Stan C. Hokanson

Morphometric variation in oaks of the Apostle Islands in Wisconsin: Evidence of hybridization between Quercus rubra and Q.ellipsoidalis (Fagaceae)

The Apostle Islands in Lake Superior are populated by trees that are clearly related to Quercus rubra L. However, several islands have trees with morphological characteristics suggestive of hybridization with Q. ellipsoidalis Hill. Leaf specimens were collected from trees in five locations: the outermost island, an intermediate island, the nearest-shore island, the northeast shoreline, and an inland forest about 24 km from the shoreline. Seventeen landmarks were digitized for two to five leaves per tree. These landmarks were used to generate nine linear characters and three angles. These characters, along with the number of bristle tips per leaf, were used in various combinations for several principal component analyses. In addition, the landmark configurations were examined using rotational-fit methods. The patterns observed in both types of analysis indicate phenotypic variation coincident with a line connecting the two most distant sample sites. The location nearest the geographic center of this line is also nearest the center of the two-dimensional view of phenotypic variation. Trees at each site illustrate a distinctive pattern in the rotational-fit analyses, and patterns of co-variation in the morphometric characters are different for each site. The observed morphometric variation is consistent with the hypothesis that there is hybridization between these two species, most likely in the form of introgression from Q. ellipsoidalis into Q. rubra.

Direct comparison of pollen-mediated movement of native and engineered genes

Despite the commercial approval of twenty-five transgenic crops in the U.S. as of mid-1996, concern is still being expressed regarding the potential risks associated with genetically engineered crops. One recurring issue is the possibility of pollen-mediated escape of engineered genes into populations of crop wild relatives. To address this concern, the scientific community has depended on literature on pollen dispersal generated from non-transgenic organisms. Utilization of this information requires the assumption that the pollen mediated movement of native and transgenes is the same. To test the validity of this assumption, we directly compared the pollen-mediated gene movement of native and engineered marker genes using melon plants (Cucumis melo L.) expressing dominant morphological and transgenic traits. Movement into both contiguous border plots and non-contiguous satellite plots were monitored. Dispersal of the native gene and transgene into the satellite plots was identical. Dispersal of the two traits into the plot borders was nearly identical. Of the nearly 4600 seedlings screened for both morphological (presence of green vs. virescent cotyledons) and transgene movement (presence of NPT II protein by ELISA), in no case was the NPT II gene observed in the absence of green cotyledons. However, 39 seedlings were green but did not express NPT II as measured by ELISA. PCR analysis revealed transgene inactivation as a cause of the NPT II ELISA-seedlings.

EFFECT OF BORDER ROWS AND TRAP/DONOR RATIOS ON POLLEN‐MEDIATED GENE MOVEMENT

One of the concerns associated with the field testing and agronomic-scale release of transgenic crops is the potential for the pollen-mediated escape of engineered genes into naturally occurring populations of wild relatives. While border rows have been used frequently to restrict the pollen-mediated escape of engineered genes from field trials, the efficacy of this approach has been little studied. To test the effectiveness of border plantings, isogenic lines of cucumber (Cucumis sativus L.) differing for the seedling marker trait blunt leaf apex (bla) were planted in four designs: 1 m2 of wild-type donor plot surrounded by a 399-m2 border of bla recipients; 1 m2 of donor plot/99 m2 border; 4 m2 of donor plot/96 m2 border; and 1-m2 of donor plot with no border. Each planting was encircled by eight 1.4-m2 satellite plots 50 m from the plot center. Progeny of plants from the satellites and borders were screened to determine the percentage of gene movement as measured by the occurrence of the dominant phenotype. Gene movement within the plot borders followed a leptokurtic distribution; there was greater movement from the 4-m2 donor plot than from the 1-m2 plot. Long-distance movement to the satellites significantly increased as the trap-to-donor ratio decreased. Although movement to individual satellites was generally consistent within a treatment, there was one instance of unusually high outcrossing to a single satellite, indicating that the effectiveness of borders was influenced by both the relative numbers of donor plants and by environmental variables.

