Determination of Helicoverpa armigera (Lepidoptera: Noctuidae) larval instars and age based on head capsule width and larval weight

Προνύμφες του Helicoverpa armigera (Lepidoptera: Noctuidae) εκτράφηκαν σε χώρο με 26°C, φωτόφαση 16 ωρών και σχετική υγρασία 60-75%. Μετρήθηκαν, ανά προνυμφικό στάδιο, το πλάτος της κεφαλικής κάψας και το βάρος κάθε προνύμφης 2-3 ημέρες μετά την έκδυση, με σκοπό τον προσδιορισμό του προνυμφικού σταδίου και της ηλικίας. Χρησιμοποιήθηκε επί πλέον το βάρος της προνύμφης γιατί δεν είναι ασφαλής ο προσδιορισμός των προνυμφικών σταδίων μόνο από το πλάτος της κεφαλικής κάψας, καθόσον υπάρχει αλληλεπικάλυψη μεταξύ πλάτους ενός σταδίου και του προηγούμενου και επόμενου του, και ακόμη παρατηρείται διαφορετικός αριθμός σταδίων μεταξύ των προνυμφών. Η ανάπτυξη συμπληρώνεται σε 5 προνυμφικά στάδια στο 75% των προνυμφών, σε 6 στο 24% και σε 7 στο1%. Το πλάτος της κεφαλικής κάψας ήταν αρκετό για τη διάκριση των προνυμφών της Ιου σταδίου μόνο και το μέγιστο πλάτος ήταν 0,4mm. Το βάρος της προνύμφης ήταν ικανό μόνο του να προσδιορίσει προνύμφες 1ης και 2ης ηλικίας. Η διαφορά μεταξύ Ιου και 2ου σταδίου ήταν lmg και μεταξύ 2ου και 3ου σταδίου 5,5mg. Συσχέτιση και ανάλυση παραλλακτικότητας των δύο παραμέτρων μας δίνει τη δυνατότητα προσδιορισμού όλων των προνυμφικών σταδίων μιας προνύμφης με πιθανότητα 96,9%,.καθώς και την ηλικία της σε ημέρες από την εκκόλαψη.Larνae of Helicoverpa armigera (Hubner) (Lepidoptera: Noctuidae) were reared in laboratory conditions (26°C, 16:8 L:D) and measurements of larval head capsule width, and body weight, were used in order to determine the boundaries of larval instars. Larvae of Η. armigera completed development in 5 to 7 instars. Head capsule width could predict the larval instar only for Ll. The upper boundary of head width for L1 was 0.4mm. Body weight could predict both L1 and L2 larval instars. Boundaries between L1-L2 instars were found to be 1 mg and for L2-L3 5,5 mg. Correlation and regression analysis suggest that a combination of head capsule width and body weight can predict both larval instars and chronological age under constant conditions in the laboratory

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

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