Sturgeon Bay Research Articles

An endemic plant and the plant-insect visitor network of a dune ecosystem

Network theory increasingly is used to quantify and evaluate mutualistic interactions, such as those among plants and their flower-visiting insects or pollinators. Some plant species have been shown to be important in community structure using network metrics; however, the roles of plant taxa, particularly rare species, are not well understood. Pitcher's thistle (Cirsium pitcheri), a threatened endemic of Great Lakes shorelines, flowers late-June to early-August, when other floral resources may be less abundant or unavailable. We performed 10 min insect visitor observations on all insect pollinated plants in 44–10 m by 10 m plots at Sturgeon Bay, northern lower MI, USA, during C. pitcheri flowering and recorded plant species, number of open flowers, species of insect visiting, and number of visits by insects. Pitcher's thistle received 18.2% of all 600 recorded visits, 61.1% more than the next most visited plant. Pitcher's thistle also received visits from 22 of the 59 different insect species in the network, twice as many as the next most visited plant species. Species-level network analysis metrics showed that Pitcher's thistle was most generalized, with greatest species strength, betweenness, and connectance scores of any other plant taxon, demonstrating network topological importance. Pitcher's thistle received significantly more insect visits relative to its abundance that did any other plant species. Therefore, conservation of C. pitcheri and of other rare taxa, particularly in xeric and low diversity systems, can be significant beyond species-level management and may extend to conservation of the plant-insect community.

Improved estimates of phytoplankton community composition based on in situ spectral fluorescence: use of ordination and field-derived norm spectra for the bbe FluoroProbe

The use of spectral fluorometers for assessing phytoplankton concentrations and taxonomic composition in aquatic environments is increasingly common. However, the accuracy of such assessments suffers because the necessary norm spectra (spectral fingerprints) are derived using selected taxa and laboratory conditions that may not adequately represent the taxa and environmental conditions in the study area. Ordination analysis of raw fluorescence data has been proposed as a better means of interpreting spectral fluorescence data. We applied nonmetric multidimensional scaling and cluster analysis to raw in situ fluorescence data from Sturgeon Bay, a small, mesotrophic embayment of Georgian Bay (Lake Huron) to obtain system-specific norm spectra for the bbe FluoroProbe. The revised spectra gave improved estimates of phytoplankton taxonomy (root mean square error of 10% versus 14%) and of dissolved organic carbon and chlorophyll a concentrations. While promising, this method should be further explored in other systems with different and (or) weaker gradients in phytoplankton biomass and taxonomic composition.

In vitro technology at the US Potato Genebank

The US Potato Genebank in Sturgeon Bay, Wisconsin, is the national germplasm collection for the world’s most important vegetable crop. It contains about 6,000 accessions of 100 species of tuber-bearing relatives of Solanum tuberosum. The potato of commerce is a clonal crop susceptible to many systemic pathogens, so the genebank routinely uses in vitro clonal maintenance and distribution for named cultivars. In vitro management is also the tool of choice for various breeding and genetic stocks of interest to breeders and researchers. Long-term backup cryopreservation of clones is done at the base collection in Fort Collins, Colorado. In vitro techniques also play an important role in virus elimination from clones. Recently, in vitro propagation has expanded to the temporary safekeeping of meristem propagules in antimicrobial medium during plant collecting expeditions in the southwest USA. The genebank’s mission includes promoting technology that supports expanded use of the germplasm, in particular, finding ways to overcome interspecific hybridization barriers. Thus, in vitro techniques such as pollen viability testing, ploidy manipulation, protoplast fusion, and embryo rescue have contributed technology for major advances in interspecific hybridization, utilization of noncommercial species, and introgression of genes from wild near-relatives. Finally, advancing in vitro technology holds promise as a tool for mass bioassay and selection of seeds, pollen, or somaclones for useful traits.

