Published Date: 2012-08-06 09:20:49
Subject: PRO/PL> Aster yellows, wheat & barley - Canada
Archive Number: 20120806.1229839
ASTER YELLOWS PHYTOPLASMA, WHEAT AND BARLEY - CANADA
A ProMED-mail post
ProMED-mail is a program of the
International Society for Infectious Diseases
Date: 31 Jul 2012
Source: Canada NewsWire [edited]
Prairie farmers may experience disappointment in wheat yields and quality due to an unusually high infestation rate of disease commonly seen in canola, now impacting wheat and other prairie crops.
Dr. Ieuan Evans, Agri-Trend, has confirmed the widespread infection of aster yellows in wheat and other crops. "It is not uncommon to find aster yellows in canola; this year , the infection rates are as high 10-40 percent. However, professionals began to notice unusual disease symptoms in wheat fields adjacent to infested canola fields together with very high levels of leaf hoppers."
In infested wheat fields, the disease has taken the form of yellowish to reddish foliage along with premature dying of randomly scattered wheat plants at anthesis or early milk stage. Areas in Manitoba, Saskatchewan, and Alberta have up to 30-40 percent of bleached or dying heads in wheat fields infected with aster yellows. This will likely result in significant yield loss.
Diseased wheat, barley, and canola samples gathered throughout the prairies have been confirmed positive for aster yellows. Additional samples are being forwarded to Agriculture Canada for testing.
"It is felt that this year , the aster yellows infestation occurred as a consequence of unusually high levels of leaf hoppers arriving in prairie Canada from the US in mid-May to early-June . Tests of the leaf hoppers by Manitoba Agriculture confirmed higher than normal levels of phytoplasmal infection," said Evans. "Additional reports are now coming in of infections in flax and barley."
[Aster yellows phytoplasma (_Candidatus_ Phytoplasma asteris, 16SrI-B taxonomic group) can infect over 300 host species including a wide variety of broadleaf (dicotyledoneous) crops such as oilseed rape, potato ("purple top"), grapevine, lucerne and some vegetables. Cereals and other monocots are usually affected to a lesser extent. Symptoms on wheat and barley may include general chlorosis, head distortion and sterility. Ornamentals and weeds can serve as pathogen reservoirs.
The phytoplasma can overwinter in the living crowns of perennials. It can be transmitted by grafting, but not in soil or by seed. The primary vector appears to be the aster leafhopper (_Macrosteles quadrilineatus_). After acquiring the pathogen, insects remain infectious for life. The pathogen may be present in host species at very low levels; however, the level can increase under favourable conditions (for example high rainfall) resulting in an outbreak with potential crop losses. Disease management in field crops, including cereals, may include vector control and removal of weeds serving as pathogen and/or vector reservoirs. For woody hosts, clean planting and/or grafting material is most important.
High levels of aster yellows are currently also reported in the broadleaf crops oilseed rape (canola) and potato from North Dakota, USA (see links below).
A range of phytoplasma species and/or strains in the aster yellows group have been isolated from different hosts, and more work is required on their exact taxonomic relationships.
Individual provinces via:
North America, overview:
Aster yellows symptoms on wheat:
Aster yellows affected barley heads:
Aster yellows symptoms on oilseed rape:
Aster yellows disease information:
Current aster yellows infections of broadleaf crops, North Dakota:
http://www.ag.ndsu.edu/cpr/plant-pathology/potato-purple-wilt-top-7-26-12 (potato purple top) and
http://www.ag.ndsu.edu/cpr/entomology/aster-leafhopper-threat-to-canola-5-24-12 (oilseed rape)
New 16SrI-B phytoplasma strain/species from cowpea, India:
_C._ Phytoplasma asteris taxonomy and strains:
Phytoplasma resource centre, information, and pictures:
A HealthMap/ProMED-mail map can be accessed at: http://healthmap.org/r/1ALd.]