Detection of plant parasitic nematodes in the soil of crop field in Meiktila area , Myanmar

The occurrence of soil nematodes from groundnut and chilli crop fields were investigated during the period from November 2013 to February 2014. From the collected soil samples, 13 genera belonging to seven families of three orders under two classes were recorded. Among the observed genera, Meloidogyene, was found to be the predominant on the soil samples of both groundnut and chilli crop fields. Moreover, Meloidogyene, Heterodera and Helicotylenchus were found with prominent values of 138, 92 and 85, respectively and occurred in 16%, 11% and 10% of all soil samples, respectively. Paratrichodorus was found to be the lowest in numbers 27 (3%). The data from recent study indicated that the soil samples of groundnut crop field showed higher incidence of nematodes (57%) than that of chilli crop field (43%).


Introduction
There is a large scale diversity in soil nematodes and are one of the most numerous soil animals.In any case, because of their little size and complex extraction from soils, they are generally seldom studied.Most taxonomic efforts have been tended to towards significant plant parasites (Huang and Cares, 2006).Usually nematodes can be found in water-filled pore spaces in the upper soil layers due to high percentage of organic sources (Lavelle and Spain, 2001).
Nematodes are ofter considered as bioindicators which indicating the quality of soil health (Wang and McSorley, 2005).They show variations in their reactions to various pollutants.Application of nematode faunal composition analysis shows the soil food-web, nutrient status and soil fertility, acidity, and the effects of soil contaminants (Bongers and Ferris, 1999).Nematodes feed on bacteria, fungi, protozoans and even other nematodes thereby cycling the nutrients and elements and sometimes attack insects, and help to control insect pests (Hay, 2013).Still some other group dwell on plants as parasites, thereby destroying agricultural crops (McSorley and Frederick, 2000).
According to the previous authors, nematodes threaten agricultural crops throughout the world, particularly in tropical and sub-tropical regions.Several hundred species of plant parasitic nematodes are known to feed on living plants causing a variety of plants diseases worldwide.In Myanmar, Sann Yi (1976) has been conducted the infestation of plant parasitic nematodes on okra, eggplants, cabbage, chilli and yard long bean at Agricultural Research Institute area, Gyogon, Yangon.
The study on plant parasitic nematodes in the soil has not been carried out in Meiktila environs previously.The aim of this study was to determine the species occurrence of plant parasitic nematodes in the soil of groundnut and chilli crop fields near Meiktila Township.

Study area
The present study was carried out in some crop fields in Mondaing village of Meiktila Township, Mandalay Region.Meiktila Township is situated between the Latitudes of 20°50′44″ and 20° 55′ North and Longitudes of 95°49′44″ and 95°N 54′ 21″ East.Groundnut and chilli cultivated fields in Mondaing village were chosen as study sites and examination of collected soil and root samples to assay nematodes were conducted at Zoology Department of Meiktila University.The study period was from November 2013 to Feb 2014.

Collection of soil samples
For collection of soil samples, firstly removed upper soil layer for nematode assay because nematodes cannot survive in upper 2-4 inches (5-10 cm) of soil due to extreme environmental conditions (hot and cold).Then three soil samples on weekly basis from each cultivated field altogether ten times were taken using a shovel and placed in separate bags.Then the collected soil samples were carried to Zoology Department for investigation the nematodes.

Preparation for nematode extraction from soil samples
Collected soil samples from each cultivated field thoroughly mixed into one composite sample.The composite soil sample was passed through a coarse sieve (mesh openings of 10 mm or ¼ inch) to remove any lumps, stones, roots, etc.Any stones or hard lumps of soil were discarded.Then the soil was also passed onto the fine sieve to get smaller soil particles.The sifted soil mixed well to obtain a uniform distribution of nematodes.In the present study, the 50 ml volume of soil was used for nematode extraction by using Whitehead tray method based on Whitehead and Hemming (1965).
Firstly, a gauze cloth (22 x 16 cm) was prepared in the plastic basket (12 x 12 cm).The basket with a gauze cloth was placed in a plastic tray (22 x 22 cm).The 50 ml of soil sample was evenly spread on a gauze cloth.Then about 300 ml of water was carefully added down the inside the edge of the plastic tray until the soil looked wet but not immersed.The extraction was left at room temperature for 24 hours after which the extraction filter (gauze cloth) was carefully removed and water (nematode suspension) poured off into a beaker for allowing to settle for 5 minutes or more.After settling, 2 ml of suspension was taken for nematode assay by using compound microscope.

Identification of plant parasitic nematodes
Plant parasitic nematodes were identified to the genus level according to Tarjan et al. (1977), Hunt et al. (2005), Mekete et al. (2012).Identification were conducted under a compound microscope based on their taxonomic characters such as body shape, head, presence or absence and shape of a stylet, the shape and overlap of the pharyngeal glands with the intestine, oesophagus, ovary, valva position, tail shape, bursa and spicules.Morphological structures of these specimens were then recorded by digital microphotographs.

