This study was conducted in Department of Horticulture, Faculty of Agriculture, University of Cukurova in 1999 and 2000. Watermelon [C itrullus lanatus (Thunb.) Matsum and Nakai] cultivar Crimson Tide was grafted onto 10 different rootstocks. Cucurbita moschata , Cucurbita maxima and Lagenaria siceraria were open pollinated cultivars, and Strong Tosa, Gold Tosa, P360 ( Cucurbita maxima × Cucurbita moschata ), Skopje, Emphasis, 216 and FRG ( Lagenaria spp.) were hybrid cultivars. The ungrafted Crimson Tide watermelon cultivar was used as the control. Plants were grown under low tunnel conditions until the outdoor temperature was suitable (22–25°C) for watermelon growth. Our results showed that while survival rate was low (65%) in Cucurbita type rootstocks, it was high (95%) in Lagenaria type rootstocks. Grafted plants flowered about 10 days earlier and showed more vigorous vegetative growth than the control plants. Grafted plants had up to 148% higher fresh weights than control plants. Similarly, grafted plants showed 42–180% higher dry weight, 58–100% more leaves and larger leaf area as compared with the control. In total yield, Lagenaria type rootstocks produced a higher yield but Cucurbita type rootstocks produced a lower yield than the control. While control plants had 6.43 kg/m2 yield, Lagenaria type rootstocks produced 27–106% higher yield than the control. In contrast, Cucurbita type rootstocks had 127–240% less yield than the control. This could be attributed to incompatibility of Cucurbita rootstocks because some of the plants died before harvest. The study showed that rootstock choices influence plant growth as well as yield and quality of scion fruit, suggesting an important consideration in the potential use of grafting applications in watermelon.

A hydroponic experiment was conducted to assess whether grafting with Cucurbita rootstocks could improve the salt tolerance of melon scions and to determine the physiological, biochemical, and nutritional responses induced by the rootstocks under salt stress. Two melon (Cucumis melo L.) cultivars (Citirex and Altinbas) were grafted onto two commercial Cucurbita rootstocks (Kardosa and Nun9075). Plants were grown in aerated nutrient solution under deep water culture (DWC) at two electrical conductivity (EC) levels (control at 1.5 dS m⁻¹ and salt at 8.0 dS m⁻¹). Hydroponic salt stress led to a significant reduction in shoot and root growths, leaf area, photosynthetic activity, and leaf chlorophyll and carotenoid contents of both grafted and nongrafted melons. Susceptible plants responded to salt stress by increasing leaf proline and malondialdehyde (MDA), ion leakage, and leaf Na⁺ and Cl⁻ contents. Statistically significant negative correlations existed between shoot dry biomass production and leaf proline (r = −0.89), leaf MDA (r = −0.85), leaf Na⁺ (r = −0.90), and leaf (r = 0.63) and root (r = −0.90) ion leakages under salt stress. Nongrafted Citirex tended to be more sensitive to salt stress than Altinbas. The Cucurbita rootstocks (Nun9075 and Kardosa) significantly improved growth and biomass production of grafted melons (scions) by inducing physiological (high leaf area and photosynthesis), biochemical (low leaf proline and MDA), and nutritional (low leaf Na⁺ and ion leakage and high K⁺ and Ca⁺⁺ contents) responses under salt stress. The highest growth performance was exhibited by the Citirex/Nun9075 and Citirex/Kardosa graft combinations. Both Cucurbita cultivars have high rootstock potential for melon, and their significant contributions to salt tolerance were closely associated with inducing physiological and biochemical responses of scions. These traits could be useful for the selection and breeding of salt-tolerant rootstocks for sustainable agriculture in the future.

In this study, two hydroponic experiments were conducted in nutrient solution growth system. Experiments were conducted in growth chamber of Erciyes University, Agricultural Faculty in Kayseri, Turkey. In the first experiment, 10 local Turkish bottle gourd genotypes and two commercial watermelon cultivars were screened under 2 N doses (0.3 mM and 3.0 mM N) in RBD design with three replications for six weeks. In the second experiment, four genotypes (N-efficient: 70-07 and 07-45, N-inefficient: 35-10 and 45-07) were selected and used as rootstock for grafting with N-inefficient watermelon cultivar (Crimson Sweet) under 2 N doses. The grafted N-efficient gourd genotypes (07-45 and 70-07) significantly contributed to growth and biomass production of the N-inefficient watermelon plants as compared to non-grafted control plants and thus showed a higher rootstock potential for watermelon. The N-efficiency of some gourd genotypes was associated with vigor root growth and active root system particularly at low N conditions. These traits could be useful characters to select ‘N-efficient’ bottle gourd rootstocks for sustainable agriculture in the future.

Plant growth-promoting rhizobacteria (PGPR) are free-existing soil-borne bacteria that can be used as bioinoculants in place of chemical fertilizers to directly or indirectly enhance plant growth. This study aimed to characterize PGPR native to the rhizosphere of alfalfa plants in Kayseri and evaluate their efficacy on the growth parameters of tomato and watermelon. A total of 56 potential PGPR isolates were isolated and 24 were selected based on their ability to produce multiple PGP traits. 16S rDNA and phylogenetic analysis characterized these isolates to be novel strains of Pseudomonas, Enterobacter, Acinetobacter, Stenotrophomonas, Staphylococcus, Lycinibacillus, and Bacillus. Sequence analysis revealed nucleotide variations and insertion/deletion mutations in their 16S rRNA genes (nucleotides 913–1408). All selected isolates demonstrated nitrogen fixation ability, whereas 54%, 83%, 71%, 54%, and 38% of isolates possessed genes for phosphate solubilization, indole-3-acetic acid (IAA) synthesis, phytase, ACC deaminase, and siderophore, respectively. Fifty-eight day old tomato and watermelon plants grown from PGPR-treated seeds showed significantly higher improvements in plant height, stem diameter, leaf area, shoot dry weight, and root fresh weight compared to non-inoculated control plants. Furthermore, treatment of watermelon seeds with these isolates significantly increased the fresh weight of shoots and the root dry weights in watermelon plants. Thus, these indigenous PGPR isolates can be used as effective seed inoculants and chemical fertilizer alternatives to enhance tomato and watermelon growth.