The study aimed at evaluating the influence of environment on sweetpotato stability and identifying superior genotype(s) with high yield stability in the farmers’ field conditions. Six sweetpotato genotypes were evaluated for two years in ‘meher’ season (July- December), 2014 and 2016; four of the six genotypes were assessed for three years in the ‘meher’ season, 2012, 2014, and 2016. Planting was done in three replications in RCBD in three unique agro-ecologies: Endayesus-dry highland, Fachagama-dry lowland, Rarhe-moist lowland. Genotypes genetic merits were predicted using BLUP. The AMMI and GGE were used to test the genotypes stability. The ANOVA for AMMI model showed high significant difference (P0.01) for genotypes, environments, seasons, and the interactions. Environment (41.67%) and the genotype main effect (35.71%) contributed largely to the cumulative variance for three years testing of four genotypes and two years testing of six genotypes, respectively. Berkume (42.44 t/ha), Tulla (33.92 t/ha) and Kulfo (33.67 t/ha) were superior for total storage root tuber yield (TTRY).Both the AMMI and GGE biplot predicted Tulla and Kulfo as ideal genotypes with dynamic stability; Berkume with static stability to Rarhe. The environment main effect had significant influence in determining how genotypes expressed their genetic potentials and stability as shown by the AMMI model and GGE biplot. The AMMI model partitioned the studied agro-ecologies of the Tigray region into two mega sweetpotato growing environments; the dry high/lowland in one environment and the moist lowland in another, completely different, but with high potentials for sweetpotato production.

Root-knot nematodes (Meloidogyne species) are the most devastating and as such they cause significant yield loss in tomato production. They are widely distributed in major tomato producing areas especially in warm climatic conditions. Because of the environmental impact of the application of pesticides, the use of nematode resistant varieties is becoming the most effective alternative to control root-knot nematodes. Several resistance genes are identified from wild tomato and other species. However, Mi-1 resistance gene is the only well characterized and used in many commercial tomato cultivars. A single dominant gene (Mi-1) with a hypersensitive response (HR), which is characterized by a local cell death at the site of nematode penetration and necrotic lesions of the surrounding tissue controls the resistance. Thus, Mi-1 gene either inhibits the penetration of second juvenile stage (J2), reduces number of gall formation, or reduces further development and reproduction rate of the nematode. However, the gene is a temperature dependent and broken by the virulent pathotypes. Plant growth hormones such as salicylic acid (SA) and jasmonic acid (JA) are involved in induced resistance, which is activated after infection. Secondary plant metabolites including amino acids, phenols, and lipophilic molecules were increased in resistant varieties as defense mechanism. The durability of the Mi-gene is a major concern since the resistance lost at high temperature. Heat stable resistance gene (Mi-9) is identified from Solannum arcanum. Hence, pyramiding of the resistance genes in commercial cultivars and genetic modification of plant metabolites might improve the durability of the gene.