Components of quantitative resistance to anthracnose (Colletotrichum gloeosporioides) in tetraploid accessions of the pasture legume Stylosanthes hamata

Abstract

Partial resistance to the anthracnose pathogen Colletotriclzum gloeosporioides was characterised in 6 tetraploid accessions and cv. Verano of the tropical pasture legume Stylosanthes hamata. Four components of resistance (incubation period, latent period, spore production, weighted infection type) were determined and compared with those of the susceptible S. scabra cv. Fitzroy. There were significant differences between the accessions for all resistance components. The mechanisms of resistance in the 3 most resistant accessions appeared to be different, with accession 55830 having a longer incubation period but higher sporulation per day than either 92715 or 92412. Spore production, weighted infection type, and latent period were significantly (P<0.05) correlated with resistance of adult plants in the field (ADPC). The weighted infection type was useful in discriminating between accessions that had similar disease severity scores. A quantitative relationship was established between 2 components, latent period and spore production per day, and the ADPC, using a multiple regression analysis (r2 = 0.9). If verified using a large number of accessions, such analysis may be used to obtain an index of resistance that may predict resistance levels in the field based on the components.