Production of high-quality tree fruit requires management of tree health and vigor during orchard establishment, especially with regard to soil-borne pathogens. Available strategies for the mitigation of soil-borne diseases include chemical fumigants, Brassicaceous seed meal (SM) soil treatments, and the use of disease-tolerant rootstock genotypes. It has been documented that superior disease suppression can be achieved using specific combinations of rootstock genotype and soil treatment that, in part, alter the soil microbiome. However, regardless of soil treatment strategy or rootstock genetics, sublethal levels of phytotoxic compounds are known to have negative effects on the reproductive output of plants. Yet the effects of SM amendments and the resultant restructuring of the soil microbiome on fruit quality are not well studied. Thus, our objective was to explore the effects of pathogen suppression strategies on at-harvest and postharvest fruit quality of ‘Gala’ apples (Malus domestica) by observing effects of both rootstock genetics [‘Malling 26’ (‘M.26’) vs. ‘Geneva 41’ (‘G.41’)] and soil treatment strategy (fumigation vs. SM). We observed that rootstock genotype generally appeared to have a stronger effect than soil treatment strategy on at-harvest fruit quality and postharvest outcomes. Further, although we did observe some fruit quality differences in each year of the study, there was no discernible pattern from year to year. We therefore conclude that, in our study, soil treatment does not have a consistent, significant influence on ‘Gala’ apple fruit quality, and importantly, efficacious ARD control using SM is without an apparent downside regarding fruit quality.
Heidi Hargarten, James Mattheis, and Loren Honaas
Sijie Wang, Haoyi Wu, Haiying Li, Yaxin Zhao, Juan Zhou, Chen Lian, Jingran Lian, and Yan Ao
Lenny Wells and Andrew Sawyer
Site selection is key to successful establishment of fruit and nut trees. The upland soils on which pecan [Carya illinoinensis (Wangenh.) K. Koch] trees are commonly planted in the southeastern United States consist of sites that have recently been in row crop cultivation or pine or hardwood timber. Anecdotal observation suggests that orchards planted to land converted from cultivated row crop fields tends to result in better tree growth and survival than those on land recently converted from timber plantations or wooded areas. The objective of this experiment was to compare growth of first- through third-leaf pecan trees planted on sites with varying land-use history [row crop cultivation or pine (Pinus spp.) tree production up to the year before planting] and to determine the effects of supplemental addition of phosphorus (P), potassium (K), and zinc (Zn) at planting on the two sites. These results suggest that the soil conditions of sites recently in pine timber production limit the growth and development of pecan trees planted to those sites. These limitations result from soil acidity and an exhaustion of soil nutrients and loss of organic matter on pine sites, making the uptake of nitrogen (N), P, K, and calcium (Ca) challenging during the establishment phase unless soils are improved before planting.
Chunlan Li, Panyun Xu, Aote Zhou, Jinlong Song, Yuxia Wu, and Tianming He
This study investigated the ploidy of ‘Mianli’ with flow cytometry and the traditional chromosome squash technique. Its pollination biology and the occurrence and formation of embryo sacs before and after flowering were observed in paraffin sections to characterize its embryo sacs. The intersimple sequence repeat (ISSR) marker technique was used to test the uniformity of progeny of ‘Mianli’ treatments. The chromosome number of ‘Mianli’ is 2n = 2x = 34. The ploidy results were consistent with those identified by flow cytometry. ‘Mianli’ is male-sterile, and the anatropous ovule has double integuments. ‘Mianli’ can bear fruit normally and produce fertile seeds under the treatments of emasculation with bagging or no emasculation with bagging, but the seed yield is very low and significantly lower than that under artificial pollination or natural pollination. The developmental process of embryo sacs under natural pollination showed that most megasporocytes develop into mature sexual embryo sacs through meiosis and a few megasporocytes degenerate. Some sexual embryo sacs continue to develop into embryos after fertilization, and some sexual embryo sacs are aborted. In addition, new aposporous initial cells are generated irregularly at each stage from the emergence of megasporocyte to the end of sexual reproduction or abortion. The observation of the development of embryo sacs under emasculation with bagging showed that after pollination is blocked, mature sexual embryo sacs degenerate, and aposporous mononucleate embryo sacs appear around the degenerated sexual embryo sacs or in the peripheral tissues. Then, the process of proembryonic masses developing into spherical embryo was observed. A genetic uniformity analysis of progeny of ‘Mianli’ using ISSR was performed. The results showed that the progeny population under emasculation with bagging has high consistency at the molecular level, with some plants having full consistency with the female parent’s banding pattern, demonstrating consistency with the maternal genetic characteristics. The progeny under artificial pollination or natural pollination do not have the same banding pattern as the female parent. Because there is no pseudogamy, all of the progeny are true hybrids. In summary, it seems that ‘Mianli’ only has sexual reproduction in the presence of pollen, and only a few ovules are stimulated to undergo apomixis after pollination is blocked.
