Journal of Applied Sciences and Environmental Management World Bank assisted National Agricultural Research Project (NARP) - University of Port Harcourt ISSN: 1119-8362 Vol. 11, Num. 4, 2007, pp. 59-62

Journal of Applied Sciences and Environmental Management, Vol. 11, No. 4, 2007, pp. 59-62

Estimation of damage caused by the burrowing Nematode, Radopholus similes (Cobb, 1893) Thorne, 1949 (Tylenchidae) (Guerot, 1970) on Musa germplasm in green house studies in Rivers State, Nigeria.

IMAFIDOR, H. O.

Animal and Environmental Biology Department, Faculty of Science. University of Port Harcourt. Port Harcourt, Rivers State. E-mail: helen_imafidor@yahoo.com. Phone No.: 08034769514

* Corresponding author: Imafidor, H. O.

Code Number: ja07095

ABSTRACT:

To define the extent of damage that Radopholus similes alone can cause in plantain (Musa sp) CV Agbagba, an inoculation experiment was conducted under greenhouse (tropical) conditions using sword suckers of Musa Sp. as test plants. Three (3) inoculum levels of Radopholus similes 50, 250 and 500 nematodes were employed. There were 4 groups of potted plants filled with sterilized soil made up of 5 replicates each. The 1st group of 5 replicates were inoculated with 50 nematode vermiforms per plant while the 2^nd and 3^rd group had 250 and 500 nematode vermiforms per plant introduced into them respectively. The 4^th group served as the control with no nematodes introduced. The period of observation was three (3) months. Damage was determined by accessing the nematodes reproduction rates. This was done by the extraction of nematode species from root samples. (Maceration – sieving method) for nematode count. Observations were made on the sensitivity of the genotype, root necrosis and plant growth parameter (freshroot weight, plant height, girth, dry root, green leaves etc). Results showed that infected plants showed a significant increase (P<0.025) in dry leaves and dry roots at all treatment levels while fresh root, plant girth and ok roots reduced mean values compared with recorded values of non-infected plants. The percentage difference between values of infected and their non-infested counterparts was 89.3 That mean values of dry leaves and dry roots of nematode infested plant recorded significantly (P<0.025) higher values than those of control showed that R. similes are damaging to plantains. Males and females of R.similis recovered at treatment levels 50, 250 and 500 were highly significantly (P <0.05) different from those recovered from control. Reproduction of nematodes occurred at all treatment levels. Plantain plants were severely damaged by R. similis as shown by increased dry roots, dry leaves and high occurrence of males (and females) which are useful growth parameters in determining susceptibility.

Phytophagous nematodes are well known as serious pests of banana and plantain worldwide. (Queeneherve, 1989; Speigher and Waale, 1997). The burrowing nematodes are the most damaging and widespread nematode attacking bananas and plantains (Ogbuji, 1976, Stover, 1972). They are probably the most important pathogen of these crops (Forgain and Gowen, 1996). They cause devastating diseases often referred to as “blackhead toppling disease” which quickly eliminate plantains (Pinochet 1988). The burrowing nematode Radopholus similes was first described from banana in Fiji by Cobb in the late nineteenth century, but its importance as a pest of commercial bananas did not receive attention until 60 years later when description of the symptoms on Cavendish bananas were published by Loos (1961) and Blake (1961). Wehunt and Edwards (1968) recorded bunch weight for treated plant (nematodes) as 29.9kg while untreated i.e. control was recorded as 20.9kg with an overall yield improvement of 26.7% for Cavendish bananas.

In Nigeria, Badra and Caveness, (1983) recorded bunch weights of 9.7kg and 14.0 – 19.1kg for untreated and treated plants respectively. The overall yield improvement was 14.4 and 19.7%. Approximately, 70 million people in West and Central Africa are estimated to derive more than one quarter of their food energy requirements from plantains, making them one of the most important sources of food energy in African lowland humid forest zone (Rony, 1990). Musa fruits are of great nutritional significance. (Nihort, 1983, Samson, 1980). They are a good source of Vitamins A and C. There are 29 proven cultivates in Nigeria (Devos, 1987). These include: plantains and banana (Red Ogoni, Agbagba) and bananas (Omini, Ikwerre banana and paranta). Studies on the biology and economic importance of burrowing nematodes in Nigeria have been restricted to the South West (Ogbuji, 1976). There is limited literature in the subject from the Southeast, specifically the Niger Delta. Studies were therefore undertaken to estimate the damage caused by R. similes on plantain Musa Spp CV Agbagba in one of the states of the Niger Delta, Rivers state.

