The vegetables play a crucial role in ensuring food and nutritional security for the expanding global population. However, the production of vegetables hindered by various factors, including both biotic factors such as pest and disease incidence, as well as abiotic factors like environmental and soil stresses
(Tirupathamma et al., 2019). Hence, farmers regularly forced to depend on agrochemicals to combat the damage caused by pests and diseases. The chemical pest management can be detrimental to the environment as well as costly and not always effective
(Colla et al., 2010). The successful mitigation of these limitations has been achieved through the advancement of novel cultivars or hybrids and the establishment of standardized crop management protocols. Grafting, a time-honored technique, has been extensively utilized in the cultivation of various fruits for the purpose of disease and pest control. This practice involves the use of carefully chosen resistant rootstocks
(Mudge et al., 2009). Grafting, a horticultural technique employed in the cultivation of fruit crops, has been a longstanding practice spanning several millennia. In recent years, there has been a growing interest in vegetable grafting among vegetable growers worldwide
(Ashok Kumar and Sanket, 2017). By employing resistant rootstock, grafting now proven to be a quick, effective and alternative method for sustainable vegetable production by reducing the need for agrochemicals that combat abiotic stresses and ameliorate soil-borne issues. To fight the Fusarium wilt problem in the late 1920s in Japan, the first attempt at vegetable grafting was made in watermelon (
Citrullus lanatus) with pumpkin (
Cucurbita moschata) rootstock
(Leonardi, 2017). Grafting has now become a common practice in vegetable crops all over the world. Currently, grafting procedures used to cultivate majority of cucurbits in greenhouse environments in Japan and Korea
(Kumar et al., 2018). Even though there were many advantages in utilizing grafted plants, not all vegetables can be grafted since the success percentage of grafted plants depends on the genetic makeup, growth characters, anatomy and biochemical and physiological aspects of the species. The Cucurbits and solanaceous crops remain as the most commonly grafted vegetable crops around the world
(Lee, 1994;
Schwarz et al., 2010). The inter-graftability of cucurbitaceous vegetables including cucumber, watermelon, bitter gourd, muskmelon and other gourds has been used and there were other related graft-compatible wild and cultivated species that could be employed as rootstocks to alleviate biotic and abiotic stresses
(Huang et al., 2014). Notable grafting methods include hole insertion grafting, tongue approach grafting, splice grafting and cleft grafting
(Mohamed et al., 2014). Intra-and interspecific grafting, a widely observed phenomenon, stands prevalent among plant belonging to the Cucurbitaceae family. The potential for implementing high-throughput techniques through automation, either with operator assistance or complete robotic control, has been explored as a means to decrease the cost associated with grafted seedlings
(Comba et al., 2016). This review delivers the information on role of grafting in improving cucurbitaceous crops.
Current status of vegetable grafting
Due to the greater preference and production of cucurbits and other grafted vegetables in East Asia, this region remain as a largest market for vegetable grafting. Watermelon grown through grafted transplants in Korea, Japan and China to varying degrees (99, 94 and 40% respectively). In case of solanaceous vegetables, about 60 and 65 per cent of tomatoes, eggplants and 10-14 per cent of peppers cultivated through grafted transplants. Grafted tomato transplants used in Netherlands for all soilless tomato production. Popularity of vegetable grafting raising rapidly everywhere especially in Eastern Europe, North and South America, India and Philippines. More than 1500 industrial nurseries in China produce grafted transplants. Vegetable transplants that have been grafted found increasingly traded internationally
(Bie et al., 2017). Around the world, cucurbitaceous crops predominate in vegetable grafting. However, this technology remain infancy in India.
Potential rootstocks for different cucurbitaceous crops
The most frequently grafted cucurbitaceous crops includes watermelon, melon and cucumber.
Cucurbita species,
Citrullus species and bottle gourd can all be utilized as rootstocks for watermelon. The three most prevalent rootstocks for watermelons are bottle gourd, interspecific hybrids between
Cucurbita moschata,
Cucurbita maxima and wild watermelon (
C. lanatus var.
citroides)
(Davis et al., 2008). Although there can be variation within a species, watermelon generally very compatible with all of these rootstocks. Melons can be grafted onto rootstocks from
Cucurbita species, bottle gourds and
C. melo. There are other examples of grafting melon onto wax gourds [
Benincasa hispida (thumb.) Cogn.] and luffas [
Luffa cylindrical (L.)] M. Roem. Each rootstock contains both advantageous and unfavourable traits
(Edelstein et al., 2004). The most widely used Cucurbita spp. rootstock as an interspecific hybrid of
Cucurbita maxima and
C. moschata, which offers non-specific but effective defense against a variety of soil-borne pathogens as well as against several abiotic stresses.
