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PubMed1999

In vitro utilization of amylopectin and high-amylose maize (Amylomaize) starch granules by human colonic bacteria.

It has been well established that a certain amount of ingested starch can escape digestion in the human small intestine and consequently enters the large intestine, where it may serve as a carbon source for bacterial fermentation. Thirty-eight types of human colonic bacteria were screened for their capacity to utilize soluble starch, gelatinized amylopectin maize starch, and high-amylose maize starch granules by measuring the clear zones on starch agar plates. The six cultures which produced clear zones on amylopectin maize starch- containing plates were selected for further studies for utilization of amylopectin maize starch and high-amylose maize starch granules A (amylose; Sigma) and B (Culture Pro 958N). Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) was used to detect bacterial starch-degrading enzymes. It was demonstrated that Bifidobacterium spp., Bacteroides spp., Fusobacterium spp., and strains of Eubacterium, Clostridium, Streptococcus, and Propionibacterium could hydrolyze the gelatinized amylopectin maize starch, while only Bifidobacterium spp. and Clostridium butyricum could efficiently utilize high-amylose maize starch granules. In fact, C. butyricum and Bifidobacterium spp. had higher specific growth rates in the autoclaved medium containing high-amylose maize starch granules and hydrolyzed 80 and 40% of the amylose, respectively. Starch-degrading enzymes were cell bound on Bifidobacterium and Bacteroides cells and were extracellular for C. butyricum. Active staining for starch-degrading enzymes on SDS-PAGE gels showed that the Bifidobacterium cells produced several starch-degrading enzymes with high relative molecular (M(r)) weights (>160,000), medium-sized relative molecular weights (>66,000), and low relative molecular weights (<66,000). It was concluded that Bifidobacterium spp. and C. butyricum degraded and utilized granules of amylomaize starch.

Amylopectin↗

PubMed2006

Maize haplotype with a helitron-amplified cytidine deaminase gene copy.

BACKGROUND: Genetic maps are based on recombination of orthologous gene sequences between different strains of the same species. Therefore, it was unexpected to find extensive non-collinearity of genes between different inbred strains of maize. Interestingly, disruption of gene collinearity can be caused among others by a rolling circle-type copy and paste mechanism facilitated by Helitrons. However, understanding the role of this type of gene amplification has been hampered by the lack of finding intact gene sequences within Helitrons. RESULTS: By aligning two haplotypes of the z1C1 locus of maize we found a Helitron that contains two genes, one encoding a putative cytidine deaminase and one a hypothetical protein with part of a 40S ribosomal protein. The cytidine deaminase gene, called ZmCDA3, has been copied from the ZmCDA1 gene on maize chromosome 7 about 4.5 million years ago (mya) after maize was formed by whole-genome duplication from two progenitors. Inbred lines contain gene copies of both progenitors, the ZmCDA1 and ZmCDA2 genes. Both genes diverged when the progenitors of maize split and are derived from the same progenitor as the rice OsCDA1 gene. The ZmCDA1 and ZmCDA2 genes are both transcribed in leaf and seed tissue, but transcripts of the paralogous ZmCDA3 gene have not been found yet. Based on their protein structure the maize CDA genes encode a nucleoside deaminase that is found in bacterial systems and is distinct from the mammalian RNA and/or DNA modifying enzymes. CONCLUSION: The conservation of a paralogous gene sequence encoding a cytidine deaminase gene over 4.5 million years suggests that Helitrons could add functional gene sequences to new chromosomal positions and thereby create new haplotypes. However, the function of such paralogous gene copies cannot be essential because they are not present in all maize strains. However, it is interesting to note that maize hybrids can outperform their inbred parents. Therefore, certain haplotypes may function only in combination with other haplotypes or under specialized environmental conditions.

Amino Acid Sequence↗

PubMed2006

Can transgenic maize affect soil microbial communities?

