Unlike most horticultural crops, blueberry (Vaccinium spp. section cyanococcus) prefers low-pH (4.2–5.5) soils. Other plants can acidify their rhizosphere to create a hospitable microenvironment. Southern highbush blueberry (SHB; Vaccinium corymbosum interspecific hybrids) plants do not acidify their rhizosphere in response to Fe deficiency, but other factors that affect rhizosphere pH have not been elucidated. We report results from two hydroponic experiments exploring N uptake effects on the rhizosphere pH of ‘Emerald’ SHB. Ammonium (NH4 +) uptake led to rhizosphere acidification, whereas nitrate (NO3 –) uptake led to rhizosphere alkalization. When grown in a split-root hydroponic system, roots that took up NH4 + acidified the rhizosphere to a greater extent that roots not exposed to NH4 +. Rhizosphere acidification was observed even in a nontreated control. These results suggest that NH4 + uptake is the main driver of rhizosphere pH in SHB. N form effects suggest that fertilization with NO3 – might lead to undesirable rhizosphere alkalization.
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Christopher S. Imler, Camila I. Arzola and Gerardo H. Nunez
Jianjun Li, Xiaoya Lian, Chenglin Ye and Lan Wang
Lonicera japonica Thunb., known as Japanese honeysuckle or golden-and-silver honeysuckle, belongs to the honeysuckle family and is native to eastern Asia, including China, Japan, and Korea. Microscopy, spectrophotometry, colorimetry, and the Royal Horticulture Society of Colorimetric Card (RHSCC) were used to compare and analyze the pigment distribution, content, and color variations in the Yujin 2 and Damaohua cultivars at different developmental stages. There were notable differences in the corolla color and the cross-section color between different developmental stages and different varieties. The lightness (L*), redness (a*), and yellowness (b*) values were calculated for each period for the two cultivars to observe variation trends. The chlorophyll content in the corollas of both cultivars showed declining trends with different rates. The chlorophyll content decreased rapidly from the young period to the two white period, and changed gradually from the two white period to the golden period. Moreover, the carotenoid content declined slightly from the young period to the silver period and rose sharply during the golden period. The ratio of these two pigment contents increased dramatically during the golden period: by 11.51 and 6.53 times in ‘Yujin 2’ and ‘Damaohua’, respectively. There were significant differences in corolla color, cross-section color, and the content of three pigments between the two varieties of honeysuckle. distribution and variation of pigments were the key factors affecting the flower color of honeysuckle. This study provides a basis for the identification and breeding of honeysuckle varieties and lays a foundation for further studies on the function and molecular mechanisms of pigments.
Rumana Yeasmin, Stephen P. Bonser, Satoru Motoki and Eiji Nishihara
Environmental conditions, specifically heat stress, are important factors in asparagus crop production. Arbuscular mycorrhizal fungi (AMF) have been shown to increase plant growth. Effects of heat stress on nutrient uptake have rarely been examined in intact plants, but the limited results indicate that heat stress will decrease uptake; no studies have examined heat stress effects on asparagus nutrient uptake. We examined the effects of AMF, Glomus intraradices, on the growth, nutrient uptake, heat stress responses, and antioxidative activity in asparagus (Asparagus officinalis L.). We grew AMF-inoculated or non–AMF-inoculated asparagus plants in sand culture at 20 to 25 °C for 14 weeks in a greenhouse and subsequently subjected to three temperature conditions (control = 20 °C/25 °C night/day, mild heating = 30 °C/35 °C night/day, and severe heating = 37 °C/42 °C night/day) in growth chambers. Morphological and physiological growth parameters were compared between AMF-inoculated and non–AMF-inoculated plants. The mycorrhizal symbiosis markedly enhanced biomass production and heat stress responses negatively in plants compared with that in the non–AMF-inoculated plants. Plants grown under non–AMF-inoculated treatment had severe rate of leaf browning (80% to 100%), whereas the mycorrhizal plants showed a minimum rate of leaf browning under heat stress conditions. The results indicated mycorrhizal-inoculated plants showed an increase activity of antioxidative enzymes, such as superoxide dismutase and ascorbate peroxidase. The 2,2-diphenyl-1picrylhydrazyl radical scavenging activity also showed a greater response in mycorrhizal plants than in the control plants under each temperature treatment. Application of AMF enhanced plant growth and mineral nutrients and alleviated heat stress damage through an increased antioxidative activity and the mycorrhizal symbiosis significantly enhanced heat stress tolerance of asparagus.
Rachel Leisso, Ines Hanrahan and Jim Mattheis
‘Honeycrisp’ apple is susceptible to the postharvest chilling disorder soft scald that renders fruit unmarketable. Reducing or preventing this disorder is an important component of ‘Honeycrisp’ postharvest management. In commercial settings, advanced fruit maturity and orchard history contribute to an estimation of soft scald susceptibility, but additional at-harvest information indicative of soft scald risk would enable better management decisions. In this study, we obtained fruit from commercial orchards for 3 successive years, and assessed field growing degree days (GDD), field chilling hours (CH), and fruit quality metrics at harvest, followed by soft scald incidence assessment at 12 weeks of cold storage. The analyses indicated starch index, soluble solids content (SSC), internal ethylene concentration, titratable acidity (TA), peel background color, firmness, GDD, or CH do not reliably indicate fruit susceptibility to soft scald. However, SSC and TA were elevated in fruit that later developed soft scald, and a higher number of GDD also sometimes preceded soft scald, which is consistent with advanced fruit maturity that can enhance soft scald risk. Overall, results suggest that other tools may be required to accurately predict postharvest soft scald on a quality control laboratory scale. The statistical analyses applied to the present study would have utility for assessing other soft scald prediction tools or markers.
