Transcriptome analysis of scions grafted to potato rootstock for improving late blight resistance

BACKGROUND

Late blight seriously threatens potato cultivation worldwide. The severe and widespread damage caused by the fungal pathogen can lead to drastic decreases in potato yield. Although grafting technology has been widely used to improve crop resistance, the effects of grafting on potato late blight resistance as well as the associated molecular mechanisms remain unclear. Therefore, we performed RNA transcriptome sequencing analysis and the late blight resistance testing of the scion when the potato late blight-resistant variety Qingshu 9 and the susceptible variety Favorita were used as the rootstock and scion, respectively, and vice versa. The objective of this study was to evaluate the influence of the rootstock on scion disease resistance and to clarify the related molecular mechanisms.

RESULTS

A Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis revealed that the expression levels of genes related to plant-pathogen interactions, plant mitogen-activated protein kinase (MAPK) signaling pathways, and plant hormone signal transduction pathways were significantly up-regulated in the scion when Qingshu 9 was used as the rootstock. Some of these genes encoded calcium-dependent protein kinases (CDPKs), chitin elicitor receptor kinases (CERKs), LRR receptor serine/threonine protein kinases (LRR-LRKs), NPR family proteins in the salicylic acid synthesis pathway, and MAPKs which were potato late blight response proteins. When Favorita was used as the rootstock, only a few genes of late blight response genes were upregulated in the scion of Qingshu 9. Grafted plants using resistant variety as rootstocks inoculated with P. infestans spores showed significant reductions in lesion size while no significant difference in lesion size was observed when susceptible variety was used as the rootstock. We also showed that this induction of disease resistance in scions, especially scions derived from susceptible potato varieties was mediated by the up-regulation of expression of genes involved in plant disease resistance in scions.

CONCLUSIONS

Our results showed that potato grafting using late blight resistant varieties as rootstocks could render or enhance resistance to late blight in scions derived from susceptible varieties via up-regulating the expression of disease resistant genes in scions. The results provide the basis for exploring the molecular mechanism underlying the effects of rootstocks on scion disease resistance.

Freezing resistance evaluation of rose stems during frost dehardening using electrical impedance tomography

BACKGROUND

Electrical impedance tomography (EIT) has rarely been applied in plant science, particularly to study plant resistance to abiotic and biotic stresses. In this study, we evaluated the freezing resistance of floribunda roses (Rosa Floribunda) during frost dehardening using the EIT technique to identify a new method for rapid and non-destructive measurement of plant freezing resistance.

RESULTS

The current was the excitation source, the boundary voltage value was measured, and then the boundary voltage reconstructed value was formed. Using an imaging algorithm, the two-dimensional (2D) distribution of impedance or impedance variation was reconstructed. The EIT reconstructed values decreased obviously with the decline in freezing temperatures. The EIT reconstructed values of stems had the best fit to the logistic equation, and subsequently, the semi-lethal temperatures were calculated. The freezing resistance results evaluated using EIT reconstructed values were linearly correlated with the results of the traditional electrolyte leakage (EL) method (r = 0.93, P < 0.01).

CONCLUSIONS

In conclusion, after freezing tests, the reconstructed values of EIT images could be used to quantitatively evaluate the freezing resistance of floribunda rose stems. The present study provides a reference for the further application of the EIT technique for non-destructive and rapid detection of plant freezing resistance.

Grafting in Hylocereus (Cactaceae) as a tool for strengthening tolerance to high temperature stress

The Hylocereus species that are grown as exotic fruit crops are very often farmed under marginal agronomic conditions, which may include exposure to high temperatures. Here we present a pioneering investigation of grafting as an agro-technique to improve heat tolerance in Hylocereus. To this end, we studied the diploid species H. undatus, the tetraploid H. megalanthus and its di-haploid gamete-derived line 2719, and the interspecific-interploid tetraploid Z-10, all grafted onto H. undatus as the rootstock. Self-grafted, grafted and non-grafted plants were acclimated for one week (to obtain baseline values) and then exposed to heat stress (45/35 °C day/night) for three days, followed by a one-week recovery period under optimal temperatures (30/22 °C). A comparison of the physiological, biochemical and molecular performances of the grafted and self-grafted plants under heat stress and during the recovery period vs those of non-stressed plants (control; 30/22 °C) showed that the grafted and self-grafted plants performed better in most of the assessments: grafted and self-grafted plants recovered more rapidly from the heat stress and suffered far less stem damage. An unexpected - but important - finding that may have implications for other crop was that the self-grafted plants showed better performance than non-grafted plants throughout the trial. Our findings provide support for grafting as a strategy for coping with the stress induced by extremely high temperatures. This study thus paves the way for further investigations of grafting in Hylocereus as a valuable technique that will maintain crop productivity in the face of increasing worldwide temperatures.

