Grafting has become a routine technique in continuous cropping systems in many parts of the world. It was first introduced in Korea and Japan in the late 1920s, when watermelon was grafted onto squash rootstocks to tackle yield losses caused by soil-borne plant diseases.
It is estimated that more than half of the world’s watermelons and cucumbers are produced in China, and over 90% of these are grafted. Using rootstocks brings several improvements: more vigorous plants that reach soil nutrients more effectively, greater resistance to soil pathogens, better tolerance of low temperatures and salinity, and lower susceptibility to the effects of high soil moisture.
The type of rootstock has been shown to have a positive effect on the growth of cucurbit plants, on yield and on fruit quality. Even so, grafting is not always the preferred technique: it is still rare in the United States, which has only recently begun to see it as a valid way to improve cucurbit growing.
Environmental tolerance
Grafting melon plants also makes it possible to grow the crop outside its normal season: only grafted plants can tolerate the climate stress that comes with off-season growing.
Growth is more vigorous, with greater uptake and translocation of soil nutrients, including nitrogen, phosphorus and potassium (macronutrients) and magnesium, iron and calcium. Higher nutrient levels help raise the rate of photosynthesis, especially when exposure and light are not ideal. Grafted plants can also be considered more environmentally friendly, because their greater efficiency in finding nutrients in the soil reduces the amount of fertiliser needed.
A grafted plant is usually chosen for greater vigour, better nutrient uptake, higher tolerance of stress conditions and better disease resistance, with a greater chance of increasing the harvest.
Higher yields are most evident where diseases and other less than ideal conditions are reduced. However, some combinations can lead to lower yields if the rootstock and the scion are not fully compatible, or if the rootstocks are not well suited to the growing conditions.
The cost of grafting
As with every part of production, grafting calls for careful cost analysis. Because the operations are mostly manual, labour becomes the main cost. Various grafting methods and procedures have been developed to reduce these costs, and grafting nurseries need to build experience and skills to find the most suitable method for producing healthy, high-quality transplants at a cost that fits the production budget.
A healthy, well-formed seedling is the first essential step towards a successful crop, which is why the choice of sound, vigorous and well-produced propagation material should never be underestimated.
