In the olive (Olea europaea L.), inflorescence and flower differentiation occur in the early spring following a period of winter chilling and dormancy of the potentially reproductive buds. We examined the size, structure, and starch content of these buds during winter rest in the field and during forcing under standard growth-chamber conditions. Basic bud structure and dimensions remained unchanged during the rest period, but starch content increased in the bud's central axis. When cuttings were forced in the growth chamber, the buds followed a morphogenetic pattern similar to that observed in the field, but the sequence of developmental events could be timed more precisely. The first changes observed were the onset of axis growth and the differentiation of axillary primordia within 3 days of transfer to the growth chamber. This was followed by the initiation of new nodes, and, at 15 to 18 days, by the first signs of floral differentiation in the terminal and axillary bud apical meristems. Bud growth and differentiation were accompanied by a decrease in starch content.
Plants of Magnolia dealbata were regenerated from zygotic embryos through somatic embryogenesis and direct organogenesis. Medium and incubation conditions were determinating factors for the development of morphogenetic responses. Photoperiodic exposure was a limiting factor in the general development of the explants, and incubation in darkness allowed their development. The highest formation of shoots per responding explant were obtained on woody plant (WP) medium supplemented with 13.3 μM or 22.2 μM 6-benzylaminopurine (BA) in combination with 2.26 μM or in absence of 2,4-dichlorophenoxyacetic acid (2,4-D) from which 2.5 shoots per explant were induced. Subcultures on WP medium, supplemented with polyvinylpyrrolidone (PUP) 40,000 1 g·L–1) avoided necrosis of explants. Somatic embryos were formed in 85% of explants cultivated on WP medium with 2,4-D (2.3 μM or 4.5 μM); 20% induced indirect embryogenesis and 65% formed direct somatic embryogenesis. The plants were transferred to soil to acclimatize under greenhouse conditions, achieving 90% survival. Somatic embryo conversion to plantlets was obtained with subculture on WP basal medium without growth regulators. In vitro culture can play a key role in the propagation and conservation of this endangered species.
Amaranthus dubius is a common weed in sweetpotato production throughout the Caribbean Basin. A field study was conducted in the Agricultural Experiment Station at Juana Diaz, P.R., during 1998 to determine the effect of A. dubius interference in sweetpotato production under tropical conditions. Interference was evaluated by using a randomized complete-block design with four replications. Plots were four 6.1-m rows divided into two sections for yield and growth determinations. Intraspecific and interspecific interference was measured for both species. A. dubius was grown at 15 and 30 plants per meter of row. Plant dry weight and leaf area were determined at 3, 6, 9, 12, 15, and 18 weeks after planting (WAP). Sweetpotato yield was determined at 29 WAP. A. dubius growing alone reached a maximum leaf area index (LAI) of 8.5 at 12 WAP. Sweetpotato, however, did not attain maximum LAI. When grown with A. dubius, sweetpotato biomass was reduced at 15 WAP. This reduction was 62% and 66% for 15 and 30 A. dubius plants per meter of row, respectively. Sweetpotato yield in weed-free plots was equivalent to 9232 kg/ha. Yield reduction was 96% for 15 A. dubius per meter of row and 100% for 30 plants.
The discovery of bruchid resistance in wild beans and the demonstration that theArcelin protein is responsible for the resistance, provide an opportunity to develop resistant cultivars of common bean, Phaseolus vulgaris L. Arcelin expression is controlled by multiple alleles, which impart different levels of insect resistance. In field tests in Honduras and Brazil, backcross-derived lines with the Arl-1 allele were most resistant, especially to Mexican bean weevil. Seed mixtures of 0.80 Arl-1:0.20 susceptible and equal amounts of Arl-1,Arl-2, and Arl-3, and Arl-4 containing seeds showed resistanc elevels and seed yields similar to lines homogeneous for Arl-1. Breeding lines uniform for appearance and agronomic performance, but heterogenous for resistance genes are being tested as potential new dry bean cultivars having stable insect resistance.
