and leaves became chlorotic after 8 days. Following 8 days of incubation, S. Minor was reisolated from all inoculated plants. Three noninoculated plants remained healthy over the incubation period. The performance of Koch's postulates confirmed that Carolina geranium is a host of S. Minor. To our knowledge, this is the first report of S. Minor on G. carolinianum. These results indicate that G. carolinianum is a potential overwintering host for S. Minor in peanut fields. Infected weed hosts allow reproduction of the fungus in the winter, potentially resulting in more disease on peanut planted in the spring. Reference: (1) J. E. Hollowell et al. Plant Dis. 87:197, 2003.

  • evaluating isolate aggressiveness and host resistance from peanut leaflet inoculations with Sclerotinia Minor
    Plant Disease, 2003
    Co-Authors: J. E. Hollowell, B B Shew, Thomas G. Isleib
    Abstract:

    ABSTRACT Sclerotinia Minor is a major pathogen of peanut in North Carolina, Virginia, Oklahoma, and Texas. Partial resistance to S. Minor has been reported based on field screening, but field performance is not always correlated with laboratory or greenhouse evaluations of resistance. More efficient screening methods and better understanding of the mechanisms contributing to Sclerotinia blight resistance are needed, and a detached leaf assay was developed and evaluated. Detached leaflets of 12 greenhouse-grown peanut lines were inoculated on the adaxial surface with a 4-mm-diameter mycelial plug of a single isolate of S. Minor. Leaflets were incubated in the dark at 20°C in Nalgene utility boxes containing moistened sand. Lesion length 3 days after inoculation ranged from 11 to 24 mm, with a mean of 19 mm. Lengths differed significantly among the entries, with GP-NC WS 12, an advanced breeding line derived from a cross of NC 6 × (NC 3033 × GP-NC WS 1), being the most resistant. Forty-eight isolates of S. ...

Alan K. Watson - One of the best experts on this subject based on the ideXlab platform.

  • Development of strain specific molecular markers for the Sclerotinia Minor bioherbicide strain IMI 344141
    Biocontrol Science and Technology, 2010
    Co-Authors: L. Pan, Gavin Ash, Byeongseok Ahn, Alan K. Watson
    Abstract:

    Abstract The plant pathogenic fungus, Sclerotinia Minor IMI 344141, has been developed as a bioherbicide for broadleaf weed control in turfgrass and a means to differentiate this biocontrol agent from like organisms is required. A strain specific molecular marker was developed to detect and monitor the Sclerotinia Minor IMI 344141 bioherbicide strain. The method was based on polymerase chain reaction (PCR) amplification of two sequence-characterized amplified regions (SCAR) primer pairs for a first round PCR, and another two sets of nested primers was used for a second round PCR if higher sensitivity was needed. Sclerotinia Minor IMI 344141 was successfully traced from both pure cultures and environmental samples originating from bioherbicide-released field trials. DNA of the S. Minor bioherbicide isolate IMI 344141 was detected in the soil 2 months after application, but was not detected in the 3- and 9-month samples after application. When applied as a bioherbicide, S. Minor (IMI 344141) did not persist...

  • RESEARCH ARTICLE Development of strain specific molecular markers for the Sclerotinia Minor bioherbicide strain IMI 344141
    2010
    Co-Authors: L. Pan, Alan K. Watson
    Abstract:

    The plant pathogenic fungus, Sclerotinia Minor IMI 344141, has been developed as a bioherbicide for broadleaf weed control in turfgrass and a means to differentiate this biocontrol agent from like organisms is required. A strain specific molecular marker was developed to detect and monitor the Sclerotinia Minor IMI 344141 bioherbicide strain. The method was based on polymerase chain reaction (PCR) amplification of two sequence-characterized amplified regions (SCAR) primer pairs for a first round PCR, and another two sets of nested primers was used for a second round PCR if higher sensitivity was needed. Sclerotinia Minor IMI 344141 was successfully traced from both pure cultures and environmental samples originating from bioherbicide-released field trials. DNA of the S. Minor bioherbicide isolate IMI 344141 was detected in the soil 2 months after application, but was not detected in the 3- and 9-month samples after application. When applied as a bioherbicide, S. Minor (IMI 344141) did not persist into the following spring season in turf environments. This molecular detection method provides a mechanism to distinguish this isolate from related organisms and a tool to monitor behavior of the biocontrol agent S. Minor IMI 344141 in nature, particularly in soil.

