Temperate Pulse Viruses: Alfalfa Mosaic Virus (AMV) (Vic)

August 2005 Temperate Pulse Viruses: Alfalfa AG1206 Mosaic Virus (AMV) ISSN 1329-8062 Angela Freeman and Mohammad Aftab, Horsham

Alfalfa mosaic virus (AMV) was first identified infecting lucerne in the USA and is now distributed worldwide. The main source of this virus is lucerne, but it has a wide host range which includes the temperate pulses (chickpeas, faba beans, field peas and lentils) and pasture legumes and weeds. The virus is spread by a number of common aphid species as well as being seed transmitted in some species. In areas where large aphid populations occur, crop losses can be high due to reduced herbage production and seed yield. Host range The host range of AMV is wide and not limited to Figure 1. Desi chickpea showing reddening of leaves and Fabaceae. Temperate pulse hosts include chickpeas, faba stunting. beans, field peas, lentils, narbon beans, grass peas and vetch. Pasture legume hosts include lucerne, burr medic and other annual medics and a number of clover species. Weed hosts, which are common in the Victorian pulse cropping areas, include bristly oxtongue, common sowthistle, clammy sowthistle and blackberry nightshade. AMV also has a number of horticultural and vegetable crop hosts. Symptoms Symptoms on the infected plant depend greatly on the virus strain, host variety, stage of growth at infection and environmental conditions. In many species, a bright yellow mottle or mosaic develops. Local or systemic necrosis and stunting may also occur. Some species recover from early Figure 2. Kabuli chickpea showing yellowing and necrosis of infections. In some species seed size may be reduced. shoot tips . Symptoms in the major temperate pulses, pasture legumes and weeds are as follows: • Desi chickpeas develop shoot tip necrosis combined with chlorosis and reddening of the leaf margin (Figure 1). • Kabuli chickpeas develop chlorosis and necrosis of shoot tips and stunting of plants (Figure 2). • Faba beans develop chlorosis, necrosis and stunting of the new shoots. Leaf rolling, ring spots on leaves and general plant stunting may occur (Figure 3).

Figure 3. Faba bean (centre) showing leaf rolling and stunting. (Courtesy J.Van Leur, DPI, NSW).

• Field peas develop chlorosis and necrosis of the new shoots. Necrotic spots or streaking on older leaves and plant stunting may occur. Pods may be malformed and fail to develop peas (Figure 4). • Lentils develop necrotic tip growth, twisting and deformation of leaves and stunting (Figure 5). • Lucerne develops mottling or mosaic symptoms and reddening of leaf margins (Figure 6). Symptoms may disappear in summer. • Clover species tend to develop vein clearing, chlorosis or necrosis of the leaves and sometimes plant stunting (Figure 7). • Some weed species develop a distinctive bright yellow Figure 4. Field pea showing chlorisis and necrosis of new shoots and malformed pods (Courtesy J.Davidson, SARDI, SA). mosaic on the leaves (Figure 8). Economic importance Surveys of lentil crops over a number of years in Vic. and SA showed that up to 17% of crops were infected with AMV, with a within crop incidence of up to 21% of plants. Surveys of faba bean and field pea crops in WA over a number of years showed that AMV incidence never exceeded 7% of crops, or 4% of plants within individual crops. However, plot trials in WA showed that herbage and seed yield reductions could be up to 40% in faba beans, 80% in lentils and 30% in burr medic. AMV was found in the majority of lucerne crops in surveys in NSW in 1982 and in WA in 2001, some paddocks having more than 50% of the plants infected. Figure 5. Lentil showing yellowing and necrosis of shoot tips and stunting of plant (left) compared to healthy plant (right). Transmission AMV is transmitted by aphids in non-persistent manner. The spread of the virus is generally over short distances and aphids only remain infective for periods from a few minutes up to a few hours. There are over 20 species of aphid capable of transmitting this virus. During surveys of the Wimmera cropping region over a number of years the following aphid vectors of AMV were found: lucerne blue green aphid (Acyrthosiphon kondoi), cowpea aphid (Aphis craccivora), foxglove aphid (Aulacorthum solani), ornate aphid (Myzus ornatus), green peach aphid (Myzus persicae), and alfalfa spotted aphid (Thryociphum maculata). AMV is transmitted via seeds in a number of host species. Seed transmission rates of 0.1-5% in lentils and 0.1-1% in Figure 6. Lucerne showing reddening of leaves from margins chickpeas have been recorded. AMV is also seed (left) and healthy leaf (right). transmitted in a range of annual pasture and forage legume species, including 0.4-19% in lucerne seed.

Management AMV is spread by sowing infected seed or by movement of aphid vectors from infected plants to healthy plants. Low levels of seed infection in pulses may lead to spread of AMV during years with high rainfall and subsequent early build up of large aphid populations. Chemical control of aphids is not an effective method for controlling AMV. Sowing healthy seed, managing weeds and other cultural practices to minimise AMV spread are recommended. Growing crops adjacent to infected lucerne or pasture will increase the risk of crop infection. Some seed companies sell lentil seed which has been tested for AMV and cucumber mosaic virus (CMV). Commercial seed testing companies will also test legume seedlots for seedborne viruses such as AMV. If farmers retain their own seed it should be selected from crops Figure 7.Subterranean clover leaves develop interveinal which do not have virus symptoms or evidence of aphids. chlorosis and purple or necrotic margins

More information Jones RAC, Coutts BA (1996) Annals of Applied Biology 129, 491-506. Latham LJ, Jones RAC (2001a) Australian Journal of Agricultural Research 52, 397-413. Latham LJ, Jones RAC (2001b) Australian Journal of Agricultural Research 52, 771-790.

Figure 8. Common sowthistle develops yellow mosaic symptoms on young and older leaves

Acknowledgement Thanks to Wendy Bedggood for assistance in preparing The advice provided in this publication is intended as a source of information only. Always read the label before using any of the this Note. products mentioned. The State of Victoria and its employees do not guarantee that the publication is without flaw of any kind or is wholly appropriate for your particular purposes and therefore disclaims all liability for any error, loss or other consequence which may arise from you relying on any information in this publication.