Abstract: The effect of coloured plastic mulches on the control of root-knot nematode (Meloidogyne javanica Treub) infections on tomato (Solanum lycopersicum) was investigated at the Federal College of Agriculture Ishiagu, Ebonyi State, Nigeria in 2009 and 2010 cropping seasons. Field experiments were performed in 2009 and 2010. The experiments were arranged in a factorial fitted into Randomized Complete Block Design (RCBD) with three replications. The varieties served as Factor A, while the coloured plastics served as Factor B. Tomato varieties used for the experiments were Ishiagu Local, Roma, Roma VF and UC82B. Black, blue and white coloured polyethene plastics of 3 mm thickness were used to randomly mulch the plots. The unmulched plots served as the control. Data were collected on number of galled roots and gall index per plant at harvest, plant height (cm) and number of leaves per plant at 50% anthesis, number of fruits and fresh fruit weight (g) per plant at harvest. All data collected were subjected to analysis of variance (ANOVA) using GENSTAT 3 EditionRelease7.2. Significant treatment means were separated using Least Significant Difference (LSD) at 5% level of probability. The coloured plastic mulches significantly (p<0.05) reduced the number of galled roots and gall indices per plant at harvest. Plants in the mulched plots significantly (p<0.05) produced higher plant heights, number of leaves, number of fruits and fresh fruit weights per plant. Black plastic mulch proved better than other plastic materials in all the parameters measured. Black plastic conserved heat around the root zone and raised the temperature of the soil to the disadvantage of the phytopathogenic nematodes. Black plastic mulch reduced significantly root knot nematode infections in Ishiagu local, Roma, Roma VF and UC82B varieties better than other mulching materials and is therefore, recommended.
INTRODUCTION
Tomato (Solanum lycopersicum) is a solanacious plant of Tropical Central and South American origin. The fruit is very rich in essential vitamins and mineral salts. The bulk of tomato production is from the dry season cropping particularly under irrigation in the Northern states and river banks in the Southern states of Nigeria. In Nigeria, tomato production amounts to 600,000 tonnes per year.
The production of tomato is limited by the attack of pests and diseases and this result in the acute shortage of fresh fruits in certain periods of the year (Ogwulumba et al., 2011). Nematodes are among the major pests of tomato globally especially in the tropical and subtropical regions. Dufour et al. (2003) reported that over sixty species of plant parasitic nematodes attack tomato but the most destructive nematodes responsible for enormous yield losses are the root knot nematode belonging to the genus Meloidogyne.
Nematode problems in Nigerian soils are effectively controlled with synthetic nematicides. These nematicides are costly, scarce and have adverse residual effects on the environment. This underscores the need to find alternative control measures which are affordable, readily available and environmentally friendly.
The aim of this study was therefore to evaluate the effect of different coloured plastic mulching materials on the control of Meloidogyne javanica infections on some varieties of tomato.
MATERIALS AND METHODS
The experiments were carried out in the Research and Teaching Farm of the Federal College of Agriculture Ishiagu SE Nigeria in 2009 and 2010 cropping seasons. Four tomato varieties (Ishiagu local, Roma, Roma VF and UC82B) were used in the field experiments. These varieties are susceptible to Meloidogyne javanica (Ogwulumba et al., 2009, 2010).
Nursery: Top soil of 0-30 cm depth collected from the experimental sites each year was mixed with poultry manure and river sand in the ratio of 3:2:1 were sterilized using electric soil sterilizer at 50°C for two hours to ensure that no micro-organism was left alive was used for the nursery medium.
Wooden boxes measuring 100x50x30 cm containing the nursery medium were used to raise the seedlings of the various varieties for four weeks. The seedlings were watered every other day depending on the intensity of the sun.
Coloured plastic mulching materials: The coloured plastics used as mulching materials in the field experiment were black, blue and white of 3 mm thickness. Soil temperatures under various plastic mulch and varieties were recorded using soil thermometer 1-2 pm at 10 cm depth weekly after transplanting. The thermometers were inserted at the middle of the sampled plots. The mean temperature for the various plastic mulches and varieties as well as the temperature in the control and varieties was recorded.
