**1. Introduction**

Root-knot nematodes (RKN), *Meloidogyne* spp., are obligate plant-parasitic nematodes that cause serious damage and yield losses in a wide range of crops [1]. This group of nematodes presents a wide range of herbaceous and woody host plants, including monocotyledons and dicotyledons [2]. Due to the importance of their economic impact, different managemen<sup>t</sup> strategies have been developing to control these plant-parasitic nematodes, such as application of live microbes (e.g., bacteria, fungi) and/or their secondary metabolites, essential oils, plant extracts, ozonated water, silicon, steaming, and solarization. These environmentally benign strategies can be considered for replacing the chemicals commonly used in agriculture [3].

*Meloidogyne graminicola* (which was first discovered by Golden and Birchfield in 1965 (Nematoda: Meloidogynidae)), commonly named as the rice RKN, is considered as one of the most important damaging parasites for upland, lowland, and deep-water rice cultivation throughout the world, particularly in South and Southeast Asia [4]. The second

**Citation:** Sacchi, S.; Torrini, G.; Marianelli, L.; Mazza, G.; Fumagalli, A.; Cavagna, B.; Ciampitti, M.; Roversi, P.F. Control of *Meloidogyne graminicola* a Root-Knot Nematode Using Rice Plants as Trap Crops: Preliminary Results. *Agriculture* **2021**, *11*, 37. https://doi.org/10.3390/ agriculture11010037

Received: 25 November 2020 Accepted: 6 January 2021 Published: 8 January 2021

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juvenile stage (J2) is the infective stage that hatches from the egg under favorable environmental conditions, finds the root, enters the meristematic zone, and induces the formation of giant galls by continuous feeding.

Rice is the most important host for rice RKN, but this nematode has a wide range of alternative hosts, including many weeds commonly found in rice fields that may offer refuge to these nematodes [5,6].

Italy is the main rice-growing country in Europe, with 217,195 ha of rice in 2018 [7]. The most important rice-growing area is the section of the Po River Valley straddling the regions of Lombardy and Piedmont (more than 202,000 hectares, 93% of the Italian rice surface [7]). *Meloidogyne graminicola* was detected for the first time in mainland Europe (in the Piedmont region, Northern Italy) in 2016 and was subsequently added to the EPPO Alert List [8,9]. To preserve the national rice production, the Italian National Plant Protection Organization (NPPO) quickly issued phytosanitary measures to limit *M. graminicola* damage and avoid its spread to new areas. The options to control *M. graminicola* are still limited and for many years, the use of nematicides has been the most efficient way to manage this pest. Due to their negative impact on the environment and the implementation of new directives and regulations to reduce chemical applications [10], alternative strategies are now needed to reduce RKN populations. Among the phytosanitary measures adopted by the Italian NPPO (reported in the Ministerial Decree of 6 July 2017), rice field flooding seems to be one of the most efficient techniques to control the size of the *M. graminicola* population, but in some areas of the Lombardy region, this practice is not applicable due to the soil structure characterized by a low water retention capacity [11]. For this reason, some field trials using rice plants as trap crops were conducted to identify new control strategies against this pest.

Trap cropping is a practice for pest nematode control that has been used since the late 1800s [12]. A susceptible host species is planted and nematode juveniles of a sedentary parasitic nematode such as root-knot nematodes are stimulated to hatch and invade the roots and establish a feeding site on the plant. Once this colonization has occurred, and the females begin to mature, they are unable to leave the plant root. Before the nematodes complete their life cycle, the crop is destroyed, avoiding a new soil infestation and thus reducing the nematode population.

In this study, among the various trap cropping techniques available, sequential trap cropping was chosen for the managemen<sup>t</sup> of the rice RKN, since this technique involves plants that are highly attractive to the pest and that are sown earlier than the main crop [13].

This study aimed to conduct a first-time evaluation of rice plant use in trap crop techniques for the managemen<sup>t</sup> of this nematode pest, in areas where the rice field flooding is not applicable.

#### **2. Materials and Methods**
