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Leafy hybrids represent a new direction in the breeding of silage maize. Not only does the increased number of leaves above the ear in these hybrids lead to an increase in dry matter production, but the large quantity of carbohydrates formed and stored in the leaves results in silage with better chemical quality. Many papers have been published abroad on this subject, but few data have been reported in Hungary.The present work aimed to examine the effect of genotype and year on six leafy and non-leafy silage maize hybrids over a period of four years (2002–2005), with special emphasis on the plant height, ear attachment height, leaf number, and fresh and dry matter yield.The results showed that the number of leaves above the ear was much higher for the two leafy hybrids (8.00 and 9.35) than the average of the other hybrids (5.56, averaged over the years). This trait was in close negative correlation (r 2 = −0.7346) with the ratio of ear attachment height to total plant height, a trait with strong genetic determination, little influenced by the year. In leafy hybrids the main ear was located far lower down, but the total plant height was similar to that of the other hybrids. The ratio of ear attachment height to plant height was 0.36 for the leafy hybrids, but ranged from 0.41 to 0.45 for the other hybrids (averaged over the years). In wetter years the hybrids were taller and had greater dry matter production per plant than in the dry year.

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The breeding of hybrid maize now has a history of over 100 years. In 1908, George H. Shull was the first to report on the high yields, great uniformity and homogeneity of hybrids derived from a cross between two inbred lines. Following this discovery, consistent self-fertilisation over a period of six to eight generations was found to be an extremely efficient method for developing maize lines. From the mid-1970s, however, with the elaboration of the monoploid ( in vivo ) and microspore culture ( in vitro ) techniques, it became possible to develop homozygous lines within a year.With the help of an efficient plant regeneration system based on anther culture, large numbers of doubled haploid (DH) lines can be produced. In the course of the experiments the seed of DH plants selected over several years was multiplied and crossed with Martonvásár testers, after which the hybrids were included in field performance trials in three consecutive years (2005–2007). The aim was to determine whether the field performance of hybrids developed in this way equalled the mean yield of standards with commercial value. The data also made it possible to calculate the general (GCA) and specific (SCA) combining ability of the parental lines, indicating the usefulness of the parental components in hybrid combinations and expressing the extent to which a given line contributes to yield surpluses in its progeny.A total of 52 maize hybrids were evaluated in the experiments in terms of yield and grain moisture content at harvest. The combinations, resulting from crosses between 12 DH lines, one control line developed by conventional inbreeding and four testers, were found to include hybrids capable of equalling the performance of the standards, and four DH lines were identified as improving the yield level of their progeny. As the experiment was carried out on a very small number of genotypes, the results are extremely promising and suggest that, if the range of genotypes used to develop DH lines is broadened and the sample number is increased, it will be possible in the future to find maize hybrids, developed with in vitro DH parental components, that surpass the performance of commercial hybrids.

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Studies involving morphological description with both dominant (RAPD) and codominant (SSR, isoenzyme) molecular markers were made on 28 maize inbred lines of known genetic background with a final aim of prediction of heterosis. The genetic distance and degree of relationship between the lines was determined using cluster analysis. Only a very limited extent of allele polymorphism could be detected in isoenzyme analyses as the 28 lines formed only 16 gel electrophoretic groups, indicating that certain lines had identical isoenzyme patterns. On the basis of RAPD and gene-specific microsatellite (SSR) markers, however, all the lines could be distinguished from each other. When the lines were grouped according to genetic background it was found that although the individual marker systems only partially reflected the actual relationships between the lines, a joint processing of the data, supplemented with morphological data, revealed a close correlation between the groups formed on the dendrogram and the genetic background.

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Acta Agronomica Hungarica
Authors:
B. Barnabás
,
T. Spitkó
,
K. Jäger
,
J. Pintér
, and
L. C. Marton

In the present study the applicability of a self-constructed doubled haploid line (DH 105) in the in vitro breeding of maize was evaluated. This line, which contained only 50% exotic (Chinese) germplasm, could be used to transmit in vitro androgenic ability into non-responsive breeding materials. F1 hybrids resulting from single crosses between the moderately responsive line DH 105 and recalcitrant genotypes with high breeding value showed a considerable heterosis effect in their androgenic responses. Most of the hybrids had favourable morphological and agronomic characters on the basis of “per se” evaluation. The data of the experiments showed that these F1 hybrid plants could be successfully used as anther donors, since numerous fertile DH plants were developed from their anther cultures. By the use of this in vitro breeding strategy the genetic variability can be widened and the effectiveness of inbred line production might be improved.