PCBs refocused: Correlation of PCB concentrations in Green Bay legacy sediments with adjacent lithophilic, invasive biota

Green Bay sediments exhibit a gradient of polychlorinated biphenyl (PCB) concentrations from the mouth of the Fox River to the northern end of the bay. This study explored whether the sediment concentration gradient was reflected along Green Bay's rocky (non-depositional) eastern coast in a suspension feeder, the invasive quagga mussel (Dreissena bugensis), as well as in the main predator on quagga mussels, the invasive round goby (Neogobius melanostomus). We performed congener-specific PCB analyses on quagga mussels and round gobies collected from ten sites along the east shore of Green Bay. PCB results were compared with sediment data. Regression analyses showed that mussel tissue PCB concentrations followed sediment PCB concentrations (F1,6=16.4, P=0.007) except at two sites near Sturgeon Bay where cleaner Lake Michigan water enters in tidal pulses. Round goby PCB concentrations also followed the sediment trends (F1,7=8.17, P=0.024). However, only a weak relationship between PCB concentrations in quagga mussel and round goby was found (P=0.085), even though the species are trophically linked. Here, ontogenetic and seasonal details of round goby diet strongly influenced PCB concentrations such that in areas adjacent to high sediment PCB concentrations, fish length dictated round goby's PCB concentration (F1,14=7.46, P=0.016). Overall, our findings indicate that these exotic benthos refocus PCBs in near-shore regions in a pattern similar to that observed in sediments. Our results also highlight the need to understand trophic details in order to track contaminant bioaccumulation accurately.

Age and growth of round gobies in Lake Michigan, with preliminary mortality estimation

The round goby (Neogobius melanostomus) is a prevalent invasive species throughout Lake Michigan, as well as other Laurentian Great Lakes, yet little information is available on spatial variation in round goby growth within one body of water. Age and growth of round goby at three areas of Lake Michigan were studied by otolith analysis from a sample of 659 specimens collected from 2008 to 2012. Total length (TL) ranged from 48 to 131mm for Sturgeon Bay, from 50 to 125mm for Waukegan, and from 54 to 129mm for Sleeping Bear Dunes. Ages ranged from 2 to 7years for Sturgeon Bay, from 2 to 5years for Waukegan, and from 2 to 6years for Sleeping Bear Dunes. Area-specific and sex-specific body–otolith relationships were used to back-calculate estimates of total length at age, which were fitted to von Bertalanffy models to estimate growth rates. For both sexes, round gobies at Sleeping Bear Dunes and Waukegan grew significantly faster than those at Sturgeon Bay. However, round goby growth did not significantly differ between Sleeping Bear Dunes and Waukegan for either sex. At all three areas of Lake Michigan, males grew significantly faster than females. Based on catch curve analysis, estimates of annual mortality rates ranged from 0.79 to 0.84. These relatively high mortality rates suggested that round gobies may be under predatory control in Lake Michigan.

Using Diets to Reveal Overlap and Egg Predation among Benthivorous Fishes in Lake Michigan

AbstractEcological stability in the Laurentian Great Lakes has been altered by nonindigenous species, such as the Round Goby Neogobius melanostomus and dreissenid mussels, and by declines in native amphipods Diporeia spp. We evaluated whether these changes could influence diet overlap between three benthivorous fishes (Slimy Sculpin Cottus cognatus, Deepwater Sculpin Myoxocephalus thompsonii, and Round Goby) and whether predation on eggs of native species was occurring. We examined diets of fish collected at depths of 69–128 m in Lake Michigan offshore of Frankfort and Muskegon, Michigan, and Two Rivers and Sturgeon Bay, Wisconsin, during January–May 2009 and 2010. Important prey (by dry weight proportion and by percent frequency of occurrence) for Slimy Sculpin were Mysis (0.34; 45%), Diporeia (0.16; 34%), and Limnocalanus macrurus (0.22; 68%); important prey for Deepwater Sculpin were Mysis (0.74; 92%) and Diporeia (0.16; 54%). Round Goby consumed mainly bivalves (i.e., dreissenids: 0.68; 95%) and Mysis (0.15; 37%). The two sculpin species consumed the eggs of Bloaters Coregonus hoyi (Slimy Sculpin: 0.04, 11%; Deepwater Sculpin: 0.02, 7%) and the eggs of Deepwater Sculpin (Slimy Sculpin: 0.03, 13%; Deepwater Sculpin: 0.05, 16%) during February–May at all sites. Round Goby also consumed eggs of these species but at lower levels (≤0.01; <1%). Diet overlap was identified between sculpin species at Frankfort and Sturgeon Bay, suggesting possible interspecific competition, but their diets did not overlap at Two Rivers; diet overlap was never observed between Round Goby and either sculpin species. Given that (1) diet overlap varied by site and (2) diet proportions varied spatially more than temporally, benthivores appear to be exhibiting localized responses to recent ecological changes. Overall, these results reveal that egg predation and interspecific competition could be important interactions to consider in future examinations of the population dynamics of these species or in ecosystem models that forecast how fisheries will respond to possible perturbations or management scenarios.

