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Screening species of stylosanthes for resistance to anthracnose disease

D.F. Cameron1, R.G. O'brien2 and J.A.G. Irwin2

1 Division of Tropical Crops & Pastures, CSIRO, Mill Rd, St. Lucia. Qld. 4067
2 Queensland Department of Primary Industries, Meiers Road, Indooroopilly. Qld. 4068

Stylo anthracnose, a fungal disease caused by Colletotrichum

gloeosporioides, is damaging seed crops and pastures of Stylosanthes in higher rainfall regions of tropical Australia. As part of a program to reduce losses from this disease we are attempting to develop disease resistant cultivars. In this paper we report on glasshouse spray inoculations used to test Stylosanthes accessions for disease resistance.

Seedlings were grown in a glasshouse for 6-8 weeks and then sprayed with a spore suspension of the fungus (c. l x 106 spores ml-1) until run-off. Separate batches of seedlings were inoculated with composite inocula of Type A (isolates 31357, 31365, 31613) and Type B (isolates 31718, 31719, 31732) disease (Irwin and Cameron 1978), transferred to a Polythene humidity chamber (relative humidity > 85%) in the glasshouse and rated for anthracnose damage after 10 days. There were two replicates of four plants of each line, with twelve standard lines in each of the two runs. 358 accessions of the seven species listed in Table 1 were screened.

TABLE l. Reaction of Stylosanthes spp. to Type A anthracnose.

Of these seven species, only S. guianensis was damaged by the Type B disease. 30% of these accessions, including cvs. Endeavour and Schofield, were severely damaged but Cook and the new cv. Graham were damaged only slightly. Both S. fruticosa and S. subsericea were severely damaged by Type A disease (Table 1) and none of the tested introductions are likely to be useful in regions where regular disease epiphytotics are experienced. Although the S. humilis cultivars Paterson and Lawson, and the new S. scabra cultivar Fitzroy are susceptible to Type A disease, many of the other accessions from S. hamata (including cv. Verano), S. scabra (including cv. Seca) and S. viscosa were resistant or slightly susceptible. With the exception of S. fruticosa and S. subsericea there thus seems to be adequate scope for the selection of accessions resistant to the present collection of disease isolates. Collaboration with field workers is being maintained to monitor fungal populations for variation in pathogenicity since race specialization has been identified in Type A isolates.

Irwin, J.A.G. and Cameron, D.F. (1978). Aust. J. agric. Res. 29: 305.

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