Rootstocks resistant to Meloidogyne incognita and compatibility of grafting in net melon

Received: 16/05/2012; Accepted: 29/05/2013. Agronomist Engineer . Departamento de Produção Vegetal, Universidade Estadual Paulista “Júlio de Mesquita Filho”, Faculdade de Ciências Agrárias e Veterinárias, Via de Acesso Professor Paulo Donato Castellane, s/n, 14884-900, Jaboticabal, São Paulo, Brazil. francinegalatti@hotmail.com (corresponding author); alexandrejfranco@hotmail.com; lucas.gaion@yahoo.com.br 2 Agronomist Engineer , Master of Science. Departamento de Produção Vegetal, Universidade Estadual Paulista “Júlio de Mesquita Filho”, Faculdade de Ciências Agrárias e Veterinárias, Via de Acesso Professor Paulo Donato Castellane, s/n, 14884-900, Jaboticabal, São Paulo, Brazil. leleakemi@yahoo.com.br 3 Agronomist Engineer , Doctor of Science. Instituto Federal de Educação, Ciência e Tecnologia do Triângulo Mineiro, Rua João Batista Ribeiro, 4000, 38964-790, Uberaba, Minas Gerais, Brazil. hamiltoncharlo@iftriangulo.edu.br 4 Agronomist Engineer , Doctor of Science. Departamento de Produção Vegetal, Universidade Estadual Paulista “Júlio de Mesquita Filho”, Faculdade de Ciências Agrárias e Veterinárias, Via de Acesso Professor Paulo Donato Castellane, s/n, 14884-900, Jaboticabal, São Paulo, Brazil. leilatb@fcav .unesp.br Francine de Souza Galatti , Alexandre Junqueira Franco , Letícia Akemi Ito , Hamilton de Oliveira Charlo , Lucas Aparecido Gaion, Leila Trevisan Braz 4 Short Communication


INTRODUCTION
The net melon (Cucumis melo var.reticulatus Naud.) belongs to the botanical group Cantalupensis of the Cucurbitacea family, and it is characterized by the netting on the husk, round to oval shape and color of pulp varying between clear green and salmon (Rizzo & Braz, 2001).Unlike the others on the market, due to its appearance, aroma and higher level of soluble solids, this melon shows competitive advantages compared to other varieties, because it has a good market value and allows production in small areas with good yield (Factor et al., 2000).
Besides, light and relative humidity, temperature is the main climatic factor that affects melon crops, from the germination of the seeds, up to the final quality of the product (Costa et al., 2002), and for these conditions to be better controlled and to increase production, it is recommended to grow melons in a greenhouse.
According to Peil (2003), intensive growing of vegetables in greenhouse has caused serious problems with infestation by soil pathogens, such as root-knot nematodes, and salinization, which are increasingly difficult to be solved by traditional control methods.Therefore, grafting has become an alternative of necessary cultivation in contaminated areas, to prevent contact of the sensitive plant with the pathogenic agent.
Another problem which has limited the production of net melon under protected conditions is the incidence of nematodes of Meloidogyne group, which cause disruption of roots's cells resulting in galls and yellowing of leaves, leaves reduction, poor fruit quality and decrease of production.The gall nematodes also interact with bacteria and fungi causing complex diseases (Zitter et al, 1996).According to these authors, the environmentally safe and economic method of control is the use of resistant plants.Cucumis metuliferus is highly resistant to M. hapla, M. incognita, M. javanica and M. arenaria, but the development of hybrids with Cucumis spp has failed.Resistance to M. incognita and M. arenaria was identified in Cucumis anguria and others wild cucurbits.
Grafting of melons is little known and used in Brazil, due to the existence of not contaminated areas, but it is a technology utilized in many parts of the world, with the purpose of overcoming these problems (Martínez-Ballesta et al., 2010).
Grafting is a very effective practice for controling diseases caused by soil pathogens such as nematodes; this technique requires specialized procedures, high costs and longer times for seedlings to reach an ideal stage for transplanting.However, according to Goto et al. (2003), the cost-benefit ratio can make this technique feasible, and even reduce very high costs.
Therefore, the aim of the present study was to evaluate 16 genotypes of Cucurbitaceae regarding to resistance to Meloidogyne incognita and grafting compatibility of resistant rootstocks with net melon.

