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Comparing the effects of cytokinin source and concentration on shoot growth in a micropropagation system of UCB-1 interspecific Pistacia rootstock
No full textProtocols for the micropropagation of pistachio rootstock are not well established, and little is knownabout the effect of different plant growth regulators (PGRs) on micropropagation systems of the UCB-1
pistachio rootstock. Two cytokinins, 6-benzylaminopurine (BAP) and meta-Topolin (mT), were tested at
three different concentrations (1uM, 5uM, 10uM) to germinate, multiply, and root UCB-1 pistachio
seedlings in vitro. UCB-1 seedlings germinated at a rate of 76% in clean culture after being split with
bypass pruning shears and a 3hr decontamination treatment in 3000ppm sodium dichloroisocyanurate
(NaDCC) solution. Data were collected on cumulative shoot length, weight, and branching of singleshoot
descent lines. The 10uM concentration of both tested cytokinins provided the greatest amount of
shoot material at the end of three transfer cycles, though no significant difference (P < 0.05) in shoot
growth was found between the two cytokinins at that concentration. Mean rooting performance was
significantly (P < 0.001) higher for shoots multiplied with BAP (87.2%) as the source of cytokinin
compared to mT (57.9%)
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Excised Leaf Desiccation (ELD) as a Tool to Distinguish Desiccation Tolerance Among Almond Genotypes
No full textWater scarcity is a major concern for almond growers worldwide. To achieve sustainable almond production, it is crucial to identify strategies for improved water use efficiency including new cultivars compatible with the improved irrigation strategies. Pulsed-irrigation strategies have been shown to provide improved water use efficiency but make orchards highly vulnerable to catastrophic irrigation failures because, while the tree-zone is continuously provided with sufficient water to meet current transpiration needs, insufficient surplus water is available in the root zone to supply tree needs if irrigation is interrupted for as little as a few hours under high heat stress (McClymont and Goodwin, 2016). Excised shoot desiccation is a method for quickly evaluating cultivar differences in rapid leaf water loss that involves exposing excised shoots to desiccation under dry environments to evaluate genetic differences in subsequent leaf tissue damage. This approach appears useful as a rapid screen for tolerance to catastrophic irrigation failures based on early field performance (Appendix A). However, the underlying physiological mechanism as well as the consequence on tree productivity are unknown. To better understand the physiological basis, leaf characteristics of twenty almond genotypes were measured to examine their relationship with plant responses to rapid and severe water stress. We hypothesize that differences in the rate of excised shoot desiccation will be determined by genetic differences in the rate of leaf water loss, primarily by water loss through stomata and secondarily by waterloss through remaining epidermal tissue, and that these basic mechanisms will also determine differences in whole tree rate of water loss under stressful field conditions.
Excised shoots of the twenty genotypes were observed over 24 hours and excised shoot desiccation (ESD) scores were determined according to standardized wilting patterns ranging from 0 to 5 (0 for no desiccation, 5 for high desiccation). In subsequent experiments, excised leaves were used as a simplified model-system to evaluate differences in water retention under stress as previously described by McCaig and Romagosa (1991). Excised leaf desiccation (ELD) scores were determined using the same standardized wilting patterns used for ESD scoring. Relative water content (RWC) of sample leaves was recorded over time and the pattern of water loss with time was analyzed to identify underlying physiological mechanisms. This ELD experiment was then repeated with five genotypes selected for high productivity and kernel quality to provide more detailed data for genetic differences in excised leaf water loss patterns under more controlled laboratory environments. A moderate negative correlation was observed between ESD value and stomata density. The pattern of RWC decline differed among genotypes and ELD scores, demonstrating significant genetic differences. ELD score was significantly associated with water loss during the first 180 minutes when stomata closure response has been reported to be the major determinant of rate of water loss (Wang and Clarke, 1993; Darwish and Fahmy, 1997). It was found that the genotypes having lower ELD scores had reduced water loss in the first 180 minutes in the controlled environment. This suggests that genotypes showing low ELD scores were more effective in closing stomata following excision and so more effective in conserving leaf water. ELD scores were also significantly correlated with epidermal conductance (EC) for the five standard genotypes evaluated indicating that post stomata-closure differences in epidermal properties also play an important role in determining rate of water loss. The genotypes
that had lower EC were also the genotypes that showed reduced water loss patterns during the later stages of leaf desiccation. Genotypes showing high yields and good quality kernels under good commercial growing conditions expressed both high as well as low ESD scores, indicating that using ESD as a rapid screen for tolerance to catastrophic irrigation failures does not preclude selections for high yields and good kernel quality. While desiccation rates of excised shoots and excised leaves represent a relatively rapid test to identify inherent vulnerabilities in new as well as traditional breeding selections and cultivars, results need to be more fully assessed in both whole-plant as well as whole-orchard trials
