Is calcium deficiency the real cause of bitter pit? A review.

Bitter pit is a disorder affecting the appearance of apples. Susceptibility is genetically controlled by both the cultivar and rootstock, with both environmental and horticultural factors affecting its severity and proportional incidence. Symptoms appear more frequently at the calyx end of the fruit and consist of circular necrotic spots, which take on a "corky" appearance visible through the peel. Bitter pit may develop before harvest, or after harvest, reducing the proportions of marketable fruit. In this review, current knowledge of the factors associated with the occurrence of bitter pit in apples is summarized and discussed along with their interactions with Ca uptake and distribution to fruit. This disorder has been previously linked with localized Ca deficiencies in fruit during its development. However, these relationships are not always clear. Even with over a century of research, the precise mechanisms involved in its development are still not fully understood. Additional factors also contribute to bitter pit development, like imbalances of mineral nutrients, low concentration of auxins, high concentration of gibberellins, changes in xylem functionality, or physiological responses to abiotic stress. Bitter pit remains a complex disorder with multiple factors contributing to its development including changes at whole plant and cellular scales. Apple growers must carefully navigate these complex interactions between genetics, environment, and management decisions to minimize bitter pit in susceptible cultivars. Accordingly, management of plant nutrition, fruit crop load, and tree vigor still stands as the most important contribution to reducing bitter pit development. Even so, there will be situations where the occurrence of bitter pit will be inevitable due to cultivar and/or abiotic stress conditions.

New insights into the role of the root system of epiphytic bromeliads: comparison of root and leaf trichome functions in acquisition of water and nutrients.

BACKGROUND: In epiphytic bromeliads, the roots used to be considered poorly functional organs in the processes of absorption and metabolization of water and nutrients, while the leaves always acted as protagonists in both functions. More recent discoveries have been changing this old view of the root system. SCOPE: In this review, we will address the old thoughts of the scientific community regarding the function performed by the roots of epiphytic bromeliads (mere holdfast structures with low physiological activity) and the importance of a reduced or lack of root system for the emergence of epiphytism. We will present indirect and direct evidence that contradicts this older hypothesis. Furthermore, the importance of the root absorptive function mainly for juvenile tankless epiphytic bromeliads and the characteristics of the root absorption process of adult epiphytic tank bromeliads will be thoroughly discussed in physiological aspects. Finally, some factors (species, substrate, environmental conditions) that influence the absorptive capability of the roots of epiphytic tank bromeliads will also be considered in this review, highlighting the importance that the absorptive role of the roots have for the plasticity of bromeliads that live on trees, which is an environment characterized by the intermittent availability of water and nutrients. CONCLUSIONS: The roots of tank-forming epiphytic bromeliads play important roles in the absorption and metabolization of nutrients and water. The importance of roots stands out mainly for juvenile tankless bromeliads since the root is the main absorptive organ. In larger plants with tank, although the leaves become the protagonists in the resource acquisition process, the roots complement the absorptive function of the leaf trichomes, resulting in a better growth of the bromeliad. The physiological and biochemical properties of the processes of absorption and distribution of resources in the tissues seem to differ between absorption by trichomes and roots.

Tripartite interactions of an endophytic entomopathogenic fungus, Asian corn borer, and host maize under elevated carbon dioxide.

BACKGROUND: Biological control of insect pests is encountering an unprecedented challenge in agricultural systems due to the ongoing rise in carbon dioxide (CO2) level. The use of entomopathogenic fungi (EPF) in these systems is gaining increased attention, and EPF as crop endophytes hold the potential for combining insect pest control and yield enhancement of crops, but the effects of increased CO2 concentration on this interaction are poorly understood. Here, the introduction of endophytic EPF was explored as an alternative sustainable management strategy benefiting crops under elevated CO2, using maize (Zea mays), Asian corn borer (Ostrinia furnacalis), and EPF (Beauveria bassiana) to test changes in damage to maize plants from O. furnacalis, and the nutritional status (content of carbon, nitrogen, phosphorus, potassium), biomass, and yield of maize. RESULTS: The results showed that endophytic B. bassiana could alleviate the damage caused by O. furnacalis larvae for maize plants under ambient CO2 concentration, and this effect was enhanced under higher CO2 concentration. Inoculation with B. bassiana effectively counteracted the adverse impact of elevated CO2 on maize plants by preserving the nitrogen content at its baseline level (comparable with ambient CO2 conditions without B. bassiana). Both simultaneous effects could explain the improvement of biomass and yield of maize under B. bassiana inoculation and elevated CO2. CONCLUSION: This finding provides key information about the multifaceted benefits of B. bassiana as a maize endophyte. Our results highlight the promising potential of incorporating EPF as endophytes into integrated pest management strategies, particularly under elevated CO2 concentrations. © 2024 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Arbuscular mycorrhizal symbiosis with Rhizophagus irregularis DAOM197198 modifies the root transcriptome of walnut trees.

