Impact of Thermotherapy and Short-Term Storage on Quercus robur L. Acorn Mycobiota and Germination

Abstract

When natural regeneration of Quercus robur stands is hampered by an insufficient acorn yield, human assisted sowing of acorns collected in non-affected stands and stored for some period of time is performed. To inhibit the development of fungi and acorn deterioration during storage, thermotherapy is usually applied by submerging acorns for 2.5 h in water heated to 41 °C. This research aimed to test the effect of four thermotherapy treatments of different durations and/or applied temperatures as well as short-term storage at −1 °C or 3 °C on acorn internal mycobiota and germination. Fungal presence in cotyledons was analyzed in 450 acorns by isolation of mycelia on artificial media, followed by a DNA-based identification. Germination of 2000 acorns was monitored in an open field trial. Thermotherapy significantly decreased fungal diversity, while storage at 3 °C increased the isolation frequency of several fungi, mainly Penicillium spp. The most frequently isolated fungi did not show a negative impact on acorn germination after short-term storage. The study confirmed the efficiency of thermotherapy in the eradication of a part of acorn internal mycobiota, but also its effect on the proliferation of fast-colonizing fungi during storage. However, the latter showed to be more stimulated by storage conditions, specifically by storage at 3 °C.

Thermotherapy and Storage Temperature Manipulations Limit the Production of Reactive Oxygen Species in Stored Pedunculate Oak Acorns

“…Presumably, SOD, CAT, POD, AsA and carotenoids contributed to maintaining the physiological concentrations of H 2 O 2 and other ROS types in pedunculate oak seeds (Figure 1). In this context, thermotherapy appears to be beneficial not only in pathogen limitations in oak acorns [13][14][15][16] but also in seed priming, resulting in increased physiological fitness. Seed coats display higher heat capacity and thermal conductivity and low thermal diffusivity [58].…”

“…Therefore, thermotherapy by hot water (2.5 h at 41 • C) was recommended to limit C. batschiana prior to oak seed storage [12,13] and was successfully applied in pedunculate oak acorns [14,15]. More precisely, the above thermotherapy efficiently eradicated a part of the mycobiota, mainly Penicillium spp., in pedunculate oak acorns, but storage temperatures and storage duration still determine the development of fast-colonizing fungi and acorn deterioration [16].…”

“…Only acorns of provenance Kobiór were subjected to thermotherapy before storage. Thermotherapy was conducted by aerated steam for 2.5 h at 41 • C as described by Delatour et al [12] and confirmed by Kranjec Orlović et al [16] when selecting the best time vs. temperature combination. All biochemical measurements were performed immediately after cooling seeds to room temperature (RT).…”

Effect of Acorn Thermotherapy and Short-Term Storage on Morphological Characteristics of Related Quercus Robur L. Seedlings

“…The use of the latter two is referred to as a thermotherapy. Thermotherapy treatment, usually conducted by submerging the acorns for 2.5 h in a water preheated to 41 • C, is proven to be effective in reducing the overall acorn mycobiota, including one of the most damaging fungal pathogens of oak acorns during the storage, Ciboria batschiana [28,[30][31][32][33]. However, not all fungi can be eliminated by this treatment, which can potentially result in their proliferation during the acorn storage and the subsequent loss of acorn quality.…”

Tree Regeneration by Seeds in Natural Forests

“…High seed production does not guarantee successful regeneration. Orlović et al [12] observed different storage regimes for pedunculate oak acorns depending on the occurrence of internal mycobiota and seed germination. The study confirmed the efficiency of thermotherapy in the eradication of a proportion of acorn internal mycobiota, but also its effect on the proliferation of fast-colonizing fungi during storage.…”