The root-knot nematode, Meloidogyne javanica, is one of the most damaging plant-parasitic nematodes, affecting chickpea and causing substantial yield losses worldwide. The damage potential and population dynamics of this nematode in chickpea in Ethiopia have yet to be investigated. In this study, six chickpea cultivars were tested using 12 ranges of initial population densities (Pi) of M. javanica second-stage juveniles (J2): 0, 0.125, 0.25, 0.5, 1, 2, 4, 8, 16, 32, 64 and 128 J2 (g dry soil)-1 in a controlled glasshouse pot experiment. The Seinhorst yield loss and population dynamics models were fitted to describe population development and the effect on different measured growth variables. The tolerance limit (TTFW) for total fresh weight ranged from 0.05 to 1.22 J2 (g dry soil)-1, with corresponding yield losses ranging from 31 to 64%. The minimum yield for seed weight (mSW) ranged from 0.29 to 0.61, with estimated yield losses of 71 and 39%. The 'Haberu' and 'Geletu' cultivars were considered good hosts, with maximum population densities (M) of 16.27 and 5.64 J2 (g dry soil)-1 and maximum multiplication rate (a) values of 6.25 and 9.23, respectively. All other cultivars are moderate hosts for M. javanica; therefore, it is crucial to initiate chickpea-breeding strategies to manage the tropical root-knot nematode M. javanica in Ethiopia.

Root-knot nematodes (RKN) are globally distributed and highly pathogenic. By determining the threshold at which damage occurs, we can create effective measures to protect plants from nematodes. In our study, we investigated the impact of ten initial population densities (Pi-log series) of M. javanica, i.e., 0, 2.38, 2.68, 2.98, 3.28, 3.58, 3.88, 4.18, 4.48 and 4.78 juveniles (J2) g(-1) soil on tomato cv. S22 plants in pots. The graphical estimation of yield losses caused by RKN was calculated using Seinhorst's yield loss model based on the relationship between the RKN population and damage to tomato plants. The relationship between initial nematode population density (Pi) and plant yield was analyzed using Seinhorst's model, where T is the tolerance limit, m is the minimum yield, and z is a constant describing yield decline. This allowed us to determine the threshold at which nematode infestation significantly reduces tomato growth. Seinhorst's model, y = m + (1-m) 0.95(Pi/T-1) for Pi > T; y = 1 for Pi <= T for RKN, was fitted to the data of shoot length and fresh weight of infected and uninoculated control plants to estimate the damage threshold level. The impact of M. javanica on plant physiological parameters, including chlorophyll content, carotenoid and nitrate reductase activity, root-gall formation, and disease incidence, was also determined in this study. The tolerance limits for relative tomato shoot length and fresh weight were 3.34 J2 of M. javanica g(-1) soil. The minimum relative values (y(m)) for shoot length and fresh weights were 0.39 and 0.42, respectively. We found that the damage threshold level was between 3.28 and 3.58. The root galls index, nematode population and reproduction factors were 3.75, 113 and 29.42, respectively, at an initial population density (Pi) of 3.58 J2 g(-1) soil. The chlorophyll (0.43 mg g(-1)), carotenoids (0.06 mg g(-1)) and nitrate reductase activity (0.21 mu mol min(-1) g(-1)). Our study highlights the importance of the accurate estimation of damage thresholds, which can guide timely and effective nematode management strategies.