Northern Root‐Knot Nematode Populations and Soil Temperature Effect on Alfalfa

Abstract

Resistance is the only practical method of controlling northern root‐knot nematode [Meloidogyne hapla (Chitwood)] on alfalfa (Medicago sativa L.). This study was conducted to determine if physiological differences in geographically separated nematode populations affected the resistance and susceptibility of alfalfa to M. hapla. The host/parasite relationship between resistant and susceptible alfalfa and five M. hapla populations was investigated at Logan, UT in regulated greenhouse and growth chamber studies. Meloidogyne hapla‐susceptible ‘Ranger’ alfalfa was 100% susceptible to all M. hapla populations, while M. hapla‐resistant Nevada Synthetic XX (Nev Syn XX) germplasm differed in the percentage of plants susceptible to California 1 (CA1), California 2 (CA2), Utah (UT), Nevada (NV), and Wyoming (WY) populations. Ranger was 100% susceptible to all populations at soil temperatures of IS to 30 °C. The Nev Syn XX was 100% susceptible to CA1 at all temperatures, but differed in the percentage of susceptibility to the other populations at temperatures of 20 to 30 °C (P < 0.05). Reproduction on Ranger for all nematode populations was greatest at 25 °C (P < 0.05), while CA1 and CA2 had a higher reproduction rate at 30 °C than the other populations. On Nev Syn XX, the greatest reproduction for CA1 occurred at 25 °C, and with the other populations at 30 °C (P < 0.05) where resistance was lost. Shoot dry weights of Ranger were less at 30 °C for CA1 and CA2, and at 25 °C for the other nematode populations (P < 0.05). The greatest reduction of Nev Syn XX shoot growth by CA1 occurred at 25 °C. Physiological differences in the virulence and reproduction of M. hapla populations and the effect of soil temperatures on expression of plant resistance should be considered in an alfalfa breeding program involving this nematode.