Protective, curative and eradicative activities of fungicides against grapevine rust/Atividade protetora, curativa e erradicante de fungicidas no controle de ferrugem da videira.
Grapevine rust, caused by the fungus Phakopsora euvitis Ono, has become a common late season foliar disease of grapevine (Vitis sp.) in some parts of Brazil (ANGELOTTI et al., 2008b). The symptoms initially appear as small yellow pustules containing uredinia, which may cover large portions of the abaxial leaf surface. Under severe rust infection, the disease can cause premature defoliation of vines, reduce plant growth and affect the development and ripening of grape berries (LEU, 1988).
The triazole fungicides tebuconazole and ciproconazole are used in Brazilian viticulture mainly to control powdery mildew and ripe rot, and strobilurin fungicides azoxystrobin and pyraclostrobin are used mainly to control downy mildew and to a lesser extent powdery mildew and ripe rot. However, only formulations with tebuconazole and pyraclostrobin + metiram (strobilurin+ditiocarbamate) are currently registered to control grapevine rust in Brazil. Thus, aiming to optimize the use of fungicides on grape production, the objective of this study was to evaluate the protective, curative and eradicative activities of fungicides against grapevine rust.
Potted 'Niagara Rosada' plants were obtained through propagation of cuttings in pots filled with 2000 [cm.sup.3] of substrate. The top two buds above ground were treated with hydrogen cyanamide at 5%, for uniform bud break. An isolate of P euvitis, obtained from a leaf collected in an orchard of 'Niagara Rosada' grapevine in Marialva, PR, was maintained on leaves of potted transplants in controlled conditions. It was used 14-day old urediniospores produced on leaves of potted 'Niagara Rosada' plants, as inocula. For inoculation, a suspension of urediniospores (1x[10.sup.5] spores per mL), amended with 0.01% of Tween 20 (Sigma Chemical Co., St. Louis, MO, USA), was sprayed to run-off onto abaxial surfaces of leaves using a hand-held spray bottle. The inoculated plants had shoots with 5-6 fully expanded leaves. After inoculation, plants were maintained in dew chamber for 12h, at 23-25[degrees]C, in darkness, and then transferred to a growth chamber at 23- 25[degrees]C with 12 hours of photoperiod. To evaluate the protective activity of fungicides, potted plants were sprayed with fungicides at four, eight and 14 days before inoculation, using manual sprayer. The following treatments were compared: azoxystrobin 50g a.i. [ha.sup.-1], tebuconazole 100g a.i. [ha.sup.-1], pyraclostrobin + metiram 50 + 550g a.i. [ha.sup.-1], ciproconazole 100g a.i. [ha.sup.-1], and "control" without fungicide. The concentration of each fungicide used in this experiment was based on the recommended for other diseases of the grapevine. The inoculation procedure and environmental conditions for disease development were the same as described above. To evaluate the curative and eradicative activities of fungicides, the plants were inoculated as previously described and treated with fungicides after two, four and eight days. The experimental design was completely randomized with four replicates, in a factorial arrangement with an additional control treatment. Individual plants were considered to be an experimental unit. The severity of the disease was assessed on all leaves of each plant for each treatment using a diagrammatic scale (ANGELOTTI et al., 2008a) on the 14th day after the inoculation, and the percent disease control was calculated as 100 x [the differences in severity values between treated and control plots]. To evaluate the eradicative effect of fungicides, the viability of urediniospores collected from leaves sprayed with fungicides was determined by the percentage of germinated spores in vitro. For this, urediniospores were collected 14 days after inoculation and a suspension was prepared using sterile water at the concentration of 105 spores [mL.sup.-1]. An aliquot of 100pL of this suspension was spread evenly across surface in each Petri plate containing agar-water 2%. The Petri plate were maintained at 25[degrees]C with a photoperiod of 12h. Germination percentages at 24h incubation were determined by means of microscopic examination of 100 urediniospores at x100 magnification in each of the triplicate dishes. Individual urediniospores were considered germinated if the germ tube was equal to or greater than the minor diameter of the parent urediniospore. The experiment was repeated twice. Data were subjected to analysis of variance (ANOVA) using Sisvar computer programme (FERREIRA, 2000). The mean square of residues of factorial analysis was calculated and used for multiple comparisons. These procedures were accomplished using GENES software (CRUZ, 1998). The Scott- Knott test at 5% probability level was used to separate significant treatment means.
All tested fungicides presented protective and residual effects when sprayed until 14 days prior to inoculation, providing 100% control of grape rust. The first rust signs on leaves of control plants were observed at seven days after inoculation, which was about the same inoculation period reported by ANGELOTTI et al. (2008b). The average rust severity of the three inoculation timings was 47.5%. The leaves that were sprayed with fungicides did not present rust signals. In the curative trial, significant effects were observed for fungicides, application timing and interaction between fungicide and application (P=0.05). The triazole fungicide tebuconazole and ciproconazole provided 100% control of grapevine rust when sprayed two and four days after inoculation. However, when sprayed eight days after inoculation provided 74.7 and 68.2 % (1st experiment) and 96.7 and 60.7% (2nd experiment), respectively (Table 1). The fungicide azoxystrobin and piraclostrobin + metiram were less efficient than the tebuconazole and ciproconazole in their curative activity against grapevine rust. In fact, these strobilurin fungicides presented more curative activity at two days after inoculation than at four or six days after inoculation.
Information about chemical control of grapevine rust is scarce in the scientific literature. Possibly, it is because the major viticultural areas of the world, which are actually in temperate regions, are free or do not have this disease as a major problem. Previous studies carried out in Brazil showed the efficiency of triazol and strobilurin on grape rust control in field (NARUZAWA et al., 2006); however, this study carried out in greenhouse approached the protective, curative and eradicative activities of these fungicides.