Walnut trees are cultivated and exploited worldwide for commercial timber and nut production. They are heterografted plants, with the rootstock selected to grow in different soil types and conditions and to provide the best anchorage, vigor, and resistance or tolerance to soil borne pests and diseases. However, no individual rootstock is tolerant of all factors that impact walnut production. In Europe, Juglans regia is mainly used as a rootstock. Like most terrestrial plants, walnut trees form arbuscular mycorrhizal symbioses, improving water and nutrient uptake and providing additional ecosystem services. Effects of arbuscular mycorrhizal symbiosis on root gene regulation, however, has never been assessed. We analyzed the response of one rootstock of J. regia to colonization by the arbuscular mycorrhizal fungus Rhizophagus irregularis DAOM197198. Plant growth as well as the nitrogen and phosphorus concentrations in roots and shoots were significantly increased in mycorrhizal plants versus non-colonized plants. In addition, we have shown that 1,549 genes were differentially expressed, with 832 and 717 genes up- and down-regulated, respectively. The analysis also revealed that some rootstock genes involved in plant nutrition through the mycorrhizal pathway, are regulated similarly as in other mycorrhizal woody species: Vitis vinifera and Populus trichocarpa. In addition, an enrichment analysis performed on GO and KEGG pathways revealed some regulation specific to J. regia (i.e., the juglone pathway). This analysis reinforces the role of arbuscular mycorrhizal symbiosis on root gene regulation and on the need to finely study the effects of diverse arbuscular mycorrhizal fungi on root gene regulation, but also of the scion on the functioning of an arbuscular mycorrhizal fungus in heterografted plants such as walnut tree.

Transcriptional and metabolic profiling of sulfur starvation response in two monocots.

BACKGROUND: Sulfur (S) is a mineral nutrient essential for plant growth and development, which is incorporated into diverse molecules fundamental for primary and secondary metabolism, plant defense, signaling, and maintaining cellular homeostasis. Although, S starvation response is well documented in the dicot model Arabidopsis thaliana, it is not clear if the same transcriptional networks control the response also in the monocots. RESULTS: We performed series of physiological, expression, and metabolite analyses in two model monocot species, one representing the C3 plants, Oryza sativa cv. kitaake, and second representing the C4 plants, Setaria viridis. Our comprehensive transcriptomic analysis revealed twice as many differentially expressed genes (DEGs) in S. viridis than in O. sativa under S-deficiency, consistent with a greater loss of sulfur and S-containing metabolites under these conditions. Surprisingly, most of the DEGs and enriched gene ontology terms were species-specific, with an intersect of only 58 common DEGs. The transcriptional networks were different in roots and shoots of both species, in particular no genes were down-regulated by S-deficiency in the roots of both species. CONCLUSIONS: Our analysis shows that S-deficiency seems to have different physiological consequences in the two monocot species and their nutrient homeostasis might be under distinct control mechanisms.

Optimizing nutrient solution for vegetative growth of Dendrobium Tubtim Siam and Phalaenopsis Taisuco Swan through plant tissue nutrient balance estimation.

