Reação de genótipos de cafeeiro à Hemileia vastatrix e à Cercospora coffeicola

Coffee plants were introduced in Brazil in the Northern State of Para around 1727. Two major diseases have affected coffee trees in the country. One is rust, caused by fungus Hemileia vastatrix and accountable for production losses up to 50%. The other one is Cercospora leaf spot, caused by fungus Cercospora coffeicola endemic to all Brazilian coffee farms and, therefore, economically critical due to production losses both in the plant nursery and in the field. Availability of resistant varieties has been a constant challenge for breeders. Research programs play an important role in the search for new resistant and/or tolerant genotypes, since over time plants can become susceptible to new, genetically variable races of pathogens. This study aimed to evaluate the incidence and severity of such diseases, the resistance of different coffee genotypes to H. vastatrix and C. coffeicola pathogens, as well as the productivity of said genotypes in dense planting system. The experimental design consisted of randomized blocks, with twelve genotypes (treatments) and two replications (blocks). SISVAR® program was used to analyze data and compare them building on Scott-Knott test and Tukey’s test with a probability of 5%. Disease incidence and severity percentage were assessed for both Cercospora leaf spot and rust. Means were used to calculate the area under the disease progress curve (AUDPC) of both diseases. As to rust, the most resistant genotypes were H586-6, IBC 12, and H556-7 H567-6. As to Cercospora leaf spot and productivity, no statistical differences were found across genotypes. The dense planting system did not impair plant development, but favored disease evolution given the microclimate it produces.

Fungicidas protetores no manejo da ferrugem da soja, processos fisiológicos e produtividade da cultura

Currently, the management recommendations for asian soybean rust (ASR) has been based on the application of protective fungicides mixed with triazoles and stronilurins. Thus, this study aimed at assessing whether the increased productivity provided by the application of protective fungicides is due solely to the fungicidal action of the product or some physiological changes in the plant and which the latter would be. The experiment was conducted from March to July 2015 at the experimental station of Udi Research and Development in Uberlândia-MG, with the cultivar 97Y07 RR. The experimental design chosen for this study was comprised of a randomized block with four replications and 16 treatments: check, fluxapyroxad + pyraclostrobin (116.55 + 58.45 g ha-1), azoxystrobin + benzovindiflupir (90 + 45 g ha-1), trifloxystrobin + prothioconazole (60 + 70 g ha-1), tebuconazole + picoxystrobin (100 + 60 g ha-1), picoxystrobin + cyproconazole (60 + 24 g ha-1), mancozeb (1125 g ha-1), azoxistrobina + tebuconazole + difenoconazole (60 + 75 + 120 g ha-1), azoxystrobin + tebuconazole + difenoconazole + chlorothalonil ( 60 + 120 + 75 + 1440 g ha-1), and mistures fluxapyroxad + pyraclostrobin + mancozeb, azoxystrobin + benzovindiflupir + mancozeb, trifloxystrobin + prothioconazole + mancozeb, tebuconazole + picoxystrobin + mancozeb, picoxystrobin + cyproconazole + mancozeb, azoxystrobin + tebuconazole + difenoconazole + mancozeb, and azoxystrobin + benzovindiflupir + chlorothalonil, from the aforesaid doses. The first application of the treatments occurred in R1, in the absence of symptoms. The number of applications, intervals and the use of adjuvants were performed according to the recommendations by manufacturers. The variables analyzed were: disease severity, concentration of chlorophylls and carotenoids, photosynthetic rate (A), transpiration rate (E), stomatal conductance (gs), internal carbon concentration (Ci), instantaneous efficiency in water use (A/E), intrinsic water use efficiency (A/gs), and carboxylation efficiency (A/C). With these data collected, this study set to date the progress curve of each variable (AUPC). At the end of the crop cycle, the average of pods per plant was quantified, grain per pod, productivity and weight of 1,000 grains. It was concluded that: the addition of mancozeb to fluxapyroxad + pyraclostrobin, azoxystrobin + benzovindiflupir, trifloxystrobin + prothioconazole and tebuconazole + picoxystrobin potentiated the ASR control; adding mancozebe to the mixture azoxystrobin + benzovindiflupir provided better control of the disease compared to the addition of chlorothalonil; mancozeb amounts to AUPC concentration of photosynthetic pigments and when added to axozystrobin + tebuconazole + difenoconazole, increases the AUPC for total chlorophyll concentration, as well as when chlorothalonil was added; mancozeb added to the mix fluxapyroxad + pyraclostrobin raised the AUPC for A/Ci and A/gs, increasing the W1,000G and crop productivity; the addition of protectors similarly reflected on the productivity of culture.

Alterações fisiológicas causadas por fungicidas em soja infectada naturalmente por oídio

Soybean crop is substantially important for both Brazilian and international markets. A relevant disease that affects soybeans is powdery mildew, caused by fungus Erysiphe diffusa. The objective of this master’s thesis was to analyze physiological changes produced by fungicides in two greenhouse-grown soybean genotypes (i.e., Anta 8500 RR and BRS Santa Cruz RR) naturally infected with powdery mildew. A complete randomized block design was used with six replications in a 2x5 factorial arrangement. Treatments consisted of applications of Azoxystrobin, Biofac (fermented solution of Penicillium sp.), Carbendazim or Picoxystrobin fungicides, and a Control (no fungicide application). Three applications were performed in the experimental period, and each eventually represented a period of data collection. Gas exchanges, chlorophyll content, fluorescence of chlorophyll a and disease severity were measured twice a week. Dry grain mass production was measured at the end of the experiment. Areas under progression curve of variables were submitted to both ANOVA and Tukey’s test at 5% significance. Treatments Azoxystrobin, Biofac and Picoxystrobin had higher photosynthetic rates than Control in the second period, with genotype Anta having higher rate than Santa Cruz. Biofac had higher transpiration rate than Control in the second period, while Biofac and Picoxystrobin had higher figures in Santa Cruz in the third period. Carbendazim had greater stomatal conductance in Anta, whilst Azoxystrobin, Biofac and Picoxystrobin had greater values than Carbendazim in Santa Cruz. Biofac and Picoxystrobin had greater intercellular CO2 concentration in Santa Cruz. Azoxystrobin and Picoxystrobin had greater instantaneous water use efficiency than Control, with Anta being more efficient than Santa Cruz. Biofac and Picoxystrobin had greater intrinsic water use efficiency in Anta, while Carbendazim increased efficiency in Santa Cruz. Azoxystrobin, Biofac and Picoxystrobin had greater carboxylation efficiency than Control in the second period, with Anta being more efficient than Santa Cruz. Azoxystrobin and Biofac had greater contents of chlorophylls a, b and a+b than Control in the second period. Azoxystrobin had greater effective quantum yield than Control and Picoxystrobin. All treatments faced increasing disease severity over time, with Anta being less resistant than Santa Cruz. As for production, data showed that: (1) Santa Cruz was more productive than Anta, having the greatest dry grain mass with Carbendazim, and (2) Anta’s lower disease severity did not translate into higher productions. In conclusion, strobilurins (Azoxystrobin and Picoxystrobin) and Biofac performed similarly as to their physiological effects on soybeans; however, these effects did not lead to increased dry grain mass by the end of the experiment.