Tiago Edu Kaspary

Habilidade competitiva de cultivares de trigo com plantas daninhas

Competitive ability is an important tool for integrated weed management. The objective of this work was to evaluate the potential of wheat cultivars in competing with the weeds Italian ryegrass and wild radish, at different periods of coexistence. The experiment was arranged in a randomized block design, in a factorial scheme 4 x 2 x 3, with three replicates. The following wheat cultivars were allocated in Factor A: BRS Guamirin - short cycle and short plant height; Fundacep Cristalino - short cycle and medium plant height; Fundacep Raizes - medium cycle and medium plant height; and BRS 296 - short cycle and tall plant height. In Factor B, absence or presence of weed control, and in Factor C, weed management time (throughout the crop cycle or until pre-harvest, up to 15 days after seeding and 30 days after seeding - DAS). The Fundacep Cristalino cultivar - short cycle and medium plant height- showed more competitive ability than the Italian ryegrass and wild radish, compared to the other cultivars, in all the periods evaluated. Weed control in wheat must be performed early, especially for cultivars with lower competitive ability.

Manejo de Conyza bonariensis resistente ao glyphosate: coberturas de inverno e herbicidas em pré-semeadura da soja

Conyza bonariensis became the main weed in soybean crop in Southern Brazil, as a consequence of the evolution of resistance to the herbicide glyphosate. The objective of this work was to evaluate the effect of different winter cover crops and the association of burn-down herbicides on the control of glyphosate-resistant C. bonariensis. A field experiment was conducted in the 2010/2011 season. The treatments were arranged in a split-plot scheme, with the winter cover crops lopsided oat, radish, common vetch, Italian ryegrass, wheat, and fallow in the main plots, and in the subplots, the following burn-down treatments: glyphosate (720 g e.a ha-1), glyphosate (720 g e.a ha-1) + 2,4-D (1.050 g e.a ha-1), glyphosate (720 g e.a ha-1) + 2,4-D (1.050 g e.a ha‑1)/paraquat (200 g i.a ha-1) + diuron (100 g i.a ha-1), glyphosate (720 g e.a ha-1) + chlorimuron-ethyl (80 g i.a ha-1), glyphosate (720 g e.a ha-1) + chlorimuron-ethyl (80 g i.a ha-1)/paraquat (200 g i.a ha-1) + diuron (100 g i.a ha-1) and mowing. Radish was the cover crop species that produced the highest amount of shoot dry mass during the winter season, while common vetch had the highest suppressive effect on germination and initial development of C. bonariensis. Associations of glyphosate with 2,4-D or chlorimuron-ethyl, followed by the sequential application of paraquat + diuron, caused the highest reductions in C. bonariensis infestation.

Dessecação pré-colheita e efeitos sobre a produtividade e qualidade fisiológica de sementes de soja

The anticipation of soybean harvest is possible with the use of pre-harvest burn-down practice, which reduces the time of permanence of seeds in the field, after reaching physiological maturation. The objective of this work was to evaluate the effect of time of application of the herbicide paraquat as burn-down during soybean pre harvest on yield and physiological quality of the seeds. The work consisted of two steps: one field experiment, conducted in Jaboticaba-RS, in 2010/2011 and the analysis of the physiological quality of seeds. The treatments consisted of three times of paraquat (240 g a.i. ha-1) application, R6, R7.1 and R7.3, as well as one untreated (without burn‑down). Yield grains and yield components were evaluated. Seed quality analysis was conducted at the Seed Production and Technology Laboratory of UFSM, Campus of Frederico Westphalen, RS, where the following evaluations were carried out : germination, first germination count, root and shoot weight, shoot dry mass of seedlings, accelerated aging, electrical conductivity, field emergence and emergence velocity index. Paraquat application as burn-down practice in soybean pre harvest, at the R6 and R7.1 soybean stages, causes high yield loss in soybean crop. Burn-down without potential yield loss is only viable after R7.3 soybean growth stage. Seeds originated from plants which received paraquat application in R6 and R7.1, show a superior percentile of germination and a higher germination velocity. However, seeds from plants which received paraquat at stage R6 have less seed vigor.

