Tomato resistance, tomatine

SchonbeckE, SchlosserE (1976) Preformed substances as potential protectants. In Heitefuss, R, WiUiams, PH (eds) Physiological plant pathology. Springer, Berlin, pp. 653-678 Pegg GE, Woodward S (1986) Synthesis and metabohsm of a-tomatine in tomato isoUnes in relation to resistance to Verticillium albo-atrum. Mol Plant Microbe Interact 28 187 Eord JE et al (1977) The detoxification of a-tomatine by Fusarium oxysporum f.sp. lycopersici. Phytochemistry 16 544... 

The existence of tomatinases in fungal-tomato pathogens supports the idea that tomatine may play a role in resistance to fungal attack because these enzymes seem to act specifically on tomatine. Such a role is also supported by the finding that at least in F. oxysporum f. sp. lycopersici, tomatinase is produced during infection both in roots and stems... 

A second major mechanism of resistance to tomatine involves enzymatic detoxification by tomatinases. Although saponins are very numerous and widely distributed in the plant kingdom, detailed studies on saponin detoxification by fungi have been restricted to pathogens of a few plant species, principally to oat and the Solanaceous tomato and potato. This is because structures and antifungal properties of oat, tomato and potato saponins are well established, and that saponin profiles of these plants are relatively simple, in contrast to other plants like alfalfa, where over 20 predominant different saponins have been identified. 

Although several authors claimed that the glycoalkaloid tomatine is not present in sufficient concentrations in roots or stems to play a major role in resistance to Fusarium oxysporum f. sp. lycopersici [7, 57, 88], the fact that tomatinase is induced in tomato plants during infection, strongly suggests that the enzyme may have a specific role in pathogenicity of tomato plant by F. oxysporum f. sp lycopersici. 

In conclusion, F. solani isolates appear to be less sensitive to tomatine than F. oxysporum f. sp. lycopersici, although they produce much lower tomatinase activity, indicating that they must possess other inherent mechanisms of resistance. One possibility is that F. solani may have a lower content of sterols in the membrane than F. oxysporum. Thus, although tomatinase activity may help F. solani to grow on green tomato tissue it does not seem to be determinant in the resistance to tomatine. 

Pegg, GE, Woodward, S. Synthesis and metabolism of alpha tomatine in tomato Lycopersicon esculentum isolines in relation to resistance to Verticilliumalbo-atrum. Physiol Mol Plant Pathol 1986 28 187-202. 

The glycoalkaloid -tomatine has been implicated in the resistance of tomato to both H. zea (4 10 18) and to L. decemllneata (8). q-Tomatine has been found in all Lycopersicon species surveyed (19, 20). It is present in both tomato foliage and fruit, although the concentration of -tomatine in the fruit decreases as the fruit matures (4, 10, 20). For at least two tomato species which have been examined (L esculentum and hlrsutum f. glabra turn), foliar K-tomatlne has been found associated with the leaf lamellae but not the tips of the type VI trlchomes (5, 21). 

Leptlnotarsa decemllneata, -Tomatine also acts as a feeding deterrent for U deceml lneata (25) and the tomatine content of the wild tomato species that are resistant to L, deceml lneata Is generally higher than that of commercial tomato cultlvars (8). Nonetheless, the evidence that -tomatine Is responsible for the resistance of any tomato genotypes to 1 decemllneata Is Inconclusive, but suggestive. 

If the role of -tomatine in resistance to L. deceml lneata is verified, It should be relatively easy to select for high levels of foliar -tomatine In a tomato breeding program because the genetic variation in -tomatine is controlled by the segregation of 2 codominant alleles at a single locus (28). One possible limitation on the utility of -tomatine-mediated resistance to L. deceml lneata is... 

Barbour, J. D. and G. G. Kennedy, Role of steroidal glycoalkaloid a-tomatine in host-plant resistance of tomato to Colorado potato beetle, J. Chem. Ecol., 17, 989-1005 (1991). 

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