PATHOGENICITY OF MELOIDOGYNE HAPLA ON ONION

Pang, W., S. L. Hafez, and P. Sundararaj. 2009. Pathogenicity of Meloidogyne hapla on onion. Nematropica 39:225-233. Meloidogyne hapla and M. incognita can both cause severe damage in onion production. Thus the objective of this study was to examine the relationship between different initial densities of M. hapla and the subsequent yield loss of onion. 'Tioga' onion seedlings were inoculated with M. hapla at 0, 3,000, 6,000, 9,000, or 12,000 J2/1500 cm3 pot in the greenhouse and 0, 40,000, 80,000, 160,000 M. hapla or 80,000 M. incognita J2/20,000 cm3 plot in the field microplot experiment. Data was collected on fresh and dry weights of the shoot, root and whole plant, bulb diameter and weight, and nematode populations in the roots and soil were collected at harvest. Onion weight was reduced with the increasing inoculum levels of M. hapla, and significant reduction began at 3,000 M. hapla J2/pot or 40,000 M. hapla J2/microplot. Root dry weight reduction ranged from 30.2% to 48.2%, with a total plant dry weight reduction of 40.6% to 59.6% in greenhouse tests. In field microplots, the maximum reduction in bulb fresh weight was 41.3% at 160,000 M. hapla J2/microplot and significantly more damage was caused by M. hapla than M. incognita at the same rate of 80,000 J2/microplot. Linear regressions indicated that for an increase of 40,000 in the initial inoculum density of M. hapla J2, there was a reduction of 0.4 cm in bulb diameter and 12 gram in bulb weight. The damage caused by M. incognita at 80,000 J2/microplot was not different from that caused by M. hapla at 40,000 J2/plot.