Significant factorial interaction was found between fungicides and application timing on P euvitis urediospores viability (Table 2). The germination of urediniospores produced on leaves treated with fungicides was significantly reduced compared to the control (P=0,05). Again, the most dramatic effects were caused by the triazole fungicides. All fungicides significantly reduced urediniospores viability even when sprayed eight days after inoculation. BUCK et al. (2011) and GACHOMO et al. (2009) found similar results using active principle of the same chemical groups when evaluating Puccinia triticina, P. hemerocallidis and Diplocarpon rosae spores germination, respectively.
The urediniospores germination phase, which occurs at pre-infection phase, is critical to pathogen establishment. Thus, the inhibition of the germination using fungicides is a fundamental practice to control the disease, since the urediniospores are the initial step for the propagation and survival of P. euvitis. Thus, any control measures that reduce the viability of urediniospores are thought also to reduce survival of this rust. Chemical control used to reduce the initial inoculum can bring economic benefit by reducing the risk of epidemics (VALDEBENITO- SANHUEZA et al., 2010).
All tested fungicides present excellent preventive activity against grapevine rust; however, tebuconazole and ciproconazole provide better curative activity than azoxystrobin and pyraclostrobin+metiram. It is expected that the information presented here can help growers to optimize the use of fungicides as well to plan effective fungicide programs to control grape diseases. Additionally, use of several groups of fungicides is important for the management of resistance of fungi to fungicides, being important to the rotation of products with different action mechanisms.
The authors would like to Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES).
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Francislene Angelotti (I) Claudia Regina Scapin Buffara (II) Dauri Jose Tessamnn (II) Rafael Augusto Vieira (II) Joao Batista Vida (II)
(I) Embrapa Semiarido, CP 23, 56302-970, Petrolina, PE, Brasil. E-mail: email@example.com. Autor para correspondencia. (II) Departamento de Agronomia, Universidade Estadual de Maringa (UEM), Maringa, PR, Brasil.
Received 11.05.12 Approved 01.27.13 Returned by the author 06.03.14 CR-2013-1085.R1
Table 1--Curative effect of fungicides in grape rust control with sprayings at two, four and eight days after inoculation (DAY) with Phakopsora euvitis--1st experiment and 2nd experiment. Treatment 2DAY Severity (%) Fungicide g active ingredient [ha.sup.-1] Tebuconazole 100 0.0 aA(1) Cyproconazole 100 0.0 aA Pyraclostrobin + Metiram 50 + 550 37.5 bA Azoxystrobin 50 39.7 bA Control 60.4 c Tebuconazole 100 0.0 aA(1) Cyproconazole 100 0.0 aA Pyraclostrobin + Metiram 50 + 550 21.8 bA Azoxystrobin 50 13.7 aA Control 67.5c Percentage of control Treatment 2DAY 4DAY Control (%) Severity (%) Control (%) Fungicide 1st experimente Tebuconazole 100.0 0.0 aA 100.0 Cyproconazole 100.0 0.11 aA 99.9 Pyraclostrobin + Metiram 77.2 58.3 bB 57.7 Azoxystrobin 76.0 59.2 bB 57.2 Control 0.0 72.1 c 0.0 2nd experimente Tebuconazole 100.0 0.0 aA 100.0 Cyproconazole 100.0 0.1 aA 99.7 Pyraclostrobin + Metiram 82.5 60.0 bB 39.7 Azoxystrobin 72.0 6.9 aA 89.0 Control 0.0 63.2b 0.0 Treatment 8DAY Severity (%) Control (%) Fungicide Tebuconazole 25.2 aB 74.7 Cyproconazole 31.7 aB 68.2 Pyraclostrobin + Metiram 82.2 cC 17.7 Azoxystrobin 81.5 bC 26.5 Control 89.9 d 0.0 Tebuconazole 2.1 aA 96.7 Cyproconazole 25.4 bB 60.7 Pyraclostrobin + Metiram 55.0 dB 15.0 Azoxystrobin 49.3 cB 23.7 Control 64.7d 0.0 In a same experiment, the means followed by the same small letter in the column differ statistically by Scott-Knott test (5% probability), and the means followed by the same capital letter in the line do not differ significantly by Scott-Knott test (5% probability). Coefficient of variation: 1st experiment = 3.96 and 2nd experiment = 14.03%. Table 2--Percentage of germination (G) and reduce germination (RG) of urediospores of Phakopsora euvitis collected in 'Niagara Rosada" grape plants treated with fungicides at two, four and eight days after inoculation. Treatment 2DAY Fungicide g active ingredient G (%) RG (%) [ha.sup.-1] Tebuconazole 100 -- (1) Cyproconazole 100 -- Pyraclostrobin + Metira 50 + 550 2.2 aA 96,2 Azoxystrobin 50 15.2 bA 74.0 Control -- 58.5 cA -- Treatment 4DAY 8DAY Fungicide G (%) G (%) G (%) G (%) Tebuconazole -- 16.7 bB2 72.8 Cyproconazole -- 19.7 bB 67.9 Pyraclostrobin + Metira 6.6 bA 89.7 24.0 bB 60.9 Azoxystrobin 13.1 bA 79.6 9.4 aA 84.7 Control 64.5 c -- 61.5 cA -- (1) Urediniospores not produced. (2) Means followed by the same small letter in the column differ statistically by Scott-Knott test (5% probability). Means followed by the same capital letter in the line do not differ significantly by Scott-Knott test (5% probability).