Cell-cell adhesion in plant grafting is facilitated by β-1,4-glucanases

Plant grafting is conducted for fruit and vegetable propagation, whereby a piece of living tissue is attached to another through cell-cell adhesion. However, graft compatibility limits combinations to closely related species, and the mechanism is poorly understood. We found that Nicotiana is capable of graft adhesion with a diverse range of angiosperms. Comparative transcriptomic analyses on graft combinations indicated that a subclade of β-1,4-glucanases secreted into the extracellular region facilitates cell wall reconstruction near the graft interface. Grafting was promoted by overexpression of the β-1,4-glucanase. Using Nicotiana stem as an interscion, we produced tomato fruits on rootstocks from other plant families. These findings demonstrate that the process of cell-cell adhesion is a potential target to enhance plant grafting techniques.

Response of grafting tobacco to low potassium stress

BACKGROUND

In the previous study, we investigated the alleviation effect of grafting on potassium uptake in roots and tobacco growth inhibition under low potassium stress. However, the effect of grafting on the low potassium stress perception and coping mechanism of tobacco at the whole plant level is not clear now. In order to clearly understand the impact of grafting on potassium deficit responding mechanism in tobacco, a mutual grafting experiment has been conducted in two varieties of tobacco ('Wufeng No.2' and 'Yunyan 87') in different K supply level (5 mmol L- 1 and 0.5 mmol L- 1 K).

RESULTS

The results show that compared with the self-rooted seedlings, grafting significantly increased the potassium content of the whole plant of Yunyan 87 (97.57 and 189.74% under normal potassium and low potassium conditions, respectively), and the increase in shoots was greater. The data of whole plant K content distribution and tobacco hypocotyls net K+ flux demonstrates that potassium stress makes plants more inclined to maintain K+ in the shoot rather than root. In addition, when K deficiency occurs, grafting could reduce the time required for downward net K+ flux in tobacco hypocotyl to decrease to stable levels. The results of net K+ flux in the roots indicated that K channel proteins and transporters play different roles in two rootstocks in terms of potassium tolerance. Transcription level analysis suggested that the increased circulating efficiency of K+ between the shoots and roots in tobacco constitutes one means to low potassium stress adaptation.

CONCLUSIONS

Grafting can activate more K+ channels in tobacco 'Yunyan 87', this means a more active K+ cycle, higher potassium content in shoot and faster response to low potassium stress signals in grafting tobacco. In addition, grafting can also change the K+ absorption mode of tobacco root from being dominated by HATS to being jointly responsible by HATS and LATS, greatly improving the ability of K+ transmembrane transportation on root surface under low potassium stress. These are undoubtedly the reasons why grafting tobacco performs better in coping with low potassium stress.

Local knowledge about sustainable harvesting and availability of wild medicinal plant species in Lemnos island, Greece

BACKGROUND

In Europe and the Mediterranean, over-exploitation and destructive harvesting techniques have been identified as two critical threats affecting the sustainable harvesting of wild medicinal plant (WMP) species. However, unsustainable harvesting is not an issue everywhere and localized assessments are needed. Local knowledge has been praised for its potential for local short-term assessments. In this study, we aimed to register the known, harvested, and locally utilized WMP species and understand local knowledge of harvesters about the ecological sustainability of WMP harvesting and the perceived changes of WMP availability.

MATERIALS AND METHODS

This study was conducted on Lemnos island, Greece, in July and August 2018. Sixteen harvesters knowledgeable about gathering and using WMP were chosen through purposeful and snowball sampling. Successive free-lists provided insights on the taxa known, harvested, and utilized by harvesters and subsequent semi-structured interviews served to understand harvesting practices and perceived changes of WMP availability. Participant observation during seven harvesting walks allowed for additional insights and facilitated the collection of voucher specimens.

RESULTS

In total, 144 different plant taxa were listed as useful and 81 had been harvested in the prior 4 years. Medicinal applications were mainly related to digestive and respiratory system issues. A number of favorable harvesting practices suggested a high potential towards an ecologically sustainable harvest. Although, a decreased availability for certain plant taxa and harvesting sites was reported and mainly attributed to external factors such as pollution, unusually dry weather, intentional pastureland burning or chemicals in agriculture, but also destructive harvesting by less knowledgeable harvesters.

CONCLUSIONS

Knowledgeable harvesters of Lemnos gather and use a considerable number of WMP taxa and possess local knowledge that supports an ecologically sustainable harvest. However, certain plant taxa and areas of the island were indicated to be under pressure from harvesting, unusual climatic conditions, and agricultural practices. Our approach confirmed that local knowledge should be taken into account for assessing the sustainability of WMP harvesting.