Cucumis spp., Cucurbita interspecific hybrids,
Cucurbita spp., wax gourd, bottle gourd, fig leaf gourd (
C. ficifolia Bouché) and luffa can all be effectively grafted with cucumber
(Sakata et al., 2008). Fig leaf gourd has historically been the most popular rootstock for cucumbers because it has a strong affinity for the plant, greater cold tolerance and resistance to Fusarium wilt. The Cucurbita interspecific hybrids remain well-liked for cucumbers grown in the summer because they offer enduring Fusarium resistance and improved heat tolerance. In addition, Cucurbita interspecific hybrids also proven some cold tolerance
(King et al., 2010).
Influence of cucurbit rootstocks to soil-borne biotic stresses
Grafting against verticillium wilt
In tomato and brinjal, grafting has been used frequently to tackle verticillium wilt, while cucurbits hardly employ it for this purpose. The main pathogen to be concerned about among all of these pathogen races is
V. dahliae. All 33 of the examined cucurbit rootstocks exhibited some signs of
V. dahlia colonisation.
Lagenaria siceraria and
Cucurbita pepo were among those that were discovered to be the most tolerant. It was discovered that watermelon and melon were both highly vulnerable
(Paplomatas et al., 2000). Increased root vigour, biomass and concomitant increase in water and nutrient uptake are some of the mechanisms used by grafting to battle Verticillium in the contaminated soils
(Bletsos et al., 2008). The impact of decreased infestation, according to Klosterman’s findings, may be caused by the poor penetration of the inoculum and colonization into vascular tissue and even though the colonization does occur, it is a long process
(Klosterman et al., 2009). A lesser amount of wilt may also be due to a pathogen’s reduced colonization in the vascular tissue
(Paplomatas et al., 2000). Another crucial aspect of root exudates is their ability to inhibit Verticillium growth in the rhizosphere of both susceptible and resistant rootstocks
(Liu et al., 2009). “Crimson Sweet” watermelon grafted onto “Emphasis” and “Strongtoza” rootstocks grew more quickly and were more resistant to
V. dahliae when compared to non-grafted plants
(Buller et al., 2013). Devi et al., (2020) found that Verticillium wilt severity differed between grafted watermelon plants and non-grafted ‘Secretariat’ watermelon plants. Grafted watermelon plants had 3.5 times less disease than non-grafted ones. The research also found that Pelops (
L. siceraria), Round (
B. hispida), Super Shintoza and Tetsukabuto (
C. maxima ´
C. moschata hybrids) all mitigated Verticillium wilt equally.
Grafting against fusarium wilt
Fusarium species can survive for years in soils by symptomless colonizing on multiple alternate hosts, hiding in soil particles, or
via long-lasting survival mechanisms like chlamydospores. Therefore, it revealed that crop rotation remain ineffective in controlling Fusarium pathogens. Fusarium species can easily be reintroduced into cultivation regions on contaminated equipment, soil and plant tissue. They have a prodigious capacity to colonize polluted soils. However, grafting has been more effective in cucurbits than in solanaceous crops for treating Fusarium wilt. Interspecific or intergeneric grafting with non-host resistance, or exploiting host pathogen incompatibility, has proven to be a successful management strategy, especially in cucurbit crops. As a result, interspecific hybrids are frequently used in the instance of watermelon. In Japan, bottle gourd considered as the significant rootstock against this watermelon pathogen
(Sugiyama et al., 2006). Because it found effective to all races of Fusarium and contributes towards stability of yield, the rootstock “Shintoza” recommended in Spain.
When rootstocks with improved yield and environmental stress tolerance were coupled with rootstocks resistant to
F. oxysporum f. sp.
cucumerinum, cucumber grafting became popular in Japan. Since the fig leaf gourd (
Cucurbita ficifolia) exhibits good to outstanding resistance to fusarium wilt and has a tolerance to low temperature stress, it is frequently used as a rootstock for cucumbers during the winter production season. For cucumber production in the summer, ISHc ‘Shintoza,’ a rootstock with fusarium wilt resistance and heat tolerance, is favoured
(Sugiyama et al., 2006).
