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Guangxin Liu, Xiaoqian Su, Lingling Guan and Fengrong Hu

Plant resistance characteristics are closely related to changes in the activities of self-defense enzymes after infection. Despite significant differences in the resistance of different lily (Lilium sp.) cultivars to leaf blight (Botrytis elliptica), few studies of their resistance physiology exist. This study explored changes in the resistance-related enzyme activity of several lily cultivars after leaf blight inoculation. Seven oriental lily cultivars (Lilium hybrids) with obvious differences in resistance were used as experimental materials. After inoculation with B. elliptica, the activities of four defense enzymes, superoxide dismutase (SOD), catalase (CAT), phenylalanine ammonia-lyase (PAL), and peroxidase (POD), were determined according to the light absorption values at different wavelengths after their reactions. The results showed that the activities of SOD and CAT differed between the highly resistant and highly susceptible hybrids. Before inoculation, SOD activity was relatively low in all cultivars. However, after inoculation, the SOD activity increased sharply in the resistant cultivars. In the moderately resistant cultivars, the SOD activity did not change drastically. In the susceptible cultivars, the SOD activity initially showed slight increases or decreases and then increased. CAT activity showed reactions similar to those of SOD. Some changes in PAL and POD activity occurred after inoculation, but no significant correlations were present between these trends and resistance characteristics. In addition, no significant changes in enzyme activities were found in the control plants of the seven cultivars during the testing period. Overall, the resistance of Lilium oriental hybrids to B. elliptica is related to SOD and CAT activity but does not show much of a relationship with PAL and POD activity. Studying the physiological metabolic pathways of SOD and CAT appears to be an important direction in research to elucidate resistance to B. elliptica in Lilium oriental hybrids.

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Joshua K. Craver, Jennifer K. Boldt and Roberto G. Lopez

High-quality young plant production in northern latitudes requires supplemental lighting (SL) to achieve a recommended daily light integral (DLI) of 10 to 12 mol·m−2·d−1. High-pressure sodium (HPS) lamps have been the industry standard for providing SL in greenhouses. However, high-intensity light-emitting diode (LED) fixtures providing blue, white, red, and/or far-red radiation have recently emerged as a possible alternative to HPS lamps for greenhouse SL. Therefore, the objectives of this study were to 1) quantify the morphology and nutrient concentration of common and specialty bedding plant seedlings grown under no SL, or SL from HPS lamps or LED fixtures; and 2) determine whether SL source during propagation or finishing influences finished plant quality or flowering. The experiment was conducted at a commercial greenhouse in West Lafayette, IN. Seeds of New Guinea impatiens (Impatiens hawkeri ‘Divine Blue Pearl’), French marigold (Tagetes patula ‘Bonanza Deep Orange’), gerbera (Gerbera jamesonii ‘Terracotta’), petunia (Petunia ×hybrida ‘Single Dreams White’), ornamental millet (Pennisetum glaucum ‘Jester’), pepper (Capsicum annuum ‘Hot Long Red Thin Cayenne’), and zinnia (Zinnia elegans ‘Zahara Fire’) were sown in 128-cell trays. On germination, trays were placed in a double-poly greenhouse under a 16-hour photoperiod of ambient solar radiation and photoperiodic lighting from compact fluorescent lamps providing a photosynthetic photon flux density (PPFD) of 2 µmol·m−2·s−1 (ambient conditions) or SL from either HPS lamps or LED fixtures providing a PPFD of 70 µmol·m−2·s−1. After propagation, seedlings were transplanted and finished under SL provided by the same HPS lamps or LED fixtures in a separate greenhouse environment. Overall, seedlings produced under SL were of greater quality [larger stem caliper, increased number of nodes, lower leaf area ratio (LAR), and greater dry mass accumulation] than those produced under no SL. However, seedlings produced under HPS or LED SL were comparable in quality. Although nutrient concentrations were greatest under ambient conditions, select macro- and micronutrient concentrations also were greater under HPS compared with LED SL. SL source during propagation and finishing had little effect on flowering and finished plant quality. Although these results indicate little difference in plant quality based on SL source, they further confirm the benefits gained from using SL for bedding plant production. In addition, with both SL sources producing a similar finished product, growers can prioritize other factors related to SL installations such as energy savings, fixture price, and fixture lifespan.