The aim of the experiment was to determine if temporal variations of belowground activity reflect the influence of the Cry1Ab protein from transgenic maize on soil bacteria and, hence, on a regulatory change of the microbial community (ability to metabolize sources belonging to different chemical guilds) and/or a change in numerical abundance of their cells. Litter placement is known for its strong influence on the soil decomposer communities. The effects of the addition of crop residues on respiration and catabolic activities of the bacterial community were examined in microcosm experiments. Four cultivars of Zea mays L. of two different isolines (each one including the conventional crop and its Bacillus thuringiensis cultivar) and one control of bulk soil were included in the experimental design. The growth models suggest a dichotomy between soils amended with either conventional or transgenic maize residues. The Cry1Ab protein appeared to influence the composition of the microbial community. The highly enhanced soil respiration observed during the first 72 h after the addition of Bt-maize residues can be interpreted as being related to the presence of the transgenic crop residues. This result was confirmed by agar plate counting, as the averages of the colony-forming units of soils in conventional treatments were about one-third of those treated with transgenic straw. Furthermore, the addition of Bt-maize appeared to induce increased microbial consumption of carbohydrates in BIOLOG EcoPlates. Three weeks after the addition of maize residues to the soils, no differences between the consumption rate of specific chemical guilds by bacteria in soils amended with transgenic maize and bacteria in soils amended with conventional maize were detectable. Reaped crop residues, comparable to post-harvest maize straw (a common practice in current agriculture), rapidly influence the soil bacterial cells at a functional level. Overall, these data support the existence of short Bt-induced ecological shifts in the microbial communities of croplands' soils.

Carbon↗

PubMed2006

Field measures of western corn rootworm (Coleoptera: Chrysomelidae) mortality caused by Cry34/35Ab1 proteins expressed in maize event 59122 and implications for trait durability.

Maize, Zea mays L., has been transformed to express the Cry34Ab1 and Cry35Ab1 proteins from Bacillus thuringiensis strain PS149B1. These two proteins act together as a binary insecticidal protein that is effective against corn rootworm (Coleoptera: Chrysomelidae) species. The design of the resistance management plan to preserve the long-term durability of this trait largely depends on the level of rootworm mortality induced by Cry34/35Ab1 corn rootworm-protected maize (frequently referred to as "dose" in this context). Here, we report on studies that showed Cry34/35Ab1-expressing maize event 59122 caused 99.1 to 99.98% mortality of western corn rootworm, Diabrotica virgifera virgifera LeConte, larvae, after adjusting adult emergence numbers for density-dependent mortality. In two of three studies, there was a short delay in time to 50% adult emergence from 59122 maize plots compared with control plots, although emergence was completed at approximately the same time from both types of maize. These data support an expectation that alleles conferring resistance to the Cry34/35Ab1 proteins in western corn rootworm will be functionally nearly completely to completely recessive on 59122 maize and that there is unlikely to be assortative mating of Cry34/35Ab1-resistant and susceptible rootworms. When incorporated into simulation models of rootworm adaptation to transgenic maize, these findings suggest that a 20% refuge is likely to be highly effective at prolonging the durability of 59122 maize.

Animals↗

PubMed1995

The effects of processing on the availability of lysine in kenkey, a Ghanaian fermented maize food.

The effects of processing steps such as soaking, fermentation, cooking and drying on the availability of lysine in kenkey were investigated. Soaking increased lysine availability by 21% and 22% for maize and maize-cowpea mixtures, respectively. Cooking of soaked samples further improved lysine availability by 68% and 31% for maize and maize-cowpea mixtures, respectively. Further significant improvements in lysine availability were effected by fermentation and cooking and values of 3.42 and 4.43 g/16 g N were recorded, respectively for maize and maize-cowpea doughs fermented for 4 days and cooked for 3 h. Cabinet drying had no significant effect on lysine availability, but drum drying of fermented maize and maize-cowpea doughs significantly lowered lysine availability in the resulting kenkey. A 1:1 mixture of cabinet and drum dried flours gave a product with higher available lysine content than the drum dried flour.

Biological Availability↗

PubMed1982

Effects of leucine/isoleucine ratio in amino acid mixture-diets simulating normal and high-lysine maize proteins on growth, nitrogen balance, and tryptophan-niacin metabolism in rats.