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Fast Assay for Salinity Tolerance (FAST): A selection method to differentiate salt sequestration potential among Prunus genotypes
No full textSalinity is a major problem for agricultural production worldwide. In the Central Valley of California where most of the state’s almond acreage is located, high salt concentrations in soils and irrigation water is becoming a major limitation to continued production. Salinity tolerance has become an important requirement for both cultivars and rootstocks. High salt concentrations damage plant growth and development at multiple levels, making it a complicated trait to study. At a basic level, the two main strategies for tolerance to high soil salt concentrations are: a) the exclusion of salt and b) the sequestration of salt away from regions of sensitive leaf and shoot growth. This study examines diverse Prunus germplasm to determine if differences in levels of hardwood salt sequestration are present. Genotypes studied include a population of standard California commercial almond scion cultivars from different genetic origins and a ((Prunus persica x Prunus davidiana) x Prunus persica) rootstock breeding population. If differences in salt sequestration levels can be distinguished, this Fast Assay for Salinity Tolerance (FAST) could prove useful as a prescreening tool for identifying differences in plant salt sequestration potential. This, in turn, could facilitate subsequent studies on salt tolerance mechanisms and genetic control. Concurrently, genotypes from the FAST cultivar and rootstock experiments were compared to their whole plant counterparts grown under conditions of high salinity. We hypothesized that genotype and duration of salt exposure play a critical role in final woody tissue SC (salt concentration) by sequestration of accumulated NaCl. The SC data was measured from stem cuttings under standardized protocols in a controlled laboratory setting. Selected genotypes from the California industry-standard almond cultivars population were advanced into a follow-up irrigation experiment, where responses in leaf Na+, K+ T/C (Treatment/Control) ratio, and Cl⁻ accumulation were measured. The goal was to determine the relationship between SC and whole plant salt tolerance or sensitivity. If toxic salts can be sequestered in stem tissue, limiting their accumulation in sensitive leaves and shoots, this may contribute to an effective salt tolerance strategy. We hypothesize that high SC and low leaf accumulations of Na⁺ and Cl⁻, and higher K⁺ T/C ratio in leaves, give indications of overall salinity tolerance.Results showed that genotype and time were both significant (P<0.05) in both populations examined (peach rootstocks and almond scions). Genotypic differences in SC remained consistent over time, with genotype rankings at Week 1 largely preserved through Week 8. This was evidence that longer evaluation times were not essential for quickly assessing differences among genotypes. Relative differences among genotypes were effectively predicted by Week 1.In the FAST assessment of California almond cultivars, a positive weak correlation was observed for Cl⁻ and SC. There was also a weak negative correlation for Na⁺ with SC. There was no correlation between K⁺ T/C ratio and SC. These results suggest that higher NaCl, particularly Na, accumulation in the woody stems may be a useful predictor of general salt tolerance. Further testing and refining of the FAST method may thus provide a rapid method to prescreen for salt sequestration differences among large and genetically diverse populations. This method may also have application to other California tree crops: such as walnut, pistachio, and possibly fresh market fruits, as well as rootstocks
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Ontogeny of Almond Vegetative Meristems during Dormancy
No full textVegetative development is crucial to orchard tree growth and productivity. Vegetative bud formation and subsequent preformed and neoformed growth patterns determine tree size and architecture (Arquero and Jarvis-Shean 2017). Because flower buds are derived from vegetative buds, the number and distribution of vegetative buds are also a major determinant in tree crop (Lamp et al. 2001). The failure or significant delay of vegetative bud development and growth weakens tree productivity in the current year through the decreased availability of new shoots and leaves for photosynthesis. Failures affect tree productivity in the following years through decreased flower-bearing wood and thus decreased potential yields. In temperate crops various types of dormancy, including paradormancy, endodormancy and ecodormancy, have evolved to suppress bud development and so make these crop species less vulnerable to adverse environments. Different cultivars have different chill and heat requirements for successful transition through dormancy. With ongoing climate change, these differences have made some cultivars more vulnerable to subsequent bud survival and growth. Such bud “pushing” failures have a range of possible causes, including virus and bacterial infections, nutrient deficiencies and insufficient winter vernalization to overcome endodormancy (Gradziel and Fresnedo-Ramírez 2019). Endodormancy is defined as growth suppression by physiological factors within the plant vegetative buds, even in favorable environments (Alonso