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Jianjun Zhang, Wei Zhu, Jaime A. Teixeira da Silva, Yongming Fan and Xiaonan Yu

The analysis of herbaceous peony (Paeonia lactiflora Pall.) floral bud initiation and differentiation from autumn to early spring is important because flower formation is strictly correlated with flowering in late spring. A clear understanding of peony flower development would allow management practices to be optimized for stable annual production and supply of cut flowers. The aim of this research was to study the time-sensitive characteristics underlying flower development in peony cultivar ‘Dafugui’. Flower bud differentiation was assessed by paraffin and hand-made slices, as well as stereomicroscopy. Both methods have strengths and weaknesses. Our observations are not entirely consistent with those of previous studies. Flower bud differentiation in ‘Dafugui’, which starts from late September to mid-April of the following year, is divided into differentiation of the lower parts (separate differentiation periods for the bracts, sepals, petals, stamens, and pistillodes) and upper parts (separate differentiation periods for the petals, stamens, and pistil), and is closely related to annual changes in ambient temperature. Differentiation of lower flower buds takes place before winter dormancy, whereas that of upper parts starts early in the following spring, and finally forms a double-flowered type. The three methods used in this article can be used to study P. lactiflora flower bud differentiation and can contribute to an understanding of this process in the future.

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Maria A. Macias-Leon and Daniel I. Leskovar

In the United States, most short-day onions are direct seeded. With this method, plant stands can be reduced because of extreme temperatures, weed pressure, and soil-borne diseases. Containerized transplants offer an alternative method of stand establishment with less seedling losses while producing uniform bulb sizes and high marketable yield. However, the use of transplants is not a widespread commercial practice because of the high cost of production. This study aims to select the best transplant strategies to improve onion crop performance in semiarid regions of southwest Texas or similar environments. Three sequential transplanting dates of early, mid, and late season (14 Nov., 8 Dec., and 9 Jan.) and two seedling densities of one seed per cell (T1) and three seeds per cell (T3) were evaluated on growth, yield, bulb quality, and phytonutrient content of three onion cultivars, two yellow (‘Caramelo’ and ‘Don Victor’), and one red (‘Lambada’). During early development, late-transplanted onions had an increase in plant height and greater leaf elongation rate than early and midtransplanted onions, whereas early plantings required more days to reach maturity than mid and late plantings. Overall, early and midtransplanting dates resulted in higher yields than late plantings. Although increasing seedling density (T3 vs. T1) did not significantly reduce marketable yield in early plantings, T1 produced a higher number of jumbo and colossal bulb sizes than T3. Onion quality was mostly affected by cultivar and not by transplant strategies. The technique of establishing onions from transplants grown from one plant per cell (T1) or multiple plants (T3) from early November to early December provides a practical and economical alternative to achieve earlier crops, while reducing the length of the production season, as planting date is delayed.

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Guangtian Cao, Tingting Song, Yingyue Shen, Qunli Jin, Weilin Feng, Lijun Fan and Weiming Cai

The Agaricus genus represents the most popular edible mushroom in the world. Wheat straw often is used as the substrate for mushroom cultivation following pretreatment to degrade the lignocellulosic biomass in agricultural waste. In this study, we investigated the changes in bacterial and fungal microflora of wheat straw substrate during different phases of composting. We collected samples of the raw material (M1), phase I aerobic fermentation (F1, F2, F3), and phase II after-fermentation (AF1) for high-throughput 16S rRNA and internal transcribed spacer (ITS) sequencing to analyze the microbial diversity in the substrate during composting. Our data revealed that among the five stages, 365 operational taxonomic units (OTUs) were shared, with Firmicutes, Proteobacteria, and Actinobacteria being the predominant bacterial phyla. In addition, Thermobispora, Thermopolyspora, Ruminiclostridium, Thermobacillus, and Bacillus were the predominant genera in F3 and AF1, with the species Thermobispora bispora and Pseudoxanthomonas taiwanensis being predominant in F2. Both principal component analysis (PCA) and nonmetric multidimensional scaling (NMDS) plots showed that the bacterial communities of five stages could be distinguished from each other based on their composting time. The Shannon and Simpson indexes of F2 were lower than M1 (P < 0.05), and the clustering dendrogram showed that the bacterial communities in AF1 were similar to F3, with Micromonosporaceae, Streptosporaceae, Thermomonosporaceae, and Vulgatibacteraceae representing the differential bacterial families by linear discriminant analysis with effect size (LEfSe) analysis. The analysis of fungal communities showed that 384 OTUs were common among the five stages, with 1054 and 454 OTUs unique to M1 and AF1, respectively. Ascomycota and Basidiomycota were the two predominant phyla in all stages, and Chytridiomycota was predominant in F2, F3, and AF1 stages. PCA and NMDS plots showed that the clusters of F2 and AF1 were more dispersed than the other stages. No differences were observed in alpha diversity between the stages, and samples of F1, F2, and F3 were closer to AF1 in the clustering dendrogram. By LEfSe analysis, Mycothermus thermophilus, Gonapodya polymorpha, and Phaeophleospora_eugeniae were identified as the predominant fungal species in AF1.

