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Open access

R. Karina Gallardo, Kara Grant, David J. Brown, James R. McFerson, Karen M. Lewis, Todd Einhorn and Mario Miranda Sazo

Advances in precision agriculture technologies provide opportunities to improve the efficiency of agricultural production systems, especially for high-value specialty crops such as fresh apples (Malus domestica). We distributed an online survey to apple growers in Washington, New York, and Michigan to elicit stakeholder perceptions of precision agriculture technologies. Findings from this study demonstrated that growers are willing to adopt precision agriculture technologies when they receive results from applied research projects and are engaged with active extension programs. The availability of customized services and purchasing and rental options may minimize the effects of the economies of size that create barriers to adopting increasing access to technologies. Finally, respondents deemed collaborative efforts between industry and academic institutions crucial for adapting the innovation to better address the needs of growers.

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Benjamin D. Toft, Mobashwer M. Alam, John D. Wilkie and Bruce L. Topp

The vigorous growth and large canopy size of commercial macadamia (Macadamia integrifolia, M. tetraphylla, and hybrids) cultivars generally restricts macadamia orchards to low-density planting. Little is known of the detailed interactions between plant architecture and yield components specific to macadamia. This chapter examines how dependent traits such as canopy size and yield might be determined by direct and indirect interactions between traits at different scales within the canopy. Fifteen genotypes (n = 3) were phenotyped in two growing seasons for architectural and reproductive traits, around the age of their transition from juvenility to maturity. Genotypes varied in canopy volume, cumulative yield, and canopy efficiency, and particular genotypes with low canopy volume and high yield were considered potentially useful for future high-density orchard systems. There was high variability in architectural, floral, and yield traits at multiple scales. Direct and indirect effects of architectural traits on the variability of yield and tree size were quantified using path coefficient analysis. Canopy volume was subject to positive direct effects from trunk cross-sectional area (TCA; 0.72), lateral branching (0.24), and branch unit (BU) length (0.24). Other traits showed significant indirect effects with canopy volume via TCA, such as branch cross-sectional area (BCA; 0.43), BU length (0.40), lateral branching (0.35), and internode length (0.32). Branch angle had a significant indirect negative effect on canopy volume via BU length (−0.11). Nut number had the strongest direct effect on yield (0.97), and this relationship was significantly indirectly influenced by raceme number (0.47), raceme length (0.50), nut number per raceme (0.33), canopy volume (0.37), and branch angle (0.35). In these relatively young trees, early yield was directly and positively influenced by canopy volume (0.12), presumably due to increased early light interception, which suggests that early canopy vigor contributes to early yield. This study suggests that yield and canopy size are determined by complex phenotypic interactions between architectural traits at different scales. Therefore, preplanting (i.e., scion and rootstock selections) and postplanting (i.e., pruning and training) manipulations that specifically manage architectural traits such as shoot length, branching, branch angle, raceme length, and nuts per raceme may result in the creation of efficient macadamia canopies.

Open access

Chad T. Miller

Plant Madness was a classroom activity developed and implemented for the Landscape Plants II identification course at Kansas State University. The game was modeled after the National Collegiate Athletic Association college basketball March Madness tournament and Bracketology. One activity objective was to provide students an opportunity to learn new and recent cultivars and plant species not specifically covered in the class curriculum. The activity also provided students opportunities to practice public speaking skills, an avenue to be creative, and simply have fun in class. In Plant Madness, each student randomly drew a plant from a hat and then students were randomly assigned tournament seed rankings (preliminary rankings). On specified game days, one student played against another student, each having 2 minutes of play. Student play varied, and consisted of defining different plant attributes, landscape appeal, and interesting facts, for example; or identifying the opposing student’s plant’s faults through riddles, poems, games, songs, or simply recitation. Referees (e.g., guest faculty, graduate students) reviewed student play and awarded points, and the student with the highest score advanced to the next round through the single-elimination tournament. A postactivity survey was administered [Spring 2016 and 2017 (n = 44)] to obtain student feedback. When asked if the students liked the activity, it was nearly unanimous, 98% liked Plant Madness. Similarly, most students (93%) self-reported the activity increased their awareness of new or recent plant cultivars. When asked to rate the activity compared with other class approaches for learning different plants based on a scale of 1 (excellent) to 5 (poor), the average rating was 1.8. Students’ average rating for their ability to be creative for Plant Madness was 1.8 (1 = to a large extent, 5 = not at all). Ninety-five percent of the students recommended repeating the activity.