To re-evaluate nutritive values of opaque-2 (o2) and brittle-2 opaque-2 (bt2o2) maize protein and to re-estimate Gopalan's hypothesis [Lancet, i, 954-957 (1960)] that pathogenesis of pellagra might be related with intake of excess leucine and with chronic consumption of maize or jowar which contains relative high leucine, rats were fed on synthetic diets composed of amino acid mixtures simulating the protein of normal and high-lysine maize, o2 and bt2o2 maize. In order to investigate the effect of intake of excess leucine, leucine was supplemented to o2 and bt2o2 diet at the level of 0.43 and 0.73%, respectively, to adjust the ratio of leucine to isoleucine to that of normal maize protein. Judging from body weight gains and carcass nitrogen of weanling rats fed on these diets, the protein quality (amino acid composition) of bt2o2 maize was 30% superior nutritionally to that of o2 maize, and body composition of bt2o2 diet group were similar to that of casein diet group. Leucine supplementation did not affect these values except for a significant decrease in plasma valine levels. In young adult rats fed on leucine supplemented o2 diet, excretion of urinary nitrogen increased significantly compared with o2 diet alone, suggesting that a slight amino acid imbalance took place. But leucine supplementation altered neither N1-methylnicotinamide level in urine nor total niacin levels in the liver and the brain. These results suggest that supplementation of leucine to a high lysine maize diet did not affect tryptophan and niacin metabolism in rats under these conditions.

Amino Acids↗

PubMed2006

Investigation of false-positive reactions for CBH351 maize in screening PCR analysis.

Examination for CBH351 maize was conducted by the qualitative polymerase chain reaction (PCR) method in maize grain and maize processed foods obtained in the Tokyo area. The numbers of samples possibly positive in the screening test were 7 of 22 (31.8%) for maize grain samples, 4 of 14 (28.6%) for semi-processed foods, 11 of 30 (36.7%) for canned products, 3 of 30 (10.0%) for maize snacks, 3 of 4 (75%) for tacos and 1 of 3 (33.3%) for tortillas. However, CBH351 maize was not detected in the confirmation test. Therefore, the results of the screening test were false-positive. Since the reaction might have been caused by the base sequences of the 3'-end of primers CaM03-5' and CBH02-3' used in the screening test, a new primer pair was designed. The PCR products obtained with the new primer pair TMC2-5'--TMS2-3' were specific for CBH351 and were not obtained with barley, wheat, rice, RRS, Bt11, or Event176. Thus, the new primer pair shows high specificity. CBH351 maize was detected from samples containing at least 0.05% CBH 351 maize DNA by using this primer pair.

Base Sequence↗

PubMedDate not supplied

Complex structure of knobs and centromeric regions in maize chromosomes.

The recovery of maize (Zea mays L.) chromosome addition lines of oat (Avena sativa L.) from oat x maize crosses enables us to analyze the structure and composition of individual maize chromosomes via the isolation and characterization of chromosome-specific cosmid clones. Restriction fragment fingerprinting, sequencing, and in situ hybridization were applied to discover a new family of knob associated tandem repeats, the TR1, which are capable of forming fold-back DNA segments, as well as a new family of centromeric tandem repeats, CentC. Analysis of knob and centromeric DNA segments revealed a complex organization in which blocks of tandemly arranged repeating units are interrupted by insertions of other repeated DNA sequences, mostly represented by individual full size copies of retrotransposable elements. There is an obvious preference for the integration/association of certain retrotransposable elements into knobs or centromere regions as well as for integration of retrotransposable elements into certain sites (hot spots) of the 180-bp repeat. DNA hybridization to a blot panel of eight individual maize chromosome addition lines revealed that CentC, TR1, and 180-bp tandem repeats are found in each of these maize chromosomes, but the copy number of each can vary significantly from about 100 to 25,000. In situ hybridization revealed variation among the maize chromosomes in the size of centromeric tandem repeats as well as in the size and composition of knob regions. It was found that knobs may be composed of either 180-bp or TR1, or both repeats, and in addition to large knobs these repeated elements may form micro clusters which are detectable only with the help of in situ hybridization. The association of the fold-back elements with knobs, knob polymorphism and complex structure suggest that maize knob may be consider as megatransposable elements. The discovery of the interspersion of retrotransposable elements among blocks of tandem repeats in maize and some other organisms suggests that this pattern may be basic to heterochromatin organization for eukaryotes.