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Marcelo A.G. Carnelossi, Edinaldo O.A. Sena, Adrian D. Berry and Steven A. Sargent

Blueberry is widely grown around the world, and the United States is the leading producer. A strategy to maintain fruit quality during commercial handling is rapid cooling using the forced-air system. Hydrocooling (HY) is an effective cooling method widely used for many crops and has potential as a cooling method for blueberry. The objective of this study was to compare the cooling efficiency of conventional forced-air cooling (FA), the current commercial method, with immersion HY alone or HY in combination with FA (HY + FA), and to determine effects on blueberry fruit quality during subsequent cold storage. ‘Emerald’ and ‘Farthing’ southern highbush blueberry were commercially harvested and packed into plastic clamshell containers. FA was accomplished by simulating commercial conditions using a small-scale unit within a cold room at 1 °C/80% relative humidity (RH) until 7/8 cooling was achieved (27 minutes). For HY, fruit in clamshells (125 g) were immersed in chlorinated ice water (200 ppm free Cl−1, pH = 7.0) and 7/8 cooling occurred in 4 minutes. For HY + FA, fruit were 7/8 hydrocooled then transferred to FA for 30 minutes to remove free water from the fruit. After the cooling treatments, clamshells were evaluated weekly for selected quality parameters during 21 days storage at 1 °C. For HY treatment, the 1/2 cooling time was 1.13 minutes for ‘Emerald’ and 1.19 minutes for ‘Farthing’, whereas for FA treatment, the 1/2 cooling times were 4.5 and 6.8 minutes, respectively. For ‘Farthing’, cooling method did not affect fruit firmness; after 21 days, there was a slight softening in fruit from all treatments. However, ‘Emerald’ fruit cooled by HY + FA were softer than those from either HY or FA after 14 days of storage. For all cooling methods ‘Emerald’ was less acidic (0.3% citric acid) and was sweeter [10.2% soluble solids content (SSC)] than ‘Farthing’ (0.6% citric acid, 9.4% SSC). There were no differences in bloom among cooling methods. Bloom ratings for ‘Emerald’ remained >4.5 (70% to 80% coverage) whereas that for ‘Farthing’ cooled by HY or HY + FA was 3.7. Anthocyanin concentration in ‘Emerald’ fruit from HY + FA cooling method decreased by 33% during 21 days of storage, whereas that for ‘Farthing’ remained constant (8.3 mg cyanidin-3-Glicoside/g) irrespective of treatment during storage. Compared with ‘Farthing’, ‘Emerald’ was more sensitive to HY, where ≈15% of fruit developed visual skin breaks (split) after 7 days storage. HY shows potential as an alternative method to rapidly and thoroughly cool southern highbush blueberries such as ‘Farthing’, thus, maintaining fruit quality, while introducing a rinsing and sanitizing treatment. HY needs to be tested on commercial cultivars to determine the incidence of fruit splitting.

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Mokhles A. Elsysy, Michael V. Mickelbart and Peter M. Hirst

Uniform annual apple (Malus ×domestica) fruit production is highly dependent on consistent flower formation from year to year, as inconsistent flowering can lead to the biennial bearing observed in some high-value cultivars. The presence of fruit on a spur has been considered the main cause of the expression of biennial bearing and the inhibition of flower initiation, with a number of theories being introduced to explain the phenomenon. In the current experiment, individual spurs of annual bearing cultivars (Gala, Ruby Jon, and Pink Lady) and biennial bearing cultivars (Honeycrisp, Fuji, and Golden Delicious) were thinned to a single fruit or completely defruited at petal fall. Spurs were sampled at the end of the growing season. Effects of fruiting on spur characteristics such as spur and bourse leaf area, stomatal density, leaf gas exchange, and flower formation were determined. Across all cultivars, the presence of fruit on a spur did not affect spur characteristics or flower formation compared with nonfruiting spurs. Similarly, flowering was unaffected by those factors associated with greater spur carbohydrate status, such as bourse leaf area and assimilation rate. Cultivars with greater transpiration and stomatal conductance (g s) rates had lower rates of flower formation. Future studies should focus on xylem flow and expression of genes regulating flowering and plant growth regulators in annual and biennial bearing cultivars.