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John R. Stommel

Small/miniature sweet and hot peppers (Capsicum annuum L.), such as snack peppers, are a rapidly growing class of specialty peppers. Low seed count is an important attribute for consumer acceptance of small-fruited specialty peppers. Four inbred U.S. Department of Agriculture (USDA) C. annuum breeding lines exhibiting uniformity for pod type and size and normal or reduced seed count were selected for producing F1 and segregating F2 and backcross generations. Seed content of F1 hybrids and progeny produced from the backcross of F1 hybrids to normal seed count parents exhibited unimodal frequency distributions and skewed toward the parent with normal seed count. Progeny produced from backcrosses to the reduced seed count parent exhibited bimodal population distributions representative of the respective parental phenotypes. F2 populations approximated 3:1 frequency distributions skewed toward normal-seeded parental phenotypes. Chi-square tests supported a single recessive gene model with potential modifiers controlling inheritance of reduced seed count. Genetic variants with reduced seed count facilitate seed production and propagation of specialty market class peppers.

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Xin Zhao, Qianqian Dong, Shubang Ni, Xiyong He, Hai Yue, Liang Tao, Yanli Nie, Caixian Tang, Fusuo Zhang and Jianbo Shen

Macadamia (Macadamia spp.) has been widely planted in southern China and has been now developed into an important industry. China has the largest area of macadamia plantation in the world but provides only 3% production of the world. Current farming systems have a fertilizer surplus of about 73 g of nitrogen (N), 103 g of phosphorus (P), and 24 g of potassium (K) per macadamia plant per year in southern China. Optimizing fertilization recommended for macadamia improves production by about 5 kg per plant. Macadamia develops cluster roots (i.e., proteoid roots) in a P-starvation environment. Overuse of P fertilizers restrains the development of cluster roots as well as rhizosphere processes, thus decreasing the P-use efficiency. Excessive fertilization, especially P fertilization, is one of the major limiting factors in China macadamia production. This study is the first to analyze current management practices and then discuss approaches of improving nutrient management based on the specific root biology of macadamia. For a sustainable macadamia industry, it is imperative to develop appropriate nutrient management by integrating root-zone soil nutrient supply, fertilizer application, and rhizosphere processes.

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Katie O’Connor, Ben Hayes, Craig Hardner, Mobashwer Alam and Bruce Topp

Current macadamia breeding programs involve a lengthy and laborious two-stage selection process: evaluation of a large number of unreplicated seedling progeny, followed by replicated trials of clonally propagated elite seedlings. Yield component traits, such as nut-in-shell weight (NW), kernel weight (KW), and kernel recovery (KR) are commercially important, are more easily measured than yield, and have a higher heritability. A genome-wide association study (GWAS) combined with marker-assisted selection offers an opportunity to reduce the time of candidate evaluation. In this study, a total of 281 progeny from 32 families, and 18 of their 29 parents have been genotyped for 7126 single nucleotide polymorphism (SNP) markers. A GWAS was performed using ASReml with 4352 SNPs. We found five SNPs significantly associated with NW, nine with KW, and one with KR. Further, three of the top 10 markers for NW and KW were shared between the two traits. Future macadamia breeding could involve prescreening of individuals for desired traits using these significantly associated markers, with only predicted elite individuals continuing to the second stage of selection, thus potentially reducing the selection process by 7 years.

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Jonathan D. Mahoney, Thao M. Hau, Bryan A. Connolly and Mark H. Brand

The genus Aronia Medik., also known as chokeberry, is a group of deciduous shrubs in the Rosaceae family, subtribe Pyrinae. The four commonly accepted species include A. arbutifolia (L.) Pers., red chokeberry; A. melanocarpa (Michx.) Elliott, black chokeberry; A. prunifolia (Marshall) Reheder, purple chokeberry; and A. mitschurinii (A.K. Skvortsov & Maitul). Wild and domesticated Aronia species are found as diploids, triploids, and tetraploids. Genetic improvement of polyploid Aronia genotypes has been limited by suspected apomixis, which may be widespread or distinct to tetraploids. The objectives of this study were to elucidate the reproductive mechanisms of Aronia species and reveal the occurrence of apomixis within the genus and along ploidy lines. Twenty-nine Aronia accessions [five A. melanocarpa (2×), five A. melanocarpa (4×), eight A. prunifolia (3×), four A. prunifolia (4×), six A. arbutifolia (4×), and one A. mitschurinii (4×)] were used in this study. Intra-accession variability was evaluated by growing out progeny from each open-pollinated maternal accession and comparing plant phenotypes, ploidy levels, and amplified fragment length polymorphism (AFLP) marker profiles between the progeny and maternal accession. Progeny of diploid and tetraploid maternal plants had ploidy levels identical to maternal plants, except for UC009 (A. melanocarpa, 2×) which produced a mix of diploids and tetraploids. UC143 and UC149 (A. prunifolia, 3×) produced all triploid offspring, whereas all other triploid accessions produced offspring with variable ploidy levels including 2×, 3×, 4×, and 5×. Pentaploid Aronia has not been previously reported. Diploid accessions produced significant AFLP genetic variation (0.68–0.78 Jaccard’s similarity coefficient) in progeny, which is indicative of sexual reproduction. Seedlings from tetraploid accessions had very little AFLP genetic variation (0.93–0.98 Jaccard’s similarity coefficient) in comparison with their maternal accession. The very limited genetic variation suggests the occurrence of limited diplosporous apomixis with one round of meiotic division in tetraploid progeny. Triploid accessions appear to reproduce sexually or apomictically, or both, depending on the individual. These results support our understanding of Aronia reproductive mechanisms and will help guide future breeding efforts of polyploid Aronia species.

