### EFFECT OF PRATYLENCHUS THORNEI AND MELOIDOGYNE INCOGNITA, ALONE AND IN COMBINATIONS, ON THE GROWTH AND OIL YIELD OF MENTHA ARVENSIS

#### Abstract

Pathogenicity of Pratylenchus thornei at various initial population densities (Pi) and its interaction with Meloidogyne incognita, in concomitant and sequential inoculations, were studied on Mentha arvensis cv. HY77 in a glasshouse pot experiment. Influence of all the Pi of P. thornei and M. incognita on the growth and oil yield of M. arvensis was inversely proportional and highly significant (P =0.01). The influence of M. incognita on plant growth was more severe (P =0.05) than P. thornei at equal Pi. In concomitant and sequential inoculations the greatest reduction in growth of M. arvensis was observed in M. incognita prior + P. thornei post followed by M. incognita+ P. thornei simultaneous, and P. thornei + M. incognita post, respectively. Final nematode population (Pf) of P. thornei and M. incognita increased with the increase of Pi and the reproduction factor (Rf) decreased with the increase of Pi. The influence of all Pi on Pf and Rf of both the nematodes was significant (P =0.05). M. incognita generally produced higher populations (P =0.05) than P. thornei at equal Pi. In concomitant and sequential inoculations of the two nematodes, their sum Pf was less than that of the 5000 P. thornei or M. incognita alone. Twenty days prior inoculations of both the nematodes resulted in higher Pf followed by simultaneous and post inoculations respectively. Root-galling index was significantly (P =0.01) higher (3.8) at 5000 J2 per pot followed by 2500 M. incognita alone (2.8), 2500 M. incognita prior (2), simultaneous (1.8) and post (1.3), respectively.