Avena↗

PubMed2002

[Uptake and distribution of Cu, Zn, Pb and Cd in maize related to metals speciation change in rhizosphere].

The behavior of heavy metals in terrestrial system and the mechanism of VAM plant in toleranting excessive heavy metals in soil were examined with VAM maize(Zea mays L.). After seven-week cultivation in sewage-sludging soil, the biomass of VAM (Glomus mosseae) maize was found 1.5 times higher than non-mycorrhizal one. Compared with non-mycorrhizal maize, the accumulation of Cu, Zn and Pb by mycorrhizal maize was reduced by 10%, 18% and 29%, respectively, but the accumulation of Cd was the same. The distribution and speciation change of Cu, Zn, Pb and Cd in rhizosphere of VAM and non-mycorrhizal maize were analyzed by using the technique of sequential extraction. Except a significant increase in exchangeable Cu in rhizosphere of VAM maize, the increased amount of test metals bound to organic matter, carbonates, iron and manganese oxides were significantly higher than those in rhizosphere of non-mycorrhizal maize, indicating that the speciation of metals in rhizosphere of mycorrhizal maize growing in contaminated soil tended to be relatively stable. Meanwhile, the influence of metal speciation in rhizosphere on its bioavailability as well as the mechanism of mycorrhizal plant in toleranting excess metals were also discussed.

Cadmium↗

PubMed2002

[Detection of the genetically modified organisms in genetically modified soybean and maize by polymerase chain reaction method].

A method for the detection of the (genetically modified organism GMOs) in genetically modified soybean (Round-up Ready soybean, RR soybean) and maize(Bt-176 maize) is described. The polymerase chain reaction (PCR) method is discussed with the genetically modified soybean and maize whose contents are known. The detection limit can be 0.1%, that is to say, we can detect the GMO in the food whose content is only 0.1%, the detection method is just a screening method. The procedure includes: (1) extraction of genomic DNA of maize and soybean, (2) amplification of the inserted genes, CaMV35S promoter and the NOS terminator inserted by means of the polymerase chain reaction (PCR) method, (3) amplification of the specific genes of maize and soybean in order to determine that the samples are maize and soybean, (4) characterization and confirmation of the PCR products by restriction enzyme analysis and the electrophoresis on agarose gel. The RR soybean contains CaMV35S promoter and NOS terminator, and the Bt-176 maize contains only CaMV35S promoter. Due to the high content of the starch in maize, the effect of the electrophororesis is not so good as of the soybean's.

DNA, Plant↗

PubMed2003

Time of planting and choice of maize hybrids in controlling WCR (Diabrotica virgifera virgifera Le Conte) in Serbia and Montenegro.