BACKGROUND: Orchids are grown without soil in many regions of the world, but there is a lack of studies to define the balanced and adequate nutrient solution for their cultivation, mainly in the vegetative growth phase. Therefore, this paper aims to evaluate the optimal concentration of the nutrient solution based on the proposal by Hoagland and Arnon (1950) in the vegetative growth phase capable of increasing the nutrient contents, growth, and dry matter production of Dendrobium Tubtim Siam and Phalaenopsis Taisuco Swan. In addition, this paper aims to estimate a new nutrient solution from the optimal nutrient contents in the dry matter of these orchid species to be used in the vegetative growth phase. RESULTS: Nutrient contents, growth, and dry matter production increased as the nutrient solution concentration increased up to an average concentration of 62 and 77% for D. Tubtim Siam and P. Taisuco Swan, respectively. We found that the Hoagland and Arnon solution presented a group of nutrients with concentrations above the requirement for P. Taisuco Swan (nitrogen, phosphor, calcium, and sulfur) and D. Tubtim Siam (phosphor, calcium, magnesium, and sulfur), while other nutrients in the solution did not meet the nutritional demand of these orchid species, inducing nutritional imbalance in the vegetative growth phase. CONCLUSION: We conclude that using a balanced nutrient solution created specifically for each orchid species in vegetative growth might favor their sustainable cultivation by optimizing the use of nutrients in the growing medium.

Functionalized biochar from waste as a slow-release nutrient source: Application on tomato plants.

Licorice processing waste was pyrolyzed at different temperatures (500 and 700 °C) to obtain biochar (BC500 and BC700) for use as a slow-release fertilizer on Solanum lycopersicum. The materials were characterized through BET analysis, SEM, elemental analysis, pHzc, and pyrolysis temperature effect was evaluated. The biochars were functionalized by the impregnation method to enrich them with nitrogen, phosphorus, and potassium (NPK), and desorption tests were performed in aqueous solution at different pHs (5 and 7). The pseudo-second-order model described well the release of all 3 macronutrients tested, BC500 was found to have slower release kinetics due to smaller pore size, reaching adsorption/desorption equilibrium after 14 days, compared with 10 for BC700, Kdes were lower in all 3 cases and NPK content was higher, initial pH did not change the release kinetics. BC500 was selected as an agricultural soil conditioner by testing at both different dosages of BC (0-25 %) and different NPK ratios (3:1:4 and 4:1:3). The treatment significance was evaluated. The best treatment resulted in BC dosage of 25 % nutrient ratio 4:1:3 which increased, compared to the control, total chlorophyll content (+38 %) and carotenoids (+15 %).

The role of Manganese in tree defenses against pests and pathogens.

Manganese (Mn) deficiency is a widespread occurrence across different landscapes, including agricultural systems and managed forests, and causes interruptions in the normal metabolic functioning of plants. The microelement is well-characterized for its role in the oxygen-evolving complex in photosystem II and maintenance of photosynthetic structures. Mn is also required for a variety of enzymatic reactions in secondary metabolism, which play a crucial role in defense strategies for trees. Despite the strong relationship between Mn availability and the biosynthesis of defense-related compounds, there are few studies addressing how Mn deficiency can impact tree defense mechanisms and the ensuing ecological patterns and processes. Understanding this relationship and highlighting the potentially deleterious effects of Mn deficiency in trees can also inform silvicultural and management decisions to build more robust forests. In this review, we address this relationship, focusing on forest trees. We describe Mn availability in forest soils, characterize the known impacts of Mn deficiency in plant susceptibility, and discuss the relationship between Mn and defense-related compounds by secondary metabolite class. In our review, we find several lines of evidence that low Mn availability is linked with lowered or altered secondary metabolite activity. Additionally, we compile documented instances where Mn limitation has altered the defense capabilities of the host plant and propose potential ecological repercussions when studies are not available. Ultimately, this review aims to highlight the importance of untangling the effects of Mn limitation on the ecophysiology of plants, with a focus on forest trees in both managed and natural stands.

Epidemiology and management of Fusarium wilt of Eucalyptus camaldulensis through systemic acquired resistance.