Phytochemical Analysis, Network Pharmacology and in Silico Investigations on Anacamptis pyramidalis Tuber Extracts

Anacamptis pyramidalis (L.) Rich. forms part of the Orchidaceae family that is highlyvalued for its horticultural as well as therapeutic benefits. The present study set out to investigatethe inhibitory activity of A. pyramidalis tubers against key biological targets for the management oftype 2 diabetes, Alzheimer disease, and skin hyperpigmentation. In addition, the antioxidantpotential of the extracts was also assessed using multiple methods. The detailed phytochemicalprofiles of the extracts were determined using high-performance liquid chromatography. Based onqualitative phytochemical fingerprint, a network pharmacology analysis was conducted as well.Parishin was identified from the water extract only, whereas gastrodin and caffeic acid derivativeswere present in the methanol extract. The methanol extract exhibited high inhibitory activityagainst tyrosinase (69.69 mg kojic acid equivalent/g extract), α-amylase (15.76 mg acarboseequivalent/g extract), and α-glucosidase (20.07 mg acarbose equivalent/g extract). Similarly, themethanol extract showed highest antioxidant potential (22.12, 44.23, 45.56, and 29.38 mg Troloxequivalent/g extract, for 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), CUPric Reducing Antioxidant Capacity (CUPRAC),and Ferric Reducing Antioxidant Power (FRAP) assays, respectively). Finally, the results ofnetwork pharmacology analysis, besides corroborating traditional uses of plant extracts in themanagement of cold and flu, confirmed a direct involvement of identified phytochemicals in theobserved enzyme inhibitory effects, especially against tyrosinase, α-amylase, and α-glucosidase.Furthermore, based on the results of both colorimetric assays and network pharmacology analysis related to the activity of A. pyramidalis extracts and identified phytocompounds on enzymesinvolved in type 2 diabetes, a docking study was conducted in order to investigate the putativeinteractions of oxo-dihydroxy octadecenoic acid trihydroxy octadecenoic acid against aldosereductase, peroxisome proliferator-activated receptor (PPAR)-α, dipeptidyl peptidase (DPP)-IV,and α-glucosidase. Docking analysis suggested the inhibitory activity of these compounds againstthe aforementioned enzymes, with a better inhibitory profile shown by oxo-dihydroxyoctadecenoic acid. Overall, the present findings supported the rationale for the use of A.pyramidalis as source of bioactive metabolites and highlight, today more than ever, for the strongnecessity of linkage strategy between wild resource valorization and conservation policy.

Influence of variation in the volumetric moisture content of the substrate on irrigation efficiency in early potato varieties

Potato is a plant with high water requirements. This factor affects not only the weight of potato tubers but also their quality parameters. In order to achieve quantity and quality goal, it is helpful if we apply the principles of precision agriculture, which also contributes to sustainable management of environmental resources. Accurate identification of the water requirements of crops is the basis for determining optimal irrigation doses and dates. After their application, it is possible to assess the effectiveness of irrigation treatments and their impact on the air-water conditions in soil with a root system. The aim of the presented study was to analyse the influence of volumetric soil moisture diversity on the vegetation of early potato varieties. Two potato varieties were subject to investigation: Denar and Julinka. Pot experiments were carried out at the Department of Horticulture of Wroclaw University of Environmental and Life Sciences. Three variants were analysed: one with a low water content in the soil (pF 2.7), one with the optimal water content (pF 2.5) and one with a high water content (pF 2.2). The basis for the selection of the frequency and application rate of water doses was soil moisture measured with an SM150-Kit set. Volumetric moisture was measured with a TDR apparatus. It was found that the water requirements of both potato varieties differ and increase along with the development of the aboveground and underground parts. Moreover, it was shown that the irrigation requirements of cv. Julinka are higher than those of Denar (31.4–33.0% higher), depending on the adopted variant. The research also showed that the most effective method of potato cultivation is to maintain soil moisture at a lower level. This should be taken into account in regions where the cultivation of this species uses supplementation of the water requirements by irrigation.

Growth response of greenhouse-produced muskmelon and tomato to sub-surface drip irrigation and soil aeration management factors

BACKGROUND

Hypoxia causes injury and yield loss. Soil aeration has been reported to accelerate the growth of plants and increase crop yield. The aim of this study was to examine growth response of greenhouse-produced muskmelon to 3 levels of sub-surface drip irrigation (I), 3 different installation depths of drip laterals in the soil (D), and 4 levels of supplemental soil aeration frequency (A). A fractional factorial experiment was designed to examine these treatment effects on marketable fresh fruit yield, leaf area index during 3 growth stages, and dry matter partitioning at harvest. In addition, we studied the response of fruit yield and dry matter of tomato to 2 levels of burial depths of subsurface tubing in combination with 3 frequency levels of soil aeration.

