Damage threshold of Meloidogyne arenaria to common bean influenced by dates of planting

Effect of root-knot nematode Meloidogyne arenaria was studied on common dry bean plants under natural infestation in the field at two different seasons of planting. In the first season, bean was grown in Autumn, 2012 while, the second season in early Spring, 2013. For the first season, the relation between nematode initial population density and bean yield was significantly negative (r = -0.6). A significant reduction in bean yield (P = 0.05) was obtained when nematode density was more than 100 J_2/200 g soil. While, damage threshold level (DT); nematode density at which yield begin to decrease; was estimated by 3 J_2/200 g soil. For the second season, no significant relation (P = 0.05) between nematode population density and bean yield was found (r = 0.33). DT was estimated as 22 J_2/200 g soil. Total protein and nitrogen element decreased in seeds of infected plants compared with those of healthy ones.