Parasites of BloaterCoregonus hoyi(Salmonidae) from Lake Michigan, U.S.A

In total, 158 bloaters Coregonus hoyi collected in September and October 2011 from 4 Lake Michigan, U.S.A., ports were examined for parasites. The ports included Waukegan (WK), Illinois; Port Washington (PW) and Sturgeon Bay (SB), Wisconsin; and Saugatuck (SG), Michigan. Parasites found in bloaters by port were cestodes Cyathocephalus truncatus (WK, PW, and SB) and Eubothrium salvelini (WK, PW, SB, and SG); the nematode Cystidicola farionis (WK, PW, SB, and SG); acanthocephalans Acanthocephalus dirus (WK and PW), Echinorhynchus salmonis (WK, PW, and SB), and Neoechinorhynchus tumidus (SB); and the copepod Salmincola corpulentus (WK and PW). Gravid individuals of all parasite species were found except for E. salvelini and A. dirus. Cystidicola farionis had the highest prevalence at each port, and the highest mean intensity and mean abundance at PW. The numbers of C. farionis at PW were significantly higher than those at WK and SB. Echinorhynchus salvelini had the highest mean intensities and mean abundances at WK, SB, and SG. The values for parasite species richness in bloaters were similar among ports. The total numbers of parasites were similar between WK and PW, but they were higher at these ports than at SB. The parasite faunas of bloaters were characterized by autogenic helminth species.

Resolution of optical gradients and pursuit of optical closure for Green Bay, Lake Michigan

Optical properties have fundamental importance to water quality, ecology, and remote sensing initiatives. Paired measurements of optically active constituents (OACs), and inherent optical properties (IOPs) and apparent optical properties (AOPs), were made in September 2010 across the optical gradients of Green Bay, extending from the Fox River to Sturgeon Bay (8 sites), and for three near-shore locations in the main basin of Lake Michigan. The array of laboratory and in situ measurements provided a robust characterization of the underwater and emergent light fields of these waters with respect to magnitudes and spectral features of the OACs, IOPs and AOPs. These measurements resolved the character and possible origins of the major gradients within the bay (5 to 10-fold differences) and the substantial differences between the bay and the main basin. The credibility of the characterizations was supported through closure analyses which demonstrated: (1) the approach to equivalence between various field and laboratory measurements, and (2) good matches of AOP observations by values predicted from measured IOPs using accepted radiative transfer expressions. The bay was demonstrated to be an optically complex case 2 system, with uncoupled variations along the spatial gradient(s) in OACs of phytoplankton biomass, colored dissolved organic material, and non-algal particulates. The documented spatial differences in optical properties rival those reported in much larger marine surveys. Radiative transfer expressions are used to predict changes in AOPs of the downwelling (underwater) attenuation coefficient and remote sensing signal in response to scenarios of changes in levels of OACs of potential ecological and management interest.