Eucalyptus camaldulensis is a multifunctional tree and is globally used for the reclamation of problematic lands. Eucalyptus camaldulensis is prone to attack by a number of pathogens, but the most important threat is the Fusarium wilt (Fusarium oxysporum). Keeping in view the importance of E. camaldulensis and to manage this disease, five plant activators, i.e., salicylic acid (C7H6O3), benzoic acid (C7H6O2), citric acid (C6H8O7), dipotassium phosphate (K2HPO4), monopotassium phosphate (KH2PO4) and nutritional mixture namely Compound (NPK) and nutriotop (Fe, Zn, Cu, B, Mn) were evaluated in the Fusarium infested field under RCBD in the Research Area, Department of Forestry and Range Management, University of Agriculture, Faisalabad (UAF). Among plant activators, salicylic acid and a combination of compound + nutriotop exhibited the lowest disease incidence and enhanced fresh and dry weight of leaves compared to other treatments and control. Results of the environmental study indicated maximum disease incidence between 35-40 °C (max. T), 6-25 °C (mini. T), 70-80% relative humidity and 1.5-2.5 km/h wind speed while pan evaporation expressed weak correlation with disease development. It was concluded that Fusarium wilt of Eucalyptus camaldulensis could be managed through activation of the basal defense system of the host plant with provision of salicylic acid and balanced nutrition by considering environmental factors. Recent exploration is expected to be helpful for future research efforts on epidemiology and ecologically sound intervention of Fusarium wilt of Eucalyptus camaldulensis.

Divergent colonization traits, convergent benefits: different species of arbuscular mycorrhizal fungi alleviate Meloidogyne incognita damage in tomato.

Arbuscular mycorrhizal fungi (AMF) can increase plant tolerance and/or resistance to pests such as the root-knot nematode Meloidogyne incognita. However, the ameliorative effects may depend on AMF species. The aim of this work was therefore to evaluate whether four AMF species differentially affect plant performance in response to M. incognita infection. Tomato plants grown in greenhouse conditions were inoculated with four different AMF isolates (Claroideoglomus claroideum, Funneliformis mosseae, Gigaspora margarita, and Rhizophagus intraradices) and infected with 100 second stage juveniles of M. incognita at two different times: simultaneously or 2 weeks after the inoculation with AMF. After 60 days, the number of galls, egg masses, and reproduction factor of the nematodes were assessed along with plant biomass, phosphorus (P), and nitrogen concentrations in roots and shoots and root colonization by AMF. Only the simultaneous nematode inoculation without AMF caused a large reduction in plant shoot biomass, while all AMF species were able to ameliorate this effect and improve plant P uptake. The AMF isolates responded differently to the interaction with nematodes, either increasing the frequency of vesicles (C. claroideum) or reducing the number of arbuscules (F. mosseae and Gi. margarita). AMF inoculation did not decrease galls; however, it reduced the number of egg masses per gall in nematode simultaneous inoculation, except for C. claroideum. This work shows the importance of biotic stress alleviation associated with an improvement in P uptake and mediated by four different AMF species, irrespective of their fungal root colonization levels and specific interactions with the parasite.

Micronutrient-microbiome interplay: a critical regulator of soil-plant health.

The delicate balance between soil micronutrients and the phytobeneficial microbiome is crucial for maintaining soil-plant health. Recently, Dai et al. established a correlation between elemental micronutrients and the soil microbiome that regulates plant quality and productivity, offering innovative and sustainable solutions to increase agricultural production in a changing climate.

Rhizosphere priming promotes plant nitrogen acquisition by microbial necromass recycling.

Nitrogen availability in the rhizosphere relies on root-microorganism interactions, where root exudates trigger soil organic matter (SOM) decomposition through the rhizosphere priming effect (RPE). Though microbial necromass contribute significantly to organically bound soil nitrogen (N), the role of RPEs in regulating necromass recycling and plant nitrogen acquisition has received limited attention. We used 15N natural abundance as a proxy for necromass-N since necromass is enriched in 15N compared to other soil-N forms. We combined studies using the same experimental design for continuous 13CO2 labelling of various plant species and the same soil type, but considering top- and subsoil. RPE were quantified as difference in SOM-decomposition between planted and unplanted soils. Results showed higher plant N uptake as RPEs increased. The positive relationship between 15N-enrichment of shoots and roots and RPEs indicated an enhanced necromass-N turnover by RPE. Moreover, our data revealed that RPEs were saturated with increasing carbon (C) input via rhizodeposition in topsoil. In subsoil, RPEs increased linearly within a small range of C input indicating a strong effect of root-released C on decomposition rates in deeper soil horizons. Overall, this study confirmed the functional importance of rhizosphere C input for plant N acquisition through enhanced necromass turnover by RPEs.

