Current Status of Phytonematodes Associated with the Rhizosphere of Some Cultivars of Maize ( Zea mays L.) in Two Types of Soil in Egypt

Phytonematodes are one of the most important pathogens of cereal crops, especially maize (corn). The current study aimed to conduct a survey of phytonematodes associated with the rhizosphere of some dominant cultivars of maize ( Zea mays L.) in clay and sandy soils in different geographical areas (Sohag and Behaira Governorates). Data revealed a significant difference between nematode population density and soil type between clay and sandy. As well as, the differentiation of maize cultivars in their ability to reproduce nematodes. Also, results showed the spread of six genera of nematodes in the rhizosphere of the maize plants in sandy soil, which belong to three families; Helicotylenchus , Heterodera , Hoplolaimus , Meloidogyne and Tylenchorhynchus . While only three of them appeared in the clay soil; Heterodera , Paratylenchus and Tylenchorhynchus . In addition, the Pioneer cultivar recorded the highest population density of nematodes (427) in the clay soil, followed by the Triple hybrid cultivar and then the cultivar of Hybrid 131(425). While in sandy soils, the Hi-tech cultivar achieved the highest population density (742) compared to the same cultivar in clay soil (471).

Phytonematodes are one of the most important pathogens of cereal crops, especially maize (corn). The current study aimed to conduct a survey of phytonematodes associated with the rhizosphere of some dominant cultivars of maize (Zea mays L.) in clay and sandy soils in different geographical areas (Sohag and Behaira Governorates). Data revealed a significant difference between nematode population density and soil type between clay and sandy. As well as, the differentiation of maize cultivars in their ability to reproduce nematodes. Also, results showed the spread of six genera of nematodes in the rhizosphere of the maize plants in sandy soil, which belong to three families; Helicotylenchus, Heterodera, Hoplolaimus, Meloidogyne and Tylenchorhynchus. While only three of them appeared in the clay soil; Heterodera, Paratylenchus and Tylenchorhynchus. In addition, the Pioneer cultivar recorded the highest population density of nematodes (427) in the clay soil, followed by the Triple hybrid cultivar and then the cultivar of Hybrid 131(425). While in sandy soils, the Hi-tech cultivar achieved the highest population density (742) compared to the same cultivar in clay soil (471).

INTRODUCTION
Phytonematodes constitute one of the most important factors determining the productivity of agricultural crops both quantitatively and qualitatively (Lazarova et al., 2021;Coyne et al., 2018). Its presence, which is often difficult to notice with the naked eye, did not take an adequate economic evaluation in the record of losses and damages caused by various agricultural pests to our main agricultural crops, especially traditional grain crops (Mandal et al., 2021;Kumar and Yadav, 2020). As these losses and damages are often caused by causes that are more obvious and easier to detect, such as insects and other plant pathogens, such as bacteria and fungi (Sivasubramaniam et al., 2020). Nematodes are microscopic organisms, which attack many plants in their roots under the soil, causing them to enlarge cells and damage tissue (Barker and Koenning,1998). It impedes the transfer of food and water from it to the rest of its parts above the soil, so symptoms appear in the form of gradual weakness of its growth, dwarfing in its size, yellowing and wilting of its leaves, eventually causing the plant to die and lose it, often without recognizing the main cause under the soil (Stirling et al., 2016;Martin, Gershuny, 1992). Many previous studies were concerned with the effect of nematode pests on both fruit trees and vegetable crops, with relatively few studies on the effect of nematodes on field crops with multiple uses (Georgis et al., 2016;El-Borai and Duncan, 2005;Luc et al., 2005), especially cereal crops, which necessitated conducting some environmental and pathological studies to know the damage caused by nematode pests on the productivity of these crops (Thompson et al., 2008;Vanstone et al., 2008).
Maize (Zea mays L.) is the most extensively cultivated highland cereal in the world and the main source of food in many developing nations (Abd El-Gawad, and Morsy, 2017). After rice and wheat, it is Egypt's third-most significant staple crop in terms of acreage and output (Absy and Abdel-Lattif, 2020). The overall area of maize cultivation in Egypt is 888329 hectares or around 25.17% of the total area of cultivated land. The average output is 7.80 tonnes per hectare. It represents roughly 21.90% of the overall production of grains (FAO, 2011). Therefore, the current study aimed to conduct a survey of phytonematodes associated with the rhizosphere of some dominant cultivars of maize in clay and sandy soils in different geographical areas.