Field experiment: Two different portions were used for the field experiments were conducted in 2009 and 2010, respectively. The fields were assayed for nematode infestations using the decanting and sieving methods (Baker, 1985) before land preparation in 2009 and 2010, respectively. This was done by taking composite soil (50 g) samples from each field for the assay of live nematodes.
The lands were cleared, ploughed, harrowed, ridged and marked into blocks in each year. The physical and chemical properties of the soil at the experimental site were analysed in the soil laboratory of National Root Crops Research Institute Umudike Umuahia, SE Nigeria.
Three coloured plastic mulching materials were used in this experiment. The materials were: White, blue and black plastics of 3 mm thickness. Land measuring 4x80 m was used for the experiment each year. Individual blocks containing a ridge of 80m long were divided into 16 plots of 0.5x4.5 m each with 0.5 m between plots and 1 m between blocks.
The plots were randomly mulched with the various coloured plastic mulches with no-mulch as the control. Four weeks old seedlings from the nursery were transplanted into the plots at a row spacing of 45 cm along the row giving a total of 10 plants/row, 40 plants/variety/block, 160 plants/block and a projected plant population of 5,556 plants/variety/ha.
The design was 4x4 factorial in Randomized Complete Block Design (RCBD) with three replications. The varieties were Factor A while the coloured plastic mulching materials including the control were Factor B thereby making it 16 treatment combinations. The plots were labelled accordingly. Six (6) plants from each treatment were randomly selected and tagged for data collection.
Data were collected on the following parameters: Number of galled roots and Gall index per plant at harvest, Plant height (cm) and Number of leaves per plant at 50% anthesis, Number of fruits and Fresh fruits weight (g) per plant at harvest. The gall indices were evaluated using the rating scheme as follows: 0 = no galls, 1 = 1-2 galls, 2 = 3-10 galls, 3 = 11-30 galls, 4 = 31-100 galls and 5≥100 galls.
Data analysis: All data collected were subjected to analysis of variance (ANOVA) using GENSTAT 3 EditionRelease7.2. Significant treatment means were separated using Least Significant Difference (LSD) at 5% level of probability.
RESULTS
The results of the field assay revealed that the fields in both years were predominantly infested with Meloidogyne javanica followed slightly by M. incognita. The results of the composite sampling indicate that 50 g soil from the field in 2009 contained 21 live nematodes and 11 live nematodes in 2010.
The results of the physical and chemical properties of the soil from the respective sites are recorded in Table 1. The results showed that both sites used in both years were characterised as sand-loamy soil.
The soil temperatures at 10cm depth under various plastic mulches and control (no mulch) recorded weekly after transplanting are shown in Table 2. The soil temperatures were taken between 1-2 pm every week. The black plastic mulch maintained higher soil temperature than other plastics. This is closely followed by the temperature obtained from the plots mulched with the white plastic.
The coloured plastic mulches significantly (p<0.05) reduced the number of galled roots (Table 3). The control had the highest numbers of galled roots, 13.00 and 15.23 which differed significantly (p<0.05) from other plastic mulches and control in 2009 and 2010, respectively. The varieties and the interactions with the coloured plastic mulch had no significant (p>0.05) effect on the number of galled roots in 2009 and 2010. In 2010, the black plastic mulch significantly (p<0.05) reduced the numbers of galled roots to 1.70 and 3.00 in Roma and Roma VF varieties, respectively. Local variety, produced the highest number of galled roots (8.25).
The coloured plastic mulches significantly (p<0.05) reduced the gall index per plant in 2009 and 2010, respectively (Table 4). The black plastic mulch produced the lowest gall index, 1.00 and 1.67 in 2009 and 2010, respectively. The varieties, the interactions between the coloured plastic mulches and the varieties did not have any significant (p>0.05) effect on the gall index in 2009 and 2010.