Dynamic interactions between SPX proteins, the ubiquitination machinery, and signalling molecules for stress adaptation at a whole-plant level.

The plant macronutrient phosphorus is a scarce resource and plant-available phosphate is limiting in most soil types. Generally, a gene regulatory module called the phosphate starvation response (PSR) enables efficient phosphate acquisition by roots and translocation to other organs. Plants growing on moderate to nutrient-rich soils need to co-ordinate availability of different nutrients and repress the highly efficient PSR to adjust phosphate acquisition to the availability of other macro- and micronutrients, and in particular nitrogen. PSR repression is mediated by a small family of single SYG1/Pho81/XPR1 (SPX) domain proteins. The SPX domain binds higher order inositol pyrophosphates that signal cellular phosphorus status and modulate SPX protein interaction with PHOSPHATE STARVATION RESPONSE1 (PHR1), the central transcriptional regulator of PSR. Sequestration by SPX repressors restricts PHR1 access to PSR gene promoters. Here we focus on SPX4 that primarily acts in shoots and sequesters many transcription factors other than PHR1 in the cytosol to control processes beyond the classical PSR, such as nitrate, auxin, and jasmonic acid signalling. Unlike SPX1 and SPX2, SPX4 is subject to proteasomal degradation not only by singular E3 ligases, but also by SCF-CRL complexes. Emerging models for these different layers of control and their consequences for plant acclimation to the environment will be discussed.

Plant-soil synchrony in nutrient cycles: Learning from ecosystems to design sustainable agrosystems.

Redesigning agrosystems to include more ecological regulations can help feed a growing human population, preserve soils for future productivity, limit dependency on synthetic fertilizers, and reduce agriculture contribution to global changes such as eutrophication and warming. However, guidelines for redesigning cropping systems from natural systems to make them more sustainable remain limited. Synthetizing the knowledge on biogeochemical cycles in natural ecosystems, we outline four ecological systems that synchronize the supply of soluble nutrients by soil biota with the fluctuating nutrient demand of plants. This synchrony limits deficiencies and excesses of soluble nutrients, which usually penalize both production and regulating services of agrosystems such as nutrient retention and soil carbon storage. In the ecological systems outlined, synchrony emerges from plant-soil and plant-plant interactions, eco-physiological processes, soil physicochemical processes, and the dynamics of various nutrient reservoirs, including soil organic matter, soil minerals, atmosphere, and a common market. We discuss the relative importance of these ecological systems in regulating nutrient cycles depending on the pedoclimatic context and on the functional diversity of plants and microbes. We offer ideas about how these systems could be stimulated within agrosystems to improve their sustainability. A review of the latest advances in agronomy shows that some of the practices suggested to promote synchrony (e.g., reduced tillage, rotation with perennial plant cover, crop diversification) have already been tested and shown to be effective in reducing nutrient losses, fertilizer use, and N2 O emissions and/or improving biomass production and soil carbon storage. Our framework also highlights new management strategies and defines the conditions for the success of these nature-based practices allowing for site-specific modifications. This new synthetized knowledge should help practitioners to improve the long-term productivity of agrosystems while reducing the negative impact of agriculture on the environment and the climate.

Zinc speciation in highly weathered tropical soils affected by large scale vegetable production.

