Grafting in solanaceous vegetable: a new technology for higher productivity in north eastern hill region of India
Authors: M. Bilashini Devi*, HD. Talang, AK. Jha, H. Rymbai and Solomon Keri
ICAR Research Complex for NEH Region, Umiam-793103, Meghalaya
Corresponding author's email: bilashini1712@gmail.com

Grafting in perennial crops such as fruits and flowers is a well known and has been widely used technology since decades ago in India. However, ‘vegetable grafting’ is a relatively recent advancement made in India. It is a unique technique for mitigating the production problems imposed by abiotic and biotic stresses in vegetable production and can be referred as uniting of two living plant parts so that they grow as a single plant. The first attempt in vegetable grafting was done by grafting watermelon (Citrullus lanatus) onto pumpkin ( Cucurbita moschata) rootstock in Japan and Korea in the late 1920s (Lee, 1994). Since then, this horticultural technology is being practiced widely in solanaceous and cucurbitaceous vegetable crops.

The northeastern hill region of India is characterized by difficult terrain and agriculture in this particular region is exposed to abiotic stresses such as high rainfall, acidic soil, toxicity of Al, Fe and Mn, deficiency of micro-nutrients such as Zn, B, Mo etc. In this scenario grafting technique could be proposed as a way to enhance vegetable productivity in the region through increased tolerance to abiotic stresses. Among biotic stresses occurring under intensive vegetable cultivation, grafting has been promising to enhance plant response under stresses determined by extreme temperature, drought, salinity and flooding. In addition, grafting proved to improve nutrient uptake under extreme conditions, reduce uptake of persistent organic pollutants from agricultural soils, improve alkalinity tolerance and limit the negative effect of boron, copper, cadmium, and manganese toxicity. All this positive impact on grafted plants can responsibly attribute to higher productivity. Besides various abiotic stresses, bacterial wilt is a soil borne disease and one of the major problems in cultivation of all the major solanaceous crops of the region. The region is bestowed with a huge diversity of wild species of solanaceous groups of vegetables especially brinjal and chilli. Therefore, proper utilization of interspecific grafting with tolerant rootstock can prove to be a great promise. This might be entire nuclear genomes can transfer between plant cells of scion and stock, leading to the formation of new alloploid derived different species (Fuentes et al., 2014).

Grafting technique is labor intensive and incurred higher cost of production when it comes to commercial scale than cultivation of non-grafted plants. However, increases in yield may outweigh the cost of introducing grafted seedlings and, therefore, this technology was quickly accepted by farmers in some part of the country. However, access to the information on scientific evidence and locally conducted systematic research for identifying compatible and promising rootstocks is limited in northeastern region. Therefore, vegetable grafting is still relatively unknown to farmers of this region, while there is a huge diversity of wild and related species of three major solanaceous vegetables (tomato, brinjal and chilli) in this region. Therefore, obtaining locally collected data regarding the performance of the different rootstocks over different pests, pathogens and abiotic stresses locally problematic to the region are crucial to adopt the technology in the region. Amongst the solanaceous vegetable crops, tomato, brinjal, chilli and king chilli ( Capsicum chinense Jacq.) are important and commercially cultivated in north eastern region of India. Grafting can be a promising strategy that improves the responses of these crops under biotic and abiotic stresses in this area.

Methods of Grafting:

A number of grafting techniques are employed in fruit bearing vegetables. Cleft, tube and tongue grafting are mostly practiced in tomato, brinjal and chilli (Kumar et al., 2015).

1. Cleft grafting: The seeds of the rootstock are sown 5-7 days earlier than those of the scion. At 4 leaf stage the scion is prepared by cutting the stem at right angle with 2-3 leaves remaining on the stem. The rootstock (at the 4 to5 leaf stage) is also cut at right angles, with 2-3 leaves remaining on the stem. The stem of the scion is cut in a wedge, and the tapered end fitted into a cleft cut in the end of the root-stock. The graft is then held firm with a plastic clip.

2. Tube Grafting: This grafting technique has been developed for vegetable seedlings grown by plug/pro-tray culture. This method of grafting is 2-3 times faster than the conventional method. In this technique the rootstock is cut under cotyledons at 45^o or sharper angle. Prepare the scion with matching hypocotyl width cut in the same angle at about 5- 10 mm below the cotyledons. Place one tube a half way down on top of the cut end of rootstock hypocotyl. Insert the scion into the grafting tube so that cut surface aligns perfectly with that of rootstock.

3. Tongue Grafting: In this method, the shoot apex of the rootstock is removed so that the shoot cannot grow. The hypocotyls of the scion and rootstock are cut in such a way that they tongue into each other and the graft is secured with a plastic clip. The hypocotyls of the scion is left to heal for 3-4 days and then crushed between the fingers. The hypocotyl is cut off with the razor blade three or four days after being crushed.

After successful completion of grafting, the grafted plants should be moved to healing chamber.

Basic pre requisites

Healing chamber/Grafting chamber : It is used for formation of better graft union. In this chamber grafts should be kept for 5-7 days. High humidity, optimum temperature and reduces light intensity should be maintained in the chamber.

Healing conditions : Healing is the most crutial stage in grafted seedling production. Temperature of 25-30^o C, RH-85-90% and low light intensity are required for healing.

Acclimatization chamber : This chamber is used for hardening the grafted seedling prior to transplanting to prevent leaf burning and wilting. The grafted seedling takes 7 to 10 days for acclimatization as hardening treatment.

Grafting for increased productivity

The use of grafted vegetables is associated with enhanced resistance to biotic and abiotic stress. But grafting can also increase yields without the presence of stress. A yield increased of about 106 percent in watermelon by grafting with certain rootstocks has been reported in Australia. Rootstock varieties specifically bred to be used as rootstocks are available in solanaceous crops, such as ‘Maxifort’ for used in greenhouse tomato cultivation. Many growers worldwide are utilizing these rootstocks to increase fruit yields, even in absence of biotic and abiotic stresses. Moreover, many researchers reported that interaction between rootstocks and scions might results in high vigor of the root system and greater water and mineral uptake leading to increased yield and fruit enhancement (Kacjan-Marsic and Osvald, 2004).

Conclusions and future prospects

Grafting is an easy and rapid vegetative propagation technique that can overcome the problem of sexual incompatibility between two different species. Identification of compatible disease resistant rootstocks with tolerance to abiotic stresses is the basic requirement for continued success of grafting in the region. Healthy grafted seedlings at reasonable price are the key point for wider use. Methods should be of low cost so that these could be adopted by farmers for commercial production. Systematic location specific research is needed to evaluate and find out the compatible rootstocks to minimize post grafting losses. Sharpening of grafting skills and healing environment need to be standardized for its application on commercial scale in the region. More awareness amongst the farmers about the techniques and benefits of grafted vegetables needs to be created.

References:

Kumar P, Rana S, Sharma P and Negi V. 2015. Vegetable grafting: a boon to vegetable growers to combat biotic and abiotic stresses. Himachal Journal of Agricultural Research 41(1): 1-5

Lee JM. 1994. Cultivation of grafted vegetables. I. Current status, grafting methods and benefits. Hort. Science, 29: 235–239.

Fuentes I, Stegemann S, Golczyk H, Karcher D, Bock R. 2014. Horizontal genome transfer as an asexulal path to the formation of new species. Nature 511 232–235 10.1038/nature13291

Kacjan Marsic N, Oswald J 2004. The influence of grafting on yield of two tomato cultivars grown in a plastic house. Acta Agriculturae Slov enica 83(2): 243-249.




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