Sampling Sites and Procedure:
A total number of 360 soil and root samples from the rhizosphere of six maize cultivars, Hi-tech, Hybrid 126, Hybrid 131, Pioneer Triple hybrid and Watania hybrid, were collected from two different locations in Egypt, geographically and in soil types: Sohag Governorate: Represents the largest provinces in the cultivation of traditional crops, especially grain crops. Samples were collected from Akhmim, Juhayna, Tahta, Tima and Maragha districts. These areas are characterized by hot and dry weather in the summer, with a temperature of 42±5 °C. With heavy to medium clay soil and a traditional irrigation system (immersion).

Behaira governorate:
Due to the dominance of vegetable crops and fruit trees, the cultivation of grain crops is spread in relatively few areas, namely Abu al-Matamir, Nubaria and Hosh Issa, from which samples were collected. areas are characterized by hot and wet weather in the summer, with a temperature of 39±5 °C. With light sandy soil and advanced irrigation systems (nets and sprinklers).
Soil and root samples were obtained by excavating the soil to a depth of 20-25 cm with stainless steel half-tubes. To count and isolate plant parasitic nematodes, the obtained samples were delivered to the lab in polyethylene bags.

Phytonematodes Extraction and Numeration:
Each soil sample (250g) was carefully combined with water before being processed for nematode extraction using Cobb's decanting and sieving methods to remove phytonematodes of various shapes and sizes, Seinhorst wet method, stirring method, and automotive zonal centrifugation and floatation method to remove Heterodera from the samples. According to Golden (1971), Mai and Lyon, and the collected phytonematodes, they were counted in a Hawksly slide and classified into genera (1975). The estimation of Population density and Frequency of occurrence is calculated by the following formula:

Frequency of occurrences = (
Number of samples containing a genus The number of samples collected ) x100 Prominence value= Absolute density χ √Absolute frequency 100 Relative frequency = ( Frequency of a genus Sum of frequencies of all genera ) x100

RESULTS AND DISCUSSION
The distribution and population density of nematodes commonly in-habiting the rhizosphere of maize fields in the crop in two types of soil; Sohag and Behaira Governorates were studied. The data presented in Tables (1,2 and3) indicated a lack of diversity in the genera associated with maize in both study areas and with different soil types. As well as the lack of genera in the clay soils compared to the sandy soils of the same cultivars of maize.
In general, the results showed the spread of six genera of nematodes in the rhizosphere of the maize plants in sandy soil belonging to three families; Helicotylenchus (Hoplolaimidae), Heterodera (Heteroderidae), Hoplolaimus (Hoplolaimidae), Meloidogyne (Meloidogynidae) and Tylenchorhynchus (Tylenchorhynchidae). While only three of them appeared in the clay soil; Heterodera, Paratylenchus and Tylenchorhynchus. Considering the population density (PD) frequency of occurrence (FO) and prominence value (PV) of each genus separately in both types of soils; sandy and clay within six cultivars of maize. In general, the current study found that the amount and kind of agricultural interventions had an impact on the population density and frequency of occurrence for specific genera. In the Hi-tech cv. the Heterodera genus achieved the highest presence in sandy soil (127, 96 and12) compared to clay soil (87, 91 and 15) respectively. On the contrary, the Paratylenchus genus achieved the highest presence in the clay soil (285, 100 and 50) compared to the sandy soil (35,48 and 2) of the same cultivar. While the results of the presence of the genus Tylenchorhynchus converged in both types of soil for the same cultivar.
Also, the study showed the absence of some genera, especially in heavy clay soils in the surveyed localities, where the genus Helicotylenchus was significantly present in the clay soil, while it disappeared in the sandy lands on the Triple hybrid cultivar. The same pattern was noted with Hoplolaimus and Meloidogyne (140, 7 and 4) and (257, 19 and 11) respectively in Hi-tech cultivar. Furthermore, in the sandy soil, the genera of Helicotylenchus, Pratylenchus, and Tylenchorhynchus appeared on Hi-tech type and disappeared on the Triple hybrid cultivar.
By comparing the distribution of genera based on cultivars (Fig. 1), the Pioneer cultivar recorded the highest population density of nematodes (427) in the clay soil, followed by the Triple hybrid cultivar and then the cultivar of Hybrid 131(425). While in sandy soils, the Hi-tech cultivar achieved the highest population density (742) compared to the same cultivar in clay soil (471).   The current study clarified the association of nematodes with the roots of the maize plants despite the different types of soil and climatic conditions, in agreement with Kheir et al., (1989). And Srivastava and Jaiswal, (2011). These findings are consistent with those of Abou-Elnaga (1979), who described 50 genera of phytonematodes belonging to 31 families, including the genera found in the current study with variable population densities that may be caused by host and soil type (Youssef, (2013). The genera of Heterodera, Paratylenchus and Tylenchorhynchus represented the most common genera in the rhizosphere maize roots in agreement with Oteifa and Taha (1964), Zirakparvar, (1979), Youssef, (2013 and Fabiyi 2020.