RESUMO
Campomanesia guazumifolia is a Brazilian fruit tree that has ecological importance and the potential to be explored by the food and medical industries (Lima et al., 2011). In February 2019, in the experimental orchard at the Universidade Tecnológica Federal do Paraná, Dois Vizinhos city, Paraná State - Brazil, disease symptoms were observed on leaves, stems, and fruits of 22 C. guazumifolia trees. Yellow uredinia were observed on upper side of the leaves, stems, and flowers, which resembled typical uredinia of Myrtaceae rust. The pustules occurred mainly on young shoots, and on flowers, they infected their sepals. Over time, tissues colonized by the pathogen exhibited deformations and mummification occurred in infected fruits. In the orchard, the fungus affected 80% yield. Twenty diseased plant parts (from each of the eleven trees) were collected at different positions in the orchard. One strain were selected as a representative for morphological characterization, multilocus phylogenetic analysis, and pathogenicity tests. The structures observed were epiphyllous uredinia (leaves), united in small groups with hyaline and obovoid or obpyriform urediniospores, which presented echinulate ornaments, germinated pores in the subequatorial and inordinate positions (Cummins; Hiratsuka, 2003) (n = 30, 14.84 x 21.12 µm). The morphology of uredinia and urediniospores was similar to the morphological characteristics of the genus Austropuccinia previously described in Young (2019). For molecular identification, genomic DNA was extracted and the internal transcribed spacer (ITS) region (White et al. 1990), ß-tubulin (TUB2) and translation elongation factor 1-alpha (TEF) (Machado et al. 2012) were amplified by PCR, and sequenced. Bayesian inference was used to reconstruct a phylogenetic tree, using MrBayes v. 3.2.1 (Ronquist et al., 2012). The multilocus phylogenetic analysis clearly distinguished the isolate APCG001 as Austropuccinia psidii separating it from all other species. The sequences were deposited in GenBank (accessions nos. ITS: ON003418, TUB2: ON568196, and TEF: ON437601). For pathogenicity tests, four healthy branches (20 leaves each) were sprayed with 2.5 mL of (APCG001) uredospore suspension (105 mL-1) and covered with a plastic bag in the orchard. The air temperature ranged from 16ºC to 25ºC. Sterile distilled water was used as a control. Three replications (pathogen and control) were performed on different trees. After 6 days, symptoms of rust appeared on the plants. Control branches did not show fungal growth. The inoculation test was repeated again, confirming the initial results. This is the first report of infection by A. psidii in C. guazumifolia trees in Brazil, causing rust, necrosis, and early senescence in fruits, leaves, and stems. Myrtaceae rust reduces the C. guazumifolia leaf area, affecting photosynthetic production and reducing fruit quality.
RESUMO
A estabilidade de complexos organo-minerais é uma característica importante quanto à química e física de solos tropicais e subtropicais. O objetivo deste estudo foi identificar variáveis relacionadas à estabilidade de complexos organo-minerais, avaliada pela energia de ultra-som necessária para a dispersão total do solo em partículas primárias, em seis solos das regiões Sul e Centro-Oeste do Brasil com textura e mineralogia distintas. A energia de ultra-som necessária para dispersão total dos solos variou de 239 a 2.389J mL-1, sendo diretamente relacionada aos teores de carbono orgânico (R²=0,799, P<0,05). A mineralogia da fração argila teve um papel determinante na estabilidade dos complexos organo-minerais, a qual foi relacionada aos teores de óxidos de ferro de baixa cristalinidade (R²=0,586, P<0,10), mas não teve relação com os teores totais de óxido de ferro pedogênicos. A análise qualitativa da fração argila, realizada por difratometria de raios-X, demonstrou que a estabilidade dos complexos organo-minerais variou positivamente em função das proporções de gibbsita e de goethita na fração argila, o que reforça o papel desses minerais na proteção física e estabilidade coloidal da matéria orgânica em solos tropicais e subtropicais.
The stability of organo-mineral complexes is an important characteristic related to the soil chemistry and physics of tropical and subtropical soils. This study was aimed at identifing the variables related to the stability of organo-mineral complexes, evaluated by ultrasonic energy necessary to complete soil dispersion, of six soils from South and West-Center regions of Brazil with distint texture and mineralogy. The ultrasonic energy to complete soil dispersion varied from 239 a 2389J mL-1, and was positively related to the soil organic carbon concentrations (R²=0.799, P<0.05). The clay mineralogy had an important role to the stability of organo-mineral complexes, which were related to the content of low cristalinity iron oxides (R²=0.586, P<0.10), but did not had relationship with the total pedogenic iron oxides. The qualitative analysis of the clay mineralogy, by X-ray diffraction, evidenced that gibbsite and goethite are the main clay minerals related to the stability of organo-mineral complexes, reinforcing the importance of these minerals on the physical protection and coloidal stability of the soil organic matter in the tropical and subtropical soils.
RESUMO
The area under no-till (NT) in Brazil reached 22 million ha in 2004-2005, of which approximately 45% was located in the southern states. From the 1970s to the mid-1980s, this region was a source of carbon dioxide to the atmosphere due to decrease of soil carbon (C) stocks and high consumption of fuel by intensive tillage. Since then, NT has partially restored the soil C lost and reduced the consumption of fossil fuels. To assess the potential of C accumulation in NT soils, four long-term experiments (7-19 yr) in subtropical soils (Paleudult, Paleudalf, and Hapludox) varying in soil texture (87-760 g kg(-1) of clay) in agroecologic southern Brazil zones (central region, northwest basaltic plateau in Rio Grande Sul, and west basaltic plateau in Santa Catarina) and with different cropping systems (soybean and maize) were investigated. The lability of soil organic matter (SOM) was calculated as the ratio of total organic carbon (TOC) to particulate organic carbon (POC), and the role of physical protection on stability of SOM was evaluated. In general, TOC and POC stocks in native grass correlated closely with clay content. Conversely, there was no clear effect of soil texture on C accumulation rates in NT soils, which ranged from 0.12 to 0.59 Mg ha(-1) yr(-1). The C accumulation was higher in NT than in conventional-till (CT) soils. The legume cover crops pigeon pea [Cajanus cajan (L.) Millsp] and velvet beans (Stizolobium cinereum Piper & Tracy) in NT maize cropping systems had the highest C accumulation rates (0.38-0.59 Mg ha(-1) yr(-1)). The intensive cropping systems also were effective in increasing the C accumulation rates in NT soils (0.25-0.34 Mg ha(-1) yr(-1)) when compared to the double-crop system used by farmers. These results stress the role of N fixation in improving the tropical and subtropical cropping systems. The physical protection of SOM within soil aggregates was an important mechanism of C accumulation in the sandy clay loam Paleudult under NT. The cropping system and NT effects on C stocks were attributed to an increase in the lability of SOM, as evidenced by the higher POC to TOC ratio, which is very important to C and energy flux through the soil.