RESULTS

Results showed that soil aeration can positively influence the yield, leaf area index, dry matter and irrigation use efficiency of the muskmelon (p < 0.05). The fruit yield of muskmelon and tomato were increased by 21.5 and 30.8% respectively with 1-d and 2-d aeration intervals compared with the no aeration treatment.

CONCLUSIONS

The results suggest that soil aeration can positively impact the plant root zone environment and more benefits can be obtained with aeration for both muskmelon and tomato plants.

Lettuce plant growth and tipburn occurrence as affected by airflow using a multi-fan system in a plant factory with artificial light

A multi-fan system (MFS) for single culture beds was developed to improve the airflow in a plant factory with artificial light. The MFS had seven fans which were installed on both the front and back sides of culture beds to generate airflow from two opposite horizontal directions. The fans that push the air into the culture bed were air inlets while those that pull the air out of the culture bed were air outlets. In this study, three airflow patterns were evaluated: T1, the front and back sides of the culture bed were air inlets; T2, the front side was an air inlet and the backside was an air outlet; and T3, both the front and back sides were air outlets. A culture bed with no MFS was used as a control (T4). Lettuce growth and tipburn occurrence were evaluated and leaf boundary layer resistance (1/gbv), sensible heat flux (Sh), and latent heat flux (Lh) of lettuce plants were estimated. The airflow pattern in T1 improved the air velocity (Va) by an average of 0.75 m s-1 and a variation coefficient of 65%. The 1/gbv decreased significantly with the increase in Va, and the lowest value of 54.0 s m-1 was observed in T1. The low resistance to heat and moisture transfer enhanced the Sh and Lh of lettuce plants. The average Sh and Lh were 40% and 46% higher in T1 compared with those in T4. The fresh and dry weights of lettuce plants in T1 were 1.13 and 1.06 higher than those in T4, respectively. No tipburn occurrence was observed in lettuce plants grown under the MFS while five leaves per plant were injured with tipburn in T4. The results indicated that improving the airflow can improve the growth of indoor cultured lettuce and alleviate the occurrence of tipburn due to the decrease in the 1/gbv and the increase in the transpiration rate.

From dangerous branches to urban banyan: Facilitating aerial root growth of Ficus rubiginosa

Large urban trees have many benefits. However, falling branches pose a serious hazard to both people and infrastructure. In several tree species, aerial roots grow down from branches to the ground. These roots are capable of thickening to support the branches, lessening the risk of tree failure. Unfortunately, in urban environments most aerial roots die before reaching the ground. Here, we report a new method for encouraging aerial roots to reach the ground, developed by the second-year botany class at UNSW Sydney. Our class tested three experimental treatments on aerial roots of Ficus rubiginosa Desf. ex Vent. (Port Jackson Fig)-PVC pipes filled with sphagnum moss, PVC pipes filled with potting mix, and PVC pipes filled with sphagnum moss and topped with funnels to catch extra rainwater. All three treatments significantly improved aerial root growth, with 26 of the 30 (87%) treatment roots reaching the ground after one year compared to 0 of the 10 control roots. Our method was successful for roots up to 3 m above the ground, suggesting the potential growth rate of aerial roots is substantial when conditions are favourable. Our novel approach is an attractive and cost-effective alternative to slings and other artificial supports. This project is an example of using undergraduate practical classes to teach science while simultaneously addressing important real-world problems.

The Molecular Determination of Hybridity and Homozygosity Estimates in Breeding Populations of Lettuce (Lactuca sativa L.)

The development of new varieties of horticultural crops benefits from the integration of conventional and molecular marker-assisted breeding schemes in order to combine phenotyping and genotyping information. In this study, a selected panel of 16 microsatellite markers were used in different steps of a breeding programme of lettuce (Lactuca sativa L., 2 n = 18). Molecular markers were first used to genotype 71 putative parental lines and to plan 89 controlled crosses designed to maximise recombination potentials. The resulting 871 progeny plants were then molecularly screened, and their marker allele profiles were compared with the profiles expected based on the parental lines. The average cross-pollination success rate was 68 ± 33%, so 602 F1 hybrids were completely identified. Unexpected genotypes were detected in 5% of cases, consistent with this species' spontaneous out-pollination rate. Finally, in a later step of the breeding programme, 47 different F3 progenies, selected by phenotyping for a number of morphological descriptors, were characterised in terms of their observed homozygosity and within-population genetic uniformity and stability. Ten of these populations had a median homozygosity above 90% and a median genetic similarity above 95% and are, therefore, particularly suitable for pre-commercial trials. In conclusion, this study shows the synergistic effects and advantages of conventional and molecular methods of selection applied in different steps of a breeding programme aimed at developing new varieties of lettuce.