et al. 2005). Genetic bud-failures include those associated with specific cultivars and in particular Noninfectious Bud Failure (NBF) in Nonpareil and Carmel, and Environmental Bud Failure (EBF) in Monterey and Bennett-Hickman (Fresnedo-Ramírez et al. 2019). NBF and EBF both result in bud-failures but differ in their induction, developmental timelines, and ultimate cause of collapse. Understanding these differences is important for both diagnosis and management.Genetic control of Noninfectious Bud Failure has been demonstrated in crossing studies with almond and peach (Gradziel and Fresnedo-Ramírez 2019; Gradziel and Shackel 2021). Noninfectious bud-failure does not result from a genetic change but rather a change in the state of a “dormancy” gene; in effect, this gene is turned off at the wrong time and this change is irreversible once a certain genetic “age” is achieved (Fresnedo-Ramírez 2017; Gradziel and Shackel 2021). Results from earlier studies (Kester et al. 2005) support the current working model that this gene is also involved in the proper functioning of a hypothesized paradormancy in almond during late summer, and that this is the initial induction or trigger of the disorder. In contrast to endodormancy, paradormancy refers to bud dormancy caused by a signal from a structure other than the buds and is often associated with apical dominance (Kester et al. 2005).A critical diagnostic for NBF is that vegetative buds are already dead (necrotic and brown at the core) going into winter dormancy in the fall, further indicating that the induction occurred during earlier growth. Mechanisms for controlling gene action without changing gene identity are known as epigenetic mechanisms and include changes in gene methylation (D’Amico- Willman et al. 2021a; D’Amico-Willman et al. 2021b), chromosome (telomere) structure (D’Amico-Willman et al. 2021c), micro-RNA composition as well as several still poorly understood processes (Gradziel and Fresnedo-Ramírez 2019).In contrast, the greater site, source and year-to-year variability in Environmental Bud Failure (EBF) suggests that while it is associated with certain highly susceptible cultivars, it is strongly influenced by environmental factors such as diseases and other stresses during the previous growing seasons as well as environmental conditions during dormancy. Environmental bud-failure is activated at some time between fall dormancy and bud-pushing the following spring, but, like NBF, the specific time (and so developmental stage) of failure has not been determined. To better characterize the time and position of such failures in bud development, useful developmental milestones for bud development prior to and during dormancy need to be identified. This study has shown that the number of leaf primordia in dormant Nonpareil as well as Monterey buds shows a uniform rate of increase throughout dormancy. This internal bud- growth pattern can be thus used to establish a developmental timeline for normal dormant-bud development as well as providing more precise estimates for the time of bud failure. While much of this work is preliminary, it opens the door to a better understanding of the ontogeny of meristem and vegetative bud development in perennial plants. Ontogenesis is defined as the development of an individual organ or anatomical feature from the earliest stage to maturity. Negron et al. (2014) have demonstrated that the relative axillary bud position on current season shoot growth was the critical determinant of subsequent shoot fate, whether flower, or vegetative shoot, or blind node. This current research demonstrates that axillary bud ontogeny, including the structure and development of meristematic tissues within individual buds, is a critical determinant of subsequent development years to decades after initial formation. Improved knowledge of such deferred fates including endodormancy, paradormancy and ecodormancy, as well as epicormic shoot induction, will lead to more effective growth management in agricultural and ecological systems, including improved diagnosis and remediation of developmental disorders
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
No full text“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Redomesticating Almond to Meet Emerging Food Safety Needs
No full textAlmond is a desirable and high-quality food source where the presence of nut allergens and a vulnerability to aflatoxin and Salmonella contamination represent threats to consumer safety. In 2019, over 1 billion kg. of almonds, representing over 80% of the world total, were produced in California from a relatively few varieties with a very narrow genetic base. To address emerging needs mandated by cultural and climate changes, new germplasm has been introduced combining peach as well as wild peach and wild almond species. Advanced breeding selections incorporating exotic germplasm into a genetic background compatible with commercial production in California have demonstrated sizable reductions in level of kernel immunoreactivity as well as opportunities for improved control of aflatoxin and Salmonella. Breeding strategies employed include direct selection for reduced kernel immunoreactivity from an introgression enriched germplasm, the integration and pyramiding of resistance to multiple components of the aflatoxin disease-insect complex, and introduction of novel nut and tree traits to facilitate mechanized catch-frame field harvesting to avoid contamination with soil-borne pathogens such as Salmonella and Escherichia coli, as well as agrochemical residues
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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