
TY  - JOUR
A1  - McKirdy, SJ 
A1  - Jones, RAC 
T1  - Infection of alternative hosts associated with annual medics (<I>Medicago</I> spp.) by alfalfa mosaic virus and its persistence between growing seasons
JF  - Australian Journal of Agricultural Research
JO  - Aust. J.  Agric. Res.
Y1  - 1994
VL  - 45
IS  - 7
SP  - 1413
EP  - 1426
KW  - alternative hosts;suscepibility persistence;sources;alfalfa mosaic virus;seed transmission;annual medics;broadacre agriculture
UR  - https://doi.org/10.1071/AR9941413 
N2  - Under conditions of natural alfalfa mosaic virus (AMV) spread, five plant species found associated with annual Medicago spp. (medics) were infected commonly and another seven sporadically. Ten of these were new records. Because seed of herbaceous plant hosts provides a possible route for virus persistence through dry summer conditions, AMV seed transmission was tested for in alternative hosts. Of ten species systemically infected by sap inoculation with AMV, seed transmission was detected in Melilotus indica (l0%), Ornithopus compressus (0 1%) and Stachys arvensis (2%). Seed of seven naturally infected potential alternative host species was tested, and seed transmission found in Crassula decumbens (0. 1%), M. indica (3%), 0. compressus (0.2%), S. arvensis (0.4%) and Trifolium subterraneum (2%). Carry-over of AMV through seed transmission was detected in seedlings of Hypochaeris glabra (0.2%) and M. indica (0.6-0.8%) that germinated naturally in the field. In grazed, self-regenerated Medicago murex and M. polymorpha swards sown in 1987, the virus persisted for at least seven growing seasons. Levels of infection in M. polymorpha seed produced each year declined, but levels in the general seed bank remained higher due to presence of older seed. It is concluded that under the conditions of broadacre agriculture in the Mediterranean-type climate of Western Australia, seed transmission in C. decumbens, H. glabra and volunteer 0. compressus is an alternative means by which AMV can persist over summer to act as sources of AMV for spread within annual medic pastures. However, persistence through seed of the annual medic cultivars sown and of naturalized annual Medicago species is the principal means of persistence. AMV persists readily from year to year following sowing of infected seed and is likely to cause a recurrent disease problem in annual medic pastures. 
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