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

An approach on yielding performance in maize under varying plant densities

The purpose of this study was to evaluate the yielding performance of F1 single maize hybrids and their mechanical mixture in three plant densities and in two different years. Experiments were conducted in the farm of TEI of Larissa in 2000 and 2001. The genetic material used was consisted of commercial and experimental F1 single-cross maize hybrids and their balanced mechanical mixture for each year. It was found that there was a tension for increasing field yields of almost all hybrids when the plant density was increasing. This was very clear for year 2000, but in 2001 this was found only for the middle density in comparison to the low density because of the presence of common smut. Only hybrid Dias was the exception, with decreasing field yield when the plant density was increasing. The increasing plant density resulted in increasing CV values and number of barren plants. The performance of the mechanical mixture of all hybrids was similar to the mean performance of the hybrids when grown separately. This kind of performance was rendered to the genetic background of modern hybrids, in a way that under stress conditions (allocompetition, density effects) they express stable performance. In general, modern commercial maize hybrids increase field yields under increasing plant density and they can be used as a mixture without decreasing yielding performance. It is possible that allocompetition is not a stronger stress factor than isocompetition in modern maize hybrids. © 2006 Asian Network for Scientific Information

The flexibility of wheat and barley genomes under salinity stress and honeycomb evaluation

The aim of this study was to find genetic variability within established cultivars of barley, bread and durum wheat, after applying salinity stress for five years. Bread wheat varieties Irnerio, Generoso and Yecora, together with durum wheat varieties Mexicali81, Simeto and Bob, and barley varieties Athinais and Cannon were used. For this purpose, certified seed of the above-mentioned varieties was sown in pots containing a mixture of soils salinized by different quantities of salt. Following a certain experimental scheme that produced progressively new treatments at the same or higher salinity level and after five cycles of evaluation, there were formed new seed partitions for final evaluation under honeycomb designs. The results showed that wheat and barley genomes are quite flexible, allowing selection within variety for certain agronomic performance. Salt stress proved to be a serious stress for the health of evaluated plants (for all species) and thus, we were not able to discover genotypes exhibiting salt tolerance. Seed germination and plant yield declined rapidly at higher concentrations of salt. In spite of this, comparing two-year honeycomb experimental data, these stress conditions resulted indirectly to drought tolerance (due to the flexibility of genomes for species used), confirmed from additional data after evaluation of barley varieties in pots. The genetic mechanism for such phenotypic behavior remains to be studied

Stress conditions for improvement of mass breeding method in maize

Mass selection during early stages of genotype evaluation is essential for maize breeding programs. The purpose of this study was to determine the proper conditions for mass selecting useful genotypes in segregating maize genetic materials. F1/F2 comparisons were made to evaluate the genetic materials and F1/F2 and F2 mixtures of genotypes were formed to ensure allocompetition conditions. Moreover, two severe stresses were applied: plant density and low inputs, in addition to full-inputs conditions. Prisma F1 and F2 were better yielding materials than Funo F1 and F2, respectively. Until 13.33 plants m -2 there was an increase in F1 field yields, followed by lower yields in increased plant density, since modern hybrids tolerate greater plant populations. Significant interaction between genetic materials and plant density found in full-inputs experiments, was eliminated under the strong low-inputs stress. The indications from Half-sib progeny evaluation showed strong relationship between progeny yield and both selected plants' yield and selection differential. High selection differential was realized under low-inputs condition due to low performance of original genetic materials. Strong allocompetition conditions may have a negative effect on HS progeny yielding performance, since mixtures of different genetic materials lead to lower yields. As a final conclusion, present findings indicated that selection of genotypes must be practiced under conditions of high selection differential. The original population mean is not as important as the selection differential. Extended experimentation must include S1 and Full-sib progenies and selection of progeny plants must include not only the highest yielding plants, but plants from the upper, mean and lower yielding areas of yield distribution, as well. © 2007 Asian Network for Scientific Information