Development of tools for studying Olea europaea: Pseudomonas savastanoi interaction

Abstract

Portugal is one of the main world olive oil producers. Consequently, the culture of olive trees is of considerable importance for our country. In order to maintain and improve our varieties, responses to environmental stresses and pests, which can seriously affect productivity, must be studied, and clones more adapted to challenge stress conditions must be found. One problem that seriously affects Portuguese olive orchards' is olive knot, a disease caused by Pseudomonas savastanoi (Pseudomonas syringae pv savastanoi) which, causing tumours in the stems and leaves of the trees, drastically reduces the production of fruits. Some varieties, like Galega Vulgar, are know to be resistant to the disease, while others, like Cordovil de Serpa, variety are know to be susceptible. With the objective of developing an in vitro system of eliciation of Olea europaea with an avirulent strain of Pseudomonas savastanoi, we have initiated suspension cell cultures of from calli of the variety Galega Vulgar. Cells in middle exponential growth phase were incubated with a suspension of P. savastanoi.Hypersensitive response was studied using XTT (sodium,3’-(1-[phenylamino-carbonyl]-3,4-tetrazolium)-bis(4-methoxy-6-nitro) benzene-sulfonic acid) by the quantification of the perhydroxyl / superoxide (H2O./O2-) radical acid-base pair associated to the oxidative burst, during the time course of elicitation. The results showed the existence of two bursts (100 and 300 min after eliciation), which are characteristic of the HR that occurs in the incompatible interactions). By screening an elicited O. europaea cDNA library a clone encoding phenylalanine ammonia lyase (PAL) was obtained. The coding region was used as probe for evaluate Pal expression levels. The results will be discussed by comparing to variation of PAL activity, during the time course of elicitation.