Squash, interspecific hybrids and watermelons have all been widely employed for their robust root systems, resilience to severe temperatures and Fusarium resistance. When grown in Fusarium-infested soils, the rootstocks “Shintoza” and “Super Shintoza,” a hybrid of
C. maxima and
C. moschata, gave watermelon tolerance. The rootstocks also boosted fruit size and yield in comparison to plants that weren’t grafted. The “Super Shintoza” rootstocks among these also offer resistance to Verticillium wilt, lowering the occurrence of microsclerotia, maintaining the structure of
Verticillium spp. and maintaining fruit output
(Gaion et al., 2018). The watermelon scions grafted onto
C. maxima x
C. moschata ‘Super Shintoza’ and
C. lanatus ‘Robusta’ demonstrated resistance to
Fusarium oxysporum f. sp.
niveum (Alvarez et al., 2015). Grafting bitter gourd onto cucurbitaceous rootstocks
viz.,
C. colocynthis,
C. metuliferus and
C. moschata with high or moderate levels of these biochemical constituents suffered less for Fusarium wilt pathogen and these rootstocks served as the best rootstocks followed by
M. charantia var.
muricata and
L. cylindrica.
Grafting against root-knot nematode
Commercial cucurbits have no known RKN resistance, therefore finding resistant rootstock has been a top focus
(Cohen et al., 2007). Cucurbit root systems are consumed by root-knot nematodes, which produce galls, which are unnatural, knotty growths on the roots. It is challenging for the plant to get water and nutrients from the roots to the above-ground plant sections due to the galls, which can reach a height of one inch or more. Cucurbits grow galls that are bigger than those found in solanaceous plants. Nematode infestations cause cucurbit crops to often be stunted as a result. They have yellow leaves and are susceptible to wilting in warm weather, but the symptoms are not alleviated by irrigation. Compared to healthy plants, infected plants produce fewer leaves, flowers and fruits and the fruits are of lesser quality.
The incidence of
Meloidogyne incognita race 3-induced galling was reduced in cantaloupes (
Cucumis melo L.) grafted on rootstocks
C. moschata and
C. metuliferus, with the latter rootstock being regarded as moderately resistant
(Pradhan et al., 2017). Strongtosa and Shintosa produced greater yields ranging from 260 to 280% than that of non-grafted plants. Grafting studies in cucumber were done to investigate the influence of several cucurbit rootstocks under the impact of root-knot nematode on growth and yield of cucumber
(Al-Debei et al., 2011).
In order to find resistant rootstocks of cucurbitaceous species for grafting cucumbers against root-knot nematode,
Punithaveni et al., (2015) did a study where,
Citrullus colocynthis and
Cucumis metuliferus were found to have resistant reactions with a root knot index (RKI) of 2. They were backed by a related screening study of cucurbitaceous species against root-knot nematode conducted by
Thangamani et al., (2018) to assess their suitability as rootstocks in grafting.
Cucurbita moschata,
Cucumis metuliferus,
Citrullus colocynthis and
Cucumis callosus were found to be resistant having an RKI-2. Although root-knot nematode tolerance can be increased through grafting, it has been shown that several common rootstocks (including interspecific Cucurbita hybrids and Lagenaria gourds) are entirely vulnerable but are tolerant due to their large root systems
(Giannakou and Karpouzas, 2003). Since these rootstocks may permit a buildup of nematodes that could potentially infect following crops, such tolerance should be handled with caution. Evidence suggests that some rootstocks have hereditary nematode resistance, which can be used to increase resistance
(Davis et al., 2008).
Influence of cucurbit rootstocks to abiotic stresses
Cold/heat stress
Losses in production of vegetable can occur as result of temperature extremes as they retard the appearance of flowers and affects the timing of fruit ripening. Due to the related physiological changes in the grafted plant, grafting can be utilized to shield plants from temperature shock and improve their yield
(Rivero et al., 2003). Grafting superior commercial cultivars onto chosen low-temperature tolerant rootstocks is seen to be a potential strategy for reducing the heat demand of vegetables as a quick and effective substitute for the often labourious breeding procedure
(Schwarz et al., 2010). To speed up the planting date during cool weather, watermelon is grafted onto rootstocks of the Shintosa type (an interspecific squash hybrid,
Cucurbita maxima ´
C. moschata). Fig leaf gourd (
Cucurbita ficifolia) and bur cucumber (
Sicos angulatus L.) are frequently utilised as rootstocks for cucumber in order to increase cold resistance. In comparison to a self-grafted cucumber, a cucumber scion grafted onto a squash rootstock (
Cucurbita moschata) might endure unfavourable conditions. Luffa [
Luffa cylindrica (L.)] rootstock-grafted cucumbers were able to tolerate heat stress (36/31°C)
(Gaion et al., 2018). Inhibition of growth caused by cold stress was greatly ameliorated in gourds (
Lagenaria siceraria) grafted onto watermelons, as manifested by physiological indices, such as much better growth parameters; much higher chlorophyll and proline contents; lower levels of ROS and lipid peroxidation; higher antioxidant enzyme activities, especially CAT and GPX; and higher expression levels of enzymes related to the Calvin cycle
(Lu et al., 2021).
