REDUCTION IN SEEDLING GROWTH OF SOME VEGETABLES DUE TO INFECTION WITH ROOT- KNOT NEMATODE (MELOIDOGYNE INCOGNITA)
Rukshshana and I. H. Mian. 2012. Reduction in seedling growth of some vegetables due to infection with root- knot nematode (Meloidogyne incognita). Bangladesh J. Plant Pathol. 28(1&2):39-44.
A pot experiment was conducted to find out the effect of root-knot nematode infection at seedling stage on plant growth of eleven vegetable crops commonly grown in Bangladesh. It was found that shoot and root growth of all eleven vegetables were significantly reduced due to inoculation with root-knot nematode at seedling stage. The reduction of height and fresh weight of shoot, and length and fresh weight of root of eleven crops varied from 16.83 to 63.65%, 15.50% to 46.652%, 23.30 to 57.53% and 22.18 to 74.00%, respectively. Number of galls and eggs per 20 g roots ranged 2.88-69.82 and 120.85-3482.00, respectively. The highest gall number was found in roots of tomato and the lowest in roots of Indian spinach. The lowest egg number was found in roots of cucumber and the highest in tomato roots. Among eleven vegetables, the highest population of L3 and L4 and immature as well as mature females were recorded from roots of tomato followed by cauliflower and eggplant. Based on findings of the present investigation it may be concluded that infection of root-knot nematodes at seedling stage causes severe reduction in plant growth of vegetable seedlings commonly grown in Bangladesh.
Root-knot nematodes (Meloidogyne spp.) are common pests of vegetable crops in Bangladesh. At least four species of root-knot nematodes occur in Bangladesh. They are M. incognita, M. javanica, M. graminicola and M. arenaria. Among them the most frequently occurring species is M. incognita (Mian 1986). The nematode larvae infect plant roots causing the development of giant cells, root galls through hypertrophy and hyperplasia. The giant cells and galls disrupt uptake of nutrients and water from soil and interfere with plant growth (Sasser 1980, Sasser and Carter 1985).
About 2000 plant species including vegetables, small grains, fruits, field crops, nursery crops, ornamentals, forages and turf grasses are attacked by root-knot nematodes. They are major pests of vegetables, impacting both the quantity and quality of marketable yields (Taylor and Sasser 1978, Widmer et al. 2011). They are common pests of cowpea (Duncan and Ferris 1983), cucumber (Dropkin 1954), eggplant (Anon. 1986), okra (Bhatti and Jain 1977), potato (Mian 1987), tomato (Dareker and Mhase 1988). A report from India reveals that root-knot nematodes can cause 27% loss in eggplant (Reddy 1986). In that country 47% yield loss in tomato due to the disease has been recorded (Bhatti and Jain 1977, Darekar and Mhase 1988).
Root-knot nematodes are the most important plant-parasitic nematodes in Bangladesh (Timm and Ameen 1960, Talukder 1974). In field surveys throughout the country, Timm and Ameen (1960), Sam (1979), Chowdhury (1985), Mian (1986) and Mian (1987) reported that root-knot nematodes are the most prevalent plant-parasitic nematodes in Bangladesh and the pests attack commonly grown vegetables such as amaranth, carrot, bottle gourd, white gourd, bitter gourd, beet, chili, coriander, cowpea, cucumber, garlic, Indian spinach, lettuce, okra, pea, potato, pumpkin, radish, ribbed gourd, sponge gourd, sugar beet and tomato. Stirling et al. (1992) reported that young plants are highly vulnerable to root-knot nematodes causing severe growth retardation.
Report on the effect of root-knot nematode infection on vegetable crop is scanty in Bangladesh. Choudhury (1985) reported from Bangladesh that root-knot disease reduced shoot and root growth of tomato. However, comprehensive reports on the effect of root-knot nematodes on the growth of common vegetables of the country are not available. Under the above circumstances the present piece of research was undertaken to find out the effect of root-knot nematode infection at seedling stage on plant growth of eleven vegetable crops commonly grown in Bangladesh.
