<p><P>We found that a dwarf tomato (<P>Another approach to understanding the mode of action of BR is to isolate BR-regulated genes and determine the mechanism of gene regulation by BR. We exploited the </HTML><P>

<p>Reactive oxygen species (ROS) are known to act as both signaling molecules and direct antimicrobial agents in plant defense against pathogens. Many plant pathogens have the ability to synthesize mannitol, a potent ROS quencher, and there is growing evidence that at least some phytopathogenic fungi use mannitol to suppress ROS mediated defenses. Here we show that mannitol production and secretion in the phytopathogenic fungus, Alternaria alternata is induced in the presence of host plant extracts. Additionally we demonstrate that the catabolic enzyme mannitol dehydrogenase (MTD) is induced in a non-mannitol-producing plant in response to both fungal elicitor and specific inducers of plant defense responses. This indicates a mechanism whereby the plant can counteract fungal suppression of ROS-mediated defenses by catabolizing mannitol of fungal origin. To further clarify this interaction, tobacco plants were transformed with celery mannitol dehydrogenase cDNA under a constitutive promoter, resulting in an enzymatically active MTD protein. This constitutive MTD expression conferred enhanced resistance to A. alternata, and this resistance did not correlate with expression of PR1a, a protein often used as an indicator of systemic acquired resistance. Constitutive Mtd expression did not enhance tolerance to two non-mannitol secreting pathogens, the fungal pathogen Cercospora nicotianae and the bacterial pathogen Pseudomonas syringae pv. tabaci. These results are consistent with the hypothesis that MTD plays a role in plant resistance to mannitol secreting fungal pathogens by catabolizing mannitol of fungal origin. <P>

<p>Root-knot nematodesrepresent a significant problem in sweetpotato, Ipomoea batatas (L.) Lam., causing reduction in yield and quality of the storageroots. The following experiments were conducted to: (1) test the use of an alternative screening method for root-knotnematode resistance; (2) assess the effect of different root-knot nematode spp. on sweetpotato cultivars; and (3) develop a setof sweetpotato differential host genotypes for Meloidogyne species. In the first study, five sweetpotato cultivars were selectedand evaluated for resistance to Meloidogyne incognita race 3, M. arenaria race 2, and M. javanica. Screening was conductedin 400-cm3 square pots and 150-cm3 Conetainers. Nematode infection was measured as the percentage of root systemgalled, percentage of root system necrosis, and the number of nematode eggs per gram of root tissue. Means of dependentvariables were not significantly different between the two container types. Conetainers were the more efficient pot type,because they required less space and permitted an easier assessment of nematode infection. Resistance responses differeddepending on the nematode species and sweetpotato cultivar. All cultivars were resistant to M. arenaria race 2, while'Hernandez', 'Excel' and 'Jewel' were also resistant to M. incognita race 3 and M. javanica. In the second study, twenty-sevensweetpotato genotypes were evaluated for their resistance to North Carolina root-knot nematode populations: M. arenaria(races 1 and 2), M. incognita (races 1, 2, 3, and 4), and M. javanica. Sweetpotato plants were evaluated in 150-cm3Conetainers. Nematode infection was assessed as the number of egg masses per root system. Different sweetpotatogenotypes were hosts for different Meloidogyne populations. Five out of the 27 genotypes ('Beauregard', L86-33, PDM P6,'Porto Rico', and 'Pelican Processor') were selected as sweetpotato differential hosts because of their resistance reaction to theMeloidogyne spp. These genotypes were tested against twelve M. incognita populations belonging to the four standardizedhost races collected from different geographical locations worldwide. Virulence of the M. incognita populations varieddepending on the sweetpotato genotype and did not always correspond to host race as classified by the North CarolinaDifferential Host Test. 'Beauregard', L86-33, and PDM P6 were hosts for the 12 nematode populations, but differences in theaggressiveness of the populations were observed among the three sweetpotato genotypes. 'Porto Rico' and 'Pelican Processor'had differential host status to the M. incognita populations irrespective of their host race. These results suggest that: 1) multiplefactors might be responsible for conferring virulence in the nematodes; 2) multiple genes could be involved in the resistance toroot-knot nematodes in sweetpotato; and 3) the final outcome of root-knot nematode resistance in sweetpotato would dependon the specific interaction of these two factors. Further, these results suggest that Meloidogyne populations should be testedagainst sweetpotato differential hosts in order to determine the pathotypes affecting sweetpotato. This would help tostandardize the evaluation of resistance to root-knot nematodes in sweetpotato breeding programs, and possibly identifyreliable sources of resistance to numerous pathotypes of Meloidogyne spp. <P>

