Research Summary: Spinach Trials
The Why
Spinach germination is commonly lower and slower than other traditionally grown crops. Low spinach germination can impact overall yield and health of the crop, leading to wasted resources. We investigated germination rates and seedling growth of four spinach cultivars to determine which ones had higher and consistent germination rates.
To note: Bolting of spinach is one of the biggest issues with this crop. When a spinach plant bolts, it begins to allocate more of its energy towards flower and seed production, rather than leaf growth. This means that the leaves on the plant will be smaller, resulting in reduced yields. Additionally, as spinach plants mature and bolt, they can develop a bitter taste, which makes them less marketable. We investigated bolting rates of 4 cultivars to determine which ones, if any, were less prone to it in a mixed-crop environment.
The What
We evaluated four spinach cultivars (Kookaburra, Bloomsdale, Space, and Sunangel) to identify a cultivar with consistently high germination rates, high yield potential and tolerance to bolting.
Description of germination enhancement treatments used:
1- Control (CN): seeds were sown unsoaked and untreated, i.e. without receiving any germination enhancement treatment.
2- Imbibition in water (IW): seeds were soaked in water for 18 hours at room temperature followed by direct sowing in rockwool.
3- Imbibition in hydrogen peroxide (IWP): seeds were soaked in H2O2 solution (0.3%) for 18 hours followed by direct sowing in rockwool.
4- Hydropriming in water (HPW): seeds were placed in paper towels wetted with 60 mL of water and placed between two paper plates for 24 hours at room temperature, followed by direct sowing in rockwool.
5- Hydropriming in hydrogen peroxide (HPP): seeds were placed in paper towels wetted with 60 mL of 0.3% hydrogen peroxide and placed between two paper plates for 24 hours at room temperature, followed by direct sowing in rockwool.
We defined germination rate as the percentage of seeds whose radicle had grown out of the seed coat (pericarp) by at least 1 millimeter. To calculate the speed of germination, we added up the number of seeds that have germinated at different time intervals (n1, n2, n3, ni), and divided that by the number of days it took for those seeds to germinate (d1, d2, d3, di).
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Results
LEGEND:Effect of germination enhancement treatments on the germination rate (A) and speed (B) of the cultivars Kookaburra, Bloomsdale, Sunangel, and Space. Data are presented as means of four replicates. Cultivars followed by the same upper-case letters within each germination enhancement treatment and germination enhancement treatments followed by the same lower-case letters within each cultivar are not statistically different at P ≤ 0.05. Bars and limit lines represent the standard error of the mean.
Germination Trials:
Kookaburra and Bloomsdale spinach had low germination rates (<50%) and slow germination speed in all germination enhancement treatments tested, including the untreated control.
Sunangel and Space spinach exhibited the highest germination rates and fastest germination speed across all germination enhancement methods tested, indicating that they are the most suitable varieties for germinating in Growcer systems.
Sunangel and Space spinach also had the longest true leaf length compared to Kookaburra and Bloomsdale in most treatments. This likely contributed to the superior overall seedling development observed in these cultivars. Larger leaves generally indicate a higher leaf area, which can increase photosynthesis and the production of carbohydrates, leading to faster and stronger plant growth.
Sunangel seeds had high germination rates (>80%) even without treatment, while Space seeds required hydropriming with hydrogen peroxide for optimal germination rates. However, hydropriming improved the speed of germination for both Sunangel and Space.
Yield Trials:
Sunangel (control) had the highest partial yield compared to Space previously treated with hydropriming. However, the average full harvest yield was not significantly affected by either cultivar or germination treatment.
Sunangel had a higher number of leaves than Space on average, indicating a potentially greater leaf production capacity.
Space exhibited a lower bolting percentage compared to Sunangel, suggesting that it may be more tolerant to bolting.
So what? The conclusion.
Based on the results of these trials, hydropriming is the recommended germination enhancement treatment, although its effectiveness may vary depending on the cultivar. In this study, hydropriming with water and hydrogen peroxide enabled germination rates of up to 91% and 88%, respectively, for Sunangel and Space spinach.
For increased yield in optimal growing conditions where bolting is not a concern, such as monocrop environmental conditions and/or when harvesting at a younger age (baby spinach), Sunangel would be the recommended cultivar.
If spinach is at risk of environmental fluctuations or other stressful conditions that may trigger bolting, Space would be the recommended cultivar due to its greater tolerance to bolting.
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