2.7.25
THE RELATIONSHIP BETWEEN PYTHIUM APHANIDERMATUM AND TOMATO ROOTS IN DEPENDENCE OF DIFFERENT INOCULUM DENSITY AND TEMPERATURE IN THE RHIZOSPHERE

A KOFOET, R GROSCH and D SCHWARZ

Institute of Vegetable and Ornamental Crops Grossbeeren/Erfurt e.V., Theodor Echtermeyer Weg 1, D-14979 Grossbeeren, Germany

Background and objectives
Alterations in root system characteristics related to infection by root pathogens during seedling or young plant development may influence the ability of a plant to withstand various environmental stresses during plant establishment and further development until the harvest. The relationship between pathogens and root growth is important in the understanding and management of such root diseases. The objective of the present study was to characterize the reactions of the root system of young tomato plants to infection with Pythium aphanidermatum (P.a.), under various inoculum densities and temperature conditions.

Materials and methods
Three tomato seedlings (Lycopersicon lycopersicum (L.) Karst. ex Farw. cv. Counter) were transplanted in one container (2 ;l) at the two-leaf-stage and cultivated in a growth chamber under temperature conditions of 25/20C, a photoperiod of 16h (600 ;pMol/m2.s) and a relative humidity of 70/90% day/night. The nutrient solution was prepared according to Voogt and Bloemhardt [1]. The seedlings were inoculated with P.a. (0.01 0.1/1/10/100/1000 oospores/ml nutrient solution) after an adaptation period of 3 ;days. After the inoculation the reactions of the roots were studied under different temperature conditions 25/20C, 30/25C and 35/25C, respectively. At 11 ;days per inoculation the fresh and dry weight of the root and shoot, the total root elongation and the root diameter were measured [2]. Each treatment included four replication in a randomized block.

Results and conclusions
The root dry weight decreased under high day temperatures of 30 or 35C in all inoculum densities, with the exception of 0.1 oospores/ml at 30C. Under 25C a minimum inoculum density of 100 oospores/ml was necessary to reduce the root dry weight. With lower densities 10 or 1 oospores/ml, respectively, only the root elongation was reduced significantly. An indicator of morphological changes is the decrease in the specific root elongation. In all treatments the root diameter was not influenced by the infection. In most inoculum density-temperature combinations the root surface and the dry weight of root and shoot were reduced. In some combinations, 25C and low inoculum densities, the root surface was reduced, but the dry matter of root and shoot were not influenced. Under these growth conditions the plant is able to compensate the reduction of root surface by a more efficient uptake of water and nutrients. The consequences of morphological changes of root systems in compensating infections by pathogens and in acquiring and transporting resources are studied in further investigations.

References
1. Voogt W, Bloemhard C, 1994. Voedingsoplossingen Glastuinbouw No. 17. 2. Tennant D, 1975. Journal of Ecology 63, 995-1001.