Abstract

In Algeria, Ascochyta blight is a major limiting factor in chickpea production. We did not record any difference between the isolates while basing ourselves on the morphological and cultural characters, but the pectinolytic activity could differentiate the ten isolates ofAscochyta rabiei. Activity of pectin methyl esterase was baseless in the presence of glucose, but variable in the presence of the citrus pectin and polygalacturonic acid. We recorded the weak production ranging between 0.19 and 0.55 µeg/ml/min; however the strong activity was between 2.97 and 5.88 µeg/ml/min in the presence of citrus pectin and polygalacturonic acid, respectively. On the other hand, the polygalacturonase activity was present in culture filtrates using three sources of carbon. Weak production was recorded in the presence of glucose (0.28 to 2.63 µmole/min), however the strong activity was recorded in the presence of 16.29 µmole/min of polygalacturonic acid. The maximal production of polygalacturonase was 11.7 µmole/min in the presence of the polygalacturonic acid and 0.9 µmole/min in the presence of glucose after six days of incubation at pH 5. The polygalacturonase activity was between 0.3 and 0.62 µmole/min after 4 days of incubation at pH 8. However, optimum production was obtained at pH 5.5. It should be noted that there is an important difference in the production of polygalacturonase with simple sugars glucose and pectin, indicating that the production of the enzyme is also stimulated by the presence of inducers. The exo-polygalacturonase is present in all carbon sources, suggesting that this enzyme could probably be of a constitutive nature in Ascochyta rabiei.

Key words: Ascochyta rabiei, pectinolytic activities, pectin méthylesterase, polygalacturonase.