MATERIALS AND METHODS

Studies were conducted in the Greenhouse at the University of Port Harcourt on the outskirts of Port Harcourt 5° N and 7° E. Relative humidity was 70 – 100% annually, mean annual temperature 30° c and the hottest period, February – April. Suckers were pared (plate 2) by removing the roots and thin slicing the corm’s back layer for a whitish skin layer to appear. They were cut to about 30cm and subjected to hot (50 – 55° c) water treatment.

Inoculation with R. Similis

Preparation of Inocula

Nematodes were extracted from carrot discs (Source I. I. T. A), which were macerated in a kitchen blender in distilled water thrice for 10 seconds at brief interval in a kitchen blender, after over a 7 hours period. Speijer and Waele, (1997). The macerated suspension was poured through a 100μm sieve placed in a bowl to separate the nematodes, which passed through the sieve, from the carrot tissue. The residue on the sieve was rinsed with tap water and the filtrate was collected in the bowl. The content of the bowl was subsequently poured through a 25μm sieve and the nematodes on the sieve were flushed into beaker with distilled water. The suspension containing the nematodes was brought to 500μm with distilled water. Air was blown through the nematode suspension with a pipette to homogenize the suspension. A 4ml sub sample was withdrawn and the nematodes (eggs, vermiform nematodes juveniles and adults) counted. The total number of nematodes in the suspension was calculated using a calibrated counting dish. A suspension containing 50 eggs and vermiform nematodes was pipetted into distilled water containing approximately 5000 eggs and vermiform nematodes. A few ml of distilled water was injected, when required into 3 -4 holes (3cm deep) the soil adjacent to the base (the root layer) of the plantain stem. The holes were filled with sand.

Inoculation process

There were 4 treatments. In treatment 1, 50 vermiform nematodes in 4 ml suspensions were inoculated into each plant; there were 5 replicates; thus, represented low population density on the scale. A total of 250 nematodes in 20ml were used at this level. At treatment level 2, 250 vermiform nematodes from five 4ml suspension were inoculated into each plant representing the medium population density. There were 5 replicates. A total of 1250 nematodes in 100ml suspension were used at this level. At treatment level 3, about 500 vermiform nematodes in ten 4ml suspension were inoculated into each sucker, representing to high population density. There were 5 replicates. A total of 2500 nematodes in 200ml were used at this level. Treatment level 4 (control) consisted of 5 nematode - free suckers. Inoculation at the 3 treatment levels was undertaken 2 – 3 weeks after planting to ensure the establishment of the root system. Inoculation was routinely in the mornings and suckers were watered daily.

Sucker were labeled as follows:

Plant/Nematode/Treatment/Replicate/Agbagba/Radopholus/Low/3 Date of inoculation = Agba/Rad./Low (3)

EXTRACTION OF NEMATODES FROM INOCULATED ROOTS

Twelve (12) weeks after inoculation, plants were taken individually and the roots washed with water into a beaker to remove soil particles. This was to ensure that no migratory R. similies was lost. Roots were carefully cut off from suckers and rewashed under flowing tap in a basin. Roots were kept in a tagged clean polysheet bag. Roots from each sucker were weighed and root weight. Five roots were randomly selected and cut into 10cm – lengths. These roots were subsequently cut into 1 cm lengths five grammes were weighed from chopped roots and blended in 100ml of water for 30 seconds (with a rest period interval). The suspension was poured overnight into an extraction sieve covered with extraction tissue on a tagged extraction plate. The supernatant was poured into a beaker and left for 6-8 hours before subsequent reduction of supernatant to 25ml. A 2ml – portion was pipetted into a counting dish under a microscope; this was undertaken 8 times. Number of nematodes was recorded (male, females and juveniles). Identifications were undertaken at x 40 magnification with the aid of keys by Thorne (1961), Southey (1970), Dropkin (1980) and Sarah (1996). Roots were sliced into halves in order to do the root health assessment (plate 7). Other growth characteristics; dry leaves, green leaves, plant height, plant girth, dry root, OK. Root, root knot, feeder root and % necrosis were assessed using Speighers protocol (Speigher and Waele, 1997).

