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Random amplified polymorphic DNA (RAPD) markers were analyzed in parents and progeny of four sweetpotato crosses. An average of 69 primers were tested and 23.5% produced well resolved polymorphic banding patterns. Each polymorphic primer had an average of 1.9 polymorphic bands resulting in 0.45 polymorphic fragments per primer tested. Phenotypic segregation ratios of 88% of polymorphic fragments fit those expected for hexaploid Mendelian inheritance. Numbers of linked polymorphic fragments and numbers of linkage groups were 13 and 5 for Cross A, 0 and 0 for Cross B, 23 and 3 for Cross C and 16 and 6 for Cross D. Those results indicated that RAPD markers have potential for a genetic linkage map in sweetpotato; however, many primers must be screened.

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The effects of high concentrations of Cl-, K+, Mg2+, and Ca2+ of the simulated waste water on the growth of turfgrass species and partitioning of these mineral element concentrations in the turfgrass-soil system have been studied. This is a two year project and the waste treatment was started in the first week of October 1993. The waste water contains 17.89 mM of K+, 97.5 mM of Ca2+, 78.1 mM of Mg2+, and 389.17 mM of Cl-. Kentucky bluegrass, perennial ryegrass, tall fescue, bermudagrass, and zoysiagrass have been irrigated with 1/5, 1/10, and 1/20 times concentration of the waste water and mowed weekly at 5 cm high. The preliminary results showed that there was no detectable growth inhibition of turfgrass by the three waste water concentrations. Waste water irrigation significantly increased the uptake of the mineral elements by the turfgrass. Significant reduction of the mineral element concentrations in the leach by the turfgrass system only found under the conditions of low concentration waste irrigation. However, the seasonal growth pattern of the turfgrass species may have significant influence on the partitioning of the element concentrations in the turfgrass-soil system and their concentrations in the leach. This prediction will be detected by the future studies.

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Intensive breeding activities of tropical orchids have given rise to many hybrids, among which genetic relationships are difficult to evaluate due to free interbreeding of different species in the same genus or even from different genera, the use of hybrids for further breeding, use of abbreviated or trade names and sometimes intentional non-disclosure of parentage for commercial considerations. We have subjected 43 popular commercial Dendrobium hybrids to fluorescence amplified length polymorphism (AFLP) analysis and their genetic relationship was estimated. The hybrids bearing flowers of similar shapes and colors were clustered into five groups. Each hybrid tested had a distinct AFLP fingerprint profile except the tissue culture mutants. Sibling hybrids were closely clustered (with genetic distance <0.09) followed by those sharing one parent. These results suggest that AFLP fingerprint profiling gives accurate and objective estimation of genetic relationship of the Dendrobium hybrids tested. Our study also found that the AFLP fingerprint profiles were uniform in different parts of tested plants, stable among individuals in vegetatively propagated populations throughout different growth periods. We conclude that AFLP fingerprint profiling has the potential to be an integral part of current new plant varieties protection sytems.

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RAPD marker analyses were completed on parents and progeny of two sweetpotato [Ipomoea batatas (L.) Lam.] crosses to determine the feasibility of genetic linkage map construction. A total of 100 primers was tested and 96 produced amplified genomic DNA fragments. The average number of polymorphisms per primer was 0.69. A total of 134 polyphorphic markers was observed and 74 (60%) segregated 1 band present : 1 band absent as needed for use in genetic linkage mapping of polyploids. The 60% of RAPD markers that segregated 1:1 shows that genetic linkage mapping of the hexaploid sweetpotato by RAPD marker analysis is feasible. Linkage was determined for all markers that segregated 1:1 and five pairs of linked markers were found. These were the first linked molecular markers found in sweetpotato and they show that construction of a genetic linkage map is feasible. A genetic linkage map will be a valuable tool to assist in genetic improvements.

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Heterotrophic bacteria present in recycled greenhouse irrigation water (RIW) were characterized and then evaluated for their effect on Pythium aphanidermatum, P. cryptoirregulare, and P. irregulare. Nutrient agar (NA) and R2A agar were used to isolate copiotrophic and oligotrophic bacteria. Bacterial isolates recovered from RIW were categorized according to whether they inhibited Pythium growth, attached to hyphae, or enhanced Pythium growth in the three Pythium species used. Three bacterial isolates were selected to determine whether their in vitro interactions with Pythium aphanidermatum, the most pathogenic of the three species used, influenced disease development in the greenhouse. An isolate of Sphingobium sp. that inhibited Pythium, Pseudomonas sp. that attached to hyphae, and Cupriavidus sp. that enhanced the growth of P. aphanidermatum in vitro were used in greenhouse experiments to examine their effects on disease development in geranium (Pelargonium ×hortorum ‘White Orbit’) grown in pasteurized potting mix in ebb and flood irrigation systems. Disease progress curves evaluating the effect of each bacterium indicate that they did not suppress or enhance disease development (P = 0.05). Thus, the effects that the bacterial isolates had in vitro differed from their effects under greenhouse conditions.

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Parents and progeny of four biparental crosses were analyzed for RAPD marker segregation. A range of 57 to 122 primers were tested in each cross, with an average of 82. Average polymorphic primers and band numbers were 22 and 53, respectively. Of the 212 polymorphic bands, phenotypic segregation ratios were as follows: 133 fitted 1 dominant: 1 recessive, 58 fitted 3:1, 11 fitted ratios 4:1 to 19:1 and 10 were distorted. The 1:1 and 3:1 ratios were expected for either diploid or hexaploid segregation, and the 4:1 to 19:1 are exclusive to hexploid. A total of 14 pairs of markers were linked at map distances ranging from 2.1 to 36.5 cM. One common pair of linked markers was found in two separate crosses.

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Increasing environmental concerns and legislation in many states and in other countries require that we take a more comprehensive sustainable “best management” approach to production techniques in nursery and greenhouse operations. This is particularly important because these production facilities are typically intense users of resources that are applied to relatively small land areas. We have developed an online knowledge center to facilitate the implementation of more sustainable practices within the nursery and greenhouse industry. A web-based knowledge center provides the most cost-effective mechanism for information delivery, as our potential audiences are extremely diverse and widespread. We currently have a registered user database of over 450 educators, growers, and industry professionals, and undergraduate and graduate students. A gateway website provides an overview of the issues and the goals of the project. The associated knowledge center currently has 25 in-depth learning modules, designed in a Moodle learning management framework. These learning modules are designed to actively engage learners in topics on substrate, irrigation, surface water, and nutrient and crop health management, which are integral to formulating farm-specific strategies for more sustainable water and nutrient management practices. Additional modules provide assessment and implementation tools for irrigation audits, irrigation methods and technologies, and water and nutrient management planning. The instructional design of the learning modules was paramount because there can be multiple strategies to improve site-specific production practices, which often require an integration of knowledge from engineering, plant science, and plant pathology disciplines. The assessment and review of current practices, and the decision to change a practice, are often not linear, nor simple. All modules were designed with this process in mind, and include numerous resources [pictures, diagrams, case studies, and assessment tools (e.g., spreadsheets and example calculations)] to enable the learner to fully understand all of the options available and to think critically about his/her decisions. Sixteen of the modules were used to teach an intensive 400-level “Principles of Water and Nutrient Management” course at the University of Maryland during Spring 2008 and 2009. The water and nutrient management planning module also supports the nursery and greenhouse Farmer Training Certification program in Maryland. The Maryland Department of Agriculture provides continuing education credits for all consultants and growers who register and complete any module in the knowledge center. Although these learning resources were developed by faculty in the eastern region of the United States, much of the information is applicable to more widespread audiences.

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