Effect of Grafting Technique on Productivity and Quality of Cantaloupe under Saline Irrigation Water

Cantaloupe (Cucumis melo L.) is a high economic vegetable crop in many countries including Egypt. It is grown in practically every country in the world under outdoor fields or greenhouses. The cultivated area of cantaloupe in Egypt is 66,434 feddan (4200m2) with total production of 846,936 tons and an average of 12.749 ton/fed. Ministry of Agric, Egypt, 2015. The most important problems facing horizontal expansion of cantaloupe in greenhouses or in open fields are the high salinity of the irrigation water or soil especially in the new reclaimed lands. As well as the recurrence of agriculture in greenhouses increases the soil salinity and thus reduces the vertical production of cantaloupe. In addition, cantaloupe is moderately salt tolerant, it has been determined that salinity causes several kinds of damage such as growth inhibition [1-3], yield and quality losses [4-6]. This leads us to use some newly trends to mitigate these negative impacts. The grafting technique is one of the most modern trends used to improve the productivity of vegetable plants, especially under adverse environmental conditions. Grafted vegetables onto resistant rootstocks offers numerous advantages on growth and yield, i.e., tolerance to salinity stress [7-10], increase yield and fruit quality in many crops such as melon [11] and watermelon [12,13]. Accordingly, the present study was conducted to investigate the possibility of using the grafting as a new promising technique for ameliorate the negative effects of the high salinity of the irrigation water on cantaloupe productivity and its quality. Abstract


Introduction
Cantaloupe (Cucumis melo L.) is a high economic vegetable crop in many countries including Egypt. It is grown in practically every country in the world under outdoor fields or greenhouses. The cultivated area of cantaloupe in Egypt is 66,434 feddan (4200m2) with total production of 846,936 tons and an average of 12.749 ton/fed. Ministry of Agric, Egypt, 2015. The most important problems facing horizontal expansion of cantaloupe in greenhouses or in open fields are the high salinity of the irrigation water or soil especially in the new reclaimed lands. As well as the recurrence of agriculture in greenhouses increases the soil salinity and thus reduces the vertical production of cantaloupe. In addition, cantaloupe is moderately salt tolerant, it has been determined that salinity causes several kinds of damage such as growth inhibition [1][2][3], yield and quality losses [4][5][6]. This leads us to use some newly trends to mitigate these negative impacts. The grafting technique is one of the most modern trends used to improve the productivity of vegetable plants, especially under adverse environmental conditions. Grafted vegetables onto resistant rootstocks offers numerous advantages on growth and yield, i.e., tolerance to salinity stress [7][8][9][10], increase yield and fruit quality in many crops such as melon [11] and watermelon [12,13]. Accordingly, the present study was conducted to investigate the possibility of using the grafting as a new promising technique for ameliorate the negative effects of the high salinity of the irrigation water on cantaloupe productivity and its quality.

Materials and Methods
This investigation was carried out in a private farm in Moshtohor village, Kalyobiya Governorate, Egypt during 2015 and 2016 autumn seasons to study the response of yield productivity and fruits quality of grafted and non-grafted cantaloupe plants to different irrigation water salinity levels. The soil was clay with pH of 8.0 and EC of 1.3dS/m. Two commercial cultivars Veleta RZ and Ideal (MG739) were grafted on the Cobalt RZ and Strong-Tosa rootstocks using modified tongue approach grafting method. The grafted and non-grafted seedlings were transplanted under net house condition, on the 21st of July in both investigation seasons. The plants were transplanted on one side of ridges 1.5m width, at 50cm apart. Four irrigation water salinity levels were applied [0.8, 3.9, 7.1 and 10 dSm −1 ] by adding NaCl to the used underground water. A split split-plot designed was adopted, with three replicates where, salinity levels were placed in main plots, meanwhile cultivars "scions" in subplots and rootstocks in sub-subplot.
The yield of the first tow pickings was considered as early yield as well as number of fruits per plant and total yield per plant (g.) were calculated in the end of the growing season. The fruit length and diameter were measured to calculate fruit shape index (fruit length/fruit diameter) and. Finally, average fruit weight (g), flesh thickness of fruit (cm) and seed cavity diameter (cm) as well as total soluble solids percentage (AOAC, 1990) were measured. Data were subjected to the statistical analysis by the method of Duncan's multiple range tests as reported by Gomez [14]. Statistical analysis was performed with SAS computer software. Based on average of two seasons, the results of total yield were used to calculate the costs, benefits and saving of using grafted and non-grafted cantaloupe plants which grown under salinity irrigation water.

