Heterosis of purple blotch (Alternaria porri (Ellis) Cif.) resistance, yield and earliness in tropical onions (Allium cepa L.)

Five open pollinated onion cultivars Red Creole, Kaharda, Koumassa, Sokoto local and Ori were crossed in a complete diallel and their progenies were evaluated in replicated trials, at Sokoto and Talata Mafara, Nigeria, during the 2004/2005 and 2005/2006 seasons. The experiments were randomised as complete block design with three replications. 30 mls of 10⁻¹ cfu of spore suspension of Alternaria porri prepared by serial dilution was poured into the centre of each plot (sunken bed) immediately after irrigation at 2 weeks after transplanting. Combined analysis across seasons and locations indicated significant (P < 0.05) differences between the populations with respect to all the characters under study. Crosses Ori x Koumassa and Koumassa x Ori recorded highly significant (P < 0.01) positive high parent heterosis for bulb diameter. Crosses Ori x Sokoto local and Ori x Koumassa recorded highly significant (P < 0.01) negative high parent heterosis for days to maturity. Cross Sokoto local x Koumassa exhibited highly significant (P < 0.01) positive high parent heterosis for number of leaves/plant. Crosses Red Creole x Kaharda and Kaharda x Red Creeole recorded highly significant (P < 0.01) positive high parent heterosis for disease incidence. Red Creole x Kaharda and Kaharda x Red Creeole also recorded highly significant (P < 0.01) positive high parent heterosis for fresh bulb yield. Cross Kaharda x Ori recorded highly significant (P < 0.01) positive high parent heterosis for bulb weight. The cross Kaharda x Sokoto local recorded significant (P < 0.05) negative high parent heterosis for days to maturity while the cross Red Creole x Kaharda recorded highly significant (P < 0.01) positive high parent heterosis for number of leaves/plant. Bulb diameter and bulb weight recorded highly significant (P < 0.01) and significant (P < 0.05) environmental correlation with days to maturity.