1.11.1
BEAN YELLOW MOSAIC POTYVIRUS INFECTION OF ANNUAL PASTURE, FORAGE AND CROP LEGUMES IN AUSTRALIA: INCI

SJ MCKIRDY and RAC JONES

CRC for Legumes in Mediterranean Agriculture, University of Western Australia, Nedlands, WA 6907, Australia; Agriculture Western Australia, Locked Bag No. 4, Bentley Delivery Centre, WA 6983, Australia

Background and objectives
Currently a major effort is under way to promote the use of a more diverse range of pasture legumes, forage legumes and pulses in southern Australia. Traditional ley farming, which is based largely around annual pastures of subterranean clover (Trifolium subterraneum) and annual medics (Medicago spp.), is being expanded by sowing a wider range of annual pasture species or by phase farming using different annual species. Annual forage legumes are also increasingly being grown. The pulses being emphasized are targeted at soils unsuitable for narrow-leafed lupin (Lupinus angustifolius). Bean yellow mosaic virus (BYMV) is endemic in annual pastures in southern Australia, especially those in higher rainfall zones. The susceptibility/sensitivity to BYMV of most of the legume species now being introduced is unknown or not well understood. Work was therefore done to determine the susceptibility and sensitivity to BYMV of these annual pasture, forage and crop legumes.

Materials and methods
Towards the end of the growing season in 1997, field inspections were made to record levels of natural BYMV infection and symptoms caused in pasture, forage and crop legume plots at diverse sites in Western Australia. Replicated field experiments to determine the susceptibility and sensitivity of lines to BYMV were done at two sites in 1996 and 1997. Test lines were sown using the experimental design of McKirdy and Jones [1]. For this, BYMV-infected subterranean clover transplants were introduced at both ends of each row and natural aphid movement spread the virus resulting in high disease pressure. The test lines sown were from the genera Trifolium, Biserrula, Ornithopus, Hedysarum, Lathyrus, Vicia, Cicer and Lens. Levels of BYMV infection were recorded at regular intervals for each plot. Leaf samples were tested for BYMV by ELISA to confirm visual diagnoses.

Results and conclusions
At 2/3 sites, inspection of pasture and forage legume plots being grown for germplasm evaluation, breeding, seed increase and field experiments revealed high levels of BYMV infection (75-100%) in crimson clover (T. incarnatum), arrowleaf clover (T. vesiculosum), biserrula (Biserrula pelecinus), T. formosum, T. nigrescens and Trigonella balansae. Eleven other species were infected at a range of lower levels. Inspection of pulse breeding and germplasm plots at three sites revealed no infection in field pea (Pisum sativum) and chickpea (Cicer arietinum) plots, but some lentil (Lens culinaris) and faba bean (Vicia faba) plots at one site were infected with BYMV. In the replicated field experiments, BYMV was detected in 37/38 test lines. These included six species not apparently previously recorded as hosts, helmet clover (Trifolium clypeatum), bladder clover (T. spumosum), T. isthmocarpus, sea clover (T. squarrosum), gland clover (T. glanduliferum) and biserrula. The most susceptible pasture species were bladder, crimson, helmet and arrowleaf clovers and biserrula (80-100% infection). The most resistant were pink serradella (Ornithopus sativus) (<10% infection) and Hedysarum coronarium (not infected). Lathyrus species are potential forage and pulse crops. L. sativus (3/5 lines) had low susceptibility (<10%) but L. cicera and L. ochrus were very susceptible to BYMV (100% infection). Of the pulse crops, narbon bean (Vicia narbonensis) and 9/10 lentil lines were extremely susceptible to BYMV (100% infection), but lentil line ILL7163 and 5/6 chickpea cultivars failed to become infected despite high disease pressure. Low levels of infection (<5%) were detected in 4/4 cultivars of faba bean. These results suggest that BYMV is likely to pose major problems for the more susceptible pasture, forage and pulse species, in particular L. cicera, narbon bean, lentil, biserrula and several of the clovers. However, BYMV was not a cause for concern in serradella, H. coronarium, L. sativus, chickpea, field pea or faba bean.

Reference
1. McKirdy SJ, Jones RAC, 1995. Australian Journal of Agricultural Research 46, 135-152.