Naked Oat×Maize Hybridization

There is a certain frequency of fertilization and embryo productivity in naked oat (Avena nuda L. ) × maize (Zea mays L. ) crosses. The maize pollen readily germinated on the naked oat stigma and more than one pollen tubes grew into the style in about 68% of florets. In a sample of 163 florets fixed after pollination, 5 (3.07%) had only an embryo, 3 (1.84%) had only an endosperm and 10 (6.13%) had both. Overall, 9 haploid and 3 diploid naked oat plants were obtained from 12 seeds which formed following application of maize pollen to about 2200 emasculated naked oat florets. Preliminary studies indicated that elimination of the maize chromosomes occurred early in the embryo and endosperm development. This method gives a new approach for obtaining haplo!d naked oat.     

Soil Type and Maize Cultivar Affect the Genetic Diversity of Maize Root–Associated Burkholderia cepacia Populations

Abstract Burkholderia cepacia populations associated with the Zea mays root system were investigated to assess the influence of soil type, maize cultivar, and root localization on the degree of their genetic diversity. A total of 180 B. cepacia isolates were identified by restriction analysis of the amplified 16S rDNA (ARDRA technique). The genetic diversity among B. cepacia isolates was analyzed by the random amplified polymorphic DNA (RAPD) technique, using the 10-mer primer AP5. The analysis of molecular variance (AMOVA) method was applied to estimate the variance components for the RAPD patterns. The results indicated that, among the factors studied, the soil was clearly the dominant one in affecting the genetic diversity of maize root–associated B. cepacia populations. In fact, the percentage of variation among populations was significantly higher between B. cepacia populations recovered from maize planted in different soils than between B. cepacia populations isolated from different maize cultivars and from distinct root compartments such as rhizoplane and rhizosphere. The analysis of the genetic relationships among B. cepacia isolates resulted in dendrograms showing bacterial populations with frequent recombinations and a nonclonal genetic structure. The dendrograms were also in agreement with the AMOVA results. We were able to group strains obtained from distinct soils on the basis of their origin, confirming that soil type had the major effect on the degree of genetic diversity of the maize root–associated B. cepacia populations analyzed. On the other hand, strains isolated from distinct root compartments exhibited a random distribution which confirmed that the rhizosphere and rhizoplane populations analyzed did not significantly differ in their genetic structure. Received: 22 January 1999; Accepted: 7 April 1999     

Genetic Characterization of a Core Set of a Tropical Maize Race Tuxpe?o for Further Use in Maize Improvement

The tropical maize race Tuxpeño is a well-known race of Mexican dent germplasm which has greatly contributed to the development of tropical and subtropical maize gene pools. In order to investigate how it could be exploited in future maize improvement, a panel of maize germplasm accessions was assembled and characterized using genome-wide Single Nucleotide Polymorphism (SNP) markers. This panel included 321 core accessions of Tuxpeño race from the International Maize and Wheat Improvement Center (CIMMYT) germplasm bank collection, 94 CIMMYT maize lines (CMLs) and 54 U.S. Germplasm Enhancement of Maize (GEM) lines. The panel also included other diverse sources of reference germplasm: 14 U.S. maize landrace accessions, 4 temperate inbred lines from the U.S. and China, and 11 CIMMYT populations (a total of 498 entries with 795 plants). Clustering analyses (CA) based on Modified Rogers Distance (MRD) clearly partitioned all 498 entries into their corresponding groups. No sub clusters were observed within the Tuxpeño core set. Various breeding strategies for using the Tuxpeño core set, based on grouping of the studied germplasm and genetic distance among them, were discussed. In order to facilitate sampling diversity within the Tuxpeño core, a minicore subset of 64 Tuxpeño accessions (20% of its usual size) representing the diversity of the core set was developed, using an approach combining phenotypic and molecular data. Untapped diversity represents further use of the Tuxpeño landrace for maize improvement through the core and/or minicore subset available to the maize community.     

Inheritance and Sequence Homology Analysis of the Maize DNA Introgressed into the Wheat Doubled Haploid Plant Through Wheat×Maize Cross

A maize (Zea mays L.) genome-specific repeated DNA sequence (clone MR64) has been transferred into one DH line of wheat through wheat (Triticum persicum Vav. ex Zhuk.) and maize cross. In the present study by RFLP analysis the authors proved that this DNA sequence could stably transmit into DH3 plants, the next generation derived from DH2 self-crossing. A similarity search in all DNA databases using BLASTN program showed that the DNA sequence of MR64 had as high as 93% identity to PREM-2 and 79% to Opie-2 in nucleotides. Both PREM-2 and Opie-2 are known as retrotransposons in maize genome, suggesting that MR64 likely is the partial sequence of a maize retrotransposon. Therefore, the results indicate that some retrotransposon might involve the DNA introgression from maize to wheat genome through wide fertilization. Stable inheritance of this maize genome-specific retrotransposon-like DNA in the wheat genome opens up the possibility of using retrotransposon as a new tool for gene tagging, function analysis, and insertional mutagenesis in wheat genome.     

