Powdery mildew and gray mold are the two most important fungal diseases in strawberry, can cause severe pre and postharvest yield and quality losses if not properly managed. Potential of
optical radiation for management of powdery mildews in wide range of crops has been reported previously. Precise application and complete canopy exposure are the major limitations in this strategy. While working on improving the precision in application, we also search for an additional environmentally friendly options that can be added to strengthen optical based management strategy.
Series of experiments were conducted at controlled environment greenhouses with plant levels to examine the potential of i) substrate properties, ii) Ascophyllum nodosum extract (ANE), and iii) biochar on suppression of powdery mildew and plant growth of strawberry cv. Korona.
Among the tested substrate mixtures, powdery mildew severity was significantly highest in strawberry plants grown in peat (100%), and peat: Celine fiber mixture. The lowest powdery
mildew severity was noticed in coconut coir (100%), and coir: Celine fiber mixture.
The number of unfolded leaves per plant was highest in strawberry plants grown in peat (100%) and peat:coconut coir substrate mixture. The lowest number of leaves per plant were observed in Celine fiber (100%) substrate.
There was significant effect of substrate drench of Ascophyllum nodosum extract (ANE) on disease severity in peat: coir substrate. There was no significant effect of ANE drench on peat or coir substrate. The foliar spray of ANE showed significant effect in all treatments in peat and peat: coir substrate. In the coir substrate, there was a disease suppressive effect of ANE when sprayed with concentration 7,5 ml L-1. There was no significant effect on plant growth of substrate type and ANE application.
Addition of 5% biochar (made from grain husks: paper fiber sludge) to the peat substrate showed significant low level of powdery mildew in strawberry plants. Increasing the proportion of biochar (above 5%) in the coconut coir substrate had slight additional suppressive effect on powdery mildew. However, the effect was not statistically significant. On the other hand, increasing the proportion of biochar (above 10%) in the peat substrate showed severity similar to strawberry plants grown in peat substrate with no biochar.
Additional experiment was executed with different types of biochar. The lowest severity was recorded with husk-paper fiber sludge-based biochar. Sewage sludge-based biochar had no effect on disease suppression compared with no-biochar control. Pine tree wood-based biochar showed slight suppression of powdery mildews, but it was not significant.
In vitro (Petri dish) experiments conducted in controlled climate chambers with Botrytis cinerea showed that brief daily exposure of 2, 4 or 8 min of UV at an irradiance of 8 ± 1 µmol/m2/s can suppress conidial germination and colony density of at room temperature (21±1 °C) in a dose dependent manner, compared with no UV control. Similar experiments with visible regions of blue, green, or red light at an irradiance of 100 ±10 µmol/m2/s showed no suppressive effect on colony area and density at room temperature.
Experiment was conducted with similar optical treatments in combination with room temperature (21±1 °C) or cold storage temperature (4±1 °C) for 12 days. Results showed that no colony growth when the samples were exposed to UV or blue in combination with cold storage temperature. Suppressed colony growth (colony area) with no conidiation was recorded under cold storage temperature with dark control. Well-developed colonies were recorded under room temperature with no UV.
Wavelengths of UV and blue were tested in combination with room or cold storage temperature for severity of gray mold and postharvest quality of the commercial strawberry cultivars Favori and Murano. All inoculated berries stored at room temperature with dark or blue light were full of gray mold with complete loss of integrity. UV or blue light in combination with cold storage showed very low level of severity with commercial value close to freshly harvested non inoculated berries.
Additional experiment was conducted with either not dipped or dipped into Aloe vera extract and stored with three different optical environments of i) no UV, ii) 8 min of daily UV, iii) blue with two different storage temperature conditions described above. Results showed that there was no effect of Aloe vera coating on suppression of gray mold severity.
Application of combined, non-chemical, treatment options effective against powdery mildew and gray mold pre and postharvest may have potential in controlling powdery mildew and gray mold with minimize use of synthetic chemical fungicides.
Potential of biochar in management of powdery mildew has been confirmed at experiment level.Further, Norwegian tree wood wastes can be used as alternative substrate with modifications of its physical and chemical properties.Outcomes of this project also showed the possible shelf life extension of strawberries combining with biochar based substrate, selective optical environment and cold storage without using synthetic fungicides.
Outcomes of this project results (potential and limitation of tree wood waste as alternative substrate) brought the industry partners involve and invest in new project (PeatFree).
Similarly outcomes of this project with optical based shelf life extension led to expansion of international collaboration with East China Normal University and achieved funding support for collaborative project (HortiFood)
This project aims to examine the potential of non-chemical, environmentally friendly, sustainable strategies and integrate them to increase yield, reduce losses throughout the strawberry production chain, and shelf life enhancement. The potential of biochar made up from Norwegian tree wood waste, beneficial rhizosphere microbes added to potting mix of coconut coir or peat with biochar, Aloe vera based coating during harvest-postharvest strawberries will be tested. In addition, viability of the experiment outcomes will be validated with commercial trial with active participation of stakeholders (extension officers, producers, and marketing agent) to ensure the responsible research benefit to the society. The expected outcomes may minimize the 1) exploitation of peat moss as potting mix by partial or complete replacement of biowaste of coconut coir, 2) use of fungicide against powdery mildew and grey mould by replacing integrated non-chemical options of optical-biochar based management, 3) postharvest losses caused by biotic and abiotic stresses via enhanced resistance/tolerances with optimized preharvest production conditions, and Aloe vera based coating of harvest-postharvest strawberries.
Success of this project will give added-value for coconut coir, tree wood waste, and Aloe vera extract. Integration of all strategies having positive effect will enhance the practical potential. This will ensure successful commercialization of the optimized products in practical level for participating companies. Pre-postharvest crop losses via abiotic and biotic factors are significant threat to strawberry production worldwide, with an increasing demand for non-chemical options. The successful outcomes of this project will have significant impact at nationally and internationally.