MANAGEMENT OF Meloidogyne incognita AND M. javanica POPULATIONS USING HOST RESISTANCE, BOTANICALS AND ORGANIC AMENDMENTS ON HOT PEPPER (Capsicum annum and C. frutescens) GENOTYPES IN ETHIOPIA

Abstract

Hot pepper is the leading vegetable crop produced in Ethiopia. It is highly valued for its nutritional and economic significance. However, its productivity is constrained by many factors such as infestations by root-knot nematodes (RKN). Thus, developing safe and cost effective integrated management methods are essential for sustainable hot pepper production and productivity. To do so, it is vital to generate information on the population dynamics and damage potential of the nematodes. Accordingly, the present study was conducted with the objectives to (1) screen Ethiopian hot pepper genotypes for resistance to Meloidogyne incognita and M. javanica species; (2) determine the damage potential and population dynamics of M. incognita and M. javanica on susceptible and resistant genotypes; and (3) evaluate the efficacy of integration of aqueous leaf extracts and organic soil amendments for management of M. incognita on hot pepper. In the glasshouse trial, eighteen hot pepper genotypes were evaluated against two populations of M. incognita and M. javanica from Ethiopia at initial population density (Pi) of 2000 J2/ 3 kg (0.67/g) soil. The treatments were arranged in a randomized complete block design (RCBD) with four replications. To evaluate egg hatching stimulation of the hot pepper genotypes, two populations from each nematode species were used in an in vitro experiment where the treatments were arranged in a completely randomized design (CRD) with six replications. An open-field pot experiment was also undertaken to examine the effect of M. incognita and M. javanica Pi on growth and yield of Oda Haro and Melka Awaze hot pepper genotypes that were susceptible and resistant, respectively in the resistance screening experiment. Moreover, the relationship between Pi and reproduction of the nematode species on the hot pepper genotypes was assessed. Ten inoculum densities of both species were used in RCBD with four replications. Seinhorst yield loss and population dynamics models were fitted to the collected data. Furthermore, efficacy of aqueous leaf extracts of Bitter Leaf (Vernonia amygdalina) and Lantana (Lantana camara) and organic soil amendments with vermicompost and poultry manure to manage M. incognita at Pi of 8 J2/g soil on Oda Haro, Acc.03, and Melka Awaze were assessed under an open-field pot trial set in a factorial RCBD with three replications.The output of the resistance screening revealed that among the tested 18 genotypes, none were immune; Acc.003 and Melka Awaze were resistant; and Oda Haro was susceptible to all nematode populations at the tested Pi. Besides, from the hatching assay it was observed that the hatching time for half of the population varied between the genotypes. Nevertheless, the cumulative egg hatching was not considerably affected by the root exudates compared to water that was used as control. The host damage and population xx dynamics trial indicated that Pi had substantial effect on growth and yield of the host plants as well as reproduction of both nematode species. All growth and yield parameters declined on both genotypes with increasing Pi of both nematode species. The yield loss analysis disclosed that the highest tolerance limit (T) of both species and greater minimum yield (m) for all growth and yield parameters was obtained from Melka Awaze. Nonetheless, the maximum number of galls, egg masses and final population (Pf) for both species were evident on Oda Haro at the highest Pi. On the other hand, Melka Awaze, the genotype considered as resistant during the resistance screening experiment, became a host for both species as Pi exceeded 1 J2/g soil. However, the values for nematode reproduction parameters were lower at all Pi compared to Oda Haro. Moreover, the output of population dynamics model elicited that the multiplication rate (a) and maximum population density (M) were higher on Oda Haro for both nematode species. From the management experiment it was observed that all treatments reduced nematode reproduction parameters except vermicompost treatment for Pf. The integration was more effective than individual treatments. There was variability among the treatments in augmenting growth and yield on the hot pepper genotypes. In summary, this study indicated that Melka Awaze and Acc. 003 genotypes are resistant to both species at Pi less than 1 J2/g soil. Furthermore, the reproduction of both nematode species on Melka Awaze is minimal even at the highest Pi of the nematode species tested compared to Oda Haro. Hence, Melka Awaze is a better option to grow in areas infested with species-complex of M. incognita and M. javanica at Pi below 1 J2/g soil as far as population build-up is concerned. A Management intervention to minimize reduction in number of pods per plant is needed on Melka Awaze only if the Pi surpasses 1.13 J2/g soil and 1.42 J2/g soil for M. incognita and M. javanica, respectively. On the other hand, caution must be taken in growing Oda Haro at hotspot areas as it results in a yield decline in number of pods per plant and intensified soil nematode population even at Pi equal to 0.4 J2/g soil for both RKN species. Besides, since tolerance is dependent on Pi, employing series of inoculum densities plus determining T, m and Pi-Pf relationship is crucial in screening for resistance. Moreover, integrating aqueous leaf extracts of V. amygdalina or L. camara with either vermicompost or poultry manure could be an alternative for management of M. incognita and M. javanica on Oda Haro, Acc. 03 and Melka Awaze up to the tested Pi. However, as the study is conducted under controlled condition, it necessitates verification under actual field situation.