Drought stress
Drought, an abiotic stressor, holds significant implications for crop productivity and quality on a global scale. Grafting high-yielding genotypes onto rootstocks that may lessen the effects of water stress on the shoot, as seen in tree crops, might be one method to reduce output losses and enhance water use efficiency under drought
(Satisha et al., 2007). Under moisture stress, mini-watermelons grafted onto a commercial rootstock (PS 1313:
Cucurbita maxima ´
Cucurbita moschata) produced a 60 per cent higher marketable yield than ungrafted melons
(Gaion et al., 2018). In cucumber, five drought stress tolerant genotypes (
i.e., rootstock) and drought-sensitive genotype Luerans (
i.e., a scion) were evaluated under water deficient conditions, which resulted in increased commercial productivity of cucumber and also increased the expression of defense related genes and increasing accumulation of GA3 and activity of antioxidant enzymes (CAT and POD), chlorophyll content, Chlorophyll fluorescence, efficiency of photosystem II (PSII) and decreased the electrolyte leakage, ABA and MDA
(Shehata et al., 2022).
Salt stress
Soil salinity affects up to 20% of irrigated agricultural land and about 7% of the world’s land area
(Shahid et al., 2018). Salinity has a deleterious impact on plant development and growth. Several approaches have been put up to mitigate the effects of salinity. A simple and effective method for increasing crop tolerance to salt stress is the adoption of resistant genotypes as the rootstocks. The ability of watermelon plants to tolerate salt increased dramatically when bottle gourd was used as a rootstock
(Yang et al., 2013). The interspecific squash rootstock (
Cucurbita maxima ´
Cucurbita moschata Duch.) increased salt tolerance, plant biomass and leaf area in the grafted muskmelon compared to non-grafted control plants, according to research by
Orsini et al., (2013) in case of the muskmelon.
Other studies showed that in salty conditions, grafted plants of the ‘Crimson Tide’ watermelon on squash (
Cucurbita maxima) and two bottle gourds (
Lagenaria siceraria (Molina) Standl.) rootstocks grew more than ungrafted plants
(Yetisir et al., 2010). When cultivated in salty conditions, melons that were grafted onto squash (
Cucurbita maxima Duch. ´
C. moschata Duch.) produced more fruit. Increased cucumber salinity tolerance may result from grafting cucumber onto pumpkin (
C. moschata). Studies have made significant advances in the use of grafting to boost cucumber salt tolerance
(Xu et al., 2017). Lower Na concentration in the scion was obtained by grafting cucumber cv. Jinchun No. 2 onto “Chaojiquanwang” rootstock (
C. moschata). Tolerance to salt in cucumber is increased by this rootstock’s greater capacity for exclusion and retention of Na in roots, which lowers Na transport to the scion
(Huang et al., 2014). The same is true for pumpkin rootstocks, which can increase resistance to both cold and salt stressors
(Xu et al., 2017). Additionally, growers employ
C. moschata rootstocks because they make it possible to produce cucumber fruits that are wax-free (bloomless). Customers favour this fruit because of its attractiveness and prolonged shelf life
(King et al., 2010). Grafting done by using highly salt tolerant rootstocks of Luffa on cucumber increased the tolerance of cucumber to salinity and significantly improved quality and yield by reducing sodium transport to the shoot
(Guo et al., 2023).
