DAMAGE POTENTIAL OF MELOIDOGYNE INCOGNITA POPULATIONS ON SELECTED TOMATO GENOTYPES IN ETHIOPIA
Reliable data are required to relate the effect of initial population density (Pi) on plant growth, biomass, and yield for specific crop-nematode associations under local conditions. In Ethiopia, no information is available on the effect and relationship between Pi of Meloidogyne incognita and damage to tomato cultivars. Hence, the effect of a series of Pi of two populations of M. incognita on tomato cultivars Assila, Chochoro, Moneymaker, and Tisey and the breeding line CLN-2366B on growth, yield, and the relationship with final nematode population density (Pf) were studied. Each tomato cultivar was inoculated with a geometric series of Pi (0, 0.125, 0.5, 1, 2, 4, 8, 16, 32, 64, 128, and 256 J2/100 g dry soil) and grown until senescence. The relationship between Pi and Pf was fitted to the Seinhorst population dynamics model (Pf = (M * Pi) / (Pi + M/a) while the effect of Pi on different plant parameters was fitted to the Seinhorst yield model (Y = Ymax*(m + (1 - m)* Z^ ((Pi-T)/T)). Based on the damage model all the tested plant parameters were negatively affected by both populations of M. incognita. The Jittu M. incognita population had greater effect on the majority of tomato parameters compared to the Babile population. Based on reproduction factors (RF), all the tomato cultivars were good hosts for both populations of M. incognita. The highest RF was obtained at lower Pis (0.125 J2/100 g dry soil) and was reduced with increasing Pi on all cultivars. Severity of root galling and number of egg masses per root system increased with increasing inoculum levels of both nematode populations. The seedlings of all tomato genotypes died at the higher Pi value (256 J2/100 g dry soil) except for Assila. The cultivar Tisey was highly susceptible to both the Babile and Jittu populations and all the seedlings died at Pi ≥ 16 J2/100 g dry soil. Moneymaker seedlings died at Pi ≥ 64 J2/100 g dry soil. For all the plant parameters studied, Tisey had the lowest damage threshold T whereas Assila (except for root weight) had greater T. A difference was observed among the tomato genotypes on minimum yield (m) for the different plant parameters against the Babile and Jittu populations. Determination of T and m of a given crop variety for the prevailing Meloidogyne species in fields to be planted (local setting) is vital.