Aurantioporthe corni gen. et comb. nov., an endophyte and pathogen of Cornus alternifolia

Cryptodiaporthe corni is the causal agent of a destructive disease called golden canker, which affects Cornus alternifolia, known as the pagoda or alternate-leaved dogwood. Due to the association between Cr. corni and pagoda dogwood, we sought to determine whether this fungus was capable of living as an endophyte in pagoda dogwood and causing this disease. Forty asymptomatic stems of plants growing in nature were sampled from five sites across Minnesota. Cryptodiaporthe corni was present in more than half (62.5%) of the stems. Asymptomatic nursery material also was sampled, and the fungus was isolated from a small percentage (20%) of them. Inoculations carried out in the field and greenhouse suggested the endophytic isolates of Cr. corni were capable of causing disease. Asymptomatic stems of trees in the field inoculated with non-colonized (control) grain seed developed golden canker as frequently as those inoculated with grain seed colonized by Cr. corni, suggesting that the fungus was already present in these plants. In greenhouse pathogenicity trials an isolate of Cr. corni obtained from an asymptomatic stem was capable of causing golden canker disease, thus demonstrating causality, fulfilling Koch’s postulates. The taxonomic placement of Cr. corni within Cryphonectriaceae was determined. Phylogenetic analysis of the ITS rDNA and β-tubulin gene regions, along with morphological characteristics, suggested Cr. corni is distinct from other genera within this family. Therefore, we propose a new genus, Aurantioporthe, as well as the new combination, A. corni, to accommodate this species within Cryphonectriaceae.

Partial resistance to black spot disease in diploid and tetraploid roses: general combining ability and implications for breeding and selection

Black spot disease, incited by the fungus Diplocarpon rosae Wolf, is the most important disease of roses (Rosa hybrida L.) in the outdoor landscape. Though partial resistance exists in cultivated germplasm, the genetic basis of this trait has not yet been elucidated. Six diploid and six tetraploid rose cultivars were crossed in two factorial combining ability arrays. Whole plant and detached leaf inoculation methods were used to assess partial resistance under two different disease pressures using a characterized single-spore isolate. Parents from both arrays had significant general combining ability effects across multiple inoculation methods and environments. Specific combining ability was not significant for either array. Parent per se performance was highly correlated with progeny performance on a family mean basis. High positive correlations among whole plant and detached leaf inoculation methods indicate that detached leaf assays can substitute for whole plant assays. Based on these results, a breeding strategy including parental selection and early, among-family selection is proposed. To our knowledge, this is the first investigation of combining ability for disease resistance in rose.

Woody Ornamentals of the Temperate Zone

Woody ornamental plants comprise a large number of genera, species, and cultivars that display a huge amount of phenotypic diversity. New introductions mainly result from natural existing variation or from selections in open-pollinated populations. Systematic commercial breeding mainly takes place in a few important genera. More advanced techniques such as interspecific hybridization and polyploidization have been successfully adopted to broaden the possibilities of woody plant improvement. Because of increased sophistication in marketing and branding, visual attractiveness at the point of sale has become one of the major breeding goals. But the real challenges continue to be biotic (disease and pest) and abiotic stress resistance (winter hardiness, heat, drought, pH, and flooding tolerance). In addition, some new trends are observed, such as breeding for sterility, breeding for multipurpose, and breeding and selecting of native plants with an ecological function. This review also provides an overview of the current status of genomics and genetic engineering in woody plants and the potential of application of genome-editing technologies to enable faster and more precise breeding.

Woody landscape plant breeding in Minnesota (45°N): It's not all about cold hardiness

The Woody Landscape Plant Breeding project at the University of Minnesota has been in existence since 1954. The project was initiated largely to develop an extended palette of cold-hardy woody landscape plants for northern landscapes. Since its inception, it has been responsible for the release of 49 woody plant cultivars including large stature shade trees, small stature flowering trees, shrubs, roses, and deciduous azaleas. Given the project’s success at building a cold-hardy germplasm pool for a number of woody taxa, recent breeding efforts have been directed towards other traits such as disease resistance in several plant taxa. Projects include an examination of the nature of resistance to powdery mildew disease (Microspharae spp.) in deciduous azalea (Rhododendron subg. Pentanthera (G. Don) Pojark) species and cultivars in both field and growth chamber studies; a physiological race and an Amplified Fragment Length Polymorphism (AFLP) molecular characterization of the rose black spot pathogen (Diplocarpon rosae Wolf) and identification of resistance genes to the disease in cultivated rose (Rosa ×hybrida). Recently, a high-throughput screening protocol to facilitate the identification of resistance to golden canker disease incited by the fungal pathogen (Cryptodiaporthe corni (Wehm.) Petrak) in a tree native to the upper midwestern U.S., Pagoda dogwood (Cornus alternifolia L.) has been initiated.