Peter M.A. Toivonen, Jared Stoochnoff, Kevin Usher, Changwen Lu, Paul A. Wiersma and Chunhua Zhou
The market value of the apple (Malus ×domestica Borkh.) cultivar Ambrosia is closely linked to the characteristic blush on the skin surface. For ‘Ambrosia’ orchards that produce consistently low levels of surface blush, the implementation of reflective rowcovering has improved surface coloration, but the reflected wavebands responsible for this enhanced color production have not been confirmed. This study consisted of two separate experiments: one conducted in the field to confirm reflective rowcovering efficacy and the other in a controlled environment cabinet to determine which waveband was enhancing red blush production. The red blush production in orchards with and without reflective rowcovering was then directly compared with the red blush produced on the surface of apples that were poorly colored at harvest and then exposed to visible, fluorescent, ultraviolet A (UVA), or ultraviolet B (UVB) light sources within the controlled environment chamber. Consequent analysis of the red blush color within the Commission Internationale de l’Eclairage a* and b* color space was conducted to evaluate the quality of the red blush pigment under each treatment in the field and the controlled environment chamber. The analysis revealed that the red blush that developed on apples from the reflective rowcover treatment most closely matched the red blush that developed in response to UVB exposure in the controlled environment cabinet. Further analysis of gene expression and anthocyanin contents in the ‘Ambrosia’ apples support the hypothesis that the primary driver for the characteristic red blush development, when reflective rowcovers are used, is increased exposure to UVB light.
Maciej A. Pszczolkowski, Kyndra Chastain, Rachel Veenstra and Martin L. Kaps
The Japanese beetle (Popillia japonica Newman) is one of the most widespread and destructive invasive insect pests in the eastern United States. Blackberry (Rubus sp.) production in the United States has increased significantly in recent years. With the introduction of new blackberry cultivars, insect resistance should become the focus of further breeding efforts. The objective of the current study was to evaluate the susceptibility of 13 blackberry cultivars to the Japanese beetle. The seasonal population dynamics of this insect, beetle damage to blackberry foliage, and beetle preference of blackberry cultivars were monitored from 2016 to 2018 on a blackberry plantation in Mountain Grove, MO. Japanese beetles feeding on blackberries occurred between 814 to 1251 cumulative degree-days (CDD; base, 10 °C) after 1 Jan. The following cultivars were evaluated: Apache, APF-40, Arapaho, Chester, Chickasaw, Kiowa, Natchez, Osage, Ouachita, Prime-Ark 45, Prime-Jan, Prime-Jim, and Triple Crown. Foliage damage incidence, defined as average percentage of leaves damaged by beetles on a given cane, did not differ among the cultivars. However, average severity of damage, estimated by rating on a scale from 0 (least) to 5 (most) of all damaged leaves on a given cane was different among cultivars. Ouachita and APF-40 exhibited the lowest damage severity rating among floricanes and primocanes, respectively. Apache (a floricane) and Prim-Jan (a primocane) were the most susceptible cultivars. Japanese beetle preferences for cultivars correlated with the degree of foliage damage. Because all blackberry cultivars exhibited similar foliage feeding incidence, but different feeding severity, we suggest the Japanese beetle does not differentiate among blackberry cultivars from a distance, but does upon contact with the foliage of a given plant.
Min Fan, Yike Gao, Yaohui Gao, Zhiping Wu, Hua Liu and Qixiang Zhang
Simple sequence repeat (SSR) markers are valuable for genetic and breeding applications, but SSR resources for the ornamental genus chrysanthemum (Chrysanthemum ×morifolium Ramat.) are still limited. Expressed sequence tags (ESTs) are sources of SSRs that represent an opportunity to develop SSRs to accelerate molecular breeding in chrysanthemum. In total, 4661 SSR loci were identified from 3823 SSR-containing unigenes in the chrysanthemum transcriptome with an average of one SSR per 6.98 kb. Of these SSR sequences, trinucleotide repeats (30.0%) predominated, followed by dinucleotide repeats (17.9%). In total, 1584 primer pairs were subsequently synthesized. By screening the parents and six individuals of the F1 progeny, 831 (52.5%) valid EST-SSR markers were identified, of which 361 (43.4%) were polymorphic. The annotation of unigenes containing polymorphic SSRs indicated that 330 (93.5%) demonstrated significant homology to other plant protein sequences. Twenty-five polymorphic EST-SSR markers were further selected for transferability analysis and exhibited 93% amplification in six Ajania species and six other Chrysanthemum species. Based on genotyping of the 59 samples, neighbor-joining analysis revealed six phylogenetic groupings, which was confirmed by population structure analysis and principal component analysis (PCA). Phylogenetic relationships among the 59 samples revealed by SSRs were highly consistent with the traditional taxonomic classification of Chrysanthemum and Ajania. The polymorphism information content (PIC) values ranged from 0.29 to 0.86, with a mean of 0.67, indicating high levels of informativeness. This research reveals the SSR distribution characteristics of chrysanthemum and provides a large number of new EST-SSR markers for further genetic diversity studies, genetic mapping, and molecular marker-assisted selection breeding for chrysanthemum.
