Sclerotinia Blight Research Articles

Greenhouse Testing of Transgenic Peanut for Resistance to Sclerotinia minor

Abstract Fungal diseases of peanut, such as Sclerotinia blight caused by Sclerotinia minor Jagger, are responsible for increased production costs and yield losses of up to 50% for peanut producers in the Southwest, North Carolina, and Virginia. A few cultivars with moderate disease resistance, such as Southwest Runner, have been developed through traditional breeding practices. An urgent need exists for developing peanut cultivars that are resistant to the broad spectrum of fungal pathogens that pose a recurring threat to peanut health. Transgenic peanut plant lines containing anti-fungal genes have been produced from somatic embryos of the susceptible cultivar Okrun and tested under greenhouse conditions for resistance to S. minor by inoculation with a mycelial plug. Disease symptoms of lesion length and vascular collapse were recorded for 30 transgenic peanut lines, non-transgenic Okrun, and Southwest Runner. The reaction of the majority of transgenic peanut lines to S. minor infection was indistinguishable from that of the susceptible cultivar Okrun. However, three transgenic lines had a significant increase in resistance to S. minor as compared to Okrun, and one line demonstrated levels of resistance comparable to the moderately resistant cultivar Southwest Runner.

An Algorithm for Predicting Outbreaks of Sclerotinia Blight of Peanut and Improving the Timing of Fungicide Sprays.

Algorithms were evaluated for computing disease risk and improving the timing of fungicide applications for control of Sclerotinia blight of peanut. Disease risk was calculated by multiplying indices of moisture, soil temperature, vine growth, and canopy density each day, and summing values for the previous 5 days to obtain a 5-day risk index (FDI). After fungicide application, the FDI was reset to zero for 3 weeks. Fluazinam at 0.58 kg a.i./ha applied at FDI 24 or 32 in 1994 and 1995 suppressed disease and increased yield as much as or more than programs of weekly scouting and applying fungicide at the initial onset of disease with additional sprays at 3- to 4-week intervals. The FDI algorithm was also more efficient than calendar sprays at 60, 90, and 120 days after planting (DAP). Environmental and host parameters were expanded in 1996 and 1997 by adding new temperature and new vine growth indices. These parameters along with DAP-dependent thresholds consistently improved the timing of fungicide sprays and disease management when using the FDI algorithm in comparison to weekly scouting or calendar sprays at 60, 90, and 120 DAP.

Wheat Straw Mulch and Its Impacts on Three Soilborne Pathogens of Peanut in Microplots.

Experiments were conducted in 1992, 1993, and 1994 to determine the effects of surface residue on incidence of Cylindrocladium black rot (CBR), Sclerotinia blight, and Southern stem rot of peanut in microplots in North Carolina. Soil was infested with either Cylindrocladium parasiticum, Sclerotium rolfsii, or Sclerotinia minor and plots were planted with the peanut cultivars NC 7 or NC 10C. Wheat straw was applied to establish 80 to 90% soil-surface coverage. Disease incidence data were collected every 2 weeks in 1992 and weekly in 1993 and 1994. Southern stem rot incidence did not increase with straw amendment but final inoculum density of Sclerotium rolfsii was highest in straw-amended plots. Straw amendment enhanced CBR incidence in 1992, but had minimal effects in 1993 and 1994. Neither root rot severity nor inoculum density of C. parasiticum was affected by straw treatment. Straw application reduced Sclerotinia blight in 1992 and 1993 but not in 1994 compared with unamended plots. Initial inoculum density had the greatest impact on final Sclerotinia minor populations. Soil temperature and moisture were monitored in 1993 and 1994. Soil at 0 to 2 cm of depth in strawamended microplots was 1 to 2°C cooler than in unamended plots.

