PhD

Chethikoduveli, Plumbago rosea L. being a newly domesticated medicinal plant, experiments were conducted to get information on the pathogenic level of the nematodes, Meloidogyne incognita (Kofoid and White, 1919) Chittwood, 1949 and Radopholus similis (Cobb, 1893) Thorne, 1949 and their effects in loss in yield. The histopathological changes due to infestation by the nematodes were also investigated. These nematode infestation also induce biochemical changes in the feeding region i.e., the root of the crop which is used for pharmacological preparations, hence these aspects were studied.
Studies were also conducted to evolve an eco-friendly management strategy for controlling nematodes using bioagents (Glomus fasciculatum, Pseudomonas fluorescens and Paecilomyces lilacinus) and selected organic amendments (neem cake and groundnut cake). The effect of green leaves (Glyricidia maculata and Clerodendron infortunatum) having antihelminthic properties available in the farmer’s field were also studied as a low cost method.
In pathogenicity and crop loss trials the results were assessed in terms of biometric characters, (height of the plant, number of leaves and number of branches) at monthly intervals and characters like shoot weight, root weight and leaf area, yield and yield characters (length, width and number of tubers) at the time of harvest of the crop. The population of the nematodes in soil was recorded at periodic intervals and at harvest of the crop. There was significant reduction in biometric characters at two and six months after inoculation onwards in the case of R. similis and M. incognita respectively. The pathogenic level of R. similis was above 100 nematodes and 1000 and above in the case of M. incognita (above 25 per cent). Both these nematodes recorded more than 25 per cent reduction in yield. In the case of crop loss there was an avoidable loss of 43.96 per cent at 1000 J2 level of M. incognita and 35.32 per cent in the case of R. similis. At 100 level the losses were 36 per cent and 29 per cent in M. incognita and R. similis respectively.
The histopathological studies revealed that the entry of second stage juveniles of M. incognita took place within five days and penetrated the root tissue and established its feeding cite on the vascular parenchyma. Formation of hypertrophy and hyperplasia took place during 10 to 15 days at the surface of the root and they produce egg mass in a gelatinous matrix. In the case of R. similis nematode entered the root and started feeding in the cortical region. After 10 days longitudinal burrows developed underneath the outer cortical cell layer. Burrows were formed due to the disintegration of cytoplasm and coalescence of cells after 15 days of entry. Then the cavities were formed and they coalesce and broke down leading to tunnel formation in 25 to 30 days.
Biochemical changes caused by various levels of M. incognita and R. similis revealed that there was considerable variation in phenol and total free amino acids. The phenol production was increased with increase in initial inoculum levels (10, 100, 1000 and 10000) in both the cases. The variation in the total free amino acids revealed that the percentage increase in different levels of inoculum were 12, 44, 96 and 216 for M. incognita and 8, 24, 104 and 240 in R. similis. The rate of reduction of plumbagin was less in R. similis infested plants when compared to M. incognita. Maximum reduction of 7.67 was recorded in 1000 J2 level while there was only 3.62 per cent increase in the case of R. similis.
The field experiment on management of nematodes revealed that G. fasciculatum @ 20 g m-2 having 100 chlamydospores / gram of media was found to be the best treatment followed by P. fluorescens @ 10 g m-2 @ 106 cells / gram and P. lilacinus @ 10 g m-2 having 106 spores / gram of media and these were seen even better than the chemical carbosulfan @ 0.1 g ai m-2, in managing nematode population and improving the biometric characters and yield of P. rosea. The yield in terms of weight of tubers revealed that G. fasciculatum, P. fluorescens, carbosulfan and P. lilacinus were statistically on par. G. fasciculatum recorded the maximum yield (231.7 g / plant). G. fasciculatum, P. fluorescens and Carbosulfan showed more than cent per cent increase while P. lilacinus recorded 98 per cent increase. The effect of neem cake and groundnut cake @ 100 g m-2 and the green leaves of G. maculata and C. infortunatum @ 5 kg m-2 were also found effective in managing the nematodes and improving the biometric characters and yield of the plant but these treatments were inferior to the above bioagents. The farmers practice of application of wood ash @ 5 kg m-2 also had some effect on nematode management and slightly increased the yield of tubers. In comparison with plants raised in denematised soil, effect of G. fasciculatum, P. fluorescens and carbosulfan were found better because of the growth promoting character of bioagents and phytotonic effect of carbosulfan. The nitrogen and phosphorus contents were maximum in the leaves of P. lilacinus (1.43 and 0.158 per cent respectively) treated plants followed by G. fasciculatum and P. fluorescens and these were on par. Neem cake and carbosulfan also showed higher ‘P’ content in the leaves as that of the above bioagents. In the ‘K’ content of leaves P. fluorescens (1.92 per cent) treated plants showed high value followed by G. fasciculatum, neem cake and carbosulfan.