Effect of grafting technique (cultivars "scions" and rootstocks) under salinity levels of irrigation water on quality of cantaloupe fruits
Data presented in Tables 1-5 indicate the effect of salinity levels of irrigation water, cultivars, rootstocks and their interaction on fruit shape index, average fruit weight, flesh thickness of fruit, seed cavity diameter and T.S.S, respectively. Fruits quality expressed as average fruit weight, flesh thickness of fruit and T.S.S. were affected by salinity levels of irrigation water but fruit shape index was not affected in both seasons of study. Where, average fruit weight and flesh thickness of fruit were decreased by increasing salinity levels [15,16] and the opposite trend was observed with T.S.S which increased by increasing salinity levels [16,17]. Concerning the effect of cultivars on these traits of fruits quality, all fruit traits except T.S.S. were significantly affected by the used cultivars (Veleta and Ideal). In general, Ideal cultivar fruits were bigger and heavier than those of cv. Veleta. While Veleta fruits were the longer little than those of Ideal and the opposite trend at the fruit diameter all over the growing season, this reflected on the fruit shape index where cv. Veleta recorded the highest value compared with cv. Ideal. Moreover, results indicate that average fruit weight, flesh thickness and seed cavity diameter were positively affected by Cobalt rootstock while no significant effect could be detected regarding to fruit shape index and T.S.S. The obtained results agreed with those stated by Colla [9] working on watermelon, [18] and Colla [8] working on cucumber who noticed that grafted plants produced fruits with highest average weight compared with of non-grafted plants.    Most fruit quality parameters, i.e., fruit shape index, average fruit weight and T.S.S. were not significantly affected by various trials of the interaction between cultivars and salinity levels and the opposite trend was found with flesh thickness and seed cavity diameter in 2015 and 2016 seasons. However, average fruit weight, flesh thickness and seed cavity diameter as well as T.S.S were significantly affected by the interaction between rootstocks and salinity levels treatments where the highest values were represented in Cobalt rootstock when irrigated by salinity levels 3.9 and 7dS/m but increasing salinity up to 10 dS/m improved T.S.S. Meanwhile fruit shape index was not affected by this interaction. In connection with the interaction treatments between cultivars "scions" and rootstocks, the average fruit weight, flesh thickness and seed cavity diameter interaction treatments among salinity levels of irrigation water, cultivars and rootstocks, there were significant interaction effects on all fruits quality parameters except fruit shape index. Under all studied factors, the best interaction effects were found in the combination of the cvs. Veleta or Ideal grafted on Cobalt rootstock under all salinity levels except the highest one (10dS/m). Where, grafted plants of Ideal/Strong-Tosa, Veleta/Cobalt and Ideal/Cobalt produced the biggest and heaviest fruits with the biggest flesh thickness in a suitable contained of T.S.S when irrigated by 3.9dS/m level of salinity levels in both seasons.

Effect of grafting technique (cultivars "scions" and rootstocks) under salinity levels of irrigation water on fruit yield and its components of cantaloupe plants.
Data presented in Tables 6-8 shows the effect of salinity levels of irrigation water, cultivars, rootstocks, and their interaction on fruits number, early and total yield (g/plant), respectively. Yield production in terms of fruits number, early yield and total yield per plant were significantly affected by salinity levels during both seasons. Where, the medium salinity level (3.9dS/m) resulted in significantly the highest of early yield, fruits number and total yield than all other salinity levels while the total yield decreased by 39.7% (as average between two seasons) with increasing salinity levels up to 10dS/m. The obtained results are in the same line with those reported by [3,5,17,[19][20][21] who showed that increasing salinity levels badly affected total melon yield. Also, early yield, fruits number and total yield per plant were affected by the used cultivars (Veleta and Ideal) where cv Ideal was higher than those of cv. Veleta. The effect of rootstocks was very clear where Cobalt rootstock produced significantly higher yield components than all other used rootstock and non-grafted plants, increased the total yield by 37.4% compare non-grafted plants, as average between two seasons. In the same context, [8] on melon as well as [22][23][24][25][26] on watermelon who noticed that grafted plants gave the highest fruit yields compared with non-grafted plants.

Calculation of Costs and Benefits of Applied Treatments
This parameter is illustrative and is not reliable in order to differentiate between the costs of using grafted and non-grafted plants under salinity of irrigation water. Assuming that, the remaining costs such as rental costs, workers, fertilizers, etc., agree on all factors of the study. Costs and benefits of grafted and nongrafted plants which grown under salinity levels of irrigation water were calculated as average between both seasons. Where, the price of non-grafted seedlings is close to the price of the grafted seedlings because it required additional costs "the costs of controlling soil diseases (1.25LE) according to Hasan (2015)". The presented results in Table 9