Development Of Cercospora Leaf Spot Research Articles

Antimicrobial Efficacy of 7-Hydroxyflavone Derived from Amycolatopsis sp. HSN-02 and Its Biocontrol Potential on Cercospora Leaf Spot Disease in Tomato Plants.

The actinomycete strain HSN-02 was isolated from the soil of a mining field in the Sandur region, Bellary, Karnataka, India. According to the morphological, cultural, physiological, and biochemical characteristics and the 16S rDNA sequence analysis, the strain HSN-02 was identified as Amycolatopsis sp. The antimicrobial activity strain HSN-02 presented stable and moderate inhibitory activity against human pathogens. In pot experiments in the greenhouse, the development of Cercospora leaf spot was markedly suppressed by treatment with the purified compound from the strain HSN-02, and the control efficacy was 45.04 ± 1.30% in Septoria lycopersici-infected tomato plants. A prominent compound was obtained from the fermentation broth of the strain HSN-02 using column chromatography and HPLC. The chemical structural analyses using UV, FTIR, HR-ESI-MS, and NMR confirmed that the compound produced by the strain HSN-02 is 7-hydroxyflavone. This investigation showed the role which the actinomycete strain can play in controlling leaf spots caused by S. lycopersici to reduce treatments with chemical fungicides.

The Biocontrol of Soil Transmitted Cercospora capsici with Lactobacillus plantarum

Microbial diseases of pepper (Capsicum species) are the most significant factors contributing to the loss of this economically important vegetable crop. Leaf spot disease caused by Cercospora capsici is one of the major constraints to pepper production in Nigeria. The disease is reportedly introduced through infected seeds. However, the development of Cercospora leaf spot on plants propagated from fungicide-treated seeds suggests an alternative perennial source of infection and also necessitates the development of an efficient, safe control measure. C. capsici was isolated from infected pepper plant through the direct plating method and subsequently characterised. Treated pepper seeds (with L. plantarum) were planted in C. capsici inoculated soil, while the emergence, seedling growth parameters and severity of leaf spot were observed. The severity index of Cercospora leaf spot on pepper plants (observed at the 20th day after planting) was significantly lower on L. plantarum treated plant set (0.07) than on pepper without seed treatment. Seed emergence rate index increased from 11.11 to 15.33% /day of untreated to treated pepper seeds sown in infected soil respectively, while the mean emergence time of untreated seeds (8.32 days) was significantly higher in C. capsici infected soil. It could therefore be deduced that seed priming with L. plantarum improved the seedling vigor and resistance of pepper to leaf spot disease caused by C. capsici.

Development of Cercospora leaf spot on Ipomoea weed species for biological control

Morning glories (Ipomoea spp.) are important weeds in non-burning sugarcane farming in Brazil, and their chemical control has low efficacy due to the straw mulching. The purpose of this work was to determine the effect of epidemiological parameters on the development of Cercospora leaf spot (Cercospora aff. canescens Ellis & G. Martin) on four Ipomoea weed species, as well as on the host range. The results demonstrated that the use of a suspension of 2 × 107 conidia ml−1 on specific host phenological stages (3–5 leaves, open flowers, and with fruit), with a minimum of a 24 h dew period, induces plant defoliation and a higher disease incidence on Ipomoea nil L. (Roth). However, the same disease incidence and defoliation on I. grandifolia (Dammer) O’Donell, I. quamoclit L., and I. hederifolia L. were not achieved. The pathogen was specific to these four Ipomoea species among 18 plant species. These results represent an important step in the development of a mycoherbicide to control morning glories.

Temporal and Spatial Development of Cercospora Leaf Spot of Faba Bean Influenced by In Situ Inoculum.

