Abstract
Temperature is one of the most significant environmental factors that affects germination of grass seeds. Reliable prediction of the optimal temperature for seed germination is crucial for determining the suitable regions and favorable sowing timing for turf grass cultivation. In this study, a back-propagation-artificial-neural-network-aided dual quintic equation (BP-ANN-QE) model was developed to improve the prediction of the optimal temperature for seed germination. This BP-ANN-QE model was used to determine optimal sowing times and suitable regions for three Cynodon dactylon cultivars (C. dactylon, ‘Savannah’ and ‘Princess VII’). Prediction of the optimal temperature for these seeds was based on comprehensive germination tests using 36 day/night (high/low) temperature regimes (both ranging from 5/5 to 40/40°C with 5°C increments). Seed germination data from these temperature regimes were used to construct temperature-germination correlation models for estimating germination percentage with confidence intervals. Our tests revealed that the optimal high/low temperature regimes required for all the three bermudagrass cultivars are 30/5, 30/10, 35/5, 35/10, 35/15, 35/20, 40/15 and 40/20°C; constant temperatures ranging from 5 to 40°C inhibited the germination of all three cultivars. While comparing different simulating methods, including DQEM, Bisquare ANN-QE, and BP-ANN-QE in establishing temperature based germination percentage rules, we found that the R2 values of germination prediction function could be significantly improved from about 0.6940–0.8177 (DQEM approach) to 0.9439–0.9813 (BP-ANN-QE). These results indicated that our BP-ANN-QE model has better performance than the rests of the compared models. Furthermore, data of the national temperature grids generated from monthly-average temperature for 25 years were fit into these functions and we were able to map the germination percentage of these C. dactylon cultivars in the national scale of China, and suggested the optimum sowing regions and times for them.
Highlights
Cynodon dactylon (Linnaeus) Persoon (Family: Poaceae, bermudagrass in English) is a perennial, creeping grass
The maximum germination percentage of C. dactylon was 87.3% at 15/35uC (Table 1); and the germination percentage at 5/30uC was only 80.7%, but it was still accepted as the optimal temperature for seed germination since the one-half of its confidence interval was 7.0% and 80.7%.(87.3%–7.0%)
Germination percentage was usually lower than 50% at constant temperature ranging from 20 to 40uC, for example the germination percentages of ‘‘Princess VII’’ (Table 1), were 0, 36.0%, 5.3%, 12.7% and 20.0% at constant temperature regimes of 20/20, 25/ 25, 30/30, 35/35 and 40/40uC, respectively
Summary
Cynodon dactylon (Linnaeus) Persoon (Family: Poaceae, bermudagrass in English) is a perennial, creeping grass. It is widely found in the tropical and warm temperate regions, bermudagrass is predominantly distributed between 45u North and 45u South latitudes [1,2]. C. dactylon is globally used as a turf grass, fodder and medicinal plant, and it was used for removal of heavy metals from contaminated soils [3,4,5] This grass is adapted to extremely variable environments, such as fertile fields, arid land, saline land, wet irrigation canals and even contaminated wastelands with high levels of Pb, Cd, Zn and Cu [6,7,8,9,10]. It has been used to treat traumatic wounding, kidney calculi [18], hypoglycemia [19], depression [20] and cancer [21,22,23]
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