In October 2001 and January 2002, in onion fields (Allium cepa L. cv Valencianita) in the Provinces of San Juan (SJ) and Mendoza (MZ), Argentina, plants were observed with chlorosis, dry leaf tips, and bulbs showing discoloration and rot. During the summer of 2002, a tan rot with white mycelium in rot cavities was also observed in stored garlic bulbs (Allium sativum) in MZ. Four monosporic cultures obtained with a micro punch adapted microscope (three from onion CSJ1, CMZ1, CMZ2 and one from garlic AMZ1) were characterized by morphology on PDA and carnation leaf agar (2). The isolates were deposited in the fungal collection of the Plant Mycosis Laboratory of the Integrated Unit Balcarce. The isolates produced abundant aerial white mycelium and a violet to vinaceous pigmentation. Club-shaped microconidia were abundant, in chains on both mono- and polyphialides. Slender, thin-walled and relatively straight macroconidia were produced only under black light and were mostly 3-septate. Chlamydospores were absent. The isolates were identified as Fusarium proliferatum. Crosses to confirm mating populations and to identify mating types were made in triplicate on carrot agar (3) with standard tester strains D-04853 (MATD-2) and D-04854 (MATD-1) as female parents and the field isolates as male parents. Crosses were examined weekly and were scored positive only if perithecia were seen oozing a cirrhus of ascospores. The identities of these isolates were confirmed as showing positive crosses with standard tester strains of Gibberella intermedia. Pathogenicity tests were conducted with healthy 45-day-old onion seedlings (cv. Valcatorce INTA). The roots of the onion seedlings were soaked in a conidial suspension (5 × 106 conidia/ml) of each isolate (CSJ1, CMZ1, CMZ2) for 2 h; the control was soaked in sterile water (SW). Seedlings were transplanted to pots in a sterile mixture of soil and sand (v/v). Five plants were used for each of 3 replications. The plants were placed in a greenhouse and irrigated with SW. After 3 weeks, symptoms were evaluated. All inoculated plants exhibited symptoms similar to those observed in the bulbs from which the pathogen was isolated and a brown rot appeared on the basal plate of the onion, later becoming dark brown. In garlic, the inoculation consisted of a wound 4.5 mm deep and 2 mm wide in superficially sterilized garlic cloves (cv. Nieve INTA). Inside the cavity, a drop (50 μl) was placed from a suspension of 5 × 106 conidia/ml (AMZ1), then covered with a drop of paraffin. Controls used SW. The garlic cloves were incubated in hermetically sealed trays at 22 ± 3°C in darkness for 3 weeks (1). Garlic showed tan rot and white mycelium in the wound. F. proliferatum was reisolated from inoculated onion seedlings and garlic cloves. The controls did not exhibit symptoms nor were any fungi recovered when tissue was excised from the inoculation points and plated on agar. F. proliferatum was previously reported in Argentina on asparagus (4) with symptoms similar to those of onion and garlic. To our knowledge, this is the first report of F. proliferatum attacking onion and garlic in Argentina. This pathogen has the potential risk of mycotoxin accumulation in contaminated bulbs. References: (1) F. M. Dugan et al. J. Phytopathol. 155:437, 2007. (2) W. Gerlach and H. Nirenberg. The genus Fusarium – A Pictorial Atlas. Mitt. Biol. Bundesanst. Land. Forstwirsch. Berl.-Dahlem, 1982. (3) C. J. R. Klittich and J. F. Leslie. Genetics 118:417, 1988. (4) G. Lori et al. Plant Dis. 82:1405, 1998.
Stem canker caused by Diaporthe phaseolorum var. caulivora is an important disease of soybean in Argentina. The objective of this study was to determine its survival ability in artificially infested straw under laboratory and field conditions. In laboratory, stem pieces of soybean, maize, sorghum, sunflower, potato and wheat were autoclaved, placed in petri dishes on Potato Dextrose Agar and Water Agar, and inoculated with a 7-day-old pathogen culture. All crop residues were colonized and produced perithecia. Debris artificially infested with D. phaseolorum var. caulivora were placed in plastic net bags and transferred to an un-cropped area in a field plot at the University of Buenos Aires. Straws were left on the ground from winter to spring season in both 2007 and 2008 years. After 6 months abundant perithecia were developed in all straws. However, a higher number of perithecia on soybean and sunflower compared to maize, sorghum and potato was determined. These findings suggest that other crops, besides soybean, could maintain alive the inoculum of Diaporthe phaseolorum var. caulivora from soybean for at least 6-7 months.
Manuscrito recibido el 27 de julio de 2015 y aceptado para su publicación el 2 de febrero de 2016. RESUMENEl cancro del tallo (CTS) ha sido la enfermedad más destructiva de la soja en el sudeste de la provincia de Buenos Aires en los últimos ciclos agrícolas. Considerando la inserción actual del cultivo en los sistemas productivos de esta zona, que el CTS es una enfermedad prevalente y que Diaporthe caulivora (Dc) es el agente causal predominante en Argentina, es importante conocer la identidad del agente prevalente en el área. Los objetivos fueron reconocer por características morfológicas las especies del complejo Diaporthe/Phomopsis presentes en cultivos de soja, en los ciclos agrícolas 2010/11-2011/12-2012/13, y confirmar molecularmente mediante PCR-RFLP, que la especie predominante causante ABSTRACTDiaporthe caulivora: predominant causal agent of stem canker in soybean crops in the southeast of Buenos Aires province.Stem canker (SC) has been the most destructive disease of soybean in the southeast of Buenos Aires in the last agricultural cycles. Considering the current inclusion of the soybean in the production systems in this area, that the SC is a prevalent disease, and that Diaporthe caulivora (Dc) is the predominant causal agent in Argentina, it is important to know the identity of the agent prevalent in the area. The objectives of the study were to recognize by morphology the species of the Diaporthe/Phomopsis complex present in soybean crops during the agricultural cycles 2010/11-2011/12-2012/13, and confirmed using PCR-RFLP that the predominant species causing symptoms of SC was Dc. Out of 39 isolates, 61% corresponded to Dc, 26% to P. longicolla,
Cultivated sunflower (Helianthus annuus L.) is susceptible to Sclerotinia sclerotiorum (Lib.) de Bary. H. petiolaris Nutt is a wild sunflower species naturalized in Argentina. The objective of this work was to evaluate the responses of some accessions of H. petiolaris to S. sclerotiorum inoculation in order to detect potential sources of resistance to be used in cultivated sunflower. An experiment was carried out at the UIB's experiment field. Inoculations were made on leaves and stems. Lesion mean on leaves was 22 mm and 24 mm on stems. The accession GRR-252 showed mean lesions on leaves significantly longer than in GRR-250. However, there were no differences for stem inoculation. Correlation analysis indicated the independence of leaf and stem responses. Results obtained after the first experimental trial suggest the possibility of detecting some H. petiolaris accessions with a higher level of resistance to S. sclerotiorum than others.
Phytophthora sojae causes root and stem rot of soybeans. In Argentina, this pathogen has shown dramatic shifts in pathotype variability since its first discovery during the 1970s. The aim of this study was to report the presence and distribution of different pathotypes of P. sojae isolates from 2013 to 2015 in the southeast of Buenos Aires Province in Argentina. Isolates were obtained from diseased soybean plants and soil in contact with the infected root. The pathotype evaluation of P. sojae was determined with a set of eight differential soybean lines. One hundred and twenty-four P. sojae isolates were obtained and forty pathotypes were determined, which is a considerable variability for a relatively new and recently infested soybean area.
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