A triple stress effect on monogenotypic and multigenotypic maize populations
The purpose of this study was to evaluate the yielding performance of maize under stress conditions involving mixing of different genotypes, plant density and low water/fertilizer inputs. The impact on yield from competition and genetic differences was analysed. Two F1 hybrids (Prisma and Funo) were used, their F2s, the mixture of the F2s and the F1+F2 mixture of the first hybrid, in a high and in a low-inputs experiment. The two F1 hybrids increased field yield until 133300 plants ha-1 and at 190000 plants ha-1 there was a decrease due to increased rate of declining individual plant yield. The rate of decrease of individual plant yield is a parameter that determines the final field yield realised under increasing plant densities. In full-inputs experiment, there was a significant interaction between genetic materials and plant densities, meaning that different materials respond in a different way under the stress of density. F2 generations were affected lesser than F1 hybrids. Genetic purity proved to be a greater stress condition than density effects. This was more apparent in the low-inputs experiment where differences between genetic materials were much more significant and plant density was a limited stress, almost eliminated by the stronger stress of lower inputs. The low-inputs condition is a major stress masking the effects of plant density. F1 yield in the low-inputs experiment was close to the F2 yielding performance in the full-inputs experiment. Higher plant densities showed lower inbreeding depression values for both hybrids in both experiments. This was due to F2s buffering, resulting in increased relative yield in comparison to the F1s. The increasing plant density resulted in increasing CV values and number of barren plants. Extreme conditions, such as plant density and low inputs, showed that the F1s are affected more than multigenotypic materials, exhibiting greater increase in CV values. F1 hybrid Funo, showed increased numbers of barren plants and this may be an indication of low seed purity, but indications from F1 Funo and Prisma yield comparisons and from F1/F2 comparisons, showed that even if there was a quantity of impure seed partition for hybrid Funo this was small. Low inputs resulted in significant soil heterogeneity, maybe stronger as a stress condition than plant density effects and allocompetition. Ranking stress conditions, low inputs is the most severe stress because of the increased needs of modern maize hybrids, followed by seed purity and soil heterogeneity. Plant density is a problem only under extremely high or low populations. © 2007 Asian Network for Scientific Information.