The plants in the plots mulched with black plastic produced the highest mean heights of 32.23 and 32.93 cm in 2009 and 2010, respectively which differed significantly (p<0.05) from other treatments and control (Table 5).
| Table 1: | Physico-chemical properties of soil |
| EA: Exchangeable acidity; ECEC: Exhaustive cation exchange capacity; BS: Base saturation | |
| Table 2: | Weekly temperature data under coloured plastic mulches at 10 cm soil depth between 1-2 pm in 2009 and 2010 |
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| Table 3: | Effects of coloured mulches X varieties on number of galled roots per plant at harvest |
| LSD0.05 for comparing any two coloured mulches means in 2009 and 2010 is: 4.83 and 8.72. LSD0.05 for comparing any two varieties and two coloured mulches X varieties means are non-significant | |
The control produced the lowest plant height of 11.53 and 13.18 cm per plant in 2009 and 2010, respectively. The varieties and the coloured plastic mulches interactions did not produce any significant (p>0.05) effects on the plant height in 2009. In 2010, the varieties had significant (p<0.05) effect on the plant height.
| Table 4: | Effects of coloured mulches X varieties on number of galls per root (gall index) per plant at harvest |
| LSD0.05 for comparing any two coloured mulches means in 2009 and 2010 is: 0.68 and 1.21. LSD0.05 for comparing any two varieties and any two coloured mulches X varieties means are non-significant | |
| Table 5: | Effects of coloured mulches X varieties on plant height (cm) per plant at 50% anthesis |
| LSD0.05 for comparing any two coloured mulches means in 2009 and 2010 is: 9.05 and 6.95. LSD0.05 for comparing any two varieties Mean±NS: 6.92. LSD0.05 for comparing any two coloured mulches X varieties means are non-significant | |
The Local variety produced the highest plant height of 28.60 cm which differed from other varieties statistically. There was no significant (p>0.05) interaction effect on the plant height by the coloured plastic mulches and varieties.
The plant in the plots mulched with black plastic produced highest mean numbers of leaves, 53.93 and 57.10 in 2009 and 2010, respectively which differed significantly (p<0.05) from the blue plastic mulch and controls (Table 6). The lowest number of leaves, 23.75 and 22.83 were obtained at the plots without mulch in 2009 and 2010, respectively. The varieties significantly (p<0.05) affected the plant leaf number. The Local variety produced the highest numbers of leaves, 48.80 and 56.20 per plant in 2009 and 2010, respectively which differed significantly (p<0.05) from Roma and Roma VF varieties. The interactions between the coloured plastic mulches and varieties did not produce any significant (p>0.05) effect on the number of leaves produced by the plants in 2009 and 2010.
The plant in the plots mulched with black plastic produced the highest number of fruits (8.50) per plant which differed significantly (p<0.05) from the control (5.25) as recorded in Table 7. The varieties as well as the interactions between the coloured plastic mulches and varieties did not have any significant (p>0.05) effects on the number of fruits per plant in 2009 and 2010.
The plants in the plots mulch with black plastic gave the highest fruit weight of 20.33 g which differed significantly (p<0.05) from the blue plastic mulch and control but remained comparable to the white plastic mulch. The control had the lowest fruit weight of 10.33 g per plant ( Table 8). The coloured plastic mulches did not have any significant (p>0.05) effect on the fruit weight per plant in 2010.
| Table 6: | Effects of coloured mulches X varieties on number of leaves per plant at 50% anthesis |
| LSD0.05 for comparing any two coloured mulches means in 2009 and 2010 is: 15.43 and 17.34. LSD0.05 for comparing any two varieties Mean±NS: 15.40, 17.30. LSD0.05 for comparing any two coloured mulches X varieties means are non-significant | |
| Table 7: | Effects of coloured mulches X varieties on number of fruits per plant at harvest |
| LSD0.05 for comparing any two coloured mulches means in 2009 and 2010 is: 1.60, NS. LSD0.05 for comparing any two varieties and any two coloured mulches X varieties means are non-significant | |
| Table 8: | Effects of coloured mulches X varieties on fruit weight (g) per plant at harvest |
| LSD0.05 for comparing any two coloured mulches means in 2009 and 2010 is: 3.94, NS. LSD0.05 for comparing any two varieties means in 2009 and 2010 are non-significant, LSD0.05 for comparing any two coloured mulches X varieties means: 7.88, NS | |
The varieties did not have any significant (p>0.05) effect on the fruit weight in 2009 and 2010. The interactions between the coloured plastic mulches and varieties significantly (p<0.05) affected the fruit weights per plant in 2009. The black plastic mulch X UC82B interaction significantly (p<0.05) produced the highest fruit weight of 20.67 g in 2009 which differed significantly (p<0.05) from the Control X Local interaction which produced the lowest fruit weight of 6.33 g. The interactions between the coloured plastic mulches and varieties did not produce any significant (p>0.05) effect on the fruit weight per plant in 2010.
