There are various challenges facing citrus orchards, including abiotic and biotic threats. In citrus orchards, nematodes are one of the significant biotic stressors that cause severe threats on growth and fruiting of citrus trees. Managing nematodes in citrus orchards reduces tree decline, decreasing various hazards of chemical nemacides on environment and humanity. Using biological control enhances tree growth, improves productivity, and protects the environment. There are different methods to manage the nematode problem in different crops, including physical techniques, crop rotation, resistant varieties, in addition to biological control. Using multiple strategies to control nematodes is beneficial and safer through reducing the use of nematicides and utilizing environmentally friendly substances, which are safer for human health and protect the environment. Presently, there is more interest in using organic nematicides to control plant-parasitic nematodes because of their positive impacts on crop productivity, soil, and the environment.
Top1. Introduction
Citrus is one of the most famous and extensively cultivated fruit crops worldwide. Citrus fruits are a rich source of vitamins, minerals, and dietary fiber that are crucial for a person's general nutritional health (Abobatta, 2019a).
The most frequently traded citrus fruit and one of the most generally farmed varieties, oranges account for more than half of global citrus output. Tangerines, lemons, and grapefruits are the next most traded citrus fruits. Over the past three decades, global citrus output and export have increased gradually, but more slowly than rival products like mangoes, avocados, and melons (FAO, 2022).
There are various challenges facing citrus groves that including abiotic and biotic threats (Abobatta, 2020). Nematode worms constitute one of the most common creatures on the planet. They comprise free-living organisms, humans, animals, plants, and insect parasites.
Nematode plant-parasitic (NPPs) are one of Ecdysozoa family, they are multicellular, microscopic, and bilaterally worms. Nematodes vary in size, they could reach up to 12 mm in a length with a width reach to 35 μ (Khan, 2015). Nematodes have a body cavity and are rounded, they possess one-way intestines with a mouth and anus at either end. They have a pseudocoelom that has been mesoderm-lined on one side and endoderm-lined on the other. The cuticle appears to be an intricate and plastic characteristic that has evolved through time, serving crucial roles in protection, body mobility, and shape maintenance. Nematodes only have longitudinal muscles, which accounts for their apparent whirling motion. Nematodes do not possess distinct circulatory or respiratory systems, although they have digestive, reproductive, nervous, and excretory systems. Nematodes can orient themselves and react to various environmental stimuli thanks to chemosensory and mechanosensory neurons located in the cuticle. About 1000 somatic cells make up an adult; hundreds of these cells are usually connected to the reproductive systems (Basyoni & Rizk, 2016).
The environmental infective larval stage of many parasitic nematodes involves host searching, a mechanism in which the infective larvae employ sensory signals to seek hosts. Olfaction, gustation, thermosensation, and humidity sensation are only a few sensory modalities used in a complicated host-seeking activity. Host seeking might be a potent target for prophylactic intervention since it is the first stage of the parasite-host interaction. Host-seeking behavior is still not well understood, though (Gang & Hallem, 2016).
Infection with nematodes interacting with soilborne disease leads to more hazards for host plants and increases deterioration symptoms. The magnitude of the damage was clearly correlated with the level of soil infection of nematodes that reduced agricultural plant output, particularly the beet cyst nematode, the precise nature of this correlation remained unclear to most researchers. Nevertheless, attempts to advise farmers on crop rotation to protect themselves against cyst nematode assault had already begun in the first half of the last century, most likely because the ability to quantify cysts in soil samples led researchers to interpret the numbers discovered (Seinhorst, 1986).
Nematodes are one of the major obstacles facing farmers around the world. They affect the various metabolic activities of plants, negatively affecting the foliage and producing organs, thus, causing significant economic losses in crops and reducing food production, there are plentiful of nematodes found in the soil, while, still some more need to explore.
Nematodes inhibit the growth and development of plants infecting the vascular system by reducing the nutrient supply, which causes high economic loss in fruit crop production. The root damaged by nematodes is very vulnerable to bacterial and fungal infection, further deteriorating the plant roots and stunting the plant growth.
The plant parasitic nematodes feed from plants (roots, stems, leaves, flowers, and seeds) with the help of stylet a specialized spear. The scars are made on plants after the nematode infection due to the withdrawal of cell contents and making them die. They affect the various metabolic activities of plants, negatively affecting the foliage and producing organs, thus, causing significant economic losses in crops and reducing food production (Khanna, et al, 2019).