Breeding system, reproductive efficiency and weed potential of A. baileyana

Acacia baileyana F.Muell. is a native environmental weed which has invaded bush areas of south-eastern Australia from ornamental plantings. There are two main colour forms, the typical green-leaf form and the variety `purpurea', which has purple new growth. Only the green form appears to have invaded natural bush. The weed potential of A. baileyana was investigated in terms of its breeding system and seed production. It was found that the purple form is as reproductively efficient as the green form. Both forms were outcrossing, highly self-incompatible, grew very rapidly and flowered by two years of age. For open, natural pollination, final pod set was low-less than 0.41%. However, seed production was high due to the high number of flowers present. Maximum flower production for a 2-year-old plant was over 300 000, resulting in more than 8000 seeds. Precocity and high flower numbers appear to be the reasons for the weed status of A. baileyana. Given the similarity in reproductive efficiency between both forms, it is postulated that the absence of the purple form as a weed could be due to it being a relatively new horticultural variety, or to the purple colour being a recessive trait.

A NEW ROOT ROT OF FLORISTS' CHRYSANTHEMUMS IN ONTARIO

An apparently undescribed root rot of Chrysanthemum morifolium Ramat. occurred in 1953 on the horticultural variety "White Shasta" in an Ontario greenhouse. The disease was characterized by a severe root rot, general stunting and a foliar chlorosis and necrosis. A species of the form genus Phoma was found associated with the roots of affected plants. The disease has been reproduced repeatedly by inoculation with monoconidal cultures of the fungus. Symptoms appear to be most severe on plants growing in infested soil maintained at temperatures between 55° and 60°F. Inoculation tests suggest that the disease is restricted to the florists' chrysanthemum. Varieties of C. morifolium do, however, vary widely in their susceptibility to this root rot. There is no evidence that the pathogen is carried within cuttings taken from infected plants. Both steam sterlization and methyl bromide fumigation have completely eliminated the pathogen from infested soils.