To map the QTLs of Fusarium moniliforme ear rot resistance in Zea mays L., a total of 230 F2 individuals, derived from a single cross between inbred maize lines R15 (resistant) and Ye478 (susceptible), were genotyped for genetic map construction using simple sequence repeat (SSR) markers and amplified fragment length polymorphism (AFLP) markers. We used 778 pairs of SSR primers and 63 combinations of AFLP primers to detect the polymorphisms between parents, R15 and Ye478. From the polymorphic 30 AFLP primer combinations and 159 SSR primers, we scored 260 loci in the F2 population, among which 8 SSR and 13 AFLP loci could not be assigned to any of the linkage groups. An integrated molecular genetic linkage map was constructed by the remaining 151 SSR and 88 AFLP markers, which distributed throughout the 10 linkage groups of maize and spanned the genome of about 3463.5 cM with an average of 14.5 cM between two markers. On 4 chromosomes, we detected 5 putative segregation distortion regions (SDRs), including 2 new ones (SDR2 and SDR7). The other 3 SDRs were located near the regions where gametophyte genes were mapped, indicating that segregation distortion could be partially caused by gametophytic factors.
Common smut in maize, caused by Ustilago maydis, reduces grain yield greatly. Agronomic and chemical approaches to control such diseases are often impractical or ineffective. Resistance breeding could be an efficient approach to minimize the losses caused by common smut. In this study, quantitative trait loci (QTL) for resistance to common smut in maize were identified. In 2005, a recombinant inbred line (RIL) population along with the resistant (Zong 3) and susceptible (87?1) parents were planted in Beijing and Zhengzhou. Significant genotypic variation in resistance to common smut was observed at both locations after artificial inoculation by injecting inoculum into the whorl of plants with a modified hog vaccinator. Basing on a genetic map containing 246 polymorphic SSR markers with an average linkage distance of 9.11 cM, resistance QTL were analysed by composite interval mapping. Six additive-effect QTL associated with resistance to common smut were identified on chromosomes 3 (three QTL), 5 (one QTL) and 8 (two QTL), and explained 3.2% to 12.4% of the phenotypic variation. Among the 6 QTL, 4 showed significant QTL ? environment (Q ? E) interaction effects, which accounted for 1.2% to 2.5% of the phenotypic variation. Nine pairs of epistatic interactions were also detected, involving 18 loci distributed on all chromosomes except 2, 6 and 10, which contributed 0.8% to 3.0% of the observed phenotypic variation. However, no significant epistasis ? environment interactions were detected. In total, additive QTL effects and Q ? E interactions explained 38.8% and 8.0% of the phenotypic variation, respectively. Epistatic effects contributed 15% of the phenotypic variation. The results showed that besides the additive QTL, both epistasis and Q ? E interactions formed an important genetic basis for the resistance to Ustilago maydis in maize.
Fusarium verticillioides is a common causal agent of maize ear rot in the Philippines. Eighty isolates were collected from healthy and infected maize cobs from Laguna province. Fifty isolates crossed with one of the mating type A testers. The ratio of MATA-1:MATA-2 is 27:23, which follows a Mendelian ratio of 1:1. The effective population number, Ne, was determined by mating type and male/hermaphrodite polymorphisms. The effective population number for mating type, Ne(mt), is 81% of the count (total population), and that for male/hermaphrodite status, Ne(f), is 36?42% of the count (total population). Sexual reproduction in Philippine isolates of F. verticillioides does not occur frequently, compared to F. verticillioides in other regions of the world.
In order to provide information for the development of molecular selection markers for drought tolerance improvement, the methods of prometric analysis, quantitative real-time PCR and field evaluation were employed for the identification of the differential expression of candidate genes under drought stress in maize. At seventeen, twenty-four and forty-eight hours of polyethylene glycol-simulated drought stress at the seventh leaf stage, leaf samples were collected from two drought-tolerant inbred lines for prometric analysis by two-dimensional electrophoresis and peptide mass fingerprinting. Fifty-eight proteins out of more than 500 were found in response to drought stress. Three drought-induced spots 2506, 3507 and 4506 showed sequence similarity with cinnamyl alcohol dehydrogenase, cytochrome protein 96A8 and S-adenosyl-L-methionine synthase, respectively. The expression of two key enzymes to lignin biosynthesis was quantified by quantitative real-time PCR among three drought-tolerant and one drought-sensitive inbred lines under drought stress and well-watered control conditions. After a decrease at the beginning of drought stress, the expression of cinnamyl alcohol dehydrogenase and caffeate O-methyltransferase recovered at twenty-four hours of the drought stress in the three drought-tolerant lines, but not in the drought-sensitive lines. Leaf lignin content, anthesis-silking interval and grain weight per plant were investigated with six inbred lines of varying drought tolerance under drought stress and well-watered control. Drought tolerance coefficients of these three characters were calculated and the correlation coefficients among these drought tolerance coefficients were estimated. Significant difference in leaf lignin content was found among the inbred lines and in response to drought stress. Close correlations were observed between the drought tolerant coefficients for leaf lignin content and grain weight per plant, and between the drought tolerant coefficients for leaf lignin content and anthesis-silking interval. These results indicate that leaf lignin content is a useful index for evaluation of drought tolerance in maize. Molecular selection markers can be developed on the basis of differential expression of the candidate genes and applied to maize improvement for drought tolerance.
The use of 2,4-D as a post pollination treatment to fertilize florets instead of GA3 provided a two-fold improvement in seed set, culturable embryos and hence green plant production from wheat and maize pollination. The efficiency of the wheat by maize pollination method for haploid production was equal to the anther culture method in F1 hybrid combinations that were responsive to anther culture. However, in recalcitrant combinations obtained from non-responsive genotypes the maize pollination method was far superior.
The paper provides an overview of the most important in vivo experiments, concerning herbicide tolerant soybean and Bt maize, quoted by the opponents of GMOs, as to justify opposition to the use of GM crops in animal feed and food production. The results of these experiments were confronted with similar studies performed by other research teams. Relatively few in vivo experiments have demonstrated significant differences in selected parameters of metabolic and health status of animals fed diets with soya or GM maize diets. Concluding on that basis that HT soybean and Bt maize may pose health threat to animals and humans is not eligible.
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