Bernadine C. Strik and Amanda J. Davis
A 6-year trial was established in Oct. 2015 in western Oregon to evaluate the effects of pruning and trellising on yield, hand- and machine-harvest efficiency, fruit quality, and costs of pruning and harvest of ‘Legacy’ highbush blueberry (complex hybrid based largely on Vaccinium corymbosum L. and Vaccinium darrowii Camp.). Pruning treatments began in Winter 2017–18 (before year 3) and continued each year through 2020–21 (year 6). Treatments included 1) recommended pruning for ‘Legacy’, removing less wood and leaving more short, thin laterals and a denser bush than is typical for most northern highbush cultivars (“control” with standard T-trellis), 2) control pruning and training to a V-trellis (“V”), and 3) standard northern highbush style pruning (“HB” with standard T-trellis). Fruit were harvested solely by hand in 2017 and 2018, and by hand for early harvests followed by machine for later harvests from 2019 to 2021. In most years, more wood was removed from HB- than control-pruned plants. On average, HB-pruned plants had a lower yield (6.7 kg/plant) than control-pruned plants, particularly those trained to a V-trellis (7.5 kg/plant). There was little effect of pruning treatment on fruiting season and hand- (7% drop) or machine-harvest efficiency (23% drop). Pruning method had no effect on berry weight, diameter, total soluble solids, or firmness over the study period or percent internal bruising in 2019. All of the ‘Legacy’ pruning methods studied required more time (358 to 561 h·ha−1) than the industry standard, ‘Duke’ (247 h·ha−1). Control and HB pruning did not differ in time to prune per unit area; however, in 2 of the 4 years, adding a V-trellis increased pruning time. On average, control and HB pruning had a similar cost per harvested fruit ($0.20 to $0.21/kg), whereas control pruning with a V-trellis ($0.23/kg) cost more than HB pruning. All treatments required the same amount of time to harvest (12.7 and 0.5 min·kg−1 for hand and machine picking, respectively). Total cost to prune and harvest ranged from $1.63/kg in 2019 to $3.43/kg in 2021 but was most heavily influenced by harvest costs rather than pruning. The one-time installation cost of $637/ha for the V-trellis was not compensated for by increased yield or efficiency of pruning or harvest compared with the control method with a standard T-trellis. Pruning according to recommended methods for ‘Legacy’ (control) increased yield without having a negative effect on fruit quality and had similar or lower costs to prune per kg of fruit harvested as typical northern highbush pruning.
Xinwang Wang, Keith Kubenka, Warren Chatwin, Tommy Thompson, and L.J. Grauke
Lijuan Fan, Wangbin Ye, Haijing Fu, Ruiyang Zhao, Gongfa Shi, Rutong Lv, Lei Yan, Zhuowen Li, and Ling Wang
Jiaqi Xia and Neil Mattson
Common ice plant (Mesembryanthemum crystallinum L.) is a novel edible succulent plant with savory flavor. It has epidermal bladder cells (EBCs) that store water and sodium chloride (NaCl) located on the epidermis of the leaves and stems. Ice plant is an obligatory halophyte that requires NaCl for optimum growth. The objective of this study was to determine the impact of NaCl on growth of ice plant for hydroponic production as an edible leafy green and to quantify the ability of ice plant to take up NaCl from the environment. Four-week-old seedlings of ice plant were transplanted into hydroponic systems, established for 1 week, and given five NaCl treatments [0 M (control), 0.05 M, 0.10 M, 0.20 M, 0.40 M NaCl]. Sequential destructive harvests to determine plant growth occurred at day 7, 14, and 21 after NaCl treatment. The 0.05 M NaCl had the greatest stimulating effect on biomass, increasing total fresh weight (FW) by 173% and shoot FW by 193% compared with the control plants. The 0.10 M NaCl also had stimulating effect as compared with 0 M, but plants were not as large as those receiving 0.05 M NaCl. The 0.20 M NaCl had little effect on plant growth compared with the control. The 0.40 M NaCl had a strong stunting effect on plant growth. All plants treated with NaCl had less root weight than the control, and higher NaCl concentration resulted in greater reduction in root weight. However, for the 0.05 and 0.10 M treatment, the gain in shoot weight exceeded the loss in root weight. Plants gained or lost water in a faster rate than dry mass, which resulted in larger differences among treatments in FW than in dry weight (DW). Plants treated with higher NaCl concentrations developed fewer, smaller, and thicker leaves but contained more EBCs per unit leaf surface area. There was high Na and Cl accumulation in leaf tissues of all salt-treated plants (e.g., 180,507 mg·kg−1 Na and 125,084 mg·kg−1 Cl in the 0.05 M treatment vs. 13,558 mg·kg−1 Na and 12,991 mg·kg−1 Cl in the 0 M treatment). This indicated potential for bioremediation of saline soil or hydroponic water. Concentrations of macronutrients such as nitrogen (N), phosphorus (P), calcium (Ca), magnesium (Mg), and sulfur (S) were reduced when plants received increasing NaCl treatments. In general, this study showed that growth of ice plant benefited from 0.05 and 0.10 M NaCl additions to the hydroponic nutrient solution. Ice plant deserves further work on its ability to reduce Na and Cl from accumulating in recirculating hydroponic nutrient solution.