DISCUSSION
The strategy adopted in this research showed good promises a method of controlling the menace of root knot nematode infections on some susceptible tomatoes in the tropics. The experiments showed that there was inverse relationship between number of galled roots and fruit weights. This therefore shows that as the number of galled roots increases, the weight of the fruit decreases. This was evident in the control experiments where the plants were not mulched thereby culminating in higher number of galled roots. The treatments adopted in this research showed anti-nematode effects thereby resulting in the decrease in the number of galled roots with concomitant increase in fresh fruit weights.
Root knot nematodes (Meloidogyne spp.) are small microscopic roundworm organisms grouped as a major pathogen of vegetable crops throughout the world, affecting the quantity and quality of marketable yields (Kingland, 2001). They infect plant roots by producing galls through their feeding habits (Nesmith, 2000). The results in 2009 and 2010 on the use of coloured plastic mulches in the control of root knot nematode infections on tomato showed that the root knot nematodes are heat sensitive as well as the tomato plants. The lower temperatures observed in the months of May and June was attributed to increased rainfall and greater crop canopy cover. The micro-climates around the roots of the plants were changed by the plastic mulches.
The black plastic reduced the infections of root knot nematodes on the tomato plant. This was attributed to the conservation of heat in the root zones which were either nemato-toxic or nemato-static. This could have affected adversely the reproduction and distribution of the second stage juveniles of the nematodes which are the most infective stages. By altering the plants’ micro-climate, the infectivity of the root knot nematodes activities was altered to the advantage of the plants. This is in line with the findings of Fortnum et al. (2000) which stated that mulch colour alters the plant’s response to root knot nematode infections by changing the distribution of egg mass in axillary shoots. The reduction in the number of galled and gall indices in the affected plants resulted in the increased fruit weight observed in the plots mulched with black plastic mulch. Kemble (2000) stated that black plastic mulch hastens maturity and yield in tomato. The results also revealed that though black plastic performed better than the other coloured plastic mulches, the advantage over the white plastic mulch was not significant.
The black plastic mulch increased the temperature of the soil around the roots of the plants by conserving heat from the sun. This adversely affected the activities of the root knot nematodes in the soil thereby creating conducive environment for the plants to make maximum use of soil nutrients by the roots. This resulted in the increase in the vegetative parameters of the plants in the mulched plots in 2009 and 2010. This agrees with the study of Fortnum et al. (1995) that growth parameters of tomatoes grown over plastic mulch were greater than those grown in the un-mulched. The differences observed in the mulched plots were as a result of different reflective qualities of the various coloured plastic mulches. The black plastic mulch conserved heat in the soil more than other coloured plastic mulches. Decoteau et al. (1988) stated that tomato grown on black polyethylene were taller than those grown on white plastic mulch.
Fruit yield and weights were higher in the plots mulched with black poly-ethene than in other mulches. Root knot nematodes were more active in the unmulched (control) plots than mulched plots thereby having greater attacking force on the tomato plants. This was attributed to the unfavourable micro-climatic conditions under the mulching materials which prevented the root knot nematode from thriving well under the mulched plots. The black plastic mulch reflected less light than the other plastic mulches thereby having increased temperature in the soil more than other mulches. Fortnum et al. (1995) stated that soil mulched with black plastic mulch reached to temperature of 38°C at a depth of 5 cm. This temperature was attributed to be inimical to the reproduction of root knot nematode.
The black plastic mulch is therefore recommended for the control of root knot nematode infections on Ishiagu Local, Roma, Roma VF and UC82B varieties farms, but the white plastic can be used in the absence of the Black plastic mulch.