Melinda A. Miller-Butler, Barbara J. Smith, Brian R. Kreiser and Eugene K. Blythe
Strawberry anthracnose diseases are caused primarily by three Colletotrichum species: C. acutatum J.H. Simmonds, C. fragariae A.N. Brooks, and C. gloeosporioides (Penz.) Penz. & Sacc. Molecular markers are being used in breeding programs to identify alleles linked to disease resistance and other positive agronomic traits. In our study, strawberry cultivars and breeding germplasm with known anthracnose susceptibility or resistance to the three anthracnose-causing Colletotrichum species were screened for two sequence characterized amplified region (SCAR) markers linked to the Rca2 gene. The Rca2 resistant allele SCAR markers were associated with varying degrees of significance for a strawberry plant’s anthracnose resistance to C. fragariae but not to C. acutatum or C. gloeosporioides. Although the presence or absence of the markers associated with the Rca2 resistance gene is an imperfect indicator of anthracnose resistance, it may serve as a useful starting point in selecting germplasm for breeding programs.
Will Wheeler, Reagan Wytsalucy, Brent Black, Grant Cardon and Bruce Bugbee
Native American tribes have been cultivating peaches [Prunus persica (L.) Batsch] since their introduction to North America in the 1600s. In the American Southwest, peach orchards derived from centuries of seed selections have been maintained in relative isolation from commercial cultivars. These Native American peach selections may be better adapted to the arid climate of the Intermountain West. We compared physiological robustness during water stress of seedling peaches from a 60-year-old orchard maintained by Navajo farmers in southwestern Utah to the commercial peach rootstock Lovell. Six replicate trees of each rootstock were subjected to eight cycles of controlled drought on an automated lysimeter system, which monitored transpiration rate continuously. Trees were selected for uniform size and transpiration rate at the start of the study. During the drought cycles, individual trees were watered when their transpiration rate decreased to less than 250 g of water per day, ≈20% of their well-watered daily transpiration rate. After the first cycle of drought, the transpiration rate of the Navajo trees was greater than the Lovell trees, so they depleted their root-zone water more rapidly and experienced greater water stress. Despite greater stress, the Navajo selection had greater leaf area and dry weight at harvest. Because the root system was confined, these results indicate that the Navajo selection may have greater resilience when experiencing drought, independent of the depth and distribution of the root system. However, this study was not able to determine whether physiological resilience during drought was a result of canopy or root characteristics. Field studies are needed to determine whether root distribution or depth also contribute to drought tolerance in the Navajo selection.
Yinping Li, Raymond A. Cloyd and Nora M. Bello
Western flower thrips, Frankliniella occidentalis, is one of the most destructive insect pests of greenhouse-grown horticultural crops. The primary method of managing western flower thrips populations involves applications of insecticides; however, there is no information associated with the effect of the insect growth regulator, pyriproxyfen, or the entomopathogenic fungus, Isaria fumosorosea, on western flower thrips pupae in growing media. Therefore, four laboratory experiments were conducted to determine the effect of pyriproxyfen and I. fumosorosea applied as a drench to growing media on western flower thrips pupae. Expt. 1 evaluated the efficacy of pyriproxyfen and I. fumosorosea on western flower thrips pupae. Based on the results from Expt. 1, Expt. 2 assessed the effect of pyriproxyfen in two growing media (LC1 and BM1) on western flower thrips pupae. Expts. 3 and 4 determined the residual activity of pyriproxyfen in growing media on western flower thrips pupae 3, 5, 7, and 14 days after treatments were applied. The pyriproxyfen treatment resulted in a significantly lower estimated mean probability of western flower thrips adults captured on yellow sticky cards (17%) compared with the water control (59%), untreated check (88%), and two I. fumosorosea treatments (46% for 1.0 g and 41% for 2.0 g of Ancora) in Expt. 1. However, for the two growing media in Expt. 2, the estimated mean probability of western flower thrips adults captured on yellow sticky cards was not significantly different between the pyriproxyfen treatment (LC1 = 15%; BM1 = 12%) and the water control (LC1 = 41%; BM1 = 24%). For either the pyriproxyfen treatment or the untreated check, there was no evidence of a significant difference between the two growing media on the estimated mean probability of western flower thrips adults captured on yellow sticky cards. Furthermore, there was no evidence of any residual activity 3 days after drench applications of pyriproxyfen. The results of the study have demonstrated that drench applications of pyriproxyfen are not affecting survival of western flower thrips pupae.