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  • Author or Editor: L. C. Marton x
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In earlier studies the inheritance of chilling tolerance in maize was investigated using the joint scaling test on six genotypes forming a systematic genetic series - P1, P2, F1, F2, B1, B2. The values of some genotypes (P1, P2, F1) were overestimated by the model, while those of the other genotypes (F2, B1, B2) were underestimated. It was thought that this could be due to the effect of the level of heterozygosity in the female parent. The level of heterozygosity of the female parent in the P1, P2, F1 genotypes is 0%, while in the F2, B1, B2 genotypes it is 100%. In addition to the m, [d] and [h] parameters, a new parameter, [fh] (female heterozygosity) was thus introduced. Analysis carried out with the new model confirmed a significant female heterozygosity effect.

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The analysis of polymorphism between 46 maize inbred lines with known genetic background and the classification of these lines in related groups was carried out by means of morphological, isoenzyme and genetic markers. The 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. Nevertheless, on the basis of RAPD and SSR markers, all the lines could be distinguished from each other. Grouping lines into related groups it was found that, while the individual marker systems only partially reflected the actual relationships, a joint analysis of genetic markers and morphological data revealed a close correlation between the groups formed on the dendrogram and genetic backgrounds.

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The climatic conditions in Hungary and in the countries to which seed is exported makes the study of maize cold tolerance and constant improvements in the cold tolerance of Martonvásár hybrids especially important. An improvement in the early spring cold tolerance of maize would allow it to be grown in more northern areas with a cooler climate, while on traditional maize-growing areas the profitability of maize production could be improved by earlier sowing, leading to a reduction in transportation and drying costs and in diseases caused by Fusarium sp. The recognition of this fact led Martonvásár researchers to start investigating this subject nearly four decades ago. The phytotron has proved an excellent tool for studying and improving the cold tolerance of maize. The review will give a brief summary of the results achieved in the field of maize cold tolerance in the Martonvásár institute in recent decades.

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The evaluation of an 8 × 8 diallel cross revealed that the mean length of the growing period was the same for inbred lines and their hybrids. However, the vegetative phase was 7-8% shorter and the generative phase 7-8% longer for the hybrids than for the inbred lines. The generative phase of the growing period, unlike the vegetative phase, proved to be extremely variable. Under dry conditions the length of the generative phase was negatively correlated with the length of the vegetative phase. The later a genotype flowered the less time remained for grain filling, due to the stress which curtailed the growing period. The shorter generative phase of late-flowering hybrids was the reason for the weakening of the growing period-yield correlation under dry conditions. This vulnerability of late-flowering hybrids makes selection for stress tolerance particularly important.

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An improvement in the early spring cold tolerance of maize would allow it to be grown in more northern areas with a cooler climate, while on traditional maize-growing areas the profitability of maize production could be improved by earlier sowing, leading to a reduction in transportation and drying costs. The cold tolerance of crosses between inbred lines and sister line crosses belonging to three related groups that combine well with each other (BSSS, Iodent, Lancaster) was tested in the Martonvásár phytotron. The results confirmed those of earlier experiments and led to the following new conclusions: - the average emergence time of the tested Iodent inbred lines was longer than that of the BSSS and Lancaster groups, - all three groups contained inbred lines with significantly earlier emergence than the others, - the average emergence percentage and individual shoot dry matter production in the Iodent group were also lower than in the other two groups, - a close negative correlation (r = -0.70) was found between the number of days to emergence and the individual dry shoot mass. The results were used to select inbred lines and sister line crosses with various genetic backgrounds that could be used in crosses aimed at improving the resistance of hybrids to cold stress in early spring.

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The effect of varying weather conditions on the moisture content of the maize grain yield was investigated in Martonvásár, Hungary from late August to late September, and from the 3rd third of September to the 1st third of Novemberbetween 1999 and 2002. In every year a close positive correlation (P=0.1%) could be observed between the moisture content in late September and the rate of drying down in October. Linear regression was used each year to determine the equilibrium moisture content, to which the moisture content of kernels returned if they contained less than this quantity of water in late September and harvesting was delayed. In the experimental years this value ranged from 15.24-19.01%.

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A comparison was made of herbicide tolerance results for two years, one dry (2003) and one wet (2004). The maximum permitted dose and twice this rate of the herbicides (mesotrione, mesotrione + atrazine, nicosulfuron, rimsulfuron) were sprayed on inbred maize lines in the 7-8-leaf stage. The effect of the herbicides on 20 inbred lines was evaluated on the basis of visible phytotoxic symptoms. In the dry year the greatest damage, averaged over the inbred lines, was caused by the double rate of rimsulfuron and nicosulfuron, but the plants had overcome this by the end of the vegetation period. In 2004 the cool wet spring weather retarded the metabolic processes of maize, leading to greater phytotoxic damage. The most severe symptoms were observed for the double rate of mesotrione +atrazine. The phytotoxic damage caused by the “normal” rates applied in commercial maize production was overcome by the lines in the wet year, too. Despite the initial visible phytotoxic damage, none of the herbicides caused significant differences in grain yield between the control and the single or double rates of treatment.

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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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A new method has been elaborated to estimate the length of the vegetation period of new maize hybrids. According to this method, the length of the vegetation period is expressed by the FAO number, calculated from the following traits:

  1. 1. 50% silking
  2. 2. Grain moisture when the average grain moisture of maturity group standards is 25%
  3. 3. Grain moisture when the average grain moisture of maturity group standards is 20%
  4. 4. Grain moisture at harvest.
The standards of the neighbouring maturity groups are also included in each experiment.The results obtained with this method were compared to the heat unit (GDD) method and to other methods of calculating FAO numbers. The new method has several advantages over previous techniques based on moisture content alone: the fluctuation of the estimated FAO number over locations and years decreased, as did the significant differences between the calculated FAO numbers; the reliability and precision of the new FAO number is less dependent on the date of harvest (moisture content); and the FAO numbers calculated with the new method are in the closest correlation with the heat unit estimates.

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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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