Effects of Application Method and Rate on Control of Sclerotinia Blight of Peanut with Iprodione and Fluazinam1

Abstract Two trials with iprodione and three trials with fluazinam were conducted to assess the effects of application method and rate on the control of Sclerotinia blight of peanut with fungicide. In order to concentrate the fungicides near the crown area where the disease causes the most damage, applications were made through a canopy opener with a single nozzle centered over the row to achieve a 30.5-cm-wide band (canopy opener), and through a single nozzle centered over the row to achieve a 46-cm-wide band (band). Broadcast applications were compared to these methods at rates of 0, 0.28, 0.56, and 1.12 kg/ha on the susceptible cultivar Okrun. Sclerotinia blight was severe, with > 70% disease incidence and < 2000 kg/ha yield for the untreated controls in each trial. Linear reductions in area under the disease progress curve (AUDPC), but not final disease incidence, with iprodione rate were significant (P < 0.05) for all methods of application. However, the rate of decrease did not differ among application methods. Linear increases in yield with rate of iprodione were greater for canopy opener compared to the band or broadcast applications. Only a 50% reduction in AUDPC and a maximum yield of < 2700 kg/ha was achieved with iprodione using the best method. At the maximum rate of 1.12 kg/ha, fluazinam provided > 75% disease control and > 4000 kg/ha yield for all application methods. Differences in disease control and yield among application methods only occurred at the 0.28 and 0.56 kg/ha rates of fluazinam. Reductions in AUDPC with fluazinam rate were quadratic for all application methods, but AUDPC values were less for the canopy opener and band methods at 0.28 and 0.56 kg/ha compared to the broadcast methods. The yield response to rate for broadcast applications of fluazinam was linear. However, predicted yield responses to fluazinam rate were quadratic for the band and canopy opener methods and approached the maximum response at 0.84 kg/ha. Targeting fungicide applications using the band and/or canopy opener methods was beneficial for fluazinam at reduced rates. Disease control with iprodione was not adequate regardless of application method.

First Report of Occurrence of Sclerotinia Blight on Petunia in Louisiana.

Petunia × hybrida Wave series cultivars were observed with symptoms of tan to brown stem lesions, wilt, and branch death in a demonstration/trial planting at Burden Research Center in Baton Rouge, LA, during January and February 2000. Disease signs included the presence of white, cottony mycelia on infected stems and the presence of black sclerotia. Seventeen of 131 plants were infected on 20 February and included individuals of cvs. Wave Purple, Wave Rose, Wave Misty Lilac, Wave Pink, Tidal Wave Hot Pink, and Tidal Wave Cherry. Isolations were made by placing diseased stem sections on acidified potato-dextrose agar. A fungus that produced white mycelia and black sclerotia was consistently isolated from infected stems and identified as Sclerotinia sclerotiorum. Pathogenicity tests were done by pipetting 1 to 2 ml of blended mycelia and sclerotia (one plate culture blended in 100 ml distilled water) at the base of flowering-age Wave series plants. Plants were held for 3 days in a dew chamber maintained at 22°C and then moved to a greenhouse held at 25°C. Wilt and branch death developed on inoculated plants after 5 days and S. sclerotiorum was reisolated. Uninoculated plants remained healthy. Wave series cultivars have a prostrate growth habit that is conducive to disease development. No plants in the trial planting were killed and infected plants had recovered by 1 May and had uniformly covered the plant bed. Sclerotinia blight was previously reported on Petunia × hybrida from Bermuda (2) and Florida (1).

Effects of root inoculation and fungicide soil drenches on sclerotinia blight of coneflower

Greenhouse studies showed that root inoculation had significant effects on sclerotinia blight (Sclerotinia sclerotiorum) of coneflower (Echinacea sp.). Seedling wilt and root rot symptoms caused by S. sclerotiorum were most severe when inoculum was placed in direct contact with seedling roots, and diminished as the distance of the inoculum from the roots increased. When colonized agar disks, colonized oat grains and sclerotia as inoculum sources were evaluated on E. angustifolia, grain inoculum was the most virulent and sclerotia the least. An in vitro bioassay was conducted, and a logistic dose-response model was developed for the fungicides benomyl, vinclozolin, iprodione and dicloran. The first three fungicides were further evaluated in greenhouse experiments. Benomyl was the most effective in controlling S. sclerotiorum in both bioassay and greenhouse evaluations. The same three fungicides were evaluated in two field experiments in Alberta, where all were effective in reducing disease incidence. Key words: Echinacea sp., Sclerotinia sclerotiorum, dose-response model