Effect of Anoxia on α-Amylase Induction in Maize Caryopsis

α -amylase as well as other enzymes involved in starch degradation under anoxia. Carbohydrates resulting from starch breakdown allow maize caryopses to avoid sugar starvation. Most interestingly, this correlates well with the ability of maize caryopses to sustain relatively prolonged anaerobiosis, in agreement with the hypothesis linking carbohydrate availability to anoxia tolerance. Received 25 September 1999/ Accepted in revised form 24 February 2000     

In Memoríam

Mental retardation is a symptom of an underlying disease process. In California state hospitals for the retarded an accurate dynamic diagnosis is possible through utilizing the knowledge of neurology, psychiatry, pediatrics, psychology, social service, rehabilitation, education, the laboratory and trained psychiatric technicians. A program of "custody" is archaic and we are returning to the concept of training, treatment, and turnover. This kind of program is essential in order to avoid building new hospitals at the cost of millions of dollars every few years.Parent organizations for retarded children are expanding in ever increasing number. Special education programs in public schools, foster care homes and sheltered workshops may make admission to hospitals unnecessary and aid return of patients to the community.     

In Memoríam

Animal experiments having indicated a nearly twofold increase in anticonvulsant protection with the use of diuretics which increase blood-brain barrier permeability, the principle was applied to treatment of humans with epilepsy. The addition of diuretics to anticonvulsant medication permitted a decrease of previously toxic dosages in ten epileptics, followed for six months, without lessening (and in some cases improving) the control of seizures. In three cases excessive diuresis and gastric distress necessitated discontinuance or decrease in dosage of the diuretic used.     

In Memoríam

Three hundred patients with the post-thrombophlebitic syndrome were studied. The lower extremities were involved in the majority of cases. Severe disabling subjective symptoms, such as burning, aching, cramping and shooting pains, occurred in approximately 15 per cent of cases regardless of the presence or absence of objective findings such as ulcerations, edema or dermatitis. Subjective symptoms occurred in about as many men as women. The persistence and severity of disabling subjective symptoms seemed to be unrelated to the possibility of compensation or pecuniary gain. No adequate explanation could be found for the perseverance of disabling subjective symptoms. There was no consistent relation of subjective symptoms and disability to psychic factors.     

Do Microtubules Control Growth in Tropism? Experiments with Maize Coleoptiles

A recently proposed hypothesis [Nick et al. (1990) Planta 181:162] suggests that, in maize coleoptiles, tropistic curvaturemight be caused by a stimulus-induced trans-organ gradient overthe orientation of cortical microtubules adjacent to the outercell wall of the outer epidermis. This gradient, in turn, iscontrolled by a light-induced redistribution of auxin. The hypothesiswas tested by following the behaviour of microtubules for variouslight stimuli using indirect immuno-fiuorescence in epidermalstrips as assay. Analysis of gravitropic straightening, nasticcurvature on the horizontal clinostat, effects of tonic irradiationwith red and/or blue light, and experiments involving opposinglight pulses demonstrate that bending direction and microtubuleorientation gradients are not as closely linked as predicted:Considerable bending can be produced without detectable gradientsof microtubule orientation, and conspicuous gradients of microtubuleorientation are not necessarily expressed as corresponding curvature.Thus, a monocausal relationship between microtubules and tropismis excluded. Furthermore, a comparison of tonic light effectson microtubules to earlier studies into the impact of lightupon auxin content indicate that the relationship between auxinand microtubules might be more complex than hitherto assumed.It is concluded that, at least in maize coleoptiles, growthcan be regulated by various mechanisms, and that microtubules,although somehow related to tropism, are probably not the causeof the fast tropistic responses. (Received April 26, 1991; Accepted July 17, 1991)     

Meiotic Studies of Diploid Perennial Teosinte and Its Hybrids with Maize

1. Open-pollinated diploid perennial teosinte Microsporocytes at pachytene stage from six different diploid perennial teosinte plants were investigated. It was found that they all had 10 pairs of chromosomes (2n = 20). All of the knobs and large chromomere were terminal (Plate Ⅰ,). The size of the knobs varied from medium to small. The short arms of chromosomes 1 and 2 and the long arms of chromosomes 2 and 3 had a small knob. A large chromomere