The objectives of this work were to estimate the capability of local populations of thrips as vectors of groundnut ringspot virus (GRSV) and tomato spotted wilt virus (TSWV), and to determine the species composition of vectors in tomato crops. Transmission assays were performed. Incidence of tospoviruses was estimated in commercial crops. Random samples of flowers were taken from tomato for identification of thrips. Of the five species of thrips tested, Frankliniella gemina (first record), F. occidentalis and F. schultzei transmitted GRSV and TSWV. F. schultzei was a significantly more efficient vector of GRSV than F. occidentalis under controlled assay conditions. The thrips were identified on flowers from six surveyed tomato crops. F. occidentalis was the most frequently identified species (43.0%), followed by F. schultzei (35.6%) and Thrips tabaci (10.1%). The incidence of tospoviruses was low (1.1-2.8%) in crops planted during August-September and greater (9.5-61.1%) in crops planted in December. GRSV was prevalent (85%) over TSWV (11%).www.blackwell-synergy.com

Fusarium basal rot (FBR), which is caused predominantly by Fusarium oxysporum and F. proliferatum, is the main limiting factor of onion crops. Resistant cultivars obtained in other countries do not behave as such in Argentina crop fields. The cultivars Antártica-INTA, Grano de Oro-Seminis, Valcatorce-INTA and TW-2007 (reported as tolerant) were tested with five Fusarium spp. isolates, using four inoculum concentrations. Disease incidence was recorded along 28 days and the area under disease progress curve was calculated. Diverse epidemiological models were fitted to experimental data. There were significant differences in the resistance level among cultivars, with TW-2007 being the most tolerant. Local Fusarium isolates were the most virulent ones. The concentration of 10,000 microconidia/ gram was the most lethal for all isolates. The absence of resistance to Fusarium in the four cultivars tested was confirmed. Inoculum concentration and isolate are critical factors in screening for resistance to FBR. Breeding based on the selection of genotypes against low virulence strains of Fusarium spp. and the presence of more aggressive strains in local fields may be one of the causes why varieties reported as resistant or tolerant behave as susceptible in our environment.

A total of 147 samples of garlic ( Allium sativum ) bulbs affected by blue mould were obtained from a variety of agroclimatic districts between December 1999 and February 2000. Penicillium species were identified using both morphological and chemotaxonomic characteristics. Penicillium allii was the predominant species isolated (81·8%) in this survey and the only species proven to be pathogenic on garlic. Other species were isolated much less frequently: P. chrysogenum (13·7%), P. brevicompactum (2·8%), P. phoeniceum (0·9%), P. aurantiogriseum (0·6%) and P. flavigenum (0·2%). Colonies of P. allii could be classified into four morphotypes and their distribution seemed to be influenced by seed trade and agricultural practices. Penicillium allii isolates were grouped into three aggressiveness phenotypes (low, medium and high) based on their ability to cause disease during field trials on susceptible (Fuego INTA) and less susceptible (Castaño INTA) garlic cultivars. The number of surviving plants at 191 days after planting and postharvest bulb weight contributed the most towards aggressiveness modelling.

Blue mould disease in garlic ( Allium sativum ) is associated worldwide with various Penicillium species, and has been attributed to significant annual crop losses in Argentina; the world's second largest exporter of garlic. To identify the pathogenic Penicillium species responsible, affected plants were sampled in La Consulta station (33 ° 45 ′ S, 69 ° 02 ′ W) and placed in a damp chamber. Characteristic disease symptoms are stunted and chlorotic plants with withered leaves and reduced bulb size. Bulbs are often covered with blue/green conidial masses. Isolations were made from fungal colonies emerging on affected bulbs. Pure cultures (IBT 26466, 26467, 26511 and 26512; CMB collection, BioCentrum-DTU, Denmark) were initially identified by micromorphology as Penicillium allii , and identifications were confirmed by comparing reversed phase-HPLC secondary metabolite profiles with those of P. allii type strains.To confirm pathogenicity, sterilized garlic cloves were injured with a needle and inoculated with 5 µ L P. allii spore suspensions (adjusted to 5 × 10 6 conidia mL − 1 ). Inoculated cloves were planted in a field not previously cultivated with garlic, and the original disease symptoms were produced on inoculated plants while water-inoculated control plants remained healthy. The survival rate of inoculated plants was 68% and P. allii was reisolated from diseased field plants.Penicillium viridicatum was first reported as the causal agent of blue mould of garlic in Argentina (Gatica & Oriolani, 1984) before the characterization of P. allii (Vincent & Pitt, 1989). Penicillium allii is micromorphologically similar to P. viridicatum and both species produce yellow exudates in pure culture. To compare pathogenic ability, standard P. viridicatum strains IBT 16939 and 15053 were inoculated into sterilized garlic cloves and incubated for 12 days. The P. viridicatum strains were not able to sporulate on the garlic cloves.Penicillium hirsutum was recently reported as a pathogen on garlic in Argentina (Cavagnaro et al ., 2005). However, P. allii but not P. hirsutum has been reported as an aggressive pathogen of garlic in comparative pathogenicity trials conducted in damp chambers (Overy et al ., 2005). The results reported here suggest that P. allii , rather than P. hirsutum or P. viridicatum , is the pathogenic species responsible for garlic crop losses due to blue mould rot in Argentina. This is the first report confirming P. allii as a field pathogen of A. sativum.

Among the factors affecting the quality and yield of garlic production, blue mold caused by -Penicillium spp. -is responsible for economical losses in many countries. Allicin, present in garlic bulbs, has been suggested as having antifungal activity against some Penicillium species. This study was conducted to evaluate the response of garlic accessions against Penicillium hirsutum infection and to compare this response with bulb allicin content. Twelve garlic accessions were inoculated with P. hirsutum, and assayed in greenhouse and growth chamber experiments. Plant growth parameters and the fungal production of conidia were evaluated. Significant differences were found among the accessions. Accessions Castan˜o and Morado were most resistant whereas AR-I-125 and Fuego were always severely affected by the disease. A low correlation was found (r = 0.17) between allicin content and tolerance, indicating that allicin is not the main factor involved in the resistance against P. hirsutum.