SEVERITY OF ROOT ROT ON TOMATO PLANTS CAUSED BY PHYTOPHTHORA NICOTIANAE AND SALT STRESS AS INDICATED BY ELISA AND PROLINE CONTENT OF LEAVES
SEVERITY OF ROOT ROT ON TOMATO PLANTS CAUSED BY PHYTOPHTHORA NICOTIANAE AND SALT STRESS AS INDICATED BY ELISA AND PROLINE CONTENT OF LEAVES Grote, D.* and W. Claussen lnstitut fur Gemuse- und Zierpflanzenbau Grobeeren/Erfurt e. V. Two different indicators were employed for quantification of the root rot pathogen Phytophthora nicotianae on tomato plants: the indirect Direct Antigen Coating-Enzyme linked Immunosorbent Assay (DAC-ELISA) and the proline content of leaves. Proline, an amino acid increasing in concentration in plant cells mainly as a consequence of water stress, is considered to be a suitable stress marker. In our investigations both abiotic salinity stress induced by three different salt concentrations of the nutrient solution (corresponding to EC 1.5, 5,0 and 8.5 dSm-1) and biotic stress caused by infection with F. nicotianae at 104 and 106 propagules/ml were Imposed on hydroponically grown tomato plants under natural light in the greenhouse and under controlled conditions in the phytotron. Progress of disease was markedly accelerated by salt stress. Differences in progress of disease induced by salinity were significant for two sets of data between all EC-levels investigated but at least between the lowest and the highest salt concentration (EC 1.5 and 8.5 dSm-1) in all experiments carried out. In most cases, proline content of leaves was significantly higher at EC 8.5 compared with EC 5 and 1.5 dSm-1, respectively. At EC 1.5 dSm-1 proline content remained rather constant throughout the experiment. The proline content of leaves at EC 5 dSm-1 was not always higher than that measured at EC 1.5 dSm-1 since stress factors such as radiation and infection contributed to the entire stress imposed on plants. At EC 5.0 dSm-1 significant differences between the proline content of infected and noninfected plants could be observed during a period of 21 days after inoculation. Therefore, the salt concentration corresponding to EC 5.0 dSm-1 was employed in further experiments carried out under controlled conditions in the phytotron in order to monitor proline content of leaves at different inoculum densities under high and low light conditions. Our results indicate, that the proline content of leaves of tomato plants is a suitable marker for stress induced by both abiotic and biotic stressors. In combination with other observations, including changes in fungal development, proline content may help to explain both the predisposition of the plant and the conditions for the progress of the disease.