Acanthocephalan Parasites of Slimy Sculpin, Cottus cognatus, and Ninespine Stickleback, Pungitius pungitius, from Lake Michigan, U.S.A

In total, 288 slimy sculpins, Cottus cognatus, were collected in September 2003 from 6 Lake Michigan, U.S.A., ports, along with 220 ninespine sticklebacks, Pungitius pungitius, from 3 ports. The ports included Waukegan, Illinois; Port Washington (PW) and Sturgeon Bay (SB), Wisconsin; and Manistique (MS), Frankfort (FF), Ludington (LD), and Saugatuck, Michigan. Echinorhynchus salmonis infected sculpins from 6 ports, Acanthocephalus dirus infected sculpins from 4 ports, and Neoechinorhynchus pungitius infected sculpins from 3 ports. Echinorhynchus salmonis infected significantly more sculpins at PW and at FF than at MS and LD. There were several significant differences in the intensities and abundances of E. salmonis among ports. Acanthocephalus dirus significantly infected more sculpins and had significantly higher abundances at FF than at PW, MS, and LD. Echinorhynchus salmonis, A. dirus, and N. pungitius infected sticklebacks from SB, MS, and FF. Neoechinorhynchus pungitius significantly infected more sculpins and more sticklebacks, and it had significantly higher abundances at MS than at FF. Neoechinorhynchus pungitius was the most common acanthocephalan in C. cognatus and P. pungitius at MS. These acanthocephalan species infecting C. cognatus and P. pungitius corresponded in their occurrence to those organisms that serve as their intermediate hosts found in the stomachs of both fish species. Potential changes in the diet of C. cognatus played a role in significant differences found for E. salmonis and N. pungitius at MS. One of these acanthocephalan species was always the most numerous helminth species found in the digestive tracts of P. pungitius and C. cognatus from these Lake Michigan ports.

Interference Fit: A Novel Method for Strong Knotless Arthroscopic Fixation of Sutures to Bone

Background The present study examined the strength of fixation of a knotless anchor system that relies on trapping the suture between an interference fit screw and its bone tunnel, a method familiar to orthopaedic surgeons during anterior cruciate ligament reconstruction. Type of study In vitro biomechanical single-pull load to failure study of fixation achieved by interference fit screws in porcine bone. A standard suture anchor with eyelet was used as a control. Methods A single-pull to failure test was carried out on a Hounsfield H20K digital tensiometer (Tinius Olsen, Hersham, PA, USA). Two suture materials were compared [braided polyester (Ethibond; Ethicon Ltd, Edinburgh, UK) and a new suture (Fibrewire; Arthrex Inc., Naples, FL, USA) that has a high molecular weight polyethylene core]. Two interference fit screws were compared: one metal and the other plastic (PEEK; Parkus Medical, Sturgeon Bay, WI, USA). Results The average values were between 262 N and 584 N. The average failure value for a standard anchor was 206 N. Clinical Relevance Interference fit fixation provides an elegant strong knotless method for securing multiple sutures to a single point.

A short-term look at potential changes in Lake Michigan slimy sculpin diets

Diporeia hoyi and Mysis relicta are the most important prey items of slimy sculpins ( Cottus cognatus) in the Great Lakes. Slimy sculpins were collected from dreissenid-infested bottoms off seven Lake Michigan ports at depths of 27–73 m in fall 2003 to study their lake-wide diets. Relatively large dreissenid biomass occurred at depths of 37- and 46-m. Quagga mussels ( Dreissena bugnesis) composed at least 50% of dreissenid biomass at Manistique, Saugatuck, and Sturgeon Bay. Mysis accounted for 82% of the sculpin diet by dry weight at eastern Lake Michigan while Diporeia composed 54–69% of the diet at western Lake Michigan and dominated the diets of slimy sculpins at all sites deeper than 46 m. In northern Lake Michigan, this diet study in new sites showed that slimy sculpin consumed more prey with low energy contents, especially chironomids, than Mysis and Diporeia in shallow sites (depth <55 m). We recommend diet studies on sedentary benthic fishes to be conducted along perimeters of the Great Lakes to observe changes in their diets that may be impacted by changing benthic macroinvertebrate communities.

