Diversity of nematode populations on cruciferous and solanaceous crops in Bagmati province of Nepal

A total of 211 soil samples were collected in different crop fields from 10 districts. Out of 211 samples, 137 samples were diagnosed for different plant parasitic nematodes. The samples were collected from the fields of cruciferous and solanaceous crops. All together twelve different nematodes were identified. The identified genera are Meloidogyne, Helicotylenchus, Pratylenchus, Tylenchus, Tylenchorhynchus, Hoplolaimus, Belonolaimus, Criconemoides, Aphelenchoides, Hirschmanniella, Longidorus and Rotylenchulus. They found either single or more than one genus in a sample. It means they are existed in both single or combine with two or more genera in a same place or root zone. The population of some of the nematode genera was recorded above the threshold level and some were below the threshold to cause significant yield loss in the crops. In potato, the population of Helicotylenchus, Tylenchorhynchus, Pratylenchus and Tylenchus were recorded equal to or more than 2 nematodes per gram of soil. Similarly, in tomato, Helicotylenchus, Meloidogyne, Hoplolaimus, and Tylenchorhynchus were recorded above threshold level. Likewise, the distribution of nematodes population in the fields of cabbage, cauliflower, chilly, capsicum, board leaf mustard, carrot and radish also had above threshold level to reduce the crops yield. Hence, lower nematode population may not show any symptom caused by nematode alone and so the effects may easily be overlooked, but nematodes become a problem when the population level surpasses the damage threshold; at that point the damage due to the pathogen is measurable and also need to manage them.