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Njung’e Vincent Michael, Pamela Moon, Yuqing Fu and Geoffrey Meru

Phytophthora capsici Leonian, the causal agent of Phytophthora crown rot in squash (Cucurbita pepo L.), is an economically important pathogen worldwide. Currently, no C. pepo cultivars immune to the pathogen are commercially available, but sources of resistance to Phytophthora crown rot have been identified in a set of 16 C. pepo plant introductions (PIs). Knowledge of the genetic relationships among these accessions and their relatedness to economically important morphotypes of C. pepo would inform breeders’ best strategies for introgressing resistance; however, this information is currently lacking. The goal of the current study was to determine genetic diversity among the resistant accessions and their genetic relatedness to susceptible morphotypes of subspecies pepo (Zucchini and Pumpkin) and texana (Acorn, Straightneck, and Crookneck) using 39 SSR markers. The markers revealed 132 alleles averaging 4.40 alleles per locus and had a mean polymorphic information content (PIC) and gene diversity of 0.44 and 0.49, respectively. CMTp235 had the highest PIC and gene diversity of 0.80 and 0.82, respectively. Hierarchical clustering by UPGMA and principal coordinate analysis (PCOA) revealed grouping into two major C. pepo subspecies, texana and pepo, with all the resistant accessions grouping in the latter. In order of increasing genetic distance (GD), the resistant accessions were least distant to Zucchini (GD = 0.34), followed by Pumpkin (GD = 0.40), Crookneck (GD = 0.56), Acorn (GD = 0.60), and Straightneck (GD = 0.61) morphotypes. Mean GD among the resistant accessions was 0.31 and was highest between PIs 615142 and 615132 (0.61). Based on genetic similarity, PIs 174185 and 181761 (disease severity ≤1.4) would be the best sources of resistance for transfer into subspecies texana and pepo, respectively. Overall, the results presented here support a closer genetic relationship between the resistant accessions and morphotypes of subspecies pepo than those of subspecies texana.

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Jinwook Lee, James P. Mattheis and David R. Rudell

‘Royal Gala’ apples can be susceptible to the incidence of fruit cracking and senescent flesh breakdown during cold storage. Because the development of these physiological disorders in other cultivars can be influenced by humidity during storage, the objective of this study was to evaluate the effect of high storage humidity on fruit quality attributes and incidence of physiological disorders in cold-stored ‘Royal Gala’ apples. Fruit obtained from a commercial orchard were kept in cardboard boxes with or without a perforated polyethylene liner during and after cold storage. High storage humidity induced by the perforated polyethylene liner reduced fresh weight loss but enhanced the change of fruit circumference after cold storage. High storage humidity contributed the most reduction of cortex lightness (L*) and hue angle (h o) in stem-end cortex tissues during shelf life. Fruit stored with liners had reduced internal ethylene concentration (IEC) and outer cortex firmness after removal from storage compared with control fruit. Furthermore, high storage humidity prevented shriveling but provoked fruit cracking. The incidence and severity of flesh breakdown were further aggravated during shelf life, compared with cold storage, regardless of a liner application. Overall, maintaining high storage humidity by applying a perforated polyethylene liner can contribute to delaying fresh weight loss, reducing IEC, and preventing fruit shriveling but can enhance cortex tissue browning, loss of flesh firmness, and incidence of fruit cracking during cold storage and shelf life.

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María Daniela Mares-Quiñones and Juan Ignacio Valiente-Banuet

Piquin pepper [Capsicum annuum L. var. glabriusculum (Dunal) Heiser and Pickergill] is a semidomesticated pepper with high commercial value and wide applications as fresh or processed products. Piquin pepper plants have been difficult to domesticate and cultivate because of low seed germination, genetic and morphologic variability, insect and disease susceptibility, and limited environmental physiology information. Currently, seed sterility is no longer considered a limiting factor as hormonal, chemical, and thermal treatments have been developed to overcome seed dormancy. In vitro propagation (primarily by direct organogenesis) is still not reliable for seedling production. Cropping systems of piquin pepper plants include traditional methods such as agroforestry and full sunlight, and under protected horticulture conditions, mainly shade nets. Shade levels and water availability affect yield and vegetative growth. Piquin pepper plants can be grown under diverse geographic and edaphic conditions. Nutrition and fertilization studies are limited. Biotic stresses that can cause economic damage to piquin pepper plants include most that affect other pepper cultivars. Piquin pepper is also considered an important genetic resource as it reports resistance to some viral groups, which could be used for genetic improvement of other cultivated peppers. Current research needs involve the development of dependable plant materials (cultivated varieties) with reduced labor needs, particularly during the harvest period. In addition, research is needed to reduce the susceptibility of piquin pepper plants to other plant diseases. This review presents an analysis of the aspects related to the production of piquin peppers under cultivated conditions.