Nineteen accessions of Stylosanthes scabra that had low terminal severities of anthracnose in the field were evaluated for their response in the glasshouse using four isolates representing three different races of Colletotrichum gloeosporioides. Accessions could be allocated to one of three groups: one showed a higher disease severity after inoculation with isolate UQ14 compared to the other isolates; the second showed a higher severity after inoculation with isolates WRS32 and/or WRS20 compared to isolates SR4 and UQ14, and the third group showed moderate to low disease severities following inoculation with all four isolates. Based on reduced disease severity and compatible infection types, a set of six accessions was selected from the three groups for further testing, two of which showed no significant difference in their response to the four isolates. Two components of resistance, incubation period and infection efficiency were studied in the selected accessions. Of these, incubation period appeared unrelated to the expression of resistance. Criteria for identifying this form of quantitatively expressed resistance are discussed.

No abstract

The relationship between stocking rate and liveweight change per animal was examined over a period of 3 years for two continuously grazed pastures, one of Brachiaria and the other consisting of guinea grass with Endeavour stylo and Siratro. On an annual basis there was no significant effect of stocking rate over the last 2 years, but on a seasonal basis there were highly significant effects in all seasons. In the dry seasons, animal gain rose as the stocking rate fell, but in the last two wet seasons gains fell with the lower stocking rates. On an annual basis the two effects cancelled out. Response surfaces for gain versus pasture yield and stocking rate were curvilinear (quadratic) during the wet season and linear during the dry. Optimum stocking rates (for maximum gain per hectare) were determined for the wet and dry seasons; the rate was greatly affected by the yield of green material during the dry season but less so during the wet. The possible causes of this reversed wetseason effect are discussed.

A lucerne-breeding programme was undertaken at Lawes, south-eastern Queensland, to transfer the creeping-rooted habit from Heinrichs's Canadian strains to subtropical lucerne varieties. Before intensive selection commenced, the inheritance and association of three characters, summer yield, winter yield, and the number of extra crowns originating as adventitious shoots from roots, were determined in the F2 and F3 generations. The F2 genotypic variances for summer yield, winter yield, and number of extra crowns were predominantly additive and were respectively 81, 53, and 54% of their phenotypic variances. The genotypic correlation coefficient for winter yield and number of extra crowns was negative ( rG = –0.18), consisting of a negative additive correlation rg = –0.55 and a positive non-additive correlation rs = 0.50. In the F3 generation the approximate genotypic correlation for these two characters was small and positive and composed of a nearly zero additive correlation and a high positive non-additive correlation. Simultaneous mass selection for summer yield, winter yield. and creeping-rootedness was undertaken in the F3 generation, and the combining ability variances and covariances for these characters were studied in the F4 generation. All three variables were positively associated in their general and specific effects, and the majority of families did not differ significantly from Hunter River in winter and summer yield. The seed production of ten F4 families was studied and it was found that eight families were significantly lower seed producers than Hunter River, their seed yields ranging from 20 to 47% of the mean for Hunter River. Covariance analysis showed seed yield and number of extra crowns to be negatively associated in the F4 generation. The changes in creeping-rootedness in the successive generations F1 to F5 were 2, 9, 34, 19, and 59% compared with a mean of 4% for Heinrichs's Canadian strains at Lawes. Creeping-rooted individuals survived better than non-creeping-rooted plants of similar genotype and better than Hunter River, particularly in the F4 generation, where the respective survival rates were 75, 27, and 23% 19 months after transplanting in the field

An experiment is described in which a large collection of Stylosanthes introductions, comprising 14 named species, was grown as spaced plants and simple morphological and agronomic data recorded. After applying various methods of numerical analysis, and integrating the results, it was found that species and forms could be delineated. The importance of non-stable agronomic characteristics in the classification of the introductions is explored and the taxonomic status of the resultant groups briefly examined; the use of these systems for plant assessment programmes is discussed.