STUDIES ON THE NATURE OF RESISTANCE IN TOMATO TO CLADOSPORIUM FULVUM COOKE

Abstract

The sugar and amino acid content of six tomato varieties were compared by paper chromatographic methods. These varieties reacted to race 1 of Cladosporium fulvum Cke. as follows: Potentate, susceptible; V-121 and Stirling Castle, resistant; Vetomold, Vinequeen, and Lycopersicon pimpinellifolium (Jusl.) Mill., immune. Potentate, Vetomold, and V-121 are closely related genetically, the last two having been developed by repeated backcrossing to Potentate of immune and resistant segregates from Potentate × L. pimpinellifolium crosses. The resistance of Stirling Castle is controlled by a gene different from the gene which conditions immunity in Vetomold and one that confers resistance on V-121, while the immunity of Vinequeen stems from L. hirsutum Humb. and Bonpl.Fructose, glucose, and sucrose occurred in all varieties, but, among the three closely related ones, the consistently low level of all three in V-121 and the low fructose in Red Currant were suggestive, while Potentate and Vetomold displayed reciprocal levels of fructose and sucrose. The two resistant varieties differed in sugar content and the three immune ones were not consistent.From four sets of extracts of all six varieties, grown under conditions optimal for disease expression, 15 amino acids were identified. The relative amounts of these differed significantly in different varieties without, however, any general causal relation to resistance being evident. The consistently lower levels of one or more of aspartic acid, serine, and glutamine in V-121 may be significant in limiting the development of the fungus in this resistant variety. The immunity of Vetomold did not seem to be conditioned by the presence or absence of specific amino acids nor did the immunity of Vinequeen. When extracts of this sort were compared with extracts from plants grown under a light experience reduced sufficiently to disturb the host–parasite relations, it was evident that this treatment significantly altered both the sugar and amino acid content of the varieties in characteristic varietal patterns. This may suggest that a suitable C/N ratio is prerequisite to compatibility. The desirability of further studies is indicated.