Geographic Relatedness and Predictability of Escherichia coli along a Peninsular Beach Complex of Lake Michigan

To determine more accurately the real-time concentration of fecal indicator bacteria (FIB) in beach water, predictive modeling has been applied in several locations around the Great Lakes to individual or small groups of similar beaches. Using 24 beaches in Door County, Wisconsin, we attempted to expand predictive models to multiple beaches of complex geography. We examined the importance of geographic location and independent variables and the consequential limitations for potential beach or beach group models. An analysis of Escherichia coli populations over 4 yr revealed a geographic gradient to the beaches, with mean E. coli concentrations decreasing with increasing distance from the city of Sturgeon Bay. Beaches grouped strongly by water type (lake, bay, Sturgeon Bay) and proximity to one another, followed by presence of a storm or creek outfall or amount of shoreline enclosure. Predictive models developed for beach groups commonly included wave height and cumulative 48-h rainfall but generally explained little E. coli variation (adj. R2=0.19-0.36). Generally low concentrations of E. coli at the beaches influenced the effectiveness of model results presumably because of low signal-to-noise ratios and the rarity of elevated concentrations. Our results highlight the importance of the sensitivity of regressors and the need for careful methods evaluation. Despite the attractiveness of predictive models as an alternative beach monitoring approach, it is likely that FIB fluctuations at some beaches defy simple prediction approaches. Regional, multi-beach, and individual beach predictive models should be explored alongside other techniques for improving monitoring reliability at Great Lakes beaches.

Total and methyl mercury accumulation in 1994–1995 Lake Michigan lake trout and forage fish

As part of the Lake Michigan Mass Balance Project, total and methyl mercury were determined for lake trout ( Salvelinus namaycush) and five forage fish species collected from Lake Michigan near Saugatuck, Michigan, and Port Washington, Sheboygan Reef, and Sturgeon Bay, Wisconsin, between 1994 and 1995. With a mean concentration of 179 ng/g wet wt., whole lake trout total mercury (Hg T) concentrations ranged between 27.6 and 348 ng/g wet wt. For combined sites, 1–4 yrs, 5–6 yrs, 7–11 yrs, and 12–15 yrs lake trout mean Hg T concentrations were 73.7, 130, 212, and 280 ng/g, respectively. Forage fish species alewife ( Alosa pseudoharengus), bloater ( Coregonus hoyi), slimy sculpin ( Cottus cognatus), deepwater sculpin ( Myoxocephalus thompsoni), and rainbow smelt ( Osmerus mordax) had mean Hg T concentrations of 63.8, 55.3, 36.7, 51.4, and 35.2 ng/g wet wt., respectively. With the exception of alewife, bloater, and slimy sculpin, all fish species contained approximately 100% methyl mercury (MeHg). Field bioaccumulation factors (BAF) were consistent with a Lake Michigan food chain that is more efficient at transferring MeHg to higher trophic levels than some inland lakes. This and other studies of lake trout from Lake Michigan document decreasing Hg T concentrations in lake trout from 1971 to 1985 and constant or increasing concentrations between 1985 and 2000. These observations were supported by a similar trend in Lake Michigan Hg sediment fluxes. To our knowledge, this is the most intense two year study of mercury in fish for any Great Lake or other large fresh water system and is one of the most complete studies of mercury cycling in the Lake Michigan food chain.

Depth Distribution Dynamics of the Sculpin Community in Lake Michigan

AbstractUsing data from our annual lakewide bottom trawl survey of Lake Michigan, we calculated the mean depths of capture for deepwater sculpin Myoxocephalus thompsonii and slimy sculpin Cottus cognatus for each combination of transect (Frankfort, Ludington, Saugatuck, and Manistique in Michigan, Waukegan in Illinois, and Port Washington and Sturgeon Bay in Wisconsin) and year (1973‐2005). The mean depth of capture of both sculpin species significantly decreased during the recovery phase of the deepwater sculpin population at four of the transects but did not significantly change for either species at the other three transects during this time. During the postrecovery phase of the deepwater sculpin population, the mean depth of capture of deepwater sculpins significantly increased at six of the seven transects, whereas that for slimy sculpins significantly increased at only four of the seven transects. The mean depth of capture of deepwater sculpins was most strongly correlated with that of slimy sculpins at Frankfort (r = 0.73); the correlation was weakest at Manistique (r = 0.00). Long‐term mean depths of capture (averaged over all years) for deepwater sculpins ranged from 90 to 108 m among the seven transects, whereas the long‐term mean depths of capture for slimy sculpins ranged from 60 to 83 m. The long‐term mean depth difference between the two species was least at Frankfort (21 m) and greatest at Manistique (38 m); at all seven transects, the mean depth difference was significantly greater than zero. We concluded that these two sculpin populations in Lake Michigan maintained some degree of spatial separation during 1973‐2005.

