LEAF SPOTS on the upper and under leaf sides, at first single, later numerous, circular, grey-brown, 2-4 mm diam, surrounded by a red brown border. At the period of formation of conidia, the center of the spots becomes silver-grey. Later, the centers become thin, papery, brittle, and may drop out leaving a ragged hole.

CONIDIOPHORES (cp) form on the upper and under leaf sides, develop from mycelium growing between cells of the leaf tissue, arise in clusters through the stomata, euseptate, olive brown, lighter or even colourless at the top, 30-50 x 4-5 µm.

PLANT HOST AND DISTRIBUTION. The plant hosts of C. beticola are Amaranthus retroflexus L., Chenopodium album L., Fagopyrum convolvulus Moench, and different species of the genus Beta (Kochman 1973).

Cercospora beticola has a worldwide distribution (Smith et al. 1988).

NOTES. Cercospora beticola causes a leaf spot of sugar-beet and garden beet.

During vegetation, conidia of C. beticola spread by wind, rainfall, and insects (Kochman 1973). Although the conidia need water to germinate and penetrate, heavy dews seem to be sufficient for abundant infection (Agrios 1988). The germ tubes of germinated conidia enter the leaves through the stomata.

The fungus is favoured by high temperatures (an optimum of 29oC).

Inoculum of C. beticola is conserved and dispersed by (1) pseudostromata forming on seeds and surviving 20-32 months; (2) spread from seed crops to nearby ordinary crops, which is the major means of carry-over from one year to the next; (3) sclerotia-bearing debris in the soil, which, like seeds, can carry the disease for over two years (Brooks 1953; Smith et al. 1988).

REFERENCES

Agrios G. N. 1988. Plant pathology, 3rd edition, Academic Press, INC. San Diego, New York, Berkeley, Boston, London, Sydney, Tokyo, Toronto.

Brooks F. T. 1953. Plant diseases. Geoffrey Cumberlege. Oxford University Press. London, New York, Toronto.

Kochman J. 1973. Fitopatologia. PWRiL. Warszawa.

Smith I. M., Dunez J., Lelliott R. A., Phillips D. H., Archer S. A. 1988. European handbook of plant diseases. Blackwell Scientific Publications.