Agriculture in highly weathered tropical soils often requires considerable application of lime and fertilizers to ensure satisfactory plant nutrient levels. The consequences of these continue long-term applications is not well understood may induce changes in soil chemical properties, the abundance, and speciation of potentially toxic trace element and as well as of micronutrients in agriculture soils. In this study, we evaluated the adsorption (at pH 5) and speciation of Zn in tropical soils (both agricultural and native vegetation) as a function of fertilization and contact time using chemical fractionation analyses and X-ray absorption spectroscopy. The soils overall had high Zn adsorption capacities (∼ 700 mg kg-1), but the agricultural soil was approximately 30 % higher than of the soil under native vegetation, and the proportion of Zn in the mobile fraction was 35 % in native vegetation and 21 % in agricultural soils. Zn speciation via linear combination analysis showed a strong relationship with soil mineralogical composition and reveled that Zn associated with organic matter decreased while Zn associated with P increased after the conversion of soils from native vegetation to highly fertilized soil. Aluminosilicate soil minerals were identified as major sinks of soil Zn, accounting for 34 % of total Zn retention regardless of soil origin and land use. Association of Zn with phosphate (i.e., hopeite) was observed in the agricultural soil samples, which might be an unexpected Zn-bearing mineral in highly weathered tropical soils and could have impacts on Zn plant nutrition.

Effects of integrated plant nutrition systems with fertilizer deep placement on rice yields and nitrogen use efficiency under different irrigation regimes.

Improved fertilizer management, with a combination of organic and inorganic inputs, has the potential to enhance rice yield while maintaining soil health. However, studies on the effects of broadcast prilled urea (PU) and urea deep placement (UDP) applied in combination with organic inputs (poultry litter [PL] and vermicompost [VC]), as integrated plant nutrition systems (IPNSs), on rice yields and nitrogen use efficiency (NUE) under alternate wetting and drying (AWD) irrigation are limited. We conducted field experiments during the dry and wet seasons of 2018, 2019, and 2020 to investigate the effects of fertilizer treatments, including control (no nitrogen), UDP, PU, and IPNSs (PU + VC, PU + PL, and UDP + PL) on rice yield and NUE under two irrigation regimes - AWD and continuous flooding (CF). The results revealed that fertilizer treatment and irrigation regime had significant (p < 0.05) interaction effects on rice yield and the agronomic efficiency of N (AEN) during the dry season. UDP significantly (p < 0.05) boosted rice yield, total dry matter (TDM), and NUE as compared to broadcast PU in both wet and dry seasons. Similarly, the IPNS treatment of UDP with PL significantly (p < 0.05) boosted rice yield, TDM, and NUE in comparison to broadcast PU. Under AWD irrigation, UDP alone produced higher rice yields than other treatments, while UDP, and UDP with PL produced similar yields under CF irrigation. During the dry season, AWD irrigation significantly (p < 0.05) increased rice yield, TDM, and AEN when compared to CF conditions, but during the wet season, AWD irrigation demonstrated a rice yield and NUE equivalent to CF. This research implies that using a UDP alone or in combination with PL as an IPNS could be a good way to boost crop productivity while also maintaining soil fertility.

The power of magnesium: unlocking the potential for increased yield, quality, and stress tolerance of horticultural crops.

Magnesium (Mg2+) is pivotal for the vitality, yield, and quality of horticultural crops. Central to plant physiology, Mg2+ powers photosynthesis as an integral component of chlorophyll, bolstering growth and biomass accumulation. Beyond basic growth, it critically affects crop quality factors, from chlorophyll synthesis to taste, texture, and shelf life. However, Mg2 + deficiency can cripple yields and impede plant development. Magnesium Transporters (MGTs) orchestrate Mg2+ dynamics, with notable variations observed in horticultural species such as Cucumis sativus, Citrullus lanatus, and Citrus sinensis. Furthermore, Mg2+ is key in fortifying plants against environmental stressors and diseases by reinforcing cell walls and spurring the synthesis of defense substances. A burgeoning area of research is the application of magnesium oxide nanoparticles (MgO-NPs), which, owing to their nanoscale size and high reactivity, optimize nutrient uptake, and enhance plant growth and stress resilience. Concurrently, modern breeding techniques provide insights into Mg2+ dynamics to develop crops with improved Mg2+ efficiency and resilience to deficiency. Effective Mg2+ management through soil tests, balanced fertilization, and pH adjustments holds promise for maximizing crop health, productivity, and sustainability. This review unravels the nuanced intricacies of Mg2+ in plant physiology and genetics, and its interplay with external factors, serving as a cornerstone for those keen on harnessing its potential for horticultural excellence.