Effects of the length of growing season of maize hybrids (FAO maturity groups 400, 500, 600 and 700) and planting dates on the maize crop, as an attractive supplemental feeding for western corn rootworm (WCR) beetles and larval survival, were observed in two locations of South Banat, during a three-year (1997-1999) and a two-year period (2001 and 2002). The feeding attraction of the maize crop for WCR beetles and survival of larvae were evaluated in dependency of the variable "plant lodging". The following results were obtained: First location: A. Plant lodging over time of planting and applied insecticides. 1. Early planting: 44.2%, 77.6%, and 76.7% for FAO 400, 500 and 600, respectively. 2. Late planting: 4.7%, 14.9%, and 7.9% for FAO 400, 500 and 600, respectively. B. Plant lodging over time of planting and cropping practices: 1. Early planting without insecticide application 72.2%, and with insecticide application 7.3%. The efficacy of application of insecticide carbofurane (Furadan 350 FS, dosage 4.0 liter/ha) in larval control was 89.9%. 2. Late planting without insecticide application, plant lodging was 47.7%, and with insecticide application 8.1%. The efficacy of application of insecticide carbofurane (Furadan 350 FS, dosage 4.0 l/ha-1) in larval control was 83.0%. Early planting resulted in greater survival of larvae; hence plant lodging was 10 times greater in early than in late planting. The percentage of lodged plants indicates that the maize crop in late planting was more attractive to imagoes. Therefore, more lodged plants were observed in the treatment where late planting preceded. Second location: Plant lodging as dependent on "treatments" 1. Regular plantings: 90.7% in untreated control and 76.2% in insecticide treated variant. The efficacy of insecticide application in control of high larval population was 16.0%. 2. Replanting date: 12.2% in untreated and 4.4% in treated variant. The efficacy of insecticide in control of low larval population increased from 16.0 to 63.9%. To successfully decrease the size and intensity of attacks of the Diabrotica v. virgifera population under conditions of applying insecticides or not, it is necessary to use maize hybrids of the earliest possible maturity group and to plant the seed on the earliest date possible in the first year of growing maize, if maize is to be followed by maize in the next year.

Agriculture↗

PubMed2025

Evolutionary dynamics and genetic diversity of transposable elements revealed by resequencing data in maize population.

Zea mays (maize) is a globally significant crop with a complex genome enriched with transposable elements (TEs), which are crucial drivers of genomic diversity and plant evolution. In this study, we identified the TE insertion loci (TILs) from resequencing data of 103 maize accessions with the developed pipeline, and 64 293 non-redundant unique TILs were obtained in 82 maize accessions after filtering; approximately 80% (51 361) of loci showed insertion polymorphisms within the population. All TE superfamilies have low frequency in the maize population except for short interspersed nuclear elements, while some TE families have high fixed TE insertions, revealing distinct evolutionary dynamics among TE superfamilies and families. Genetic analysis using the transposon insertion polymorphism information from the maize population showed that the TE polymorphism loci can reflect their geographical origin and evolutionary relationships. Furthermore, TE insertions could also significantly impact gene expression, implying functional consequences for maize phenotypes and adaptation. These findings provide valuable insights into the evolutionary dynamics and genetic diversity of maize genomes, offering a valuable resource for molecular markers and association studies.

Zea mays↗

PubMed2006

Induction of wheat and maize glutathione S-transferase by some herbicide safeners and their effect on enzyme activity against butachlor and terbuthylazine.

The expression of glutathione S-transferase (GST) activity in wheat and maize shoots was investigated in response to treatments with the herbicide safeners benoxacor, cloquintocet-mexyl, fenchlorazole-ethyl, fenclorim, fluxofenim and oxabetrinil. These safeners significantly enhanced the GST activity towards 1-chloro-2,4-dinitrobenzene (CDNB) as a 'standard' substrate, with the exception of oxabetrinil in maize. The enhancements of GST (CDNB) activity were found to be concomitant with increases in V(max) (the reaction rate when the enzyme is fully saturated by the substrate) in wheat following cloquintocet-mexyl and fenchlorazole-ethyl treatments, and in maize following fenchlorazole-ethyl treatment. Otherwise, decreases in V(max) were observed in wheat and maize following fenclorim and fluxofenim treatments. With the exception of oxabetrinil, all the safeners significantly reduced the apparent K(M) (the substrate concentration required for 50% of maximum GST activity) of both wheat and maize GST. The V(max) and K(M) variations following safener treatments are discussed in terms of an increased expression of GST enzymes and an increased affinity for the CDNB substrate. The activity of wheat and maize GST was also assayed towards butachlor and terbuthylazine respectively; the results indicate the ability of cloquintocet-mexyl, fenchlorazole-ethyl and fluxofenim to enhance the enzyme activity in wheat and of benoxacor and fenchlorazole-ethyl to do so in maize.

Acetanilides↗

PubMed1991

Direct genetic selection of a maize cDNA for dihydrodipicolinate synthase in an Escherichia coli dapA- auxotroph.

Dihydrodipicolinate synthase (DHPS; EC 4.2.1.52) is the first committed enzyme in the lysine branch of the aspartate-derived amino acid biosynthesis pathway and is common to bacteria and plants. Due to feedback inhibition by lysine, DHPS serves in a regulatory role for this pathway in plant metabolism. To elucidate the molecular genetic characteristics of DHPS, we isolated a putative full-length cDNA clone for maize DHPS by direct genetic selection in an Escherichia coli dapA- auxotroph. The maize DHPS activity expressed in the complemented E. coli auxotroph showed the lysine inhibition characteristics of purified maize DHPS, indicating that the cDNA encoded sequences for both the catalytic function and regulatory properties of the enzyme. The N-terminal amino acid sequence of purified maize DHPS was determined by direct sequencing and showed homology to a sequence within the cDNA, indicating that the clone contained the entire coding region for a mature polypeptide of 326 amino acids plus a 54 amino acid transit peptide sequence. The molecular weight of 35,854, predicted from the deduced amino acid sequence, was similar to the 38,000 Mr determined by SDS-polyacrylamide gel electrophoresis (SDS-PAGE) for the purified enzyme from maize. DHPS mRNAs complementary to the cDNA were detected in RNA isolated from developing maize endosperm and embryo tissues. Southern blots indicated the presence of more than one genomic sequence homologous to DHPS per haploid maize genome.

Amino Acid Sequence↗

PubMed1989

Characterization of the ndhC-psbG-ORF157/159 operon of maize plastid DNA and of the cyanobacterium Synechocystis sp. PCC6803.

The ndhC and ORF159 genes of the maize plastid DNA (ptDNA) were sequenced and maize ORF159 was used to screen a library of genomic DNA of the blue-green alga Synechocystis sp. PCC 6803. The cyanobacterial gene homologous to ORF159 (ORF157) was isolated and sequenced. In sequencing the region upstream of ORF157, reading frames with homology to the ndhC and psbG genes of maize ptDNA were identified. The ndhC and psbG genes overlap in the ptDNAs of maize, tobacco and Marchantia polymorpha, but are separated by a noncoding spacer in Synechocystis. Northern blot analysis showed that the ndhC, psbG and ORF157/159 genes are cotranscribed in maize and Synechocystis. The three genes occur in the same order in ptDNA of maize, tobacco, and M. polymorpha as in Synechocystis 6803. The amino acid sequences of the NDH-C, PSII-G and the ORF157/159 proteins deduced from the maize genes are 65%, 52% and 53% homologous to those of Synechocystis. However, the cyanobacterial and higher plant NDH-C protein sequences are only 23% homologous to the mitochondrial NDH-3 protein. Protein products of in vitro transcription/translation of the Synechocystis transcription unit had apparent molecular masses of 6 kDa (NDH-C), 25 kDa (PSII-G) and 22 kDa (ORF157) on lithium dodecyl sulfate (LDS) polyacrylamide gel electrophoresis. If these are components of an NADH dehydrogenase, cyanobacteria appear to resemble mitochondria more than they do Escherichia coli and Rhodopseudomonas capsulata with regard to this enzyme complex.

Amino Acid Sequence↗

PubMed1987

Characterization of the gene urf13-T and an unidentified reading frame, ORF 25, in maize and tobacco mitochondria.

We have previously identified two large open reading frames, designated ORF13 and ORF25, in the Texas male-sterile cytoplasm (cms-T) of maize mitochondrial DNA (mtDNA). ORF13 is a single copy gene of chimeric origin that is uniquely transcribed and translated in the mitochondria of cms-T maize, where it produces a polypeptide of approximately 13,000 Mr. The ORF13 reading frame does not occur in the maize N, C or S cytoplasms or Nicotiana tabacum. ORF25 exists as a single copy and is transcribed in the four major maize cytoplasms (N, T, C and S) and N. tabacum. The predicted ORF25 polypeptide has a molecular weight of 24,374 in normal maize and 22,439 in tobacco. Several nucleotide and predicted amino acid changes have occurred in the ORF25 gene among the four maize cytoplasms and N. tabacum. Properties such as transcription and conservation of the sequence between two diverse species suggests that ORF25 encodes a functional plant mitochondrial gene. The ORF25 sequence of maize contains a chloroplast DNA insert homologous to a tRNA-Arg gene; this chloroplast DNA insert is absent in the tobacco ORF25 sequence. Comparison of the ORF25 and ORF13 sequences in restored and non-restored cms-T indicates no differences in their nucleotide sequences. Thus fertility restoration does not alter the primary sequences of ORF13 or ORF25.

