SOLUBLE CARBOHYDRATE-LEVELS IN TOBACCO SYSTEMICALLY PROTECTED AGAINSTBLUE MOLD BY STEM INJECTION WITH PERONOSPORA-TABACINA OR LEAF INOCULATION WITH TOBACCO MOSAIC-VIRUS

Susceptible tobacco plants were systemically protected against blue mo ld (Peronospora tabacina) by stem injection with sporangiospores of P. tabacina or inoculation of three to four lower leaves with tobacco mo saic virus (TMV). After stem injection (9-13 days), higher soluble car bohydrate levels were detected in stem tissues at the sites of injecti on and distant from the sites of injection in P. tabacina-injected pla nts as compared with control plants. Thirteen days after stem injectio n, higher soluble carbohydrate levels were detected in nonchallenged l eaves of P. tabacina-injected plants than in those of control plants. The differences in carbohydrate levels between P. tabacina-induced and control plants increased as the protection against blue mold increase d. After challenge with P. tabacina, the soluble carbohydrate levels i n challenged leaves of both P. tabacina-induced and control plants dec reased, but the levels in the induced plants remained higher than thos e in the control plants during the entire period after challenge. In c ontrast, there was no difference in soluble carbohydrate levels betwee n TMV-induced and control plants in the inoculated lower leaves or uni noculated upper leaves before or after challenge. This suggests that s oluble carbohydrates which accumulated in tobacco plants systemically protected by P. tabacina are unlikely to be important in either the in duction of resistance or as resistance mechanisms.