STATISTICAL TOOLS

Computer Analysis: Computer based 4-way analysis of variance was used for the calculations of nematode means from all variables (fresh root weight, dry leaves, green leaves, plant height, plant girth, etc), followed by T. test.

RESULTS

R. similes infested landrace plantain in Agbagba, recorded mean at treatment level of 50 for freshweights, dry leaves, green leaves, plant height, plant girth, dry root and O.K root were 75.5, 3.0, 5.8, 54.5, 14.4, 10.2 and 42.6 respectively. Those of non-infested plants were 95.0, 1.4, 6.4, 58.1, 15.4, 2.4 and 44.8 respectively (Table 1). Mean values at level 250 and 500 are shown in Table 2 and 3. There was a significant difference (P > 0.05) in mean values of dry leaves and dry roots when R. similes infested plants were compared with their non-infested counterparts: mean values of dry leaves, green leaves, plant height and dry roots were also found in infested plants were also significantly differerent from those of non infested plants at treatment levels 250 and 500 (P<0.02). (This is summarized in Tables 1, 2 and 3)

DISCUSSION

The migratory feeding behaviour of this nematode in the root tissues caused the formation of lesions, which may enlarge and coalesce, resulting in the large necrotic areas and this accounts for the high percent root necrosis observed. The role of R. Similes in root damage of plantain had also been reported by Speijer and Waele, (1997). The significant differences observed between growth parameters of infested plants and non-infested were measurable indices of severe nematode attack. Root damage by nematodes affect the function of the root system at two levels, the anchor role and it’s ability to absorb and transport water and nutrients. The decrease in these abilities leads to; toppling over or uprooting of plants; stunting; chlorosis; lengthening of the crop cycle; reduction in size, number of leaves and bunch weight; reduction in the productive cycle of the plantation.

The dependence of the yield of a crop on root growth was demonstrated for Egyptian cotton by Balls (1953) who showed that restriction of root growth, whether laterally by very close or in-depth planting, or by any other means resulted in diminution of yield. Roots are considered laterals of limited growth; unlike branches, they do not grow indefinitely, but terminate when they have reached a certain size (Fogg, 1975). Leaves manufacture food materials for the use of plants. The exchange of gases between the atmosphere and the plants takes place usually through the stomata on the leaves. Transportation takes place mostly through the leaves. The significantly higher value of dry leaves and roots in R. similes infested plant compared to non-infested plants is confirmation of the destructive role of R. similes on plantain.

The wide spread damage caused by R. similes on bananas and plantains had been highlighted by Stover (1972); Ogbuji (1976) confirmed that in the absence of R. similes, Meloidogyne Spp. Become major nematode pests. Values on plant girth, O.K. root, plant height and green leaves of infested plant showed no significant difference among treatment levels. Although the above ground growth parameter may be useful, height is generally an unsatisfactory measure of growth (Fogg, 1975). It is only the overgrown part of the plant that is measured, no account is taken of thickness, degree of branching or spread. The disadvantage of fresh weight as a measure of plant growth is that 75% is water, and considerable portions are lost or gained independent of growth. Windham and Williams (1994) found that reduction in growth parameters was more pronounced with higher inoculation levels of R. similes on plantains.

Harvest in 50 and 500 treatment levels, number of females were double those of males; numbers of juveniles rose with increase in concentrations of inocula. The sex ratio plant parasitic nematodes is variable (Stover, 1972); although in some groups the male- female ratio is 1:1. It had been observed that during periods of stress, numbers of males increased, while those of female declined (Speijer and Waele, 1977). This may probably explain the high number of females recorded in this study, when feed was not a limiting factor. It was therefore not surprising that there were juvenile populations. R. similes has a high reproductive potential and short development cycle of 18 – 20 days (Stover, 1977). Nematodes do not survive for 10 minutes at 500C (Speiger, and Waele, 1977). However, during these investigations, some R. similes were found in non-infested plants, although the corns were pared and subjected to water treatment at 50 – 550C for 10 minutes.

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