Determination of photosynthetic pigments in fleabane biotypes susceptible and resistant to the Herbicide Glyphosate

Chlorophylls and carotenoids are the main photosynthetic pigment in plants. In the weeds, the greatest amount of photosynthetic pigments can result in high competitiveness of the species. The aim of this study was to quantify the content of photosynthetic pigments in biotypes of fleabane (Conyza bonariensis) susceptible and resistant to glyphosate, by two different methods, as well as a correlation between chlorophyll content obtained by portable and classical methodology (extractable chlorophyll). An experiment was conducted in greenhouse and laboratory, 2 x 5 factorial scheme, where factor A was equivalent to biotypes of fleabane (resistant and susceptible to glyphosate) and factor B to developmental stages plants (rosette vegetative I, II and III and reproduction). At all stages of development, fleabane plants were evaluated with the portable determiner (chlorophyll content) and then the same leaves were subjected to classical methodology laboratory (extractable pigments). The resistant biotype of fleabane showed higher contents of chlorophyll a, b, and total carotenoids, inferring a greater competitive potential regarding the susceptible population to the herbicide. The portable determiner of chlorophyll showed high correlation with the classical method of determination of photosynthetic pigments, and can thus be used to accurately assess this, saving time and reagents.

Growth, phenology, and seed viability between glyphosate-resistant and glyphosate-susceptible hary fleabane

Glyphosate is the herbicide most used worldwide. In cropping systems that rely on repeated applications of glyphosate or cultivate genetically modified soyabean crop, there are numerous cases of glyphosate resistant weeds, including Conyza bonariensis. Differences among competitive ability of Conyza spp. have been found. However, little information is available on the fitness costs related to glyphosate resistance in Conyza bonariensis. We evaluated growth, phenology, and seed viability of glyphosate-resistant (GR) and glyphosate-susceptible (GS) Conyza bonariensis from Brazil, in 2012 (fall/winter) and 2013 (spring/summer). When grown alone, in pots, C. bonariensis GR biotype developed more rapidly than the GS biotype, as evidenced by their earlier bolting, flowering, and seed set. In 2012, GR biotype showed 221.9 cm of plant height compared to 181.1 cm from GS, at the flowering time. In both years, the seed production per plant was superior for GR biotype, showing germination higher than 80% against 66.5% from the GS biotype. Thus, C. bonariensis GR biotype confirmed no fitness penalty also showing characteristics that allow us to infer in superior competitive with the absence of the herbicide. It is important to point out that the biotypes evaluated here have different genetic background and the differences between them may not be fully attributed to the resistance to glyphosate. However, the GR biotype can persist in the environment and outcompete with GS biotypes regardless of further glyphosate selection of pressure.

Phytosociological variability of weeds in soybean field

Understanding spatial distribution of weeds in the crop enables to perform localized herbicide applications, increasing the technical and economic efficiency of operations and reducing environmental impacts. This work aimed to characterize the spatial and phytosociological variability of weeds occurring in soybean commercial field. It was conducted in an agricultural area located at the municipality of Boa Vista das Missoes - RS, during the 2010/2011 harvest season. The area, that had been managed under no-tillage with soybean monoculture (summer) for five years, was divided in regular squares of 50 x 50 m (0.25 ha), totalizing 356 points. For species identification, 0.5 x 0.5 m sample squares were used. During the survey, 1,739 individuals were identified, distributed in 19 species of 13 families. The weed species Cardiospermum halicacabum, Digitaria horizontalis, Urochloa plantaginea and Raphanus raphanistrum showed the highest population variation in the area; however, only C. halicacabum, U. plantaginea and R. raphanistrum stood out based on the Importance Index Value (IVI). Localized management strategies considering the spatial variability of weed species placed in the Magnoliopsidas and Liliopsidas group show a high potential for use in soybean crop. The results show that the sampling method through regular grid was capable of characterizing the occurrence, population density and spatial variability of weed species in soybean crop.

