Crossability of Arachis valida and B genome Arachis species.

The peanut (Arachis hypogaea) is an important food crop in much of the tropical and semi-tropical parts of the world. The peanut is an allotetraploid with an AABB genome formula derived from diploids A. duranensis (A genome) and A. ipaënsis (B genome). The success of an introgression program that aims to improve cultivated varieties of the peanut depends on whether the chosen B genome species is homologous with the B genome of the peanut. While not directly involved in the origin of the peanut to the best of our knowledge, Arachis valida is a B genome species that could potentially be a bridge species or a source of new and different alleles, because of its resistance to diseases and pests. In this study, we investigated the crossability of A. valida with five other B genome species of section Arachis. Eight cross-combinations were made with A. valida and A. gregoryi, A. ipaënsis, A. magna, A. valida, and A. williamsii. Two hundred and forty pollinations were made yielding 61 fruit segments, 61 seeds, one abortion, and 24 hybrid plants. An analysis of the morphological characteristics and pollen viability confirmed that the plants were hybrids. Our results indicated that higher pollen viability of hybrid plants corresponded with higher affinity between parent plants used in crossings. This conclusion corroborates much of previous research carried out by many other authors in the past.

Improving the utility of nematode resistance in groundnut.

Host resistance to pests and pathogens, to be useful, must be introgressed into cultivars that possess the high yield potential and other important agronomic quality traits desired by the growers. The root-knot nematodes M. arenaria and M. javanica are only a subset of the several important pests and pathogens attacking groundnut. The resistance that was transferred from wild Arachis spp. to cultivated groundnut will provide nearly complete control of these important pathogens; however, growers have been reluctant to use this resistance because the resistant cultivars lack other desired traits. The introgression of nematode resistance into genotypes that have multiple disease resistance, higher yield potential, and the important agronomic trait of the high O/L ratio will provide growers with a cultivar that satisfies most of their needs. Our current efforts are aimed at providing growers with high quality cultivars with high levels of resistance to multiple diseases. Development of germplasm with these multiple traits will ensure that potential benefits of host resistance are realized.

Acetylecholinesterase-based biosensor electrodes for organophosphate pesticide detection. II. Immobilization and stabilization of acetylecholinesterase.

The dry and wet stability of Drosophila acetylcholinesterase non-covalently immobilized onto polyethyleneimine modified screen-printed carbon electrodes was improved when compared to non-immobilized acetylcholinesterase, and acetylcholinesterase covalently immobilized onto dialdehyde and polyethyleneimine modified electrodes. Stabilizer mixtures were characterized for additional stabilization of acetylcholinesterase during storage in the dry state, with dextran-sulphate/sucrose and polygalacturonic acid/sucrose mixtures proving highly effective for long-term storage of biosensor electrodes.

A Recessive Gene for Resistance to Meloidogyne arenaria in Interspecific Arachis spp. Hybrids.

A single dominant gene for resistance to Meloidogyne arenaria was identified previously in two peanut cultivars, Arachis hypogaea 'COAN' and 'NemaTAM'. The interspecific Arachis hybrid TxAG-6 was the source of this resistance and the donor parent in a backcross breeding program to introgress resistance into cultivated peanut. To determine if other resistance genes were present in TxAG-6 and derived breeding populations from the third backcross generation (BC), F individuals were evaluated for the resistance phenotype. The ratio of the resistant and susceptible individuals for all F populations fit the expected ratio for resistance being governed by one dominant gene and one recessive gene. Evaluation of the F generation from four susceptible F individuals (two from TxAG-6 x A. hypogaea and two from the BC population) confirmed that a recessive gene for resistance to M. arenaria was present in each of the tested populations. The identification of a second gene for resistance in the A. hypogaea germplasm may improve the durability of the resistance phenotype.

Acetylcholinesterase-based biosensor electrodes for organophosphate pesticide detection. I. Modification of carbon surface for immobilization of acetylcholinesterase.

