GENETIC VARIATION AND ENVIRONMENTAL STABILITY OF ONION YIELD UNDER ORGANIC AND MINERAL FERTILIZATION

The aim of this study was to evaluate yield mean performance and stability in five onion cultivars grown in conventional (mineral fertilization) and organic (without fertilization, farmyard manure, bacterial fertilizer) production systems. The two-year (2009, 2010) trial has been conducted at the experimental field of the Institute for Vegetable Crops, Smederevska Palanka, Serbia. As expected, the highest yields have been measured for onion grown on plots treated with mineral fertilizer. Out of three organic production systems, onion grown under bacterial fertilization had the highest yield, whereas no significant yield differences have been observed between unfertilized and farmyard manure fertilized plots. Factorial analysis of variance revealed statistically significant yield differences among the tested onion cultivars, treatments and years, with significant values for genotype/ treatment, genotype/year, treatment/year and genotype/treatment/year interactions; implying the possibility for breeding cultivars adapted for specific organic environments. Two-dimensional biplots have been constructed in order to evaluate genotype mean performance and stability across the tested environments, as well as to visualize genotype adaptation to the particular environments. Principal components 1 and 2 in the biplots explained 85.4 and 9.3% of variation in the genotype main effect and genotype/environment interaction. Not a single onion cultivar included in the trial exhibited both high yield and stability across conventional and organic environments. Therefore, breeding onion cultivars highly adapted to the organic production systems is required in order to obtain satisfactory high and stable yields.