Nematodes Attacking the purple Passion Fruit (passiflora Edulls) Plants In Kenya And Studies On The Biology Of Two Common Species, Meloidogyne Javanica And M. Incognita With Special Reference To their Pathogenicity And Chemical Control
Kanyagia, S T
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In a survey of plant parasitic nematodes on passion fruit in Kenya 10 genera of nematodes were discovered. Of these, 8 were identified to species level, two of which attempts were made to determine the existence of races. The 4 genera which were not identified to species were Pratylenchus, Criconemoides, Aphelenchoides and Criconema and the 8 species were Meloidogyne javanica (Treub) Chitwood, M. incognita (Kofoid and White), Chitwood, Helicotylenchus dihystera (Cobb) Sher, !i. pseudorobustus (Steiner) Golden, Rotylenchus robustus (De man), Filipjev, Aphelenchus avenae Bostian, Hoplolaimus pararobustus Sher and Tylenchorhynchus dubius Thorne. These nematodes were distributed in various areas and their number in the soil varied according to area of their distribution. However, M. javanica, M. incognita and Helicotylenchus dihystera were widespread and abundant in all areas. In each of the two dominant species, namely M. javanica and M. incognita, experiments , were conducted to determine existence of races by infecting various host plants with different nematode populations. Results revealed that M. javanica and M. incognita existed as races 1 and 2 respectively within populations of the two nematode species. Studies on development of M. javanica and M. incognita were made by studying their life cycle by cuticle moulting. Results showed that the 2nd, 3rd and 4th moults occurred on 22nd, 24th and 26th days respectively after inoculation. Full-grown females were observed by the 27th day while the eggs of both species were noted on the galls by the 31 st day after inoculation. In the histopathological studies, results demonstrated that M. javanica M. incognita caused damage to cortical and vascular tissue of passion fruit. The roots were susceptible to both nematode species whose feeding activity induced the formation of multinucleate giant cells by the root around the nematode head. Experiments on pathogenicity studies were conducted in the greenhouse to determine the effect of M. javanica and M. incognita on selected growth parameters (shoot height, root and shoot weights) of passion fruit. Results showed that plant height, root and shoot weights were significantly reduced at all inoculum levels except at 500 larvae per pot. Studies on nematode control involved the testing of the efficacy of nematicides Furadan, Nemacur and Rugby in field trials. The three rates of Furadan and Nemacur used were 3.2, 4.8 and 6.4 kg a.i/ha each and those of Rugby were 6.4, 9.6 and 10.8 kg a.i/ha. Results showed that whilst there was no significant difference in nematode population prior to soil treatment, all the rates of the three nematicides caused significant reductions but no significant differences existed between the rates. Thus, treatment of the soil with nematicides against nematodes resulted in significant fruit yield. Since passion fruit farming is gaining considerable significance in the fledgling horticultural industry in Kenya, it would appear from these studies that in order to increase production of passion fruits control and management of nematodes in the field is necessary. This could be achieved through the Ministry of Agriculture advising the farrners to control the nematodes on passion fruit with nematlcides such as Furadan, Nemacur and Rugby.