<p>NEPPL, GRANT P. Efficient trialing methods for watermelon (Citrullus lanatus (Thumb.) Matsum. & Nakai). (Under the direction of Dr. Todd C. Wehner) Researchers interested in evaluating watermelon (Citrullus lanatus (Thunb.) Matsum. & Nakai) cultivars for yield use multiple-row plots to simulate the monoculture system growers use, or single-row plots to save on land, labor, and seeds. We were interested in whether there is a significant interaction of border with center row when diverse cultivars are planted in adjacent rows. Charleston Gray, Crimson Sweet, and Sugar Baby were chosen to represent long, medium, and short vined cultivars, respectively. Cultivars were planted in three-row plots with all nine combinations of the three represented in border and center rows. Each cultivar combination of center row and border rows represented one treatment. The experiment was a randomized complete block with nine plot treatments, two locations (Kinston, Clinton), and three replications. Vine length was measured during the season, and fruit were graded (marketable and cull), counted and weighed at four harvests. Results showed that Charleston Gray had the longest vines, followed by Crimson Sweet and Sugar Baby. In the analysis of variance, the largest effects (F ratio size) on yield were from cultivar, location, and the interaction of the two. The smallest effects were due to the interaction of center with border row, although center by border interactions were significant (5% level) in some cases. Therefore, researchers interested in running trials with many cultivars and small seed quantities can obtain good data using single-row plots. However, there is a small (but significant) interaction of center with border in some cases, so testing at the final stage should be with trials having multiple-row plots or grouping cultivars by vine length. Cultivars having extreme plant types (dwarf vines for example) should be tested in separate trials. One of the most expensive stages of breeding is field testing. This encourages breeders and researchers to make efficient use of limited land, labor and seed in order to maximize information obtained while minimizing the costs of trialing. We were interested in whether smaller single-row plots could be used that would effectively be able to achieve and predict yields obtained from plots with larger dimensions when diverse cultivars were evaluated. The 13 cultivars Allsweet, Fiesta, Regency, Starbrite, Sultan, Florida Favorite, Charleston Gray, Hopi Red Flesh, Crimson Sweet, Jubilee, Navajo Sweet, New Hampshire Midget, and Sugar Baby were used to represent a wide range in yield. Cultivars were planted in single-row plots of three different plot lengths (7.3 m, 3.7 m, and 2.4 m) with all cultivars represented in each plot size. Each combination of cultivar and plot size represented one treatment. The experiment was a randomized complete block with 39 plot treatments, two locations (Kinston and Clinton) and three replications. Fruit were graded (marketable and cull), counted and weighed at five harvests. Analysis of variance indicated the largest effects (F ratio size) on plot yields were from location, plot size and cultivar. The smallest effects were due to the interactions of location with plot size, and cultivar by location by plot size. A location by cultivar interaction was also present, but F ratios were small indicating a small effect. Yields from 7.3 m and 3.7 m plots were consistently no different from each other. Regression analysis of 2.4 m and 3.7 m plots in prediction of 7.3 m plot yields showed 3.7 m plots to have higher R2 (0.90), lower mean square error, lower standard deviations and a lower coefficient of variation than was found for 2.4 m plots. Therefore, researchers interested in maximizing information obtained while minimizing costs in trials with many cultivars can obtain data representative of large 7.3 m plots using 3.7 m plots. However, alleys separating 7.3 m and 3.7 m plots required a yield correction to compensate for the extra growing space allotted to these plots.<P>