Screen-printed carbon electrodes modified with the dialdehydes, glutaraldehyde and terephthaldicarboxaldehyde, and then polyethyleneimine have been utilized for production of pesticide biosensors based on acetylcholinesterase. To improve the extent of dialdehyde modification, the electrodes were NH2-derivatized, initially by electrochemical reduction of 4-nitrobenzenediazonium to a nitroaryl radical permitting attachment to the carbon surface. Subsequent reduction of the 4-nitrobenzene yields a 4-aminobenzene modified carbon surface. Drosophila melanogaster acetylcholinesterase was immobilized either covalently onto dialdehyde modified electrodes or non-covalently onto polyethyleneimine modified electrodes. Internal diffusion limitations due to the dialdehyde and polyethyleneimine modifications increased the apparent Km of the immobilized enzyme. The thiocholine sensitivity was about 90% for dialdehyde modified electrodes and about 10% for polyethyleneimine modified electrodes as compared with non-modified carbon electrodes. The detection limit of the biosensors produced by non-covalent immobilization of acetylcholinesterase onto polyethyleneimine modified carbon electrodes was found to be about 10(-10) M for the organophosphate pesticide dichlorvos.

Transmission genetics of chromatin from a synthetic amphidiploid to cultivated peanut (Arachis hypogaea L.). broadening the gene pool of a monophyletic polyploid species.

Polyploidy creates severe genetic bottlenecks, contributing to the genetic vulnerability of leading crops. Cultivated peanut is thought to be of monophyletic origin, harboring relatively little genetic diversity. To introduce variability from diploid wild species into tetraploid cultivated Arachis hypogaea, a synthetic amphidiploid [[A. batizocoi K9484 x (A. cardenasii GKP10017 x A. diogoi GKP10602)](4x)] was used as donor parent to generate a backcross population of 78 progeny. Three hundred seventy RFLP loci were mapped onto 23 linkage groups, spanning 2210 cM. Chromatin derived from the two A-genome diploid ancestors (A. cardenasii and A. diogoi) comprised mosaic chromosomes, reflecting crossing over in the diploid A-genome interspecific F(1) hybrid. Recombination between chromosomes in the tetraploid progeny was similar to chromosome pairing reported for A. hypogaea, with recombination generally between chromosomes of the same subgenomic affinity. Segregation distortion was observed for 25% of the markers, distributed over 20 linkage groups. Unexpectedly, 68% of the markers deviating from expected segregation showed an excess of the synthetic parent allele. Genetic consequences, relationship to species origins, and significance for comparative genetics are discussed.

Genetics and Mechanism of Resistance to Meloidogyne arenaria in Peanut Germplasm.

Segregation of resistance to Meloidogyne arenaria in six BCF peanut breeding populations was examined in greenhouse tests. Chi-square analysis indicated that segregation of resistance was consistent with resistance being conditioned by a single gene in three breeding populations (TP259-3, TP262-3, and TP271-2), whereas two resistance genes may be present in the breeding populations TP259-2, TP263-2, and TP268-3. Nematode development in clonally propagated lines of resistant individuals of TP262-3 and TP263-2 was compared to that of the susceptible cultivar Florunner. Juvenile nematodes readily penetrated roots of all peanut genotypes, but rate of development was slower (P = 0.05) in the resistant genotypes than in Florunner. Host cell necrosis indicative of a hypersensitive response was not consistently observed in resistant genotypes of either population. Three RFLP loci linked to resistance at distances of 4.2 to 11.0 centiMorgans were identified. Resistant and susceptible alleles for RFLP loci R2430E and R2545E were quite distinct and are useful for identifying individuals homozygous for resistance in segregating populations.

Resistance of Interspecific Arachis Breeding Lines to Meloidogyne javanica and an Undescribed Meloidogyne Species.

