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  • Author or Editor: David A. Dierig x
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Vernonia galamensis (Cass.) Less. (Asteraceae) constitutes a species complex of six subspecies, one of which contains four varieties. Crossing barriers between the subspecies and varieties are being examined. In the analysis of microspore mother cells, no differences in chromosome number (n=9) were found, and meiosis appeared to be normal within and between subspecies. However, an extended delay in time was observed in all subspecies in which chromosomes remained condensed during the post-meiotic tetrad stage. No apparent effect on pollen formation or pollen tube growth was observed from this unusual phenomenon. Self and reciprocal intraspecific crosses are being made, and pollen tube growth into the ovules assessed by fluorescent microscopy. These techniques are being used to characterize self-incompatibility within subspecies and varieties, and to determine the possible barriers to pollen tube growth and autofertility.

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Genetic markers have not yet been described for Lesquerella fendleri (Gray) Wats. a potential new industrial oilseed crop. Seeds of this species are also utilized as a primary component in some desert wildflower seed mixes. Allozyme variation was analyzed for aconitase (ACO), phosphoglucomutase (PGM), and phosphoglucose isomerase (PGI). Four codominant loci, useful as markers, were clearly resolved. In an open-pollinated population, an outcrossing rate and pollen gene frequency was obtained from 20 random families, using these loci. This initial estimate indicated that seed production primarily resulted from outcrossing. Male sterility was discovered in six bulk populations derived from single plant selections. The frequency of this trait, which could affect the outcrossing rate, was found to occur in 15 percent of the plants. Additional populations will be analyzed for validation.

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Lesquerella fendleri (Gray) Wats. (lesquerella, Brassicaceae), native to the southwestern United States, is a potentially useful industrial oilseed crop. The seed oil contains hydroxy fatty acids, similar to castor (Ricinus communis L.) seed oil. The unique properties of the oil, along with coproducts, allow additional applications that would not compete with castor oil. Plants with vestigial anthers (male-sterile) were discovered in a greenhouse-grown, nonselected population in 1993. The inheritance of the trait was investigated through four crop seasons. Crosses were made among male-sterile and male-fertile plants from an open pollinated population, thus, they were heterozygous for many traits. Statistical analysis indicated that male sterility is expressed as a result of two nonlinked nuclear genes with epistatic relations and different cytoplasms, which cause partial or total fertility restoration. These ratios fit a 13:3 epistatic ratio, indicating that male sterility is controlled by homozygous recessive alleles at one locus in combination with at least one dominant allele at the second locus, i.e., ms1ms1 Ms2_. Some cross results were skewed in favor of fertile phenotypes presumably due to cytoplasmic effects causing partial fertility restoration. Male-sterile lines could be used for hybrid development and this information will be helpful in implementing a strategy for hybrid development. Hybrid plants and higher yields will enhance the potential for commercialization of this new alternative crop.

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Guayule (Parthenium argentatum Gray), a latex-producing perennial desert shrub and potential industrial crop for semiarid regions, exhibits reproductive modes ranging from sexual, self-sterile diploids to predominantly apomictic, self-compatible polyploids. The objectives of this study were to develop and evaluate a rapid, simple technique for characterizing apomictic potential (percentage of ovules that produce apomictic embryos) in guayule breeding lines. Initial in vivo experiments were based on an auxin test that permitted quantification of apomictic frequency in grasses. In our trials, floral application of NAA or IBA resulted in embryo production similar to that of open-pollinated controls, but 2,4-D inhibited embryo production. Breeding lines could be separated based on embryo production using an in vivo auxin test; however, accuracy of the results was questionable because 1) pollen release and insect activity within isolation bags prevented distinguishing between sexual and apomictic embryos, and 2) high temperatures and large humidity fluctuations could have affected results. Thus, in vitro flower culture was investigated using liquid medium, because it would provide better control of these factors. Flowers developed normally in vitro, except that pollen was not released from the anthers; therefore, any embryos produced in vitro were considered to be apomictic. Embryo production was similar on both Nitsch and Nitsch and Woody Plant Media. Addition of growth regulators inhibited embryo production. Embryo production was tested on Nitsch and Nitsch medium without growth regulators for seven breeding lines. Based on statistical analyses, four classes of apomictic potential were identified, ranging from none (sexual) to high. Chemical names used: 2,4-dichlorophenoxy acetic acid (2,4-D); indole-3-butyric acid (IBA); α-naphthaleneacetic acid (NAA).

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Five interspecific Cuphea hybrids were examined for isozyme banding patterns. In three of the five hybrids (C. viscosissima × C. lutea, C. ignea × C. angustifolia, and C. lanceolata × C. viscosissima), F1 plants could be distinguished from either parental species. Phosphoglucomutase and 6-phosphogluconic dehydrogenase enzyme stains produced distinct F1 band patterns for all three hybrids. Phosphoglucose isomerase and shikimate dehydrogenase enzyme stains produced distinct F1 band patterns for C. viscosissima × C. lutea and C. lanceolata× C. viscosissima, respectively. For the C. lanceolata × C. viscosissima hybrid. the banding patterns were used to identify 32 selfs among 161 putative F1 plants.

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Vernonia galamensis is a potential new crop for production of epoxidized oil with many industrial applications. This plant is native to equatorial Africa, and not adapted for culture in temperate zones since it requires a short daylength to initiate flowering and subsequent seed development. One collection of V. galamensis ssp. galamensis var. petitiana, flowered freely and produced seeds during long-day conditions throughout the United States. This variety lacks important plant characters for successful commercialization. The favorable genetic recombination of day-neutral response with more desirable plant growth characteristics, desirable seed oil and fatty acid content from other accessions of V. galamensis has been accomplished in hybrids and segregating populations, and selections are being widely evaluated throughout the U.S..

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Abstract

Single plant selections from a diverse guayule (Parthenium argentatum Gray) breeding population were evaluated for rubber and resin concentration, rubber and resin yield, and 12 growth characteristics. Thirty-seven superior selections (≈9% of the total of 421 single plant selections) exhibit combinations of satisfactory biomass production, high rubber yield, and strong regeneration and survival after harvesting by clipping the branches at a height of 0.10 m. Rubber concentration (%) was not highly correlated with the 12 plant characteristics measured. In contrast, rubber yield (g/plant) was highly correlated with plant dry weight and other plant characters related to biomass production. Twelve of the 37 superior selections had yields >125 g of rubber per plant, and the rubber concentration of seven of these 12 plants exceeded the mean (7.1%) of the 37 superior selections. Selection for high rubber concentration and yield with strong top regrowth after clipping appears to be feasible, and should expedite the development of a multiple harvesting system and rapid commercialization of guayule as a new domestic source of natural rubber.

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