Evaluation of fungicides for the management of sclerotinia blight of peanut

Three trials were conducted in the Burnett region of southern Queensland, Australia, in the 1993–94 and 1994–95 seasons to determine the efficacy of fluazinam, procymidone, and iprodione for managing sclerotinia blight of peanut. Different combinations of rates, nozzle types, and spraying times were used in each trial. Two or 3 sprays of fluazinam at 0.75 and 1.0 kg a.i./ha, and of procymidone at 0.688 and 0.75 kg a.i./ha, were the most effective combinations that reduced disease incidence and increased yield. Iprodione at rates up to 0.5 kg a.i./ha did not significantly improve the yield compared with unsprayed treatments in any trial. In one trial at Tingoora in 1994–95, pre-infection treatments in which the first spray of fluazinam or procymidone was applied before symptoms appeared were more effective than post-infection treatments in which the first spray was applied soon after symptoms were seen. At J. Bjelke-Petersen Research Station (JBPRS) in 1994–95, a banded spray of procymidone at 0.688 kg a.i./ha using a single flat-fan 8004VB nozzle centred over the row significantly increased yield and reduced disease incidence compared with a spray using 3 hollow-cone nozzles (HB4-70) per row, with 1 nozzle over the row and 1 drop nozzle on each side of the row directed at the bases of the plants. At JBPRS in 1993–94, a band spray of fluazinam at 0.333 kg a.i./120 L.ha, applied with a single flat-fan 80015EVB nozzle immediately after the appearance of symptoms, was as effective in reducing the rate of disease development for 3 weeks, as was a directed application using three 80015EVB nozzles at the same time and concentration, but at 3 times the rate per area (1.0 kg a.i./360 L.ha).

Abstracts, Saskatchewan-Alberta Regional Meeting, The Canadian Phytopathological Society, 1998

Abstracts, Saskatchewan-Alberta Regional Meeting, The Canadian Phytopathological Society, 1998

Integrated Management of Sclerotinia Blight in Peanut: Utilizing Canopy Morphology, Mechanical Pruning, and Fungicide Timing.

Sclerotinia blight of peanut, caused by Sclerotinia minor, generally becomes severe only after vines meet in the row middles and a dense canopy develops. Dense foliage appears to support a microclimate conducive to the colonization of peanut limbs by S. minor. Removal of excess foliage before and during a Sclerotinia blight epidemic on the susceptible genotype NC 7 has been shown to reduce the rate of disease progress. Field tests in 1993 and 1994 examined control of Sclerotinia blight among four peanut genotypes (NC 7, VA 93B, NC Ac 18016, and Tam-span 90) with diverse canopy morphologies. Each cultivar had foliage pruned with a rotary mower once (1993 and 1994) or twice (1994) during the season. Applications of fluazinam (9.2 kg a.i./ha) were imposed on the genotype × pruning treatments. Soil temperatures under the canopy of each genotype and pruning treatment were measured and compared. Disease data were collected weekly by counting the number of feet of plants exhibiting lesions with visible fungus growth. Tamspan 90, a resistant Spanish peanut, had the least Sclerotinia blight incidence. Pruning measurably affected soil temperature for approximately 2 weeks following pruning. Removal of foliage reduced disease and increased disease control affected by fluazi-nam in fields with high disease pressure. In some tests, yields were increased by pruning through a reduction in disease pressure. Yields were lower when peanuts were pruned excessively, especially late in the season. Pruning of excessive vine growth can be an alternative, or complement, to fungicide treatments when done in midseason during favorable weather when moderate to high disease pressure occurs.

Effect of Crop Pruning on Sclerotinia Blight of Peanut.

Sclerotinia blight of peanut, incited by Sclerotinia minor, causes serious losses when cool, moist conditions prevail in the plant canopy. The effects of altering canopy structure by pruning were investigated in this study. Disease incidence was used to calculate area under the disease progress curve (AUDPC) for field plots receiving various shoot-pruning treatments. In 1990, pruned plots and iprodione-sprayed plots did not differ in AUDPC, but pruned plots produced higher yields. Disease levels and yield of July top-pruned plants did not differ from those of August top-pruned plants. Pruning tops and sides in August reduced yields compared to pruning tops and sides in July, even though August pruning produced lower AUDPC. Without fungicide treatment, the 1991 pruned plots had less disease than nonpruned plots, although yields did not differ significantly. Pruned plots treated with fungicides for control of Sclerotinia blight had less disease than nonpruned plots treated with these fungicides, but there were no differences in yield. Pruning peanut canopies to alter microclimate or enhance fungicide penetration may reduce disease and increase yield when S. minor damage is yield limiting.