MATERIAL AND METHODS
The experiments were carried out in a greenhouse at the School of Agricultural and Veterinary Sciences (FCAV-UNESP), Campus Jaboticabal.
Rev. Ceres, Viçosa, v. 60, n.3, p. 432-436, mai/jun, 2013 The seedlings were obtained by first seeding in Styrofoam trays, and 15 days after sowing, the seedlings were transplanted to pots.On the day of transplanting, 10 individual seedlings of each genotype were inoculated with eggs and/or second-stage juveniles of M. incognita, which consisted of the replicates.Inoculation was performed using a 10-mL graduated pipette to transfer the suspension of 300 eggs and/or second-stage juveniles / mL, henceforth referred to as the initial population (IP).
At 50 days after transplanting, the seedlings were removed from the pots, the aerial part discarded and the roots washed for the determination of the reproduction factor.
The resistance of the materials was defined based on the reproduction of the nematode in each genotype, in accordance with the concept of Roberts et al. (1998), where the resistance of a plant to a nematode is measured by the ability of the plant to suppress the development or reproduction of the pest.Thus, evaluation of the genotypes resistance to M. incognita was evaluated according to the reproduction factor (RF), as described by Oostenbrink (1966).
The population obtained for each root system, designated the final population (FP), was divided by the number of eggs and juveniles according to the stage injected into the plants (IP), where the mean reproduction factor (RF) values are determined for each genotype.Genotypes were considered resistant if they showed an RF<1.All genotypes that exhibited an RF>1 were considered susceptible.
The Cucurbitaceae genotypes that were resistant to M. incognita were utilized as rootstocks for the net melon 'Bonus no.2'.
Cleft grafting was used as described by Yamakawa (1982), because according to Choe (1989), cleft grafting can promote to the seedlings a graft take rate of up to 93%.After grafting, the seedlings were placed in a humid room until local healing, when the percentage of graft take was evaluated.
All the other genotypes evaluated, such as the hybrid Bonus no.2, showed a reproduction factor >1, being considered susceptible to M. incognita.Cucumber 'Rubi' showed the highest reproduction factor of 6.26, followed by the squash Coroa with 5.12.
Among the rootstocks considered resistant, grafting compatibility between them and the scion (melon 'Bonus no.2') can be seen in Figure 1, where melon 'Redondo Amarelo' showed the highest graft take rate, at 100%.
After melon 'Redondo Amarelo', the pumpkin 'Mini-Paulista' had a graft take percentage of 94%, also showing good compatibility between scion and rootstock.Therefore, these two rootstocks appear to be very compatible with netmelon 'Bonus no.2'.
The rootstocks Sponge gourd, watermelon 'Charleston Gray' and pumpkin 'Goianinha' had low graft take percentages: 66%, 62% and 50%, respectively, showing that, despite being resistant to M. incognita, they would not be so interesting for use as rootstocks.

DISCUSSION
There are numerous studies with rootstocks aimed to achieving resistance to M. incognita.Despite the large diversity among the Cucurbitaceae family, which include 118 genera and 825 species, only 23 species are cultivated as vegetables in many regions of the world (Almeida, 2002).Thus, it is difficult to compare studies that utilize the same species as possible rootstocks.Singuenza et al. (2005) demonstrated the possibility of using Cucumis metuliferus as rootstock for melon in the control of M. incognita.Xingfang et al. (2006) used Sicyos angulatus L. as rootstock for cucumber in soils with M. incognita, observing little effect on the height of the plant and taste of fruits.Chandra et al. (2010) evaluated the pathogenic potential of M. incoginta in four species of Cucurbitaceae: Lagenaria siceraria, Cucumis sativus, Momordica charantia and Cucurbita pepo, and all were highly or moderately susceptible to the phytonematode, which limited the water and nutrients translocation in the plant.Santos et al. (1999), working with another variable of resistance to nematodes in which grades were attributed based on the presence or absence of galls, evaluated 54 experimental genotypes of melon regarding to M. incognita resistance and only two of them were considered resistant, while the others were considered moderately resistant, susceptible and highly susceptible.In the present study, the melon 'Redondo Amarelo' was considered resistant, however, differently from observed by Santos et al. (1999) this melon is commercial and not a genotype in study.
In the present study, it was not possible to count galls, since the roots showed high infestation and the galls were almost invisible to naked eyes, making it difficult to count them.Therefore, the parameter used was the reproduction factor described by Oostenbrink (1966).temperature and relative humidity during and after grafting, as well as contact surface and salinity, which could have a negative influence on wound healing (callus formation).Poor wound healing can result in reduction of leaves, slow growth and low survival rate of seedlings (Oda et al., 2005;Johkan et al., 2009).
Thus, the movement of water and translocation of nutrients can be determined by the vascular connection or continuity of the cambium between scion and rootstock, thereby affecting other physiological characteristics.