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Celery cultivars (Apium graveolens var. dulce) in North America have a narrow genetic base. Twenty-two celery, one celeriac and one annual cultivar were screened for polymorphic RAPD (Random Amplified Polymorphic DNA) markers with 28 arbitrary 10-mer primers. Among the total 231 bands obtained, 28 (12%) of the bands were polymorphic among the 24 accessions screened, but only 18 (7.8%) were polymorphic within the 22 celery cultivars. These markers are sufficient to distinguish each of the cultivars used. The average number of marker differences is 6.2 between two celery cultivars, 13.5 between the celeriac and the remaining cultivars, and 16.5 between the annual and the other cultivars. The relationship among the celery cultivars disclosed from this study is basically consistent with that observed using total protein and isozyme markers. RAPD technology provides a new alternative for cultivar identification in celery.

To characterize the celery (Apium graveolens L. var. dulce, 2n = 2x = 22) genome, 126 celery cDNA clones and 340 random 10-mer primers were used to generate restriction fragment-length polymorphism (RFLP) and randomly amplified polymorphic DNA (RAPD) markers between two cultivated types. Different abundance classes of the genomic sequences represented by the cDNA clones and the RAPD markers were observed. Most of the cDNA clones were single-copy sequences, suggesting the true diploid nature of the celery genome. Nearly half of the 39 RAPD markers tested by Southern hybridization were multiple-copy sequences. Of the RAPD markers tested, 28% was single- and low-copy, and 26% was high-copy sequences. The polymorphism level of the cDNA clones was 23% when tested with four restriction enzymes (Eco RI, Eco RV, Hin dIII, and Hae III). A positive association was observed between RFLP level and the size of cDNA inserts or hybridized restriction fragments. Deletion, insertion, and base substitution were important in the formation of the RFLP markers. Eighty-two (23%) of the 340 primers tested yielded useful RAPD markers, but only 3.8% of the amplified products were polymorphic. Base substitution may be the most important mechanism for the RAPD markers in celery. The RAPD fragments revealed no RFLP markers when tested by Southern hybridization, implying that RAPD markers are an important complement to RFLP markers in genomic mapping in celery. Random methylation of cytosine was determined in 5S rDNA on Bam HI and Hin dIII cutting sites that produced ladder patterns characteristic of tandem repeats.

Nitrogen and potassium are two crucial nutrient elements that affect the yield and quality of crops. The aim of this study was to quantify the impacts of potassium on growth dynamics and quality of muskmelon, so as to optimize potassium management for muskmelon in a plastic greenhouse, and develop a coupling model of nitrogen and potassium. For this purpose, four experiments (two experiments with different levels of potassium treatment and planting dates, and the other two experiments with different ratios of nitrogen and potassium, and planting dates) on muskmelon (Cucumis melo L. ‘Nanhaimi’ and ‘Xizhoumi 25’) were conducted in a plastic greenhouse located at Sanya from Jan. 2014 to Sept. 2015. The quantitative relationship between leaf potassium content and growth dynamics and yield of muskmelon was determined and incorporated into a photosynthesis-driven crop growth model (SUCROS). Independent experimental data were used to validate the model. The critical leaf potassium content at the flowering stage for muskmelon ‘Nanhaimi’ and ‘Xizhoumi 25’ were 55.0 and 46.0 mg·g⁻¹. The result showed that the coefficient of determination (r ²) between the predicted and measured values of leaf area index (LAI), direct weight of shoot (DWSH), direct weight of stem (DWST), dry weight of leaf (DWL), dry weight of fruit (DWF), fresh weight of fruit (FWF), soluble sugar content (SU), soluble protein content (PR), vitamin C (Vc), and soluble solids content (SO) of potassium model were 0.93, 0.98, 0.83, 0.96, 0.98, 0.99, 0.94, 0.94, 0.89, 0.85, and 0.90, respectively; and the relative root-mean-squared error (rRMSE) were 10.8%, 19.6%, 30.3%, 21.1%, 11.9%, 17.2%, 13.9%, 27.8%, 20.6%, and 10.1%, respectively. The two ways of nitrogen and potassium coupling (multiplicative coupling and minimum coupling) were compared, and the multiplicative coupling was used in model development finally. The r ² between the predicted and measured values of LAI, DWSH, DWST, DWL, DWF, FWF, SU, PR, Vc, and SO of nitrogen and potassium coupling model were 0.78, 0.91, 0.93, 0.94, 0.83, 0.89, 0.92, 0.95, 0.91, and 0.93, respectively; and their rRMSE were 9.2%, 12.4%, 11.8%, 43.2%, 6.6%, 7.2%, 6.85%, 4.98%, 6.61%, and 4.35%, respectively. The models could be used for the optimization of potassium, nitrogen, and potassium coupling management for muskmelon production in a plastic greenhouse.

The aim of this study was to quantitatively investigate the impacts of nitrogen on growth dynamics and yield, so as to facilitate the optimization of nitrogen management for muskmelon crop in plastic greenhouse. For this purpose, four experiments with different levels of nitrogen treatment and planting dates on muskmelon (Cucumis melo L. ‘Nanhaimi’ and ‘Xizhoumi 25’) were conducted in plastic greenhouse located at Sanya from Nov. 2012 to Sept. 2014. The quantitative relationship between leaf nitrogen content and growth dynamics and yield of muskmelon was determined and incorporated into a photosynthesis-driven crop growth model (SUCROS). Independent experimental data were used to validate the model. The critical leaf nitrogen content at flowering stage for muskmelon ‘Nanhaimi’ and ‘Xizhoumi 25’ were 19.8 and 21.0 mg·g⁻¹. The coefficient of determination (r ²) and the relative root-mean-squared error (rRMSE) between the predicted and measured value of growth dynamics and yield were, respectively, 0.91 and 10.8% for leaf area index (LAI), 0.90 and 19.6% for dry weight of shoot (DWSH), 0.76 and 30.3%, 0.82 and 21.1%, and 0.92 and 11.9% for dry weight of leaf (DWL), stem (DWST), and fruit (DWF), 0.91 and 17.3%, 0.89 and 13.9%, 0.86 and 27.8%, and 0.88 and 20.6% for soluble sugar content (SU), soluble protein content (PR), vitamin C content (VC), and soluble solids content (SO) of fruit, and 0.90 and 10.1% for fresh weight of fruit (FWF). The model could be used for the optimization of nitrogen management for muskmelon production in plastic greenhouse. Further calibration and test would be needed during the application of the model in wider range of conditions and muskmelon cultivars.