Resistance to a peanut-parasitic population of Meloidogyne javanica and an undescribed Meloidogyne sp. in peanut breeding lines selected for resistance to Meloidogyne javanica was examined in greenhouse tests. The interspecific hybrid TxAG-7 was resistant to reproduction of Meloidogyne javanica, M. javanica, and Meloidogyne sp. An Meloidogyne javanica-resistant selection from the second backcross (BC) of TxAG-7 to the susceptible cultivar Florunner also was resistant to M. javanica but appeared to be segregating for resistance to the Meloidogyne sp. When reproduction of M. javanica and Meloidogyne javanica were compared on five BC4F3 peanut breeding lines, each derived from Meloidogyne javanica-susceptible BC4F2 individuals, all five lines segregated for resistance to M. javanica, whereas four of the lines appeared to be susceptible to Meloidogyne javanica. These data indicate that several peanut lines selected for resistance to Meloidogyne javanica also contain genes for resistance to populations of M. javanica and the undescribed Meloidogyne sp. that are parasitic on peanut. Further, differences in segregation patterns suggest that resistance to each Meloidogyne sp. is conditioned by different genes.

Additive Effects of Meloidogyne arenaria and Sclerotinin rolfsii on Peanut.

Field observations have suggested that infection of peanut by Meloidogyne arenaria increases the incidence of southern blight caused by Sclerotium rolfsii. Three factorial experiments in microplots were conducted to determine if interactions between M. arenaria and S. rolfsii influenced final nematode population densities, incidence of southern blight, or pod yield. Treatments included four or five initial population densities of M. arenaria and three inoculum rates of S. rolfsii. Final nematode population densities were affected by initial nematode densities in all experiments (P = 0.01) and by S. rolfsii in one of three experiments (P = 0.01). Incidence of southern blight increased with increasing inoculum rates of S. rolfsii in all experiments and by the presence of the nematodes in one experiment (P = 0.01). Pod yield decreased with inoculation with S. rolfsii in all experiments (P = 0.05) and by M. arenaria in two of three experiments (P = 0.05). In no experiment was the interaction among treatments significant with respect to final nematode population densities, incidence of southern blight, or pod yield (P = 0.05). The apparent disease complex between M. arenaria and S. rolfsii on peanut is due to additive effects of the two pathogens.

Increasing the pool of qualified minority medical school applicants: premedical training at historically black colleges and universities.

Historically black colleges and universities have educated significant numbers of black students preparing for careers in medicine. These institutions have the potential to make even greater contributions to the pool of black medical school applicants and ultimately to the supply of black physicians. The Division of Disadvantaged Assistance, Bureau of Health Professions, Health Resources and Services Administration within the Public Health Service, commissioned a study of the curriculums and other factors related to premedical education. The study was conducted at the historically black colleges and universities that graduate a large number of students who gain admission to medical school, and the historically black colleges and universities whose students are less successful in gaining admission to medical school. Nine historically black colleges and universities participated in a self-assessment of their undergraduate premedical curriculums. The findings from schools with higher acceptance rates were compared with those of schools with lower acceptance rates to identify factors contributing to the production of significant numbers of successful medical school applicants. Comparisons of data on these schools revealed several important factors that may be related to differences in acceptance rates: Those schools that devoted greater effort to premedical training (for example, advising students about how to prepare for medical school, curriculum development, maintaining premedical or pre-health professions offices and clubs--the staff of these offices provide students with information on medical or other health professions schools--to identify and recruit students) tended to have higher acceptance rates. * Schools with higher acceptance rates had larger proportions of biology and chemistry majors aspiring to medical and dental careers and stronger affiliations with medical schools than schools with lower acceptance rates.* Institutions with higher acceptance rates offered a broader range of externally sponsored enrichment programs; the highest medical school acceptance rates were found among those schools with continuing Health Careers Opportunity Program projects that served significant percentages of students interested in careers in medicine.* Mean Medical College Admission Test scores were somewhat lower for applicants from schools with lower acceptance rates, but the great variation in acceptance rates for these schools is not reflected in a comparable variation in the Medical College Admission Test scores.

The current and future need for minority medical faculty.