First Report of Sclerotium rolfsii Causing Stem Rot of Luffa cylindrica in Brazil

Luffa cylindrica (L.) Roem. (Cucurbitaceae) is an Asian vine widely known as the source of loofah (Purseglove 1968). In Brazil (local name bucha), it is cultivated by small-scale producers as a cash crop. In February 2017, L. cylindrica plants with rotted and girdled stem bases were found in a commercial field (27°22′S; 53°25′W) in Frederico Westphalen, Rio Grande do Sul, Brazil. Disease symptoms later led to a collapse of stems. Necrotic areas were covered with white cotton mycelium as well as abundant spherical sclerotia. The fungus was isolated in pure culture by direct transfer of sclerotia in aseptic plates with potato dextrose agar (PDA). After 7 days, cottony white colonies started to appear, often forming fans, primary hyphae 2.0 to 5.0 μm in diameter, and bearing clamp connections; sclerotia formed after 10 days, initially white and becoming dark brown with age, and 0.65 to 2.15 mm in diameter. A specimen was deposited in the herbarium (Federal University of Pelotas Herbarium, Rio Grande do Sul State, Brazil) under accession no. LPS0025. Molecular characterization was performed by amplifying and sequencing the internal transcribed spacer (ITS) region using ITS1 and ITS4 primers (White et al. 1990) and the translation elongation factor (TEF-1α) gene region using primers EF595F and EF1160R (Wendland and Kothe 1997). Sequences of the studied DNA regions were submitted to GenBank (ITS: MF425542; and TEF-1α: MF434828). BLAST searches in GenBank showed 99 to 100% identity with the existing sequences of Athelia rolfsii (Curzi) C. C. Tu & Kimbr (anamorph: Sclerotium rolfsii Sacc.) (ITS: KU128903, KX139196, DQ059578, and GU080230; and TEF-1α: KM521767, JF267808, JF267798, and JF267798). To fulfill Koch’s postulates, 10 healthy, 20-day-old L. cylindrica seedlings were inoculated with sclerotia obtained from a 15-day-old culture. Dry sclerotia were placed directly at the base of the plant (four sclerotia per plant). Ten uninoculated L. cylindrica seedlings were used as the control treatment. The inoculated and uninoculated plants were incubated in a humid growth at 26°C for 24 h and then maintained in a greenhouse. Seven days later, pathogen-inoculated plants showed typical symptoms similar to those observed under natural conditions, but no symptoms were seen on the control plants. The pathogenicity tests were carried out three times. The fungus was reisolated from the artificially inoculated plants. According to morphological and molecular characteristic combinations, the isolate was confirmed as S. rolfsii. S. rolfsii has been reported on Citrullus lanatus, Cucumis sativus, Cucurbita pepo, and other species in the Cucurbitaceae family in Brazil (Queiroz et al. 2002), but not on Luffa cylindrica. To our knowledge, this is the first report of S. rolfsii causing disease on L. cylindrica in Brazil.

Control of wheat stink bugs (Hemiptera: Pentatomidae) in southern Brazil using the fungus Metarhizium anisopliae

Stink bugs of the species Nezara viridula and Dichelops melacanthus are considered as some of the main insect pests associated with wheat production in Brazil. The use of the entomopathogenic fungus Metarhizium anisopliae might be an alternative for the management of these insects with chemical insecticides. Thus, the aim of this study was to evaluate and ascertain the pathogenicity of different isolates of M. anisopliae on N. viridula and D. melacanthus adults under laboratory and greenhouse conditions. In the laboratory, the fungal isolates 05RA, 11RA, 08RA, and 02RA, which were collected in the field from adults of N. viridula and D. melacanthus infected with M. anisopliae, were highly pathogenic, leading to 100% mortality in adults of N. viridula and D. melacanthus at 8 days after application (DAA). However, the isolate 08RA presented higher pathogenicity in a shorter period of time for N. viridula (mean mortality time “MMT” = 2.8 days) and D. melacanthus (MMT = 4.0 days) than the remaining isolates. At the greenhouse, the isolate 08RA led to a mortality of 44.9% (N. viridula) and 35.7% (D. melacanthus) at eight DAA; however, the mortality was 100% for both species at 14 DAA, with an MMT of 8 and 10 days for N. viridula and D. melacanthus, respectively. The fungus M. anisopliae constitutes a promising alternative agent to control the growth of adult populations of N. viridula and D. melacanthus in wheat cultures.

Meloidogyne ethiopica and Meloidogyne arenaria parasitizing Oxalis corniculata in Brazil

Meloidogyne ethiopica and Meloidogyne arenaria were identified morphologically and via isozyme profiles of female nematodes extracted from Oxalis corniculata root samples collected from plantations in the municipality of Caiçara, Rio Grande do Sul State, Brazil. To the best of our knowledge, this is the first report of M. ethiopica and M. arenaria parasitizing O. corniculata in Brazil.