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Six single-cross hybrids and their parental lines were inoculated with the FG36 Fusarium graminearum isolate in 2005 and 2006. In both years the degree of infection increased after artificial inoculation for both the hybrids and the inbred lines compared with the level of natural infection. The more severe stalk infection recorded in 2005 than in 2006 could be attributed to the weather conditions during flowering and harvesting.The 18 genotypes examined exhibited different levels of resistance to fusarium stalk rot. It could be concluded from the results that the resistance level of the female parent was decisive in the inheritance of the response to fusarium stalk rot (female component-hybrid r = 0.88, male component-hybrid r = 0.39).Some genotypes may be severely affected in epidemic years, while exhibiting a lower rate of infection in years with lower pathogen pressure. This suggests that successful breeding for resistance can only be carried out efficiently by means of artificial inoculation.

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The adaptability of twelve single cross maize hybrids was investigated at five different locations in Hungary over a three-year period. The characters examined were individual plant production (total mass of the ears on a single plant), thousand kernel mass, number of kernel rows, ear length, number of kernels per row, shelling % and the assimilating leaf area above the main ear.Among these yield components, the individual plant production, the ear length, the number of kernels per row and the grain-cob ratio (shelling %) were influenced to the greatest extent by the year, followed by the variety and the location. The greatest average yield was achieved by the tested hybrids at all five locations in 1997 (263 g/plant). The average yields in 1998 and 1999 were significantly lower (221 and 203 g/plant, respectively). The outstanding yields achieved in 1997 could be attributed to the favourable ecological conditions, which led to the development of secondary ears in Keszthely and Sopronhorpács. At the other three locations there was only one ear per plant, but these ears were longer than in the following years. The greatest year effect was recorded in Sopronhorpács, where the individual plant production amounted to 305 g/plant in 1997 and 238 g/plant in the worst year, 1999. In Gyöngyös conditions were very dry in all three years, so the year effect was least pronounced at this location (grand mean of 195 g/plant in 1997 and 201 g/plant in 1999). Stability analysis was carried out using the coefficient of variance for individual plant production. Hybrids Mv 3, Mv 5, Mv 9 and Mv 12 were found to have the best adaptability. The shelling % was not significantly influenced by the location; the grain-cob ratio is relatively stable for maize hybrids. A correlation was found between the individual plant production and the leaf area above the main ear (R 2 =0.66). Hybrids with the largest leaf area above the main ear also had the greatest ear mass.

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Inbred maize lines were treated with normal and double rates of post-emergence herbicides in a small-plot field experiment in one dry and one wet year. The chlorophyll a + b content of symptom-free ear-leaves was determined using a spectrophotometer after 50% silking in order to determine whether various rates of post-emergence herbicides had any effect on the chlorophyll content at flowering and how this was influenced by the type of year. The chlorophyll a + b content of the inbred lines was greatly dependent on the year, with values twice as high in the wet year as in the dry year. Treatment with tembotrione + isoxadifen-ethyl had no effect on the chlorophyll content in either year. Both rates of mesotrione + terbutylazine reduced the chlorophyll a + b content of one stress-sensitive inbred line in the dry year, but not in the wet year. In the wet year bentazone + dicamba increased the chlorophyll content, but only for one line was this effect significant irrespective of the dose. In the dry year the double dose caused a significant increase in this genotype, but the chlorophyll contents of the other lines did not differ significantly from the control.

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Kernel samples of two maize hybrids (46308 and 463017) with different levels of resistance to Fusarium ear rot were collected from artificially and naturally infected plants. The spectral characteristics of the samples were analysed with an ASD Fieldspec 3 MAX spectroradiometer in the wavelength range of 350 to 2500 nm using an ex situ method. The different extents of artificial and natural Fusarium infection on the maize kernels resulted in spectral differences detectable with a spectroradiometer. The data showed that for both genotypes the level of Fusarium infection generated by artificial inoculation was significantly higher than that caused by natural infection over a wavelength range of 2030 to 2080 nm. Principal Component Analysis (PCA) on the data set for this range revealed that the first component explained 77.0% of the variability for hybrid 46308 and 97.0% for hybrid 46317.

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