Two anthracnose diseases caused by Colletotrichum gloeosporioides have been found in Stylosanthes spp. in northern Australia. The two diseases can be readily distinguished by their symptoms and their pure-culture characteristics. The disease classified as type A was widespread, but the other, type B, was found at only two localities. In spray-inoculation tests under controlled conditions, S. guianensis cv. Endeavour was highly susceptible to type B isolates, and some lines of S. fruticosa, S. humilis, S. scabra and S. viscosa were highly susceptible to the type A isolates. Two pathogenic races of type A were recognized from the reaction of S. viscosa 33941 towards them. The importance of these diseases is discussed, together with aspects of disease dissemination and future control strategies.
Chromosome numbers have been determined for 19 accessions representing 10 species of Stylosanthes Sw. Diploids (2n = 20), tetraploids (2n = 40), and one hexaploid (2n = 60) have been found. There are differences in chromosome size and morphology. The significance of these differences in the evolution of the genus is discussed.
Yield losses from the fungal disease anthracnose, caused by Colletotrichum gloeospovioides, were estimated for 3 species of Stylosanthes grown in northern Queensland. Naturally infected control plots of S. scabra cv. Fitzroy, S. hamata cv. Verano and S. guianensis cv. Graham were compared with plots protected by 3 benomyl spray treatments designed to restrict anthracnose development to 0, 25 and 50% of the level sustained in the unsprayed control plots. Following initial infection in early February 1984, disease incidence and severity in Fitzroy and Verano reached a maximum during early March. This rapid build up of disease was associated with a period of sustained wet weather. Graham only became infected much later in the season as the plants matured, and sustained severe anthracnose lesions on both leaves and stems even though weather conditions appeared unsuitable for an epidemic. Yield losses were severe in all 3 cultivars. Average dry matter yields of the unsprayed controls were only 21.6, 66.7, and 53.5% respectively of the yields of the disease free plots for Fitzroy, Verano and Graham. Corresponding seed yields were 15.6, 48.9 and 42.5% respectively. Highly significant negative correlations were found between dry matter and seed yields of the 3 species and the incidence and severity of anthracnose disease.
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.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.