The temporal and spatial dynamics of Cercospora leaf spot on susceptible and resistant lines of faba bean grown in or at defined distances from soil with residues infested by Cercospora zonata were examined in South Australia in 2005 and 2006. The disease was first observed on susceptible seedlings 49 days after sowing (DAS) in soil that had been sown with faba bean every 3 years since 1997 (positive soil zone for C. zonata) but was delayed by 1 week in adjacent soil (0 to 16 m away) with no history of cultivation of faba bean (negative soil zone). The incidence of diseased seedlings from 49 to 63 DAS showed a gradient from 4 to 16 m from the infested soil and was significantly greater for susceptible plants grown in the positive versus negative soil zones in field trials conducted in 2005 and 2006 (92 versus 30% in 2005, χ21 = 32.2, P < 0.001; 98 versus 55% in 2006, χ21 = 12.1, P < 0.001). The incidence of Cercospora leaf spot on the resistant line 1322/2 was significantly less (χ26 = 171.7; P < 0.001) than on the susceptible line 'Farah' at that time in both years, with fewer than 5% of the seedlings showing the disease. However, a gradient was shown at 70 to 84 DAS, where disease incidence was significantly greater on line 1322/2 in the positive soil zone than on plants in the negative soil zone in both years (62 and 18%, respectively, with χ21 = 27.9, P < 0.001 in the 2005 trial; and 47 and 6%, respectively, with χ21 = 33.3, P < 0.001 in the 2006 trial). At peak disease severity on Farah, Cercospora leaf spot mean leaf area diseased (%LAD) was severe (85 ± 4.3%) on leaves of the three nodes closest to the soil surface, and much less severe (1 ± 0.6%) in the upper canopy. Defoliation combined with %LAD was used to describe the loss of photosynthetic leaf area (%LPLA) in both cultivars, on both soil zones, in each year. Nonlinear regression analyses using a logistic model described disease development over time on susceptible plants grown in infested soil (e.g., for +12-m blocks within infested soil, y = 2.66 + 46.08/[1 + exp(-0.23 × [X - 40.92])] in 2005 and y = 0.49 + 5.02/[1 + exp(-0.14 × [X - 28.30])] in 2006, where X = DAS and y = %LPLA, with both regressions significant at P < 0.001), whereas an exponential model (e.g., for -12-m blocks from infested soil, y = 0.23 + 0.77 × 1.04X in 2005 and y = 0.44 + 0.56 × 1.04X in 2006, both at P < 0.001) best described disease gradients with increasing distance from the inoculum source. Paired t tests of %LPLA at 77 and 98 DAS showed significant differences in disease severity in the positive versus negative soil zones and a steep gradient in %LPLA from 0 to 4 m from the inoculum source. The role of infested faba bean residue in survival of C. zonata over time was also examined using a pot-bioassay and in situ field assay. When residues were removed from the soil surface or depleted rapidly by animal grazing, the amount of C. zonata inoculum in the soil was significantly less (P < 0.001) than for soil with residue remaining on the soil surface. C. zonata survived in soil and remained infective for at least 30 months after harvest of an infected faba bean crop.

Management of Late Leaf Spot of Groundnut by Different Fungicides and Their Impact on Yield

In vitro experiments were carried out with Phaeoisariopsis personata isolate to determine its sensitivity/tolerance to different fungicides viz., Tebuconazole (0.05%), Tebuconazole (0.10%), Tebuconazole (0.15%), Tebuconazole (0.20%), Tebuconazole (0.40%), Folicur (0.10%) and Mancozeb (0.30%) using poisoned food technique both in solid and liquid medium. In the solid medium method, visual observation was taken 20 days after inoculation of the pathogen. There was no significant difference among the different fungicides in their efficacy against P. personata, compared to control. In case of liquid medium the observations were taken after 25 days of inoculation and the results are presented. There was significant difference between the fungicides in per cent inhibition against the mycelial growth of the pathogen, P. personata. Among all the fungicides, Tebuconazole 0.4% (87.97%t) showed maximum inhibition followed by Tebuconazole 0.2% (85.24%) and Tebuconazole 0.15% (83.50%), among these Tebuconazole 0.15% was found to be optimum. Application of fungicidal sprays influenced the development of Cercospora leaf spot and reduced its intensity. Among these applications of different fungicides, Tebuconazole (0.15%) gave best result and reduced the disease intensity to 52.42%. Area under disease progress curve (AUDPC) greatly varied among different fungicidal treatments and showed significant difference in yield data. Impact of fungicides used for disease control was apparent on yield per plot. Tebuconazole (0.15%) gave best result and increased yield up to 67% as compared to 39% increase by Tebuconazole (0.10 %).

Effect of Production System and Pruning on Temporal Development of Cercospora depazeoides and on Berry Yield in Black Elderberry Orchards.