Use and Development of the Wetland Macrophyte Index to Detect Water Quality Impairment in Fish Habitat of Great Lakes Coastal Marshes

Indices have been developed with invertebrates, fish, and water quality parameters to detect the impact of human disturbance on coastal wetlands, but a macrophyte index of fish habitat for the Great Lakes does not currently exist. Because wetland macrophytes are directly influenced by water quality, any impairment in wetland quality should be reflected by taxonomic composition of the aquatic plant community. We developed a wetland macrophyte index (WMI) with plant presence/absence data for 127 coastal wetlands (154 wetland-years) from all five Great Lakes, using results of a canonical correspondence analysis (CCA) to ordinate plant species along a water quality gradient (CCA axis 1). We validated the WMI with data collected before and after the implementation of remedial actions plans (RAPs) in Sturgeon Bay (Severn Sound) and Cootes Paradise Marsh. Consistent with predictions, WMI scores for Sturgeon Bay were significantly higher after the implementation of the RAP. Historical data from Cootes Paradise Marsh were used to track the declining condition of the plant community from the 1940s to 1990s. Subsequently, when remedial actions had been implemented in 1997, the calculated WMI scores showed improvement, but when the presence of exotic species (WMIadj) was accounted for, improvements in ecological integrity of the aquatic-plant community were no longer evident. We show how WMI scores can be used by environmental agencies to assess the historic, current, and future ecological status of wetland ecosystems in two Canadian national parks, Point Pelee National Park (PPNP) and Fathom Five National Marine Park (FFNMP).

Evaluation of a short-day adapted tetraploid potato population with horizontal resistance toPhytophthora infestans under long-day conditions in northern Maine

Phytophthora infestans (Mont.) de Bary, the cause of late blight, has rapidly overcome major (R) gene resistance in potatoes. A population of short-day adapted tetraploid potatoes with horizontal resistance to late blight was developed at the International Potato Center in Lima, Peru. True seed from this population was obtained from the NRSP-6 Project at Sturgeon Bay, WI for the purpose of evaluating its potential to contribute to the breeding effort for late blight resistance in the United States. In 1996, 552 single hills were planted on Chapman Farm, Presque Isle, ME; only 448 tuberized. In 1997, these clones were planted on Chapman Farm for increase; 129 were saved, 53 failed to tuberize, and 266 were discarded because they were sprouted at harvest. In 1998 and 1999, 69 clones were tested for their reaction to late blight in replicated plots on Aroostook Farm, Presque Isle, ME. Percent infected foliage was estimated three times toward the end of the season and used to compute area under the disease progress curve. Broad-sense heritability for horizontal resistance to late blight was estimated as 0.78 with a 95% confidence interval of 0.64 to 0.86. Using detached leaflet assays, these clones were inoculated with US-8 strains ofP. infestans, and the diameter of the lesion was measured 7, 8, 9, 10 and 11 days after inoculation. The correlation between field resistance and the detached leaflet assay was very low (0.18<r<0.24). Some clones from this population are highly resistant to the US-8 strain of P.infestans and represent another source of breeding material for developing late blight resistant varieties in the future. However, very late maturity, short dormancy, poor tuberization and low fertility levels may limit the usefulness of this germplasm in northern USA latitudes.