Weather-Based Crop and Disease Advisories for Peanuts in Virginia.

orld peanut production averages 23 million metric tons from harvest of approximately 20 million hectares on six continents (2). India, China, and the United States produced 70% of the world’s peanuts in 1990 and 1991. Production in the United States is concentrated in the southeast (Georgia, Florida, and Alabama), southwest (Texas and Oklahoma), and the mid-Atlantic region (Virginia, North Carolina, and South Carolina). Peanuts are grown in sandy-textured soils in warm, moist climates having a growing season of 140 or more days. Southeastern Virginia provides an excellent environment for commercial production, as evidenced by high yield and quality dating back to the Civil War (8). Today, the industries of producing, shelling, and processing peanuts are major pillars of the economy in southeastern Virginia. These industries are concentrated in an eight-county area, where the value of the crop to growers often ranges from $80 to $102 million, as in 1994 and 1990, respectively. Unfortunately, the warm and moist climate necessary for peanut production makes fungal diseases a chronic threat to profits. The rapid spread and the unforgiving nature of early leaf spot, caused by Cercospora arachidicola S. Hori, have earned the respect of growers in Virginia and around the world. Peanut growers are also keenly aware of soilborne diseases caused by fungi such as Sclerotinia minor Jagger (Sclerotinia blight), Sclerotium rolfsii Sacc. (southern stem rot), and Cylindrocladium parasiticum Crous, Wingfield & Alfenas (Cylindrocladium black rot). In 1990 and 1991, a systematic survey of peanut growers in southeastern Virginia was conducted to evaluate their perception of losses of yield to specific diseases and the use of pesticides (11; P. M. Phipps, unpublished). Sclerotinia blight and southern stem rot were named most frequently as responsible for yield losses exceeding 10% (Table 1). Sclerotinia blight was considered by the highest percentage of growers to be the most damaging disease. Clinical records, on-farm tests, and reports by extension agents and specialists supported these estimates, except for the claims of yield losses to southern stem rot. In this case, it was thought that the growers’ estimate of losses may have been excessive and possibly reflected some confusion with Sclerotinia blight. Peanuts require intensive management because of the crop’s vulnerability to yield losses caused by diseases, insects, and weeds. Chemicals play a major role in pest management strategies for peanut production due to the limited availability of acceptable alternatives. Based on the 1990 survey of peanut growers in Virginia, the input of pesticide active ingredients (a.i.) totaled 747 t and averaged 19 kg/ha (Table 2). The cost of these materials averaged $293 per ha. With the dramatic increase in the use of metam sodium for control of Cylindrocladium black rot (CBR) in 1991, the estimated input of pesticide a.i. totaled 970 t and averaged 25 kg/ha at a cost of $322 per ha. Metam sodium accounted for 36% of the total a.i. and 9% of cost. Chemicals for disease management alone accounted for 37 and 42% of the total cost of pesticides for production in 1990 and 1991, respectively. Recent changes in government programs (1) that control production quotas and prices growers receive for U.S. peanuts were expected to cause up to a 10% reduction in acreage and a 10% reduction in

Diseases of groundnut in the Southern African Development Community (SADC) region and their management

Groundnut is an important food and cash crop in the Southern African Development Community (SADC) region, and is grown largely by smallholder farmers under low input conditions. Constraints are many and varied, both between and within the member states, but diseases are generally regarded as major constraints to groundnut production throughout the region. A large number of fungal, viral, nematode, and bacterial diseases of groundnut have been reported. Most of the diseases are widespread, but only a few of them are economically important on a regional basis. In this paper, the current distribution and economic importance of leaf spots, web blotch, rust, gray mould, pod rots, blackhull, Sclerotinia blight, stem rot, seedling diseases, aflatoxin contamination, rosette, groundnut streak necrosis, pod nematode, and pod scab nematode diseases, and various options (chemical control, host-plant resistance and cultural practices) for their management, are briefly reviewed. Future research needs on groundnut diseases in the region are discussed.

