TOMATO & WATERMELON GRAFTING
In vegetable production one of the consequences from continuous cropping is the buildup of soil-borne pathogens such as Fusarium wilt, Bacterial wilt and Nematodes. Grafting of vegetable plants is becoming an effective option to assist to overcome these problems. In addition to disease resistance, grafting of a vigorous rootstock to traditional vegetable cultivars can increase yield and improve water and nutrient uptake.
The use of a vigorous rootstock will increase the vigour of the plant due to the stronger root system. This results in improved leaf area and stem diameter and enables the plant to continue growing under cool conditions and extends the productive life of the crop.
The use of chemicals against soil diseases can be reduced. Stronger plants reduce the chance of successful attacks by secondary parasites. A graft combination of a vigorous scion on an equally vigorous rootstock can reduce the amount of fertilizer required. Field experience has shown on tomatoes, that rootstock resistance against Verticillium infers a high tolerance against Pepino Mosaic Virus in the crop.
Different rootstocks have different characteristics; there are generative rootstocks, vegetative rootstocks, and differences in growing power and power of endurance.
The crops most commonly grafted are Watermelon, Tomato and Eggplant.
Grafting on Tomatoes and Eggplants
Tomato and eggplant are grafted on the same rootstock (Lycopersicon esculentum).
The most common method used involves both the scion (variety) and the rootstock seedlings being cut at a 45° angle and the scion being placed on the rootstock. They are fixed together using a silicon grafting clip.
The rootstock is seeded about 5 to 10 days before the scion variety, and should be kept at a lower temperature (18° to 20°C) to develop thicker and sturdier seedlings. The scion seedlings can be grown as normal.
Grafting takes place after about 17 or 18 days and grafted plants are then kept at a constant temperature of 25°C. Grafting should be done in an area with no direct sunlight and under sterile conditions with disinfected hands, razor blades and anything in touch with the plants.
On the fifth day the plants can begin to be exposed to normal light depending upon the condition of the plants. It is preferred to make a small gap and to check each hour the condition of the plants; after day 7 normal plant raising procedures can be followed.
This grafting procedure is highly specialized and is carried out highly successfully by several nurseries in Australia. It is important for growers to consult their nursery and discuss their specific requirements for their own conditions and whether they require specific disease resistances or added vigour.
Grafting on watermelon
Watermelon is commonly grafted on bottlegourd (Lagenaria siceraria), interspecific Cucurbita hybrids, (Cucurbita maxima x moschata ), Cucumus melo, and various melon wild types.
There are several methods of grafting in watermelon but we will only cover two here.
Tongue Approach grafting
This method is relatively simple, is the oldest grafting style, and has a relatively low care requirement. The watermelon seed should be planted five days before the rootstock seed. When at least one true leaf is present, a cut is made, using a sharp blade, downwards in the stem of the rootstock and upwards in the stem of the scion; the two parts are fitted together and sealed with an aluminum wrap to allow healing to take place. The two attached plants are then placed with both of their root-balls into a single cell in a seedling tray.
Seven days after grafting the scion root is cut, and the rootstock shoot is cut and the aluminum wrap can be removed allowing the new graft to depend solely on the new rootstock.
The disadvantage of using this method is the substantial labour requirement.
One Cotyledon Graft
This graft is performed by hand or machine, is less labour intensive, and is by far the most widely used technique in Europe. Plants are ready to graft when there is at least one true leaf on both the scion and the rootstock. The rootstock is cut downwards at 45°C removing the shoot and one cotyledon, and the shoot of the scion cut at 45°C is placed on the cut rootstock. This is then fixed in place using a grafting clip.
Following the grafting, the plants require shade, high humidity and temperatures around 25°C for three days; light can be increased and humidity decreased after the third day to gradually begin normalizing plants to the environment.
The main disadvantage is a need for a good acclimating facility because poor environmental controls in humidity, light and temperature may cause high losses. It also required the diameters of the stems of the rootstock and scion to be well matched.
Lefroy Valley has two outstanding watermelon rootstock varieties which offer market leading options to the grower and nursery staff. Watermelon rootstock should be selected very carefully because they may have an adverse effect upon fruit quality.
VIGORE F1 is an interspecific hybrid ( Cucurbita moschata x maxima ) which offers intermediate resistance to Fusarium, and outstanding vigour which enables the grafted plant to develop well under difficult conditions. In addition it can assist to provide outstanding yields of very firm fruit.
ROYAL FORTE is a bottle gourd or Lagenaria rootstock which has provided good feedback from growers and nursery staff. It has good matching ability in the nursery and provides medium vigour and intermediate resistance to Fusarium in the field. ROYAL FORTE has been shown to have no effect upon fruit quality whilst assisting to provide improved yield in situations where Fusarium is a problem.
Grafting of tomato and watermelon plants is a specialized operation best left to the experts. Grafted plants provide options to growers to overcome cultural and disease problems. The nature of the variety will change once grafted, and management practices need to be adopted accordingly to optimize the benefits of the rootstock.