Open access

Maria Gannett, Marvin P. Pritts and Johannes Lehmann

Soil amendments with varying carbon:nitrogen (C:N) ratios [grass clippings, wheat (Triticum aestivum), straw, sawdust] were pre-plant incorporated into 12 × 15-ft field plots at ≈4 tons/acre in fall and then planted to perennial strawberry (Fragaria ×ananassa) the following spring and grown 4 years. These amendments were intended to alter soil biological activity as measured by a suite of soil tests referred to as “soil health indicators” which, in turn, were hypothesized to affect strawberry plant growth and yield. In addition, plots were either tilled deeply or shallowly to determine if intensity of tillage affected soil health indicators. After the first and second years, amendments were reapplied between rows and soil and plant variables continued to be monitored. Soil respiration was consistently higher in plots with higher C:N amendments, with up to a 189% increase in respiration in sawdust-amended plots over unamended plots. The respiration rate was highest in sawdust-amended shallow-tilled plots; however, in most cases, tillage depth had no effect on other soil or plant variables. Potentially mineralizable N was higher in sawdust-amended plots in May both years, but not throughout the rest of the season. Soil moisture and pH were 21% and 2% higher, respectively, between the rows of strawberries than within the rows by September of the planting year, and remained that way throughout the next year. Neither the C:N ratio of the soil nor the foliar nutrient concentration of strawberry leaves was affected by the C:N ratio of the amendments. Most significantly, plant density and yield were depressed up to 42% and 26%, respectively, by planting into straw-amended soil, but planting into other amendments did not have this effect. After the second fruiting year (the third growing season), only straw was incorporated into half of the plots after harvest to mimic winter straw mulch incorporation, and yield was measured again the following spring. However, incorporation of straw between rows after plants were established did not affect yield. This study corroborates the general recommendation to avoid new strawberry plantings in locations that were recently planted to strawberry, as old fields likely harbor pathogens and contain undecomposed straw residue from previous years’ mulching that could depress yield. Despite differences in soil health indicators between amendment and tillage treatments, yield differences were not correlated with them. These observations suggest that alternative soil health indicators may be better suited for perennial strawberry.

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Feras Almasri, Husein A. Ajwa, Sanjai J. Parikh and Kassim Al-Khatib

Methyl bromide (MeBr) was identified as a stratospheric ozone depletory; therefore, the use of MeBr was phased out in the United States in 2005. Chloropicrin (CP) and allyl isothiocyanate (AITC) are MeBr replacements. A mixture of CP and AITC is commonly applied to broaden the pest control spectrum. These two fumigants have low soil mobility; however, their efficacy could be improved if their soil mobility were enhanced. This research was conducted to study the effects of surfactants applied at 5% (v/v) for CP mobility and AITC mobility in soils. Mobility of the CP/AITC mixture applied with a nonionic surfactant comprising oleic, linoleic, and palmitic acids (nonionic-1) and mobility of the CP/AITC mixture applied with a nonionic surfactant comprising C9 hydrocarbon aromatics and calcium alkylarylsuphonate (nonionic-2) were compared with mobility of the CP/AITC mixture applied without surfactants in three soils (Elder sandy loam, Chualar loam, and Blanco clay loam) during a laboratory study. Nonionic-1 surfactant increased the concentration of total leachate collected for AITC by five and CP by 11 compared with CP/AITC applied alone. Surfactants may influence the fumigant mobility in soil by affecting the sorption/desorption equilibrium. Our research suggested that increased AITC mobility and CP mobility in soil with the addition of adding nonionic-1 surfactant may be due to the adsorption behavior of the surfactant in the soil and the solubilizing capability of the surfactant with pesticides.

Open access