In a 2-year study, the temporal development of Cercospora leaf spot (Cercospora depazeoides) and berry yield were evaluated in two production systems (integrated and organic) and in two winter pruning treatments (trees pruned to four and eight scaffolds) in two black elderberry (Sambucus nigra) orchards in Hungary. Under organic production, leaf spot onset occurred 2 to 4 weeks earlier (mid- and late July) in both years and both orchards compared with the integrated program. Disease then continuously progressed until the final assessment date (late September) in both years, reaching a maximum final disease incidence of 15.9% in the integrated system and of 38.2% in the organic system. In general, disease progress after late August was greater on trees pruned to eight scaffolds than on trees pruned to four scaffolds in both production systems. Both final disease incidence and area under the disease progress curves (AUDPC) were significantly lower (P < 0.001) in the integrated treatments compared with organic ones. Across all treatments, both disease measures were significantly (P < 0.05) lower on trees pruned to four scaffolds compared with trees pruned to eight scaffolds. However, when the effect of pruning on final disease incidence and AUDPC was analyzed separately for integrated and organic systems, pruning caused uniformly significant differences in disease development only for the organic system. Berry yield was significantly higher (P < 0.05) in the integrated system compared with the organic system, but pruning showed no significant effect on yield. Overall, pruning to four scaffolds resulted in consistently lower disease development in organic production compared to integrated. Thus, winter pruning may be useful as a Cercospora leaf spot management practice in organic elderberry orchards.

Influence of Nitrogen Rate on Cercospora Leaf Spot and Growth of Crapemyrtle

The impact of N rate on development of Cercospora leaf spot on field grown ‘Carolina Beauty’ crapemyrtle and the impact of this disease, as well as N rate, on plant growth was assessed in Alabama. From 2002 to 2005, ammonium nitrate was applied at an N rate of 2, 4.1, 8.3, 16.5, 33.0, and 66.0 g/m2. Heritage 50W fungicide was applied to one tree in each plot, while the second tree was not treated. Powdery mildew was very sporadic and was not related to N rate. An N rate-related reduction in Cercospora leaf spot intensity and defoliation was noted on the non-fungicide and fungicide treated trees in 2005 but not in 2003 and 2004. In 2005, reductions in disease intensity and defoliation were obtained at the three highest N rates of 16.5, 33, and 66 g/m2 compared to the two lowest N rates of 2 and 4.1 g/m2. Regardless of N rate, Heritage 50W suppressed Cercospora leaf spot. Despite considerable leaf spotting and premature defoliation, Cercospora leaf spot did not impact crapemyrtle growth. Increasing N rates was less effective than Heritage 50W fungicide in controlling Cercospora leaf spot and also failed to enhance tree growth. Accepted for publication 10 September 2009. Published 14 December 2009.

Synthetic and Biorational Fungicides Compared for the Control of Three Foliar Diseases of Flowering Dogwood

Abstract The biorational fungicides Neem Concentrate, SunSpray Ultra Fine Oil®, Rhapsody® were compared with the synthetic fungicides Eagle® 40W, Immunox®, Liquid Systemic Fungicide®, and 3336™ 50W for the control of spot anthracnose, Cercospora leaf spot, and powdery mildew on ‘Rubra’ flowering dogwood. In 2003, 2004, and 2005, fungicide treatments were applied at label rates at 1- and/or 2-week intervals over a period that coincided with the onset spot anthracnose and powdery mildew but before the appearance of Cercospora leaf spot. With few exceptions, the synthetic fungicides gave better control of the above diseases than biorational fungicides. Eagle 40W, Immunox, Liquid Systemic Fungicide, and 3336 50W gave equal control of the bract and leaf spot phases of spot anthracnose. Most notable was the carryover of control of the bract spot phase of spot anthracnose into the spring of the following year with the synthetic fungicides. While some control of spot anthracnose was seen in at least one year with the biorational fungicides, none was as effective as the synthetic fungicides. In 2003 and 2004, Neem Concentrate, SunSpray Ultra Fine Oil, and Rhapsody, when applied weekly controlled powdery mildew as effectively as the synthetic fungicides. Efficacy of the biorational fungicides declined under severe powdery mildew pressure in 2005. While Cercospora leaf spot development was slowed by the Eagle 40W, Liquid Systemic Fungicide, and 3336 50W, the biorational fungicides as well as the retail product Immunox also gave some control. An objectionable mottling of the leaves was noted on the flowering dogwood treated with SunSpray Ultra Fine Oil. Control of these diseases with the synthetic or biorational fungicides did not result in an increase in tree height or trunk diameter. While the biorational fungicides demonstrated sufficient efficacy for controlling powdery mildew on flowering dogwood in the landscape, they often failed to provide the level of control of this disease as well as spot anthracnose and Cercospora leaf spot needed to produce quality container- and field-grown nursery stock.