Hortus Officinarum – Breeding of a Wilt-Tolerant St. John's Wort Variety for Organic Cultivation

|   Heilpflanzen, Präparateforschung

Ruth Richter

With the increasing demand for and cultivation of St. John's wort (Hypericum perforatum), infestation by St. John's wilt (Colletotrichum cf. gloeosporioides) has increased sharply in Europe since the 1990s. There is great interest among growers for tolerant varieties that are suitable for organic cultivation. This demand was the reason that Hortus Offinarum selected starting material for breeding a wilt-tolerant variety under biodynamic conditions from 69 accessions of Hypericum perforatum at the Swiss gene bank.

The breeding project was carried out from 2019–2022 in collaboration with Sativa Rheinau and the Wala nursery in Eckwälden. The aim was to breed 1–2 varieties from resistant lines that would prove themselves in organic cultivation. Further breeding goals were agronomic and morphological properties such as stability, homogeneous crop development with uniform height, a crowded flowering horizon and early and uniform flowering of the crop. Pharmaceutical requirements were a high flower content and a minimum content of hypericin.

The special reproductive aspects of Hypericum perforatum with its negligible cross-pollination rate, enabled easy propagation of particularly wilt-tolerant plants without pollinator protection. In 2019, 26 wilt-tolerant varieties were grown at three locations in comparison with two wilt-tolerant reference varieties. Due to heavy wilt infestation at all locations, large infestation differences between the plots, with relatively homogeneous behaviour within the plot, showed that wilt tolerance is clearly genetically influenced (left). We were able to select rigorously.

In 2020, 13 and in 2021, 11 different breeding lines were planted and evaluated. In the summer of 2022 it became clear to us that heavier rainfall can be expected in the future. We therefore gave double weight to the parameter of "stability".

In 2022, the evaluation of the ratings from the first and second year of cultivation resulted in four candidate varieties for trial cultivation on different farms – two breeding lines each of two different growth types: a fine-stemmed type that quickly suppresses weeds in the first year with rather creeping growth and good ground cover and only straightens up in the second year, and a type that grows upright from the start with a narrow flowering horizon and is well suited for mechanical harvesting (right).

The analysis of the four breeding lines for hypericin content yielded medium to very good results in comparison with the two reference varieties. Fortunately, with regard to wilt infestation, our favoured breeding lines performed well at all locations this year – the infestation was between 0 and 17 %. We are curious to see how our breeding lines will prove themselves in larger cultivation.

Upright growing St. John's wort type in main flower.
Photo from the beginning of August. The differences in wilt susceptibility between the genetically different varieties are clearly visible.