DEVELOPMENT AND IMPLEMENTATION OF A BULLETIN BOARD SYSTEM FOR INFORMATION TRANSFER TO THE VIRGINIA PEANUT AND COTTON INDUSTRY

The Peanut/Cotton InfoNet, an electronic bulletin board system (BBS), was established at the TidewaterAgricultural Research and Extension Center for the distribution of weather and crop information in southeastern Virginia.EnviroCaster (Neogen Corp., Lansing, Mich.) weather stations collected data and provided daily weather summaries,peanut leaf spot advisories, sclerotinia blight advisories and heat unit reports for peanut and cotton. Collected dataincluded air temperature, wet bulb temperature, soil temperature at 5 (2 in.) and 10 cm (4 in.) depths, relative humidity,and rainfall. A data processing computer collected, processed, archived, and transferred useful information to the BBScomputer. Frost advisories, corn earworm reports, and updates concerning cultural practices and pesticiderecommendations were also available on the BBS. Wildcat! software provided the user-friendly BBS interface. TheInfoNet BBS system including eight weather stations, a BBS computer, and data processing computer cost $52,366.48.The system logged 984 calls and 1678 system downloads from county agent, grower, industry, and unspecified users in1995. The BBS was offered to county agents from 15 May to 31 October and to the general public from 24 August through31 October.

An Assessment of Environmental Conditions Preceding Outbreaks of Sclerotinia Blight of Peanut in Virginia1

Abstract Records of outbreaks of Sclerotinia blight of peanut at the Tidewater Center in Suffolk were summarized over a 16-yr period (1978–93). Initial outbreaks of the disease were determined through intensive scouting of fields at weekly intervals. First occurrences of Sclerotinia blight occurred between 10 July and 7 Sept., or 62 to 120 d after planting (DAP). The mean and median dates of initial outbreaks were 28 July (79 DAP) and 25 July (76 DAP), respectively. The initial onset of disease always occurred after vines were within 15 cm of touching between rows or after vines had lapped between rows. Under these conditions, a canopy of dense foliage shaded the soil surface and infection sites inside rows from direct sunlight. Rainfall summaries showed the heaviest accumulations were from 6 to 15 d before disease outbreaks. Maximum and minimum air temperatures over the 15-d period prior to disease onset averaged ca. 32 C and 20 C, respectively. Maximum and minimum soil temperatures at the 10-cm depth averaged ca. 30 and 25 C, respectively, during this same period. The results of this study provide evidence that vine growth and rainfall are primary determinants in triggering the onset of Sclerotinia blight of peanut in southeastern Virginia.

Fluazinam: A New Fungicide for Control of Sclerotinia Blight and Other Soilborne Pathogens of Peanut1

Abstract Fluazinam provided effective control of Sclerotinia blight (Sclerotinia minor Jagger) of peanut in six field trials during a 4-yr period. Applications of fluazinam (0.56 kg/ha) at the onset of Sclerotinia blight and 4 wk later provided an average of 69% suppression of disease incidence and increased yields by 1598 kg/ha compared to untreated plots. Performance of fluazinam was significantly better than iprodione, the material currently used for control of Sclerotinia blight. Two applications of iprodione at 1.12 kg/ha provided only 31% suppression of disease incidence and increased yield by 718 kg/ha. Fungicides were also evaluated in 1990 as tank-mixes with chlorothalonil (1.26 kg/ha) that were applied in foliar sprays according to the Virginia peanut leafspot advisory program. Treatments consisted of no fungicide, chlorothalonil alone, and tank-mixes of chlorothalonil plus either dicloran at 2.10 kg/ha, fluazinam at 0.56 kg/ha, or iprodione at 0.84 kg/ha. Sclerotinia blight at harvest in untreated plots and plots treated with chlorothalonil alone averaged 27.8 and 35.8 disease foci per plot, whereas yields averaged 3624 and 2251 kg/ha, respectively. Compared to plots treated with chlorothalonil alone, Sclerotinia blight was suppressed by 92, 25, and 25%, and yield was increased by 4020, 1925, and 1684 kg/ha in plots treated with chlorothalonil plus either fluazinam, iprodione, or dicloran, respectively. Applications of tank-mixes containing fluazinam plus chlorothalonil in 1991 provided additional evidence that this approach was a highly effective means of controlling both Sclerotinia blight and early leafspot, a previously unattainable goal. Fluazinam did not control early leafspot (Cercospora arachidicola S. Hori) in field trials; however, the fungicide was fungitoxic in vitro to Sclerotium rolfsii Sacc. and Rhizoctonia solani Kühn.