Data analyzing
Species composition and relative abundance of plant parasitic nematodes were calculated followed after Bisht et al. (2004).

Systematic position of recorded nematodes
A total of 13 genera belonging to seven families of the three orders under two classes of Phylum Nematoda were recorded (Table 1, Fig. 1).Recorded nematodes were identified according to Tarjan et al. (1977), Hunt et al. (2005), Mekete et al. (2012).
DNA or isozyme analysis is required to identify nematodes to the species level (Lambert and Bekal, 2002).In the present study, the identification of recorded specimen was also conducted only to the genus level.
Males do not penetrate roots (Evans et al., 1993).In recent study, females were found to be attached to the plant root hairs and males were free living in the soil.Tylenchulus were low numbers in yard long bean and chilli in the study conducted by Aye Aye Thant ( 2009) and the data were similar to that of present study.
Aye Aye Thant ( 2009) found high numbers of Pratylenchus in okra, yard long bean, and low numbers in chilli.In the recent study, the genus Pratylenchus found about 8% in all soil samples.So, the data from recent findings were slightly differed from that of Aye Aye Thant.Rotylenchulus occurred in low number.But in the present study, the higher number of Rotylenchulus found to be equally infested in both groundnut and chilli fields.
According to O'Bannon, and Inserra (1989), most of Helicotylenchus inserted their stylets into root epidermis to feed.From the examination of recent study, they were also found to be inserted into root hairs.Wallingford (2007) reported that major host of Helicotylenchus was chill and minor hosts were eggplant and yard long bean.In the present investigation, there high numbers of Helicotylenchus in the rhizosphere of chilli.
In the study of soil nematodes by Sann Yi (1976), Thylenchulus, Hoplolaimus, Pratylenchus and Meloidogyne in Myaung Mya, Helicotylenchus in Meiktila were found in okra.There was no record for the genus Radopholus in the analyzing by Sann Yi.Higher numbers of Radopholus (6%) found in the present study.
Netscher and Sikora (1990) stated that the plant parasitic nematodes found from chilli were Rotylenchulus, Nacobbus, Trichodorus, and Paratrichodorus.During the study period, the genus Nacobbus were found more numbers in the soil samples of groundnut field than that of chilli field.
Aye Aye Thant (2009) pointed that there were high numbers of Tylenchorhynchus in eggplant, okra, yard long bean and chill.This observation probably differed from those in the recent work.But the numbers of Tylenchorhynchus were greater in the soil of groundnut than in the soil of chilli.
Eisenback and Hirschmann (1991) mentioned that root-knot nematodes, are important group of obligate parasites of various plant.In recent study, both adult's males and females were observed from nearly all soil samples and root tissues of plants.Wallingford (2007) also reported that major host of Meloidogyne were chilli, eggplant, okra and yard long bean.In present study, high numbers of Meloidogyne were found to be infested in the soil of chilli.Therefore, the result of this study was similar to those reported by Wallingford (2007).Wallingford (2007) pointed that the minor hosts of Xiphinema were chilli, okra, eggplant and yard long bean.Sann Yi (1976) recorded that the numbers of Xiphinema were significantly higher in than those in chilli and yard long bean.The present result was not consistent with the finding of Sann Yi but the same as the Wallingford (2007).
In the assay of nematodes conducted by Aye Aye Thant (2009), there were high numbers of Trichodorus and Paratrichodorus in eggplant and cabbage.This study did not agree with Aye Aye Thant ( 2009).
In the study conducted by Anwar and McKenry (2012), Meloidogyne incognita were detected to be the most abundant plant parasitic nematodes in the examination of 325 root and soil samples.This data had consistency with the recent findings.
According to the recent findings, the numbers of nematode from the soil samples in the groundnut fields was found to be higher (57%) than that of chilli fields (43%).The tap roots of groundnut having numerous root hairs with galls and pods of groundnut underneath of the soil may more preferred by soil dwelling nematodes for their nourishment than soil of chilli crop fields.Moreover, more space of soil particles with slits from groundnut fields may allow for easily movement of the nematodes than a large percentage of clay types of soil from chilli crop fields.So, the incidence and severity of nematodes on groundnut may be related to soil texture.
Furthermore, Pankaj et al. (2006) conducted field experiments and they pointed out ploughing decreased nematode population densities significantly.The figures from recent investigation, community structure were zero or small after ploughing.So, the findings had consistency with Pankaj et al. (2006).
The present study may provide important information to extension specialists and plant scientists to consider that nematodes are major damaging pests of crops and start searching plant parasitic nematode managements.
There is need for concerted effort to control the pest nematodes on plantation area without damaging the beneficial soil organisms including nematodes.

Fig. 2
Fig. 2 Number of recoded nematode species in different families.

Table 1 .
Recorded nematodes in collected soil samples.
Fig. 1.Number of nematodes in soil samples from groundnut and chilli fields.

Table 2 .
Species composition and relative abundance of nematodes in all soil samples.