  • effect of plant age and turfgrass competition on the efficacy of the Sclerotinia Minor granular bioherbicide on broadleaf plantain and prostrate knotweed
    Biocontrol Science and Technology, 2010
    Co-Authors: Mohammed H Abudieyeh, Inaam Y Shaheen, Alan K. Watson
    Abstract:

    Abstract Broadleaf plantain and prostrate knotweed are important weeds of turfgrass systems. The fungus Sclerotinia Minor Jagger (IMI 344141) has been registered as a biological herbicide (Sarritor™) for dandelion (Taraxacum officinale) in Canadian turfgrass habitats. The objective of this study was to evaluate the effect of plant age and turfgrass environment on the efficacy of S. Minor against two additional weeds; broadleaf plantain and prostrate knotweed. The turfgrass environment alone exerted significant reduction of above and below ground biomass of broadleaf plantain, to the same magnitude as the S. Minor treatment in a grass-free environment. Prostrate knotweed biomass, however, was not reduced to this extent by competition with turfgrass. In the presence of grass, S. Minor caused a significant biocontrol effect on all studied variables with more than 90% above ground damage on both weed species. Severe damage occurred on 3–6-week-old plantains with 100% above and below ground reduction, although...

  • physiological characterization of the dandelion bioherbicide Sclerotinia Minor imi 344141
    Biocontrol Science and Technology, 2010
    Co-Authors: Inaam Y Shaheen, Gavin Ash, Mohammed H Abudieyeh, Alan K. Watson
    Abstract:

    Abstract The fungus Sclerotinia Minor (IMI 344141) is being developed as a biological control for dandelion and other broadleaf weeds in turfgrass environments. Being a microbial pest control agent (MPCA), the S. Minor strain must be characterized to show relatedness to like organisms and to distinguish the MPCA from related microorganisms. Phenotypic variation among 30 isolates of S. Minor, collected from different regions and hosts, was studied on potato dextrose agar (PDA) and oatmeal agar (OMA). Isolates varied significantly in sclerotia shape (length/width ratio) and number, but did not vary in colony morphology or growth rates. There was high diversity (0.6) among the mycelial compatibility groups (MCG) as seven multi-member and 11 single member groups were recognized. Isolates were categorized into highly virulent, virulent, moderately virulent, and hypo virulent based on 48 h post mycelial growth on detached dandelion leaves. When assessed on dandelion plants in the greenhouse, isolate IMI 344141 ...

  • efficacy of Sclerotinia Minor for dandelion control effect of dandelion accession age and grass competition
    Weed Research, 2007
    Co-Authors: Mohammed H Abudieyeh, Alan K. Watson
    Abstract:

    Summary Control of Taraxacum officinale (common dandelion) and other broad-leaved weeds in temperate turfgrass has been readily achieved with phenoxy herbicides. The herbicide option has been revoked through municipal and provincial legislation in many regions of Canada, necessitating alternative approaches. We examined the effects of dandelion accessions, age and grass competition on the performance of Sclerotinia Minor (IMI 344141) as a biological control for dandelion in turfgrass. Disease symptoms were identical on all 14 different accessions of dandelion and the above- and below-ground biomass were reduced by 94% and 96%, respectively, with no difference among accessions. Foliar damage and dandelion mortality caused by S. Minor was affected by plant age and the presence of grass competition. Dandelions of all ages were more severely affected by S. Minor in the presence of grass competition. Grass competition had greater impact on foliar biomass, whereas the fungus had a greater impact on root biomass of newly established dandelions. In addition to competition for resources, we were hypothesised that the grass sward provides a microenvironment favouring the success of S. Minor as a biological control agent of dandelion. Thus, proper management of the turfgrass environment may be complementary to the efficacy of S. Minor as a biocontrol for dandelion.

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  • optimizing fungicide inputs for management of lettuce drop caused by Sclerotinia Minor and s sclerotiorum
    Plant Health Progress, 2019
    Co-Authors: Michael E Matheron, Martin Porchas
    Abstract:

    Lettuce drop, caused by the soilborne fungi Sclerotinia Minor and S. sclerotiorum, continues to be an important disease on this crop in Arizona. Trials were conducted over a 5-year period to compar...

  • impact of summer flooding on viability of Sclerotinia Minor and s sclerotiorum sclerotia in soil
    Plant Health Progress, 2018
    Co-Authors: Michael E Matheron, Martin Porchas
    Abstract:

    Lettuce drop, caused by the soilborne fungi Sclerotinia Minor and S. sclerotiorum, is an important and destructive disease of lettuce. Research trials in Arizona have shown that some fungicides, su...

