March 30, 2006
From: ProMED-mail<promed@promedmail.org>
Source: American Phytopathological Society, Plant Disease Notes, April 2006 [edited] <http://www.apsnet.org/pd/searchnotes/2006/PD-90-0524A.asp>


Occurrence of charcoal rot caused by Macrophomina phaseolina on canola in Argentina
SA Gaetan, L Fernandez, M Madia, Catedra de Fitopatologia, Facultad de Agronomia, Universidad de Buenos Aires, Avda San Martin 4453, CP 1417 DSE, Buenos Aires, Argentina. Plant Dis 2006; 90: 524, published online as DOI: 10.1094/PD-90-0524A. Accepted for publication 11 Jan 2006.

Canola (_Brassica napus_) is an important oleaginous crop in Argentina. About 16 000 ha are grown commercially in the southern region of Buenos Aires Province. In 2003, typical symptoms and signs of charcoal rot were
observed on canola plants in experimental plots located at the School of Agricultural Sciences, University of Buenos Aires in Buenos Aires. Average disease incidence across 3 plants 5-6 months old (cvs. Monty, Rivette, and
Trooper) was 12 per cent (range 7-17 per cent). Affected plants appeared in patches following the rows at pod-filling stage. Symptoms included wilted foliage, premature senescence, and death of plants. Black, spherical microsclerotia 78-95 micrometres in diameter were present in vascular tissue of basal stems and taproots. The affected plants were stunted and had unfilled pods. In advanced phases of the disease, areas of silver gray-to-black discoloration were observed in the stem cortex; many plants were killed during late-grain fill, and plants could be pulled easily from the ground because basal stems were shredded. Four samples consisting of 5 symptomatic plants per sample were randomly collected from experimental plots. Pieces (1 cm long) taken from taproots and basal stems of diseased plants were surface sterilized with 1 per cent NaOCl for 2 min and then
placed on potato dextrose agar (PDA). Plates were incubated in the dark at 26 deg C for 4 days and then exposed to 12-h NUV light/12-h dark for 6 days. Five resulting isolates were identified as _Macrophomina phaseolina_ (Tassi) Goidanich (1) based on the gray color of the colony and the presence of microsclerotia 71 to 94 micrometers in diameter. Two colonies developed globose pycnidia with one-celled, hyaline, and elliptic conidia. Pathogenicity tests were conducted using 4 inoculated and 3 noninoculated control plants potted in a sterilized soil mix (soil/sand, 3:1) in a greenhouse at 25 deg C and 75 percent relative humidity with no supplemental light. Crown inoculations were carried out by placing a disk taken from an actively growing culture of _M. phaseolina_ into wounds made with a sterile scalpel. Control plants received disks of sterile PDA.

Inoculated and control plants were covered with polyethylene bags for 48 h after inoculation. Three isolates caused disease on 7-week-old canola plants (cvs. Master, Mistral, Rivette, and Trooper). Characteristic symptoms similar to the original observations developed for all 3 isolates within 21 days after inoculation on 80 per cent of inoculated plants. The pathogen was successfully reisolated from diseased stem tissue in all instances. Symptoms included leaf necrosis, stunting, decay and collapse of seedlings, and plant death. Control plants remained asymptomatic. The experiment was repeated once with similar results. To our knowledge, this is the first report of the occurrence of _M. phaseolina_ causing charcoal rot on canola in Argentina. This pathogen has been previously reported in the United States (2,3). The results demonstrate the potential importance of this pathogen in Argentina, since 2 commercial cultivars (Master and Mistral) were apparently susceptible to _M. phaseolina_. More studies are needed to determine the presence of charcoal rot in canola-growing areas of Argentina.

References:
1. Anon. _Macrophomina phaseolina_. No. 275 in: Descriptions of Plant Pathogenic Fungi and Bacteria. Kew, UK: CMI, 1970.
2. RE Baird, et al. Plant Dis 1994; 78: 316.
3. DF Farr, et al. Fungi on plants and plant products in the United States. St Paul, MN: American Phytopathological Society, 1989.

--
ProMED-mail
<promed@promedmail.org>

[The oil-crop plant canola, _Brassica napus_, is an alternative crop to wheat in Argentina. It develops symptoms of the disease charcoal rot when infected by the fungus _Macrophomina phaseolina_ (Mp), which is a highly
variable fungus, with isolates differing in microsclerotial size and the ability to produce pycnidia. The pathogen also infects and causes diseases of corn/maize, soybeans, and sunflower. It is a weak pathogen killing plants that are stressed, especially by high temperatures. It is an important pathogen in southern USA, Mexico, and Africa. Sclerotia survive in soil, thus providing inoculum for future infections of the crop. Crop rotation, use of early maturing varieties to avoid late season heat/drought stress, and water management are methods used to manage the disease.

Map: Argentina, Buenos Aires
<http://worldatlas.com/webimage/countrys/samerica/ar.htm>

Links:
<http://highplainsipm.org/HpIPMSearch/Docs/CharcoalRot-CanolaMustard.htm>  
Mod.JAD]

[see also in the archive:
2005
---
Blackleg, canola - Argentina (02) 20050813.2368
Charcoal rot, soybean - USA (IA): 1st report 20050416.1092
Fusarium wilt, canola - Argentina: 1st report 20050414.1073
Blackleg, canola - Argentina: 1st report 20050319.0807
Gray leaf spot, canola - Argentina 20050218.0534
2004
---
Powdery mildew, canola - Argentina 20041101.2956
2003
---
Charcoal rot, soybean - USA (Illinois) 20031001.2469
Charcoal rot, soybean - USA (North Dakota) 20030606.1394
2002
---
Charcoal rot, sunflower - USA (N. & S. Dakota) 20020816.5066]