Amino Acid Sequence↗

PubMed2004

Recovery of exotic alleles in semiexotic maize inbreds derived from crosses between Latin American accessions and a temperate line.

Genetic diversity of elite maize germplasm in the United States is narrow relative to the species worldwide. Tropical maize represents the most diverse source of germplasm. To incorporate germplasm from tropical maize landraces into the temperate gene pool, 23 Latin American maize accessions were crossed to temperate inbred line Mo44. During inbred line development, selection was practiced in temperate environments, potentially resulting in the loss of substantial proportions of tropical alleles. Genotyping 161 semiexotic inbreds at 51 simple sequence repeat (SSR) loci permitted the classification of their alleles as either Mo44 or tropical and allowed estimation of the proportion of detectable tropical alleles retained in these lines. On average, the percentage of detectable tropical alleles ranged among lines from 15% to 56%, with a mean of 31%. These are conservative, lower-bound estimates of the proportion of tropical germplasm within lines, because it is not known how frequently Mo44 and the tropical maize accession parental populations shared SSR alleles. These results suggest that substantial proportions of exotic germplasm were recovered in the semiexotic lines, despite their selection in temperate environments. The percent of tropical germplasm in semiexotic lines was not correlated to grain yield or moisture of lines testcrossed to a Corn Belt Dent tester, indicating that the incorporation of a substantial percentage of tropical germplasm in an inbred line does not necessarily negatively impact its combining ability. Thus, tropical maize accessions represent a good source of exotic germplasm to broaden the genetic base of temperate maize without hindering agronomic performance.

Agriculture↗

PubMed2002

Rock phosphate solubilization and colonization of maize rhizosphere by wild and genetically modified strains of Penicillium rugulosum.

Maize root colonization and phosphate solubilizing activity of the fungus Penicillium rugulosum were assessed in a greenhouse trial using soil-plant microcosms. The bacterial gene hph conferring resistance to hygromicin B was introduced by electroporation in the wild-type strain IR-94MF1 of P. rugulosum and one transformant, w-T3, was selected. Maize plants were grown for 5 weeks in a P-poor soil and fertilized with a Florida apatite mineral, with Navay, an apatite rock deposit from Venezuela, or with simple superphosphate. Inoculation treatments included strain IR-94MF1, transformant w-T3 and two IR-94MF1 UV-induced mutants with enhanced (Mps++) or reduced (Mps-) in vitro mineral phosphate solubilizing activity. In the absence of P fertilization, inoculation with any P. rugulosum isolate significantly reduced the size of the total and P-solubilizing bacterial community present in maize rhizosphere. The bacterial community significantly increased in maize inoculated with IR-94MF1 and w-T3 when P was added as apatites Navay or Florida. All P. rugulosum strains were able to stimulate the growth of maize plants as indicated by 3.6 to 28.6% increases in dry matter yields. In the presence of rock phosphate, P uptake by maize plants inoculated with the two mutants Mps++ and Mps- was not always in agreement with their P-solubilizing phenotypes. Strain IR-94MF1 and transformant w-T3 increased P assimilation by the plants fertilized with Navay rock phosphate by 26 and 38%, respectively. In this treatment, w-T3 showed its highest significant maize rhizosphere colonization. With the simple superphosphate treatment, w-T3 increased P uptake in plants by 8% over the uninoculated control and also decreased significantly the community size of total bacteria, total fungi, and P-solubilizing fungi in the rhizosphere.

Biological Transport↗