  • influence of soil temperature and moisture on eruptive germination and viability of sclerotia of Sclerotinia Minor and s sclerotiorum
    Plant Disease, 2005
    Co-Authors: Michael E Matheron, Martin Porchas
    Abstract:

    ABSTRACT The effect of soil temperature and moisture on eruptive germination and viability of sclerotia of Sclerotinia Minor and S. sclerotiorum in field soil was examined. In two trials at constant temperatures, the proportion of sclerotia of both pathogens that germinated in wet soil ( ≥-0.02 MPa) tended to decrease as soil temperature increased from 15 to 40°C, with no germination of sclerotia of S. Minor and S. sclerotiorum detected after 1 and 2 weeks, respectively, at 40°C. In contrast, after 1 to 4 weeks in dry soil ( ≤-100 MPa) at 40°C, germination of sclerotia of S. Minor and S. sclerotiorum ranged from 28 to 55% and 42 to 77%, respectively. In field trials, the germination rate of sclerotia of S. Minor and S. sclerotiorum after 2 to 8 weeks in irrigated soil on the surface or buried at a depth of 5 cm was significantly lower than that for sclerotia maintained in dry soil at the same depths. On the other hand, after burial at a depth of 10 cm, germination of sclerotia in irrigated and dry soil di...

  • influence of soil temperature and moisture on eruptive germination and viability of sclerotia of Sclerotinia Minor and s sclerotiorum
    Plant Disease, 2005
    Co-Authors: Michael E Matheron, Martin Porchas
    Abstract:

    Matheron, M. E., and Porchas, M. 2005. Influence of soil temperature and moisture on eruptive germination and viability of sclerotia of Sclerotinia Minor and S. sclerotiorum. Plant Dis. 89:5054. The effect of soil temperature and moisture on eruptive germination and viability of sclerotia of Sclerotinia Minor and S. sclerotiorum in field soil was examined. In two trials at constant temperatures, the proportion of sclerotia of both pathogens that germinated in wet soil (≥–0.02 MPa) tended to decrease as soil temperature increased from 15 to 40°C, with no germination of sclerotia of S. Minor and S. sclerotiorum detected after 1 and 2 weeks, respectively, at 40°C. In contrast, after 1 to 4 weeks in dry soil (≤–100 MPa) at 40°C, germination of sclerotia of S. Minor and S. sclerotiorum ranged from 28 to 55% and 42 to 77%, respectively. In field trials, the germination rate of sclerotia of S. Minor and S. sclerotiorum after 2 to 8 weeks in irrigated soil on the surface or buried at a depth of 5 cm was significantly lower than that for sclerotia maintained in dry soil at the same depths. On the other hand, after burial at a depth of 10 cm, germination of sclerotia in irrigated and dry soil did not differ significantly after 2 to 8 weeks for S. Minor and after 2, 4, and 8 weeks for S. sclerotiorum. For both pathogens, germination of sclerotia from 2 to 8 weeks in irrigated soil with a mean temperature of 32°C was significantly lower than that for sclerotia in irrigated soil with a mean temperature of 26°C. In microplot trials conducted in July and August, no sclerotia of S. Minor and S. sclerotiorum germinated after 2 and 3 weeks, respectively, after recovery from flooded soil with mean soil temperatures ranging from 30 to 33°C. A flood irrigation is often applied to fields for salt management during July or August in the Yuma lettuce production region. Results from these studies suggest that maintaining this flooding event for 2 to 3 weeks in fields with a history of lettuce drop caused by S. Minor and S. sclerotiorum could significantly reduce the population of viable sclerotia.

  • activity of boscalid fenhexamid fluazinam fludioxonil and vinclozolin on growth of Sclerotinia Minor and s sclerotiorum and development of lettuce drop
    Plant Disease, 2004
    Co-Authors: Michael E Matheron, Martin Porchas
    Abstract:

    ABSTRACT Sclerotinia drop is a major disease of lettuce caused by two soilborne fungi, Sclerotinia Minor and S. sclerotiorum. Fungicides such as dicloran (Botran), iprodione (Rovral), and vinclozolin (Ronilan) are currently available in the United States to manage this disease. Studies were conducted to investigate the relative effect of some new fungicides, including boscalid, fenhexamid, fluazinam, and fludioxonil, in comparison with vinclozolin, on growth of S. Minor and S. sclerotiorum in agar plate tests as well as control of lettuce drop in the field. At a rate of 0.001 μg/ml, all tested compounds only suppressed mycelial growth of either pathogen from 0 to 20%. At 0.01 μg/ml, mycelial growth of S. Minor was reduced 82 to 84% by fludioxonil and fluazinam and only 1 to 16% by boscalid, fenhexamid, and vinclozolin. At the same rate, mycelial growth of S. sclerotiorum was reduced 78% by fluazinam and from 0 to 12% by boscalid, fludioxonil, fenhexamid, and vinclozolin. At 0.1 μg/ml, all tested chemistri...