Plant health and quality

Summary
The overall objective of the project was to determine which general strategies show the greatest and most significant variation in selected secondary metabolites with particular importance for plant health and quality, in order to establish a knowledge base whidh can be exploited in future applied projects to optimise these characteristics. From investigations of wild plants and theoretical considerations it was expected that growth conditions and cultivar choice would have great, to some extent predictable, effects on contents of compounds with different physiological functions in the plant.

Phenols are important for plant health, e.g. infection by some fungi, but the main function of some phenols is believed to be protection against UV-irradiation, and if so these are not involved in defense reactions. The phenols, including anthocyanin, are also of interest from the nutritional point of view because as antioxidants they are assumed to reduce the risk of cancer and cardiovascular disease. Volatiles (aroma compounds) determine taste and are also important for infestation by insects and mites. Alkaloids (e.g. gramine and hor-denine in barley) are often toxic and are part of the plants’ defense mechanisms.

The model plants chosen were black currant, barley and pea.

Black currant
Contents of phenolc compounds in leaves vere measured in parallel with recordings of the field resistance (infection by fungi) of black currant plants in plants of 5 cultivars grown with different types of cover crops or sprayed with sulphur, and volatiles in leaves and presence of big bud mites were also measured. Quality characteristics (anthocyanins, vitamin C and aroma compounds) in berries of the same cultivars were also measured. Extent of infection of several diseases was correlated with contents of particular phenolic acid derivatives. Neither the type of cover crop nor sulphur treatments affected the phenolics and the (UV-absorbing) flavonoids showed no corrlation with fungal infections. A planned Ph.D. study for Carsten Iversen was given up due to personal matters.

Barley
Phenolics and alklaoids were investigated in this species. In barley gramine is expected to be important for insect infestation, by retarding the propagation of aphids. Gramine and hordenine ar exuded to soil from the roots and may retard the germination of other plants. So the aim was to investigate the exudation from the roots and the effects of the compounds on germinating seeds of weed species.

The results ragarding gramine show significant systematic cultivar differences in the content in leaves and root exudates. Modern cultivars lack gramine in fully developed leaves, but some can exude alkaloids from roots. Effects on weeds and aphids were shown, however they were still somewhat ambiguous. The weed realted work continues in a new peoject under the programme ”Organic plant protection”. Most phenolic compounds in both barley and wheat were isolated and identified, including two new unknown flavonoids, one in each species. The contents of phenolic acid derivatives was strongly correlated with e.g. nutrient supply and plant age, while the contents of flavonoids, the most abundant phenolics, were not correlated with factors of importance for resistance. Only shade, which is not in itself of importance for disease severity, affect the flavonoids more than the phenolic acids. So it is now shown for the first time under field conditions which mechanism is behind increased disease susceptibility due to overfertilisation.

Pea
In pea also a phenolic compound, pisatin, was supposed to be investigated in different platn parts and cultivars, in healthy plants and plants infected with Aphanomyces euteiches. But the international collaboraters were unable to fulfill their promise of reference material of pisatin, and our own investigations showed the presence of several compounds with very similar characteristivcs which others have probably measured as one. We found at least one compound whid consistently appeared in larger amounts in infected roots than in healthy ones, but it was not pisatin, and the content was too small for isolation and identification. In addition several mishaps occurred in connection with cultivation and sample storage, so this work was given much lower priority in favour of cereals.

Across the species our data confirms that different types of phenols have different physiological roles in the leaves, and that this ”division of labour” appears in as different species as balrey, wheat and black currant. The project also showed that the differences due to cultivar and growth conditions were independent, so additive effects can be obtained by both choosing the best cultivar and growing it under those conditions which best support the desired characteristics, e.g. resistance.