Resistance to Sclerotinia Blight and Early Leafspot in Chinese Peanut Germplasm1

Abstract Sclerotinia minor, causal agent of Sclerotinia blight, and Cercospora arachidicola, causal agent of early leafspot, are two of the most important pathogens of peanut (Arachis hypogaea L.) in Virginia and North Carolina. Twenty-two Chinese peanut germplasm lines were screened to identify resistance to these two pathogens, and evaluated for agronomic characteristics including seed size, testa color, and pod yield. Germplasm lines with PI numbers 476824 and 476843 exhibited more resistance to S. minor than other Chinese plant introductions, or the U.S. cultivars Florigiant and VA 81B. PI 476823 and PI 476837 were most resistant to C. arachidicola. Resistance to one pathogen was often associated with high levels of susceptibility to the other pathogen. Resistance to S. minor was also associated with undesirable characteristics for large-seeded virginia-type peanuts such as tan testa color and small seed size.

Evaluation of Ammonium Bicarbonate for Control of Soilborne Peanut Pathogens

Abstract Ammonium bicarbonate was evaluated for efficacy against southern stem rot and Sclerotinia blight of peanut in Georgia and Virginia, respectively. In vitro studies indicated the material provided little inhibition of mycelial growth by Sclerotinia minor and Sclerotium rolfsii, and negligible inhibition of mycelial growth of Rhizoctonia solani AG-4. However, ammonium bicarbonate did effectively inhibit formation of sclerotia by S. rolfsii in vitro. In the field, it was phytotoxic when applied as a granule or as a foliar spray and in general was not effective in controlling disease or increasing pod yield.

A Rapid Method for Evaluating Genotype Resistance, Fungicide Activity, and Isolate Pathogenicity of Sclerotinia minor in Peanut.1

Abstract Peanut stem segments 8.5-cm long were inoculated at leaf nodes with mycelial plugs of Sclerotinia minor and incubated in moist chambers at 20 C. Water-soaked lesions were often visible after 24 hr. The rate of lesion elongation was used to quantitatively assess the physiological resistance of peanut genotypes to Sclerotinia blight, screen chemicals for fungicidal activity, and evaluate the pathogenicity of S. minor isolates. The age and/or developmental state of lateral limbs of plants had a marked effect on lesion development; 3 days after inoculation, mean lesion lengths were 58.8, 46.8, and 38.9 mm for terminal, median and basal parts of stems, respectively. The speed, simplicity and adaptability of this method make it a valuable tool for research on Sclerotinia blight of peanut.

Effects of Modification of the Plant Canopy Environment on Sclerotinia Blight of Peanut

Abstract The development of Sclerotinia blight, caused by Sclerotinia minor Jagger under various environmental conditions, was studied in field plots of peanuts (Arachis hypogaea L.). The peanut plant canopy was modified to produce desired environmental parameters. The modifications included the thinning of canopy foliage to allow air circulation that would decrease canopy humidity and the addition of water-filled troughs under an unthinned canopy that would increase humidity. Canopy relative humidity and soil moisture under the canopy was decreased by canopy thinning. Following infection by S. minor, the number of infection foci and disease development was reduced in the thinned canopy; however, thinning also reduced pod yield. Disease development was not increased, nor was yield affected by the addition of the water-filled troughs which increased humidity levels in the canopy. Soil moisture and canopy light interception were important variables in multiple linear regression models for the disease severity index and longest lesion length in the thinned and unthinned-trough plots.

Sclerotinia Blight of Peanut: Relationship Between in vitro Resistance and Field Efficacy of Dicarboximide Fungicides

Sclerotinia Blight of Peanut: Relationship Between in vitro Resistance and Field Efficacy of Dicarboximide Fungicides