Pang, W., S. L. Hafez, and P. Sundararaj. 2009. Concomitant Interaction of Pratylenchus penetrans and Meloidogyne hapla on Onion. Nematropica 39:297-303. Pratylenchus penetrans and Meloidogyne hapla often exist together in Idaho onion fields; however, there is no information available about the yield loss of onion when they exist simultaneously in soil. The objectives of this research were to determine onion yield loss when the two species were inoculated simultaneously; and to determine the effects of each nematode on the multiplication of the other. Seedlings of 'Tioga' onion were inoculated with 6000 P. penetrans, 6000 M. hapla, or 6000 P. penetrans + 6000 M. hapla/ pot in a greenhouse and compared to a non-inoculated control. Onion bulb diameter, shoot height, whole plant fresh and dry weights, and nematode population in the root and soil were recorded at harvest. Meloidogyne hapla and P. penetrans alone reduced onion growth compared with the non-inoculated control (P ≤ 0.05). More damage was induced by P. penetrans compared to M. hapla. However, maximum reduction in plant growth occurred when P. penetrans and M. hapla were simultaneously inoculated. The two nematode species suppressed the multiplication of each other on onion and the suppressive effect of P. penetrans on M. hapla was more severe than that of M. hapla on P. penetrans.