Kaitlin A. Hopkins, Michael A. Arnold, Charles R. Hall, H. Brent Pemberton, and Marco A. Palma
Variation in floral characteristics and growth habits within the native range of the North American wildflower Ratibida columnifera (Nutt.) Wooton & Standl. suggests potential for breeding and selection efforts to develop improved cultivars for commercial and residential landscapes. Experiments in seed propagation were performed to enable perpetuation of unique germplasms. Overnight hydration, storage condition variations, stratification and scarification, and seed maturation effects were assessed to determine impacts on viability and percent germination. Overnight hydration had no impact on percent germination. Germplasm had a significant effect on germination for all remaining experiments. Seed maintained viability at the same rate through 18 months, when slight reductions were noted. Cold storage at 3 °C had no effect on viability or percent germination of dry seed compared with storage at 23 °C. All three germplasms exhibited increased percent germination with some stratification period, and declined significantly in percent germination with all acid scarification treatments. Experiments indicated that most germplasms benefit from between 30 to 60 days of cold, moist stratification. There was a significant interaction effect among germplasms, location on the inflorescences, and maturity stages for R. columnifera. Data suggest that seed should be harvested as close as possible to when natural dispersal would occur for optimum germination. The degree of improvement in viability and percent germination associated with harvesting at various developmental stages, seed pretreatments, and storage conditions suggests that to achieve germination success, pretreatments should be used for propagation of seed from mature inflorescences and that variation can be expected within different genotypes of this species.
Justin J. Lombardoni, Josh A. Honig, Jennifer N. Vaiciunas, Ronald S. Revord, and Thomas J. Molnar
The perennial stem canker disease eastern filbert blight (EFB), caused by Anisogramma anomala, is devastating to most trees of European hazelnut (Corylus avellana), as genetic resistance is rare in the species. The pathogen is harbored by the wild American hazelnut (Corylus americana) found throughout much of eastern North America. Wild American hazelnut is generally resistant or tolerant to EFB, and is fully cross compatible with C. avellana, the species grown commercially for its nuts, making it a valuable resource for disease resistance breeding. The objective of this study was to identify quantitative trait loci (QTLs) associated with EFB resistance and tolerance in these two species. Three unrelated EFB-resistant C. americana selections [Oregon State University (OSU) 533.069 from Pennsylvania, OSU 403.040 from Nebraska, and OSU 557.122 from Wisconsin] were crossed with C. avellana ‘Tonda di Giffoni’ (TdG), a cultivar from Italy known to be tolerant of EFB. Their progenies, each containing 124 trees, were exposed to A. anomala through field inoculations and natural spread over 7 years, then each tree was evaluated for cumulative disease response. Results showed that disease response of all three populations exhibited a roughly normal distribution, indicating that resistance/tolerance was under multigenic control. An average of 2869 total markers were used to construct each population’s linkage map following genotyping, which included an average of 121 published simple sequence repeat markers to anchor linkage groups (LGs) to those of previous studies. Linkage maps were constructed for each parent of each population and used to map QTLs associated with EFB response. The subsequent analysis resolved five EFB-related QTLs across the three populations, highlighting three genic regions. Unexpectedly, only one QTL was identified from one of the three resistant C. americana parents, located on LG11 of the map of OSU 403.040, whereas three QTLs were found in a similar region on LG10 across the three maps of TdG, and a fifth QTL was found on LG6 of one TdG map. The lack of strong QTLs identified from the three EFB-resistant C. americana parents suggests that their resistance may be highly quantitative and not resolved within the constraints of this study. In contrast, tolerance from TdG appears to be conferred by a limited number of genes with relatively strong effects. Based on prior mapping work in European and American hazelnut where R genes have been located on LG2, LG6, and LG7, the QTLs associated with resistance/tolerance on LG10 and LG11 represent novel resistance regions. These QTLs present new targets for marker aided breeding, especially when pyramiding EFB resistance genes is a goal.