Results from the U.S. Great Lakes Fish Monitoring Program and Effects of Lake Processes on Bioaccumulative Contaminant Concentrations

An analysis of composite samples of 820 lake trout, walleye, steelhead, Chinook, and coho from the Laurentian Great Lakes reveals differences in contaminant processing among and between lakes which results in differing concentrations of bioaccumulative contaminants. Generally, contaminants are most concentrated in fish from Lake Michigan and least concentrated in fish from Lake Superior, with the notable exceptions of toxaphene and alpha-HCH. Differences in contamination patterns, however, are apparent not only among the lakes but between sites within a lake or even fish within a site. Lake trout composites from Lake Superior show an increase in the degree of chlorination of PCBs with increasing total PCBs. The PCB congener profile of lake trout from the Sturgeon Bay site of Lake Michigan is substantially different from that of the Saugatuck site of Lake Michigan, possibly due to the influence of contamination from nearby Green Bay. Finally, the ratios of selected PBDE and PCB congeners are much different in Lake Superior fish compared to fishes from all the other lakes. We hypothesize that this is a result of the colder temperatures and associated lower plankton growth rates in Lake Superior allowing PCB and PBDE uptake by phytoplankton to reach near equilibrium, thus enhancing the relative concentrations, in phytoplankton and the food web in general, of congeners that may be kinetically limited in other lakes.

Rootstock Effects on Growth and Quality of `Gala' Apples

The effect of rootstock on apple size is not clear due to inconsistent results of published studies. This study was conducted over 3 years at the Peninsular Agricultural Research Station near Sturgeon Bay, WI on 6-year-old `Gala' apple trees (Malus domestica Borkh) grafted on Malling 26 (M.26), Ottawa 3, M.9 Pajam 1, and Vineland (V)-605 rootstocks. Fruit diameter was measured weekly. Fruit weight and volume were estimated by a quadratic regression of weekly measurements. Fruit weight was positively correlated with fruit volume. Rootstock had no effect on fruit growth and final size even with the removal of crop load effects. Crop load was a highly significant covariate for fruit size, but canopy light interception and seed count were not. Trees on M.26 EMLA had slightly higher yield in 2000 but rootstock did not affect yield efficiency any year. Rootstock had no influence on fruit quality attributes during 2001; however, in 2002, fruit obtained from trees on Pajam-1 tended to be less firm. Generally, apple fruit size was influenced by crop load and other factors, but not by rootstock.

Verticillium wilt resistant germplasm-release of clone LRC18-21 and derivatives

Verticillium wilt is an important disease affecting potato tuber yield and quality. In North America the major commercial cultivars are susceptible, and management strategies for control rely mainly on soil fumigation and crop rotation. We describe aSolanum chacoense clone (LRC18-21) with single gene (Vc) resistance to Verticillium wilt as well as germplasm derived from the original clone. LRC18-21 (diploidS. cha-coense), LRC418-21 (tetraploidS. chacoense) and LRC373-5 (diploidS. tuberosum/chacoense hybrid) and LRC4373-5 (tetraploidS. tuberosum/chacoense hybrid) have been released to Potato Introduction Station (NRSP-6, Sturgeon Bay, WI) for distribution to interested parties. Transfer of the Vc gene to commercial cultivars could provide effective and economical control of verticillium wilt.

Rootstock Effects on Growth, Cell Number, and Cell Size of `Gala' Apples

The effects of rootstock on growth of fruit cell number and size of `Gala' apple trees (Malus domestica Borkh) were investigated over three consecutive seasons (2000-02) growing on Malling 26 (M.26), Ottawa-3, Pajam-1, and Vineland (V)-605 rootstocks at the Peninsular Agricultural Research Station near Sturgeon Bay, WI. Fruit growth as a function of cell division and expansion was monitored from full bloom until harvest using scanning electron microscopy (SEM). Cell count and cell size measurements showed that rootstock had no affect on fruit growth and final size even when crop load effects were removed. Cell division ceased about 5 to 6 weeks after full bloom (WAFB) followed by cell expansion. Fruit size was positively correlated (r2 = 0.85) with cell size, suggesting that differences in fruit size were primarily a result of changes in cell size rather than cell number or intercellular space (IS).