Temesgen Addis

Life history trait analysis of the entomopathogenic nematode Steinernema riobrave

Life history traits (LHT) of Steinernema riobrave strain Sr 7-12 and Sr HYB19 were assessed at 25°C in monoxenic culture using a hanging drop technique. The LHT were studied with 5 × 109, 10 × 109 and 20 × 109 cells ml−1 of Xenorhabdus cabanillasii in semi-solid Nematode Growth Gelrite. Increased X. cabanillasii densities had a significant positive influence on offspring production on both Sr 7-12 and the hybrid Sr HYB19. At the higher bacterial food density, the total fertility rate (TFR) per female of Sr 7-12 was 2022 offspring and the net reproductive rate (R0) reached 1904 offspring. Similarly, for Sr HYB19, the TFR per female was 2434 and R0 was 1903. The percentage offspring produced via intra-uterine development (endotokia matricida) was relatively higher at 5 × 109 bacterial cells ml−1 than at higher bacterial density, with 64% and 66% of the total offspring produced by Sr 7-12 and Sr HYB19, respectively. A positive correlation (R=0.648) was recorded for offspring production and bacterial food density and for female body volume with bacterial density (R=0.610). Female nematodes survived longer at higher bacterial food density; however, females of both strains could not survive longer than 7.8 days, beginning from hatching and always ending 1 day after initiation of endotokia matricida. Based on LHT results, there is a potential to maximise yield of dauer juveniles in liquid culture through increasing bacterial food density.

Ethnic-based diversity and distribution of enset (Ensete ventricosum) clones in southern Ethiopia

Enset cultivation in southern and south-western Ethiopia is practiced mainly in densely populated areas. A survey covering 280 farm households and seven districts was conducted in seven zones of southern Ethiopia with the main objective of assessing the diversity and distribution of enset clones. Interviews using structured and semi-structured questionnaires were conducted to generate data. A total of 218 enset clones were recorded in the surveyed areas. The number of clones cultivated on individual farms ranged from two to 26 (mean of 8.9 ± 0.9). The highest richness of enset was recorded in Hadiya (59 clones) whereas the lowest was in Sidama zone (30); the mean richness being 39.7 ± 3.8 clones per zone. Exchange of clones among farmers in different ethnic groups in enset growing regions revealed that strong cultural and linguistic similarities exist between zones. Farmers reported that clones such as Gena and Mazia are replacing previously grown clones due to their resistance to Xanthomonas wilt. Several enset clones previously known by farmers have disappeared in recent years due to disease, extended drought and wild animals, pointing to genetic erosion and the necessity of genetic conservation. Key words: Abundance, Gurage, Kembata, Mazia, richness, Wolaita.

Applying inbreeding, hybridization and mutagenesis to improve oxidative stress tolerance and longevity of the entomopathogenic nematode Heterorhabditis bacteriophora

Poor shelf-life and sensitivity to environmental stress of entomopathogenic nematodes (EPNs) are traits, which deserve attention for improvement. Recently, a strong positive correlation between oxidative stress tolerance and longevity of Heterorhabditis bacteriophora dauer juveniles (DJs) has been reported. In this study, the improvement of H. bacteriophora DJ longevity was achieved by hybridization and mutagenesis. A hybrid pool deriving from two oxidative stress tolerant and long-living parental strains was generated. This hybrid AU1 × HU2 survived 2.6 days and 18 days longer than its best parent under oxidative stress and control conditions, respectively. In addition to the natural genetic variability, an EMS-mutant pool (M-OXI) with high longevity was generated and one of the derived mutagenized inbred lines (MOX-IL6) survived 5.8 days and 28.4 days longer than its donor line (IL3) under oxidative stress and control conditions, respectively. A genetic cross between the mutagenized inbred line and its donor line (MOX-IL × IL3) still survived 2.5 days and 18.5 days longer than the donor line under oxidative stress and control conditions, respectively. Concerning virulence and reproductive potential, trade-off effects were not observed as a result of hybridization and mutagenesis. These results underline the potential of classical genetic approaches for trait improvement in the nematode H. bacteriophora.

Research on plant-parasitic and entomopathogenic nematodes in Ethiopia: a review of current state and future direction

Food self-sufficiency is Ethiopia’s national priority goal. Given that pest management seriously impacts agriculture, research on crop diseases is of paramount significance to the national goal. Here we provide a comprehensive account of research on plant-parasitic and entomopathogenic nematodes in Ethiopia. We show that the limited information available indicates that plant-parasitic nematodes impact crop production. There exists a serious gap in knowledge with regard to the effects of plant-parasitic nematodes on almost all major crops. This gap includes surveys with appropriate levels of identification, distribution, and yield loss and damage threshold studies on target crops. The current state of knowledge hinders the nation’s ability to design and implement appropriate control strategies for plant-parasitic nematodes. We propose a strategic assessment of plant-parasitic nematodes of all major crops, the need for systematic manpower training and continued search for entomopathogenic nematodes in the major agro-ecological zones of the nation and further research on those entomopathogenic nematodes already identified.