One of the most important members of the Potyviridae is Zucchini yellow mosaic virus (ZYMV). It affects watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] as well as other cucurbits in most parts of the world. Although several genotypes have been reported as having resistance to ZYMV, differential responses to ZYMV strains are known to occur. Using a Puerto Rico strain of ZYMV (ZYMV-PR, GenBank accession number MN422959), we tested the response of 11 genotypes [PIs from the U.S. Department of Agriculture (USDA) National Genetic Resources Program] previously reported as having resistance to this virus. In two greenhouse trials, the first three leaves of seedlings of each genotype were mechanically inoculated with ZYMV-PR. An enzyme-linked immunosorbent assay (ELISA) was done on each seedling’s fourth leaf and symptom severity was rated on the first, third, fifth, and seventh leaves. There were significant genotype × trial interactions for most variables, but some genotypes performed consistently in both trials. All seedlings of PI 537277 tested negative for ELISA (absorbance < 0.200) across both trials. PI 537277, PI 595200, PI 595201, and PI 595203 were generally among the accessions with the lowest symptom severity scores. Overall, symptom severity correlated poorly with ELISA readings. But all plants of PI 537277, and most plants of PI 595201 and PI 595203, had low ELISA readings and low severity scores. Despite having low severity scores, PI 595200 was among the genotypes with the highest ELISA readings in trial 2. For the plant breeder, the most useful genotypes are those that exhibit reduced severity as well as low ELISA. PI 537277, PI 595201, and PI 595203 met those criteria in this study. Of these three accessions, PI 595203 would be the most useful in a breeding program because it has shown resistance to the Puerto Rico, Florida, and China strains of ZYMV.
poinsettia with Euphorbia cornastra , a species native to Mexico. This novel cultivar was named Eckespoint ‘Dulce Rosa’. The bracts of ‘Dulce Rosa’ have a unique florescent pink color never previously seen in poinsettia; furthermore, through shading
Abstract
During the past two decades, Europe has seen a marked increase in acreage of vegetables and flowers grown under plastic. The increase in production is most pronounced in the Mediterranean countries, where increased light intensity and favorable winter temperatures made culture under plastic without fossil-fueled heating possible. The migration of the greenhouse industry southward in Europe reflects: a) prohibitive cost of fossil fuels; b) development of simple technologies suitable for small and poorly trained growers; c) decreased investment in structures per square meter and per unit of product produced.
Nitrogen and potassium changes in poinsettia `Supjibi Red' were evaluated at four stages: vegetative growth, inductive stage, bract development and flowering. Nitrogen doses were 100, 200, 300, 400, and 500 mg·L-1 and those of potassium were: 175, 250, 325, and 400 mg·L-1, which were applied constantly with irrigation. Plants were grown in 7-inch pots with tezontle as the substrate. A completly random experimental design with nine treatments and 10 replicates was used. Short photoperiod was applied from 61 days after transplant, covering plants for 14 hours from 7 pm on. Samples for nitrogen and potassium evaluations were taken from recently grown-up leaves at 25, 50, 75, 100 and 125 days after transplant. Nitrogen absorption increased up to 75 days after transplant; treatments with 400 and 500 mg·L-1 of nitrogen induced the highest foliar levels 2.44% and 2.6%, respectively. In the following sampling dates, nitrogen decreased for all treatments. Potassium content decreased as plants developed; highest levels were obtained 25 days after transplant. The 325 and 400 mg·L-1
K treatments induced the highest concentrations in leaves 7.04% and 7.02%, respectively. Thus, it is confirmed that nitrogen is required throughout vegetative growth, and potassium just in the initial stage of vegetative growth.
Random amplified polymorphic DNA (RAPD) analysis was performed on the main Mediterranean cultivars of olive (Olea europaea L.) from the Germplasm Bank of the Centro de Investigación y Formación Agraria “Alameda del Obispo” in Cordoba, Spain. One hundred and ninety reproducible amplification fragments were identified using 46 random primers followed by agarose gel electrophoresis. Some 63.2% of the amplification products were polymorphic, with an average of 2.6 RAPD markers obtained for each primer. The combination of polymorphic markers resulted in 244 banding patterns. The high degree of polymorphism detected made identification of all the cultivars (51) possible by combining the RAPD banding patterns of just only four primers: OPA-01, OPK-08, OPX-01, and OPX-03. Cultivar-specific RAPD markers and banding patterns were also found. A dendrogram based on unweighted pair-group method cluster analysis was constructed using a similarity matrix derived from the RAPD amplification products generated by the 46 primers. Three major groups of cultivars could be distinguished by RAPD analysis: 1) cultivars from east and northeast Spain, 2) Turkish, Syrian, and Tunisian cultivars, and 3) the majority of common olive cultivars in Spain. The dendrogram thus showed a good correlation between the banding patterns of olive cultivars and their geographic origin. A higher level of polymorphism was observed when polyacrylamide gel electrophoresis was used to separate the amplification products. Thus, adequate use of RAPD technology offers a valuable tool to distinguish between olive cultivars.