Intensity of nematode infestation in mandarin orange crop in the nilgiris hill region

Random survey of mandarin orange (Citrus reticulata) growing areas was conducted in the Nilgiris district of Tamil Nadu. Ninety five holdings coming under seven revenue villages in the district were covered in the study. Six genera of plant parasitic nematodes viz., Tylenchulus semipenetrans, Helicotylenchus spp., Rotylenchulus reniformis, Xiphinema basiri, Hemicriconemoides sp. and Pratylenchus coffeae were found associated with this crop. Among them, the citrus nematode T. semipenetrans was the predominant nematode pest with an absolute frequency and relative frequency of 90.52 and 37.07 per cent respectively in soil and 75.78 and 33.02 per cent respectively in root. Among the seven villages surveyed, Kengarai and Kotagiri villages in Kotagiri taluk surveyed, recorded severe and moderately severe infestations respectively. High degree of decline and dieback symptoms were observed in the citrus nematode infested areas.