Flooding stress
Because they are extremely sensitive to flooding, many vegetable crops are negatively impacted by excessive moisture caused by unpredictably heavy rainfall and some of the vegetables are intolerant to flooded soil conditions throughout their growth and development
(Singh et al., 2020). By modifying photosynthesis and the water potential, high soil moisture reduces the amount of oxygen in the roots of plants. Grafting has been shown to increase flooding tolerance in a variety of vegetable crops by numerous research groups
(Bhatt et al., 2015). Chlorosis signs were seen in watermelon grafted onto the landrace
Lagenaria siceraria, albeit they were less severe in grafted plants in flood circumstances
(Singh et al., 2020). Hazardous pollutants, heavy metals and nutritional stress are examples of additional pressures (deficient nutrient availability, excessive nutrient availability). When cultivated in heavy metal-contaminated soils, watermelon cv. Arava grafted onto cucurbita rootstock displayed reduced levels of B, Zn, Sr, Mn, Cu, Ti, Cr, Ni and Cd. Interspecific hybrids (
C. maxima ´
C. moschata) have been shown to increase resistance to cadmium, nickel and nitrate
(Gao et al., 2015; Savvas et al., 2013). Additionally,
Allevato et al., (2019) showed in a hydroponic experiment that the melon cultivar Proteo may be grafted onto two intraspecific (Dinero and Magnus) and three interspecific (RS841, Shintoza and Strongtosa) hybrids to lessen the negative effects of a heavy metal like arsenic. The interspecific hybrid RS841 was the most effective rootstock for maintaining crop productivity in the presence of heavy metals and was also able to lessen the amount of arsenic that transferred to the fruits.
Influence of cucurbit rootstocks on qualitative and quantitative characters
Grafting is a popular and valuable method among farmers since it raises the fruit output and improves overall plant vigour through effective and increased water and nutrient uptake during the growth season
(Lee et al., 2010). Yield, quality and size of the fruits from grafted plants are indeed influenced by rootstock/scion combinations, both immediately following postharvest and throughout extended storage. Similar to this,
Xu et al., (2006) and
Wu et al., (2006) stated that grafting technology can boost yield because grafted plants have strong root systems, higher photosynthesis and resistance to soil-borne disease. Many workers across the globe have noticed the impact of grafting on increased production. Cucumber cv Kalaam grafted onto
Lagenaria siceraria rootstocks showed highly compatibility and also significant increase in vegetative growth, maximum fruit yield and quality of cucumber fruits than the other cucurbitaceous rootstocks like ridge gourd, bitter gourd and pumpkin
(Noor et al., 2019). Similarly, grafted cucumber plants on pumpkin rootstocks had 27% more marketable fruit per plant than non-grafted cucumber plants, according to
Seong et al., (2003). Cucumber grafted onto commercial cucurbita rootstocks under copper toxicity produced a higher yield (8.4 kg/vine) than non-grafted plants, according to
Rouphael et al., (2008). Pugalendhi et al., (2019) found that grafted bitter gourd plants produced a yield that was higher than the self-rooted plant by 63.2%. Parallel to these findings,
Tamilselvi and Pugalendhi (2017) and
Tamilselvi et al., (2015) found that Palee F1 scion grafted onto “pumpkin (
Cucurbita moschata)” rootstock produced more fruit (28.02 fruits) and more fruit per vine (3.55 kg/vine) than other graft combinations or non-grafted plants. The ‘RS841’ and ‘Shintoza Camelforce’ watermelon grafted on Lagenaria and
C. maxima rootstocks, respectively, had fruits that were 24% and 27% firmer than ungrafted plants.
(Yetisir et al., 2003) According to studies by
Yetisir et al., (2003) and
Proietti et al., (2008), fruits from grafted watermelon vines had a rind thickness that is 21 per cent and 17 per cent higher respectively. Even though this physical property improvement led to comparatively more waste during consumption, it also ensured better postharvest handling safety and injury prevention.
Challenges ahead
The labour and skills needed for the grafting process as well as the post-graft care of grafted seedlings for speedy healing for 7 to 10 days are the main issues with grafting.
The rural farmers may not have or understood correctly the proper knowledge of rootstock-scion compatibility, which is necessary.
Synchronization and good scion and rootstock germination rates, as well as higher success rate of grafts and stand establishment following transplant, are necessary for the successful production of grafted plants, however these conditions may not always be met
(Sen et al., 2018).
For the grafts to successfully establish themselves, it is crucial to maintain ideal conditions for temperature, humidity and light intensity during the post-grafting stage, which is particularly challenging in open field conditions. For grafts to heal, a regulated environment is necessary.
Grafting can increase the danger of disease dissemination, particularly for infections in the nursery that are disseminated by seed. Heat stress and discomfort are issues that grafting workers in a greenhouse and growth chamber must deal with
(Maurya et al., 2019).
A significant problem in large-scale manufacturing is ensuring a consistent and timely supply of promising rootstocks. Large-scale adoption is discouraged by the requirement to prepare or buy the seedlings every season. Expensive rootstock seeds, grafting tools,
etc., also contribute to a significant problem.