MATERIALS AND METHODS
Eleven vegetable crops namely bottle gourd (Lagenaria siceraria), sweet gourd (Cucurbita pepo), white gourd (Benincasa hispada), cucumber (Cucumis sativus), eggplant (Solanum melongena), tomato (Lycopersicon esculentum), okra (Abelmoschus eslentus), Indian spinach (Basella alba), cauliflower (Brassica oleracea var. botrytis), green amaranth (Amaranthus
viridus) and red amaranth (Amaranthus tricolor) were selected for the experiment.
The pot experiment was conducted in a pot house of Plant Pathology Department, Bangabandhu Sheikh Mujibur Rahman Agricultural University (BSMRAU), Gazipur during Kharif season (June to August) of 2010. Sandy loam soil was collected and steam sterilized for 4 hours. Urea, TSP and MOP were mixed with the soil at recommended doses (Anon. 1985). The prepared soil was poured into plastic pot (15 cm diameter) at 4 kg/pot. The pots were placed in the pot house following completely randomized design and kept for 48 hours for cooling of the soil.
The seeds of the selected crops were surface sterilized with 1.0% chlorox for 30 minutes and rinsed in sterilized water for three times. The surface sterilized seeds were planted in the pots. Each pot received 10-20 seeds depending on seed size. After germination the seedlings were thinned to have five healthy plants per pot. Eight pots (replication) were used for each crop.
Seven days old seedlings of each vegertable raised in 4 pots were inoculated with freshly hatched second stage active larvae of Meloidoyne incognita suspended in tap water at 2500 larvae per milliliter of water. Each pot received 1 ml of larval suspension. For inoculation, soil was removed from the base of the seedling and the larval suspension was spread uniformly near the exposed roots. After application of the inoculum suspension, the bases of the seedlings were covered with the soil. Immediately after inoculation water was sprayed over the pot soil. Seedlings in another 4 pots were not inoculated, which served as control for comparison. The seedlings were allowed to grow for 20 days providing necessary water and nutrients.
After 20 days of inoculation, both inoculated and uninoculated seedlings of each crop were removed carefully from the soil. At the time of uprooting precaution was taken to minimize root damage. The root systems were washed with running tap water to remove the adhering soil, wiped with tissue paper and number of galls per root system, height and fresh weight of shoot, and length and fresh weight of roots were recorded.
Populations of 2nd, 3rd, 4th stage larvae, immature and mature females in each root system of inoculated seedling were also recorded. To make the nematode in the root easily visible, the root system was stained following lactophenol cotton blue method (Mian 1994). The populations of L2, L3, L4, immature female, mature female and eggs per root system were counted and their populations were expressed in number/20 g roots.
Collected data on all parameters related to plant growth, gall development and nematode population were analyzed using MSTAT-C software. Paired-t test was performed to compare growth of inoculated and uninoculated seedlings. Means were compared following Duncan’s Multiple Range Test using the same computer program. Whenever, necessary data were transformed following suitable method. Relationships among some selected variables were also determined using MSTAT-C program.
RESULTS AND DISCUSSION
Reduction in height and weight of shoot
Infection of seedlings of all crops with M. incognita caused significant (P=0.01) reduction in shoot height within the range of 16.83 to 63.65% over uninoculated control. The reduction in okra, eggplant, tomato, Indian spinach and cauliflower was statistically similar and significantly lower compared to bottle gourd, sweet gourd and white gourd. Reduction in shoot height of latter three crops was also ot significantly different (Table 1).
Fresh shoot weight of eleven vegetable crops was reduced by 15.50% to 46.652% over uninfected seedlings under control. The reduction was highly significant (P=0.01). The lowest reduction was recorded from cucumber followed by tomato, eggplant, bottle gourd, okra sweet gourd and red amaranth. Differences in their shoot weight were not significantly different. The maximum reduction was found in cauliflower followed by white gourd and Indian spinach. The differences in the parameter among three crops were also not significant (Table 2).
Reduction in length and weight of root
Infection with M. incognita at seedling stage caused reduction in root length of all crops significantly over control within the range of 23.30 to 57.53%. Difference in root length of inoculated and uninoculated plants of every crop was highly significant. The maximum decrease in root length was recorded from cucumber followed by sweet gourd, red amaranth, bottle gourd, white gourd, Indian spinach and green amaranth. Differences in root length reduction of those six crops were statistically similar and significantly higher compared to only okra, tomato and eggplant (Table 3).