<p>ABSTRACTSweetpotato virus disease (SPVD) is a devastating disease due to the dual infection and synergistic interaction of sweetpotato feathery mottle potyvirus (SPFMV) and sweetpotato chlorotic stunt crinivirus (SPCSV). This study was conducted to: 1) determine the inheritance of resistance to SPVD in sweetpotato; 2) estimate the nature of genetic variance; and 3) evaluate methods for screening large populations for resistance to SPVD. The genetic basis of resistance to SPVD was investigated in three studies. The first genetic study consisted of a randomized block design at two sites in Uganda, during 1998-2000, using 45 full-sib diallel (half) families of 10 parental clones varying in SPVD resistance. The second study also conducted in Uganda, examined progeny from 15 promising sweetpotato diallel families (1352 genotypes), while the third examined two of the most promising families (294 genotypes) from the same diallel at the International Potato Center (CIP), Lima, Peru. Genetic component analysis of the 45 diallel families showed significant general combining ability (GCA) and specific combining ability (SCA) effects for resistance to SPVD. GCA to SCA variance components ratios were large (0.51-0.87) and resistant parents exhibited high GCA, indicating that additive gene effects were predominant in the inheritance of resistance to SPVD and recovery. Use of a suitable sweetpotato genotype for increase of SPVD inoculum and modified cleft graft inoculation led to rapid progress in screening large populations for SPVD resistance. The distribution of SPVD scores in the promising families was skewed toward highly susceptible categories, in Uganda and Peru. Inoculation of the two families at CIP with either SPCSV or SPFMV, and Mendelian segregation analysis for resistant versus susceptible categories for the two viruses suggest that resistance to SPCSV and SPFMV is conditioned by two, separate recessive genes. In the proposed model for inheritance, the two genes are unlinked and they are inherited in a hexasomic or tetradisomic manner. Based on amplified fragment length polymorphism (AFLP) and quantitative trait (QTL) loci analyses we identified two AFLP unlinked markers associated with loci conferring resistance to SPCSV and SPFMV in these progenies. We propose spcsv1 and spfmv1 to be the names of the genes. <P>

<p>The purpose of this research has been to determine the nature of strawberry fruit resistance to anthracnose fruit rot. Production in the United States and North Carolina is heavily dependent upon two cultivars, Chandler and Camarosa. Both cultivars are susceptible to anthracnose fruit rot (AFR), caused by the imperfect fungus . Results from this research will be used to further our understanding of the strawberry- system and to control AFR through breeding strategies or cultural practices. Components of resistance in strawberry to AFR were studied under field and controlled environment conditions; five strawberry genotypes were inoculated with conidia of under field conditions and seven genotypes were inoculated with either five inoculum concentrations or three isolates of in growth chambers. Strawberry genotypes responded differently to in the field and in a controlled environment. Components of resistance to AFR included rate-limiting resistance, reduced percent lesion, reduced probability of lesion formation due to fruit age and genotype, and plant canopy architecture. Rates of disease progress were different among genotypes, inoculum concentrations, isolates, and the genotype x isolate interaction. Susceptible genotypes and virulent isolates had faster rates of disease progress. Differences were observed among genotypes for yield, percent by weight, and number of berries with AFR. Plant canopy architecture influenced the hours of fruit wetness and the yield of berries with AFR; a loose open canopy had fewer hours. Young and old fruit were less susceptible to AFR than fruit of median age.<P>