Little progress has been made in increasing the number of minority faculty members at US medical schools. From 1975 through 1989, underrepresented minority medical faculty increased only 0.3%--from 2.7% to 3.0%. In the field of medicine in general, only 3% of physicians are African-American and 3% are Hispanic, while the African-American and Hispanic populations are approximately 12% and 7%, respectively, of the total US population. A number of factors have caused the persistent underrepresentation of minority health professions trainees: inadequate or inappropriate career counseling, admissions policies, relatively high attrition rates after matriculation, substantial costs of education, and lack of appropriate mentors and role models. Helping minority students overcome these obstacles requires providing them with appropriate information, preparation, motivation, and opportunities at all stages of the educational process. Attention must focus on recruiting minority students into the scientific, academic professions if an increase is to occur in numbers of underrepresented minorities in all specialties of medicine. The Health Resources and Services Administration and private foundations have committed to providing funds to educational institutions to help encourage minority students to pursue academic careers. Leadership at these institutions must also commit to increasing the numbers of underrepresented minority faculty and senior administrators.

RFLP variability in peanut (Arachis hypogaea L.) cultivars and wild species.

RFLP variability was studied in eight U.S. peanut cultivars, representing the four market types, and in 14 wild Arachis species accessions, using random genomic clones from a PstI library. Very low levels of RFLP variability were found among the allotetraploids, which included the U.S. cultivars and Arachis monticola, a wild species. The diploid wild species were very diverse, however. RFLP patterns of the allotetraploids were more complex than the diploids, and the two constituent genomes could usually be distinguished. On the basis of RFLP band sharing, A. ipaensis, A. duranensis, and A. spegazzinii appeared most closely related to the diploid progenitor species of the allotetraploids. A dendrogram of relationships among the diploid wild species was constructed based on band sharing.

Resistance to Meloidogyne arenaria in Arachis spp. Germplasm.

Field and greenhouse evaluations of 116 wild Arachis spp. genotypes demonstrated the presence of resistance to reproduction of the root-knot nematode Meloidogyne arenaria race 1. Resistance in greenhouse tests was based on test lines having

Factors affecting the supply of minority physicians in 2000.

There was a substantial increase in the number of black and Hispanic physicians between 1970 and 1985. During the next 15 years, 1985 to 2000, the increase is projected to continue. The factors that will determine the size of the increase and the changes in physician to population ratios include black and Hispanic population increases, medical school costs, availability of student support, minority enrollment in undergraduate schools and the pool of these students who will be applicants to medical school, attrition during medical school, competition from other professions for talented minority students, and the effects of intervention programs such as the Health Careers Opportunity Program. The most likely outcome would seem to be that the increases in black and Hispanic physicians will continue to 2000 at 1985 levels because the data show neither strong positive nor strong negative net influences for the factors examined.

Holographic optical element for visual display applications.

Off-axis and off-bisector reflection-type holographic visual display elements have been recorded in dichromated gelatin deposited on planar or spherical shell substrates of glass or Plexiglas. A procedure for bonding gelatin to Plexiglas is given. Holographic elements are recorded at the argon wavelength of 514.5 nm and reconstructed with spectral lines from a low pressure mercury arc lamp. Measured image characteristics for a flat substrate hologram agree with ray-tracing calculations. A swelling of the gelatin by approximately 6.6% after processing does not perceptibly affect the dispersion, astigmatism, or distortion in the image, that is, the grating equation depends on the spacing between the fringes on the surface of the gelatin and is not affected by the swelling or shrinking. However, the Bragg equation depends on the distance normal to the fringe planes and is affected by thickness changes of the gelatin. Therefore, this thickness change is taken as an independent parameter and used to adjust the wavelength for maximum diffraction efficiency, without affecting the image angle. Data reveal a near linear relationship between the dichromate concentration of 0.5-10% used to photosensitive the gelatin and the display wavelength of maximum diffraction efficiency. Lateral dispersion is 0.12 +/- 0.01 degrees / nanometer for both planar and spherical shell substrate elements recorded in quite similar geometry, but their astigmatisms are not alike.