Reduction in root weight
Difference in root weight of uninoculated and inoculated plants of each crop tested was highly significant (P=0.01). The reduction ranged 22.18-74.00% in different crop species. The lowest reduction of root weight over control was observed in cauliflower and cucumber, which were statistically similar to bottle gourd, sweet gourd, eggplant, tomato and red amaranth. The reduction in root weight of seedling of Indian spinach, green amaranth and okra was also statistically similar but significantly higher compared to other crops (Table 4). Significantly the highest egg number was found in roots of bottle gourd. The second highest gall number was found in roots of sweet gourd, which was statistically similar to white gourd. The egg number in roots of cucumber, cauliflower and tomato was statistically similar but significantly lower compared to all other vegetable seedlings. The gall number in roots of red amaranth, green amaranth and okra was also statistically similar and significantly lower compared to three gourds. Gall number in roots of eggplant was also significantly lower compared to three gourds (Table 5).
Population of 2nd, 3rd and 4th stage larvae, immature and mature female
The population of second stage larvae (L2) in different vegetables ranged 0.27-4.99/20 g of root. The maximum number L2 was found in roots of cauliflower followed by tomato and eggplant. Their population in those three crops was not significantly different. The lowest number of L2 was recorded from the roots of Indian spinach, which was statistically similar to green amaranth, red amaranth, bottle gourd, sweet gourd, white gourd, cucumber and Okra (Table 6). The maximum of 12.08 third stage larvae per 20 g of root was found in tomato, which was statistically similar to only cauliflower. The third highest L3 population was observed in roots of eggplant, which was statistically similar to cauliflower. Their lowest population of 0.42/20 g root was recorded from roots of Indian spinach followed by green amaranth, red amaranth, white gourd, okra, bottle gourd and sweet gourd. Differences in their populations in roots of those seven vegetables were not significant. The trends in population dynamics of the fourth stage larvae (L4) developed in roots of eleven vegetable seedlings were almost similar to the population dynamics of L3 (Table 6).
Population of immature and mature females
In case of immature and mature females, significantly the highest populations were found in roots of tomato. The second highest populations of the nematodes were found in roots of cauliflower, which was statistically similar to cucumber and eggplant. Their lowest populations were found in roots of Indian spinach, which was statistically similar to red amaranth, green amaranth, okra, and three gourds (Table 6).
Results of the present experiment show that shoot and root growth of vegetables are significantly reduced over control due to inoculation with root-knot nematode at seedling stage. Reduction of height and fresh weight of shoot and length and fresh weight of root varied from 16.83 to 63.65, 15.50 to 46.652, 23.30 to 57.53 and 22.18 to 74.00%, respectively among different crop species. Number of galls and eggs per 20 g roots ranged 2.88-69.82 and 120.85-3482.00, respectively. The highest gall number was found in roots of tomato and the lowest in roots of Indian spinach. The lowest egg number was found in roots of cucumber and the highest in tomato roots. Among eleven vegetables, the highest population of L3 and L4 larvae, and immature as well as mature females were recorded from roots of tomato followed by cauliflower and eggplant. On the other hand, the maximum number of L2 was found in roots of cauliflower followed by tomato and eggplant. It indicates that tomato is highly vulnerable to the nematode followed by eggplant and cauliflower.
The findings of the present investigation are in agreements with the findings of many other investigators worked with different crops including most of them tested in the present experiment. They reported appreciable reduction in plant growth and crop yield of cucumber (Dropkin 1954), eggplant (Anon. 1986), tomato (Chowdhury 1985, Dareker and Mhase 1988) and okra (Bhatti and Jain 1977). A report from India, reveals that root-knot nematodes can cause yield loss in eggplant (Reddy 1986) and 47% in tomato (Zahid and Ahmed 1986, Darekar and Mhase 1988). Based on findings of the present investigation it may be concluded that infection of root-knot nematodes at seedling stage causes severe reduction in plant growth of vegetable seedlings commonly grown in Bangladesh.
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