Résumé
A 10 kD elicitor protein (infestin) produced by Phytopthora infestans was purified and its efficacy for induction of systemic resistance in resistant and susceptible varieties of Solanum tuberosum was studied. Culture filtrates from P. infestans with and without purified elicitor (infestin) were used as elicitors to understand the effect of purified elicitor (infestin) on development of systemic resistance. Culture filtrate and purified elicitor (infestin) were found to induce hypersensitive reaction on the leaves of resistant varieties, but not on susceptible varieties after 48 h. Culture filtrate devoid of purified elicitor (infestin) did not induce any necrotic spots even on resistant variety. Purified elicitor (infestin) was found to induce glucose oxidase, NADPH oxidase, superoxide dismutase, glutathione reductase, catalase and peroxidase enzymes in resistant S. tuberosum plants, however the induction of these enzymes was low in susceptible varieties. The oxidative enzymes were found to induce earlier than antioxidative enzymes and there was negative correlation between these two groups of enzymes. Levels of salicylic acid, phenylalanine ammonia lyase (PAL), -1, 3 glucanase and chitinase activities were also found higher in resistant than in susceptible varieties. It was observed that purified elicitor (infestin) was superior to crude culture filtrate, but was not capable of inducing systemic resistance in susceptible varieties.
Résumé
Culture filtrate of Lasiodiplodia theobromae increased respiration rate, phenylalanine ammonia lyase activity, and levels of hydrogen peroxide, lipid peroxides and salicylic acid in B. nigra plants. Salicylic acid (SA) level increased for 1 hr of interaction and reduced later. Development of systemic acquired resistance (SAR) was found restricted in plants infected with L. theobromae due to deficiency of SA, which is a major signal for development of SAR. Exogenously supplied SA did develop resistance and plant death was delayed. It was hypothesized that deficiency of SA could be due to jasmonic acid produced by fungus that inhibits SA biosynthesis.