February 24, 2006
From: ProMED-mail<promed@promedmail.org>
Source: British Society for Plant Pathology, New Disease Reports, Vol. 13 [edited] <http://www.bspp.org.uk/ndr/july2006/2006-12.asp >


First report of Penicillium allii as a field pathogen of garlic (Allium sativum)
J. G. Valdez (1), M. A. Makuch(1), A. F. Ordovini1, R. W. Masuelli(1), D.P. Overy (2,3) and R. J. Piccolo(1)
1 INTA La Consulta. CC 8 (5567), Mendoza, Argentina
2 CMB, BioCentrum-DTU, Bldg. 221, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark
3 IBS, Edward Llwyd Bldg., University of Wales, Aberystwyth, UK. SY23 3DA

Accepted for publication 14 Feb 2006

Blue mold disease in garlic is associated worldwide with various _Penicillium_ species and has been [caused] significant annual crop losses in Argentina; the world's 2nd largest exporter of garlic. To identify the responsible pathogenic _Penicillium_ species, symptomatic plants were sampled in La Consulta station (33 deg 45 min S, 69 deg 02 min W) and damp-chambered. 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 micro-morphology as _Penicillium allii_ and identifications were confirmed by comparing RP-HPLC secondary metabolite profiles with those of type _P. allii_ strains.

To confirm pathogenicity, sterilised garlic cloves were injured with a needle and inoculated with 5 micro-litres of _P. allii_ spore suspensions (adjusted to 5x106 conidia per ml). Cloves were planted in a field not previously
cultivated with garlic (4 replications and an untreated control). The original disease symptoms were produced on inoculated plants while control plants remained healthy. The survival rate of inoculated plants was 68 percent. _P.
allii was re-isolated from symptomatic field plants.

_P. viridicatum_ was first reported as the causal agent of blue mould of garlic in Argentina (Gatica & Oriolani, 1984) before the characterisation of _P. allii_ (Vincent & Pitt, 1989). _P. allii_ is micro-morphologically 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 sterilised garlic cloves and incubated for 12 days. The _P. viridicatum_ strains were not able to sporulate on the garlic cloves.

_P. 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 moisture chambers(Overy et al., 2005). Our results suggest that _P. allii_, rather than _P. hirsutum_ or _P. viridicatum_, is the pathogenic species responsible for garlic crop losses due to blue mold rot in
Argentina. This is the first report confirming _P. allii_ as a field pathogen of _A. sativum_.

Acknowledgements
This work was partly supported by project Pict # 0803687 of Argentina.

References

Cavagnaro PF, Camargo A, Piccolo RJ, Garcia Lampasona S, Burba JL, Masuelli RW, 2005. Resistance to _Penicillium hirsutum_ Dierckx in garlic accessions. European Journal of Plant Pathology 112, 195-9.

Gatica M, Oriolani E, 1984. _Penicillium viridicatum_ Westling, agente causal de la "podredumbre verde o moho azul" del ajo (_Allium sativum_ L.) en Mendoza, Republica Argentina. Informativo de Investigaciones Agrarias 421/424, 1-7.

Overy DP, Frisvad JC, Steinmeier U, Thrane U, 2005. Clarification of the agents causing blue mould storage rot upon various flower and vegetable bulbs: implications for mycotoxin contamination. Postharvest Biology and Technology 35, 217-21.

Vincent MA, Pitt JI, 1989. _Penicillium allii_, a new species from Egyptian garlic. Mycologia 81, 300-03.
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[The results presented demonstrate that _Penicillium allii_, rather than _P. hirsutum_ or _P. viridicatum_, is the pathogenic species responsible for garlic crop losses during storage due to blue mold in Argentina. This is the
1st report confirming _P. allii_ as a field pathogen of _Allium sativum_. The general problem of correct diagnosis of _Penicillium_ species on onions and garlic is exemplified by this study. This plant disease in garlic is managed
by storing bulbs with a minimum of bruising, wounding, or insect damage. Prompt curing of bulbs so the necks are dry and storing bulbs at temperatures of 41 deg F (5 deg C) or less with low relative humidity minimizes disease losses.

Map: <http://www.maplandia.com/argentina/mendoza/>
Pictures: <http://www.bspp.org.uk/ndr/july2006/2006-12-1th.jpg>

Links:
<http://www.agr.unipi.it/sipav/jpp/volumes/0105/010507.pdf>
<http://www.ipm.ucdavis.edu/PMG/r584101011.html>
- Mod.JAD]