Sequential Post-Heading Applications for Controlling Wheat Blast: A 9-Year Summary of Fungicide Performance in Brazil.

Wheat blast, caused by Pyricularia oryzae Triticum lineage, is a major constraint to wheat production, mainly in the tropics of Brazil, where severe epidemics have been more frequent. We analyzed disease and wheat yield data from 42 uniform field trials conducted over 9 years (2012 to 2020) to assess whether the percent control and yield response were influenced by fungicide type, region (tropical or subtropical), and year. Six treatments were selected, all evaluated in at least 19 trials. Two fungicides were applied as solo active ingredients (MANCozeb, and TEBUconazole), and four were premixes (AZOXystrobin plus TEBU, TriFLoXystrobin plus PROThioconazole, TFLX plus TEBU, and PYRAclostrobin plus EPOXiconazole). Percent control, calculated from back-transforming estimates by a meta-analysis network model fitted to the log of the means, ranged from 43 to 58%, with all but PYRA plus EPOX showing efficacy >52% on average, not differing among them. The variation in both efficacy and yield response was explained by region, and all but TEBU performed better in the subtropics than in the tropics. Yield response from using three sequential sprays was approximately two times greater in the subtropics (319 to 532 kg/ha) than in the tropics (149 to 241.3 kg/ha). No significant decline in fungicide efficacy or yield response was observed in 9 years of study for any of the fungicides. These results reinforce the need to improve control by adopting an integrated management approach in the tropics given poorer performance and lower profitability, especially for the premixes, than in the subtropics.

False Bean Smut Caused by Slime Mold.

Identification of the "bean smut" reported in 1998 in abstracts from two conferences was later disseminated by a Plant Disease Note; citations in books, papers, and blogs; and in several official sites, including databases curated by the United States Department of Agriculture and Embrapa-Brazil. After seeing the illustration of the syndrome in 2002, the need became clear for a review of the so-called bean smut. Field collections indicated that it is common in no-till bean and soybean farming in Brazil. Our studies revealed that the "bean smut" attributed to Ustilago sp. or "Ustilago phaseoli" and, later, to "Microbotryum phaseoli" is not a real smut but is Physarum cinereum (Physaraceae, Physarales, Myxomycetes), sporulating superficially on leaves, stems, and pods of dry bean and soybean. To unravel this imbroglio, we produced detailed morphological documentation supported by molecular treatment. This will correct the spread and further incorporation of an error in the literature based upon mistaken taxonomical work related to a plant-associated nonpathogenic organism.

Fusarium paranaense sp. nov., a member of the Fusarium solani species complex causes root rot on soybean in Brazil.

Isolates of Fusarium obtained from soybean plants showing symptoms of root rot collected in subtropical southern and tropical central Brazil were characterized based on phylogenetic analyses, sexual crossing, morphology, and pathogenicity tests. A novel species within the Fusarium solani species complex (FSSC) causing soybean root rot is formally described herein as Fusarium paranaense. This species can be distinguished from the other soybean root rot pathogens in the FSSC, which are commonly associated with soybean sudden death syndrome (SDS) based on analyses of the combined DNA sequences of translation elongation factor 1-α and the second largest subunit of RNA polymerase II and on interspecies mating compatibility. Bayesian and maximum parsimony phylogenetic analyses showed that isolates of F. paranaense formed a distinct group in clade 3 of the FSSC in contrast to the pathogens currently known to cause SDS, which are in clade 2. Female fertile tester strains were developed that can be used for the identification of this new species in the FSSC based on sexual crosses. All isolates were heterothallic and belonged to a distinct mating population. Fusarium tucumaniae, a known SDS pathogen, was found in the subtropical southern region of the country.

A new chitinase-like xylanase inhibitor protein (XIP) from coffee (Coffea arabica) affects Soybean Asian rust (Phakopsora pachyrhizi) spore germination.

BACKGROUND: Asian rust (Phakopsora pachyrhizi) is a common disease in Brazilian soybean fields and it is difficult to control. To identify a biochemical candidate with potential to combat this disease, a new chitinase-like xylanase inhibitor protein (XIP) from coffee (Coffea arabica) (CaclXIP) leaves was cloned into the pGAPZα-B vector for expression in Pichia pastoris. RESULTS: A cDNA encoding a chitinase-like xylanase inhibitor protein (XIP) from coffee (Coffea arabica) (CaclXIP), was isolated from leaves. The amino acid sequence predicts a (ß/α)8 topology common to Class III Chitinases (glycoside hydrolase family 18 proteins; GH18), and shares similarity with other GH18 members, although it lacks the glutamic acid residue essential for catalysis, which is replaced by glutamine. CaclXIP was expressed as a recombinant protein in Pichia pastoris. Enzymatic assay showed that purified recombinant CaclXIP had only residual chitinolytic activity. However, it inhibited xylanases from Acrophialophora nainiana by approx. 60% when present at 12:1 (w/w) enzyme:inhibitor ratio. Additionally, CaclXIP at 1.5 µg/µL inhibited the germination of spores of Phakopsora pachyrhizi by 45%. CONCLUSIONS: Our data suggests that CaclXIP belongs to a class of naturally inactive chitinases that have evolved to act in plant cell defence as xylanase inhibitors. Its role on inhibiting germination of fungal spores makes it an eligible candidate gene for the control of Asian rust.

Fungal pathogens of Miconia calvescens (Melastomataceae) from Brazil, with reference to classical biological control.

A survey of fungal pathogens of Miconia calvescens was carried out in Brazil aimed at finding potential classical biocontrol agents for management of this invasive alien weed in Hawaii. Coccodiella miconiae, Glomerella cingulata (= Colletotrichum gloeosporioides f. sp. miconiae) and the new species Guignardia miconiae and Korunomyces prostratus were found associated with foliar diseases and are described herein. Two previously undescribed spore stages of Coccodiella miconiae also were obtained allowing a complete description of this species. Pseudocercospora tamonae associated with leaf spots of other species of Miconia also was collected and also was proven to be pathogenic to M. calvescens.