Screening for susceptibility and tolerance to Meloidogyne incognita and M. javanica in okra cultivars in Iraq

Kandouh, B.H., A.E. Hasan, A.M. Abd-Al-Rasoul and B.S. Sipes. 2019. Screening for susceptibility and tolerance to Meloidogyne incognita and M. javanica in okra cultivars in Iraq. Arab Journal of Plant Protection, 37(3): 279-285. Ten okra cultivars were screened for their susceptibility and resistance/tolerance to the root-knot nematodes Meloidogyne incognita and M. javanicain in a two-trial experiment under ambient conditions. 14 days old okra seedlings were inoculated with 3000 egg/J2 of M. incognita or M. javanica. The nematode reproduction factor (Rf) was used to determine susceptibility or resistance among tested cultivars, and cultivars were considered highly susceptibleif Rf ≥ 2, susceptible if 2 >Rf ≥ 1 and resistant if Rf< 1. Whereas, magnitude of reduction in plant shoot weight (ShW) over the control indicated tolerance and the categories tolerant, moderately tolerant and intolerant were established, when ShW reduction was <10%, 10-20% and >20%, respectively. Most of the cultivars tested were susceptible at various levels. Although Rf of M. javanica was always higher than that of M. incognita, but the plant growth (Shoot weight) was rather more highly affected by M. incognita than by M. javanica. Lahluba was the only resistant cv. to both nematode species, tolerant to M. javanica but intolerant to M. incognita (>30% ShW reduction). Taiwan Hybrid F1 was resistant/intolerant (shoot and root weight were decreased) to M. javanica and susceptible/moderately tolerant to M. incognita. Although M. incognita infected Musoliya, it showed high rates of egg masses (EMR) and galling (GR), thus it was moderately resistant and highly tolerant. Betraa was the most susceptible to both nematode species with moderate tolerance to M. javanica and intolerant to M. incognita. Clemson Spineless was susceptible/tolerant to M. incognita despite of EMR, GR and Rf high values. All the other cultivars failed in the category of susceptible/intolerant. The galling index did not always reflect the reproduction index or the rate of shoot weight reduction. Nematode reproduction Rf was reliable as susceptibility-resistance indicator as well as the extent of ShW reduction for tolerance assessment. The severe root weight reduction due to nematode infection may also indicate plant intolerance. Different levels of resistance and tolerance to nematode infection can be found among okra varieties. Selecting okra cultivars resistant and tolerant to Meloidogyne spp. is an effective approach to maintain high yield, mitigate yield costs and manage the nematode population.