Basil Hassan Kandouh Noamani

Ten okra cultivars were screened for their susceptibility (resistance) and tolerance to the Root-knot nematodes Meloidogyne incognita and M. javanica in a two trial experiment under the ambient condition. Okra seedlings at 14 days old were inoculated with 3000 egg/J2 of M. incognita or M. javanica. The nematode reproduction factor Rf (Rf= final population (Pf)/initial population (Pi)) was used to determine susceptibility or resistance among cultivars, cultivars considered highly susceptible if Rf ≥ 2, susceptible where 2 > Rf ≥ 1 or resistant with Rf < 1.While reduction in plant shoot weight (ShW) over the control indicated tolerance and categorized into tolerant, moderately tolerant and intolerant where the ShW reduction at < 10%, 10-20% and >20%, respectively. Most 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 highly affected by M. incognita than M. javanica. Lahluba was the only resistant 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 showed high rates of egg masses (EMR) and galling (GR), it was moderately resistant and highly tolerant. Betraa was the most susceptible to both nematode species with moderate tolerance to M. javanica and intolerance 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 sever 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.

Red food coloring artificial dye Carmoisine can be used in totally safe, low cost and environment friendly nematode staining procedure. Both egg masses on the root surface and nematodes in the root tissue stained perfectly with the Carmoisine. Egg masses stained the best at higher stain concentrations (3, 4 and 5%). 30-60 min root submersion in the stain resulted in best contrast. White vinegar can be used efficiently to store egg mass bearing roots. Nematodes in the root tissue were stained the best at low stain concentrations (0.1 and 0.2%) with 5% vinegar. 70% sucrose solution acidified with 0.5% vinegar was comparable to acidified glycerin for destaining. Stained nematodes were still visible with high contrast even after being stored for 8 to 11 months at room temperature.

Root-knot nematode Meloidogyne spp. were investigated for their occurrence, incidence and severity in 41 okra fields and farms located in six different districts of Najaf. Only two species, Meoidogyne javanica and M. incognita, were detected in all the districts under this survey. Of all samples identified, 69% were M. javanica while M. incognita constituted 31%. All the districts were infested with the two nematode species, but none of the fields was infected with mix population of both species. The infection was undetectable in only 2% of investigated fields. The perineal pattern was analyzed for 80 M. incognita and 140 M. javanica females. Morphological variations within each nematode species were observed. M. incognita showed high dorsal arch that slightly shouldered or squarish in most samples (72%), or medium dorsal arch closely surrounding the tail terminus 24%, while the rest (4%) were rounded with smooth striae. The prineal pattern of M. javanica on the other hand was found to possess more variations. Distinct lateral lines were detected in all perineal patterns. High proportion (40%) exhibited low to medium high dorsal arch with moderate wavy to smooth striae and 34% had much higher dorsal arch with squarish, while oval to round shaped with wavy striae were found in the lowest proportion. Most okra fields were highly infested and infection severity was affected by plant cultivar, irrigation method and cropping system. Winter surveys on other vegetable crops might be required to confirm the absence of other Meloidogyne species.