<p><p>ABSTRACT</p><p>JUDGE, CAREN ANN. Predicting Herbicide Dissipation in Container Nursery Crop Production ? A Method for Improving Herbicide Performance and Reducing Hand Weeding. (Under the direction of Joseph C. Neal.)</p>In southeastern U.S. container nursery crop production, frequent applications of preemergence herbicides supplemented by hand weeding are relied upon for broad-spectrum weed control during the growing season. Experiments were conducted to determine the aqueous concentrations required for weed control, to relate this to surface-applied rates, and to determine trifluralin dissipation in container substrates. Petri dish experiments were conducted to determine the aqueous concentration required for control of common nursery weeds including ) were also included as potential bioassay species. Herbicides evaluated were isoxaben, oryzalin, and trifluralin. The relative response of weeds to aqueous concentrations was similar to that observed in efficacy trials. Concentrations of Gallery required for 80% inhibition (I80) were 1.3 and 0.4 for eclipta, 0.4 and 3.9 for hairy bittercress, 0.5 and 0.3 for spotted spurge, 1.5 and 0.3 for large crabgrass, and 1.6 and 0.1 ug ai/mL for lettuce shoot and root, respectively. I80 values for Surflan were 9.8 and 0.4 for eclipta, 5.9 and 1.6 for hairy bittercress, 1.2 and 1.4 for spotted spurge, 1.2 and 0.1 for large crabgrass, and 17.4 and 0.6 ug ai/mL for lettuce shoot and root, respectively. I80 values for Treflan were 73.8 and 3.4 for eclipta, 17.3 and 7.4 for hairy bittercress, 6.2 and 9.2 for spotted spurge, 1.1 and 0.5 for large crabgrass, 7.2 and 8.4 for lettuce, and 0.9 and 1.2 ug ai/mL for perennial ryegrass shoot and root, respectively. Oat I80 values were well beyond the concentration range tested and extrapolated values were not realistic for Gallery and Surflan. However, Treflan I80 values were 0.5 and 2.1 ug ai/mL for shoot and root inhibition, respectively. Treflan dose-response experiments were conducted in the greenhouse and outdoors to determine the surface-applied rates necessary for preemergence control of large crabgrass and perennial ryegrass. The rates of Treflan in the greenhouse were 0.07 to 2.24 kg ai/ha and outdoors were 0.14 to 4.48 kg ai/ha. Percent control was estimated 3 and 6 weeks after treatment (WAT); shoot fresh weights were measured 6 WAT. In the greenhouse, approximately 1.0 kg ai/ha was necessary to control both species. Outdoors, less than 2.0 kg ai/ha was needed for control of both species 3 WAT. By 6 WAT, 2.6 and 3.4 kg ai/ha were required to control perennial ryegrass and large crabgrass, respectively. Additionally, an experiment was conducted at two locations to determine the dissipation of Preen (trifluralin) in a pine bark plus sand potting substrate and to compare grass inhibition over time. Preen was surface applied at 4.5 kg ai/ha, then large crabgrass and perennial ryegrass were seeded 0, 1, 2, 4, 6 and 8 WAT. Shoot and root growth were measured two weeks after seeding. Substrate samples taken 0, 1 and 3 days after treatment and 1, 2, 4, 6 and 8 WAT from the top 2 cm of the potting substrate were extracted and trifluralin content quantified by gas chromatographic techniques. In the March to May test, 50% weed growth occurred approximately 7 WAT, at which time weeds emerged and flourished. However, in the May to July test, trifluralin dissipated more rapidly. Growth (50%) occurred within 2 to 7 weeks after application, depending on species. These data suggest that trifluralin residues in the surface of the potting substrate decrease rapidly after application and slowly thereafter reaching what may be considered critically low levels approximately 4 to 6 weeks after application. These results suggest that for trifluralin, the common reapplication interval of 8 to 10 weeks in the southeastern U.S. may need to be shortened to 4 to 6 weeks. <P>

<p>Seeds of southern seaoats (.<P>

Thesis (M.Phil.) - University of Queensland, 2003. / Includes bibliography.

No description available.