Early Leaf Research Articles

Occurrence of early leaf spot disease (Cercospora arachidicola Hori.) of groundnut (Arachis hypogaea L.) in Bikaner region of Rajasthan

Groundnut (Arachis hypogaea L.) is the major oil seed legume crop in the world. The production and productivity of groundnut is highly affected by collar rot, early leaf spot, Late leaf spot, rust and stem rot diseases. Among the foliar fungal diseases, early leaf spot (ELS) caused by Cercospora arachidicola Hori is one of the most destructive disease in Rajasthan. The early leaf spot infected leaves of groundnut was found to produce typical symptoms, such as presence of light brown to black circular to irregular lesions with chlorotic hallow on the upper surface of the leaves. A proper investigation needs a perfect scrutiny. So, the survey was carried out during Kharif-2019 in the three major groundnut growing tehsils (Nokha, Lunkaransar and Shri Dungargarh) of Bikaner district revealed that none of the locations were free from the disease. However, maximum disease intensity of early leaf spot was observed in Shri Dungargarh tehsil (25.87%) followed by Lunkaransar tehsil (19.32%) at the crop age 45-60 days after sowing.

Genetic Diversity Analysis of Groundnut Germplasm Lines in Respect to Early and Late Leaf Spot Diseases and Biochemical Traits

Background: Groundnut (Arachis hypogaea L.) is one of the most nutritious crops having versatile use. Its yield is mostly exaggerated by two foliar fungal diseases i.e., early and late leaf spot. In present investigation 96 germplasm lines were screened for early and late leaf spot diseases along with diverse biochemical parameters including protein, oil, fatty acids, proline and sugar contents. Methods: Early and late leaf spot diseases have been screened under field condition as well as employing SSR molecular markers. Nutritional profiling has also been done for protein, oil, fatty acids viz., oleic acid, linoleic acid, stearic acid and palmitic acid, proline and sugar contents. Result: In correlation analysis, oleic acid is negatively correlated with linoleic acid (r= -0.911) and palmitic acid (r= -0.688) at 1% level of significance, whereas stearic acid is positively and highly significantly correlated with oil percentage (r=0.381) at 1% significance level. The gene diversity value varied between 0.1866 to 0.4837 for markers ipahm103 and GM1536 with an average of 0.4014 and polymorphic information content (PIC) values ranged between 0.1692 to 0.3855 for the markers pahm103 to GM1536 respectively with a mean value of 0.3183.

The genetic interaction of REVOLUTA and WRKY53 links plant development, senescence, and immune responses.

In annual plants, tight coordination of successive developmental events is of primary importance to optimize performance under fluctuating environmental conditions. The recent finding of the genetic interaction of WRKY53, a key senescence-related gene with REVOLUTA, a master regulator of early leaf patterning, raises the question of how early and late developmental events are connected. Here, we investigated the developmental and metabolic consequences of an alteration of the REVOLUTA and WRKY53 gene expression, from seedling to fruiting. Our results show that REVOLUTA critically controls late developmental phases and reproduction while inversely WRKY53 determines vegetative growth at early developmental stages. We further show that these regulators of distinct developmental phases frequently, but not continuously, interact throughout ontogeny and demonstrated that their genetic interaction is mediated by the salicylic acid (SA). Moreover, we showed that REVOLUTA and WRKY53 are keys regulatory nodes of development and plant immunity thought their role in SA metabolic pathways, which also highlights the role of REV in pathogen defence. Together, our findings demonstrate how late and early developmental events are tightly intertwined by molecular hubs. These hubs interact with each other throughout ontogeny, and participate in the interplay between plant development and immunity.

Integration of transcriptomic and proteomic analyses reveals several levels of metabolic regulation in the excess starch and early senescent leaf mutant lses1 in rice

BackgroundThe normal metabolism of transitory starch in leaves plays an important role in ensuring photosynthesis, delaying senescence and maintaining high yield in crops. OsCKI1 (casein kinase I1) plays crucial regulatory roles in multiple important physiological processes, including root development, hormonal signaling and low temperature-treatment adaptive growth in rice; however, its potential role in regulating temporary starch metabolism or premature leaf senescence remains unclear. To reveal the molecular regulatory mechanism of OsCKI1 in rice leaves, physiological, transcriptomic and proteomic analyses of leaves of osckI1 allele mutant lses1 (leaf starch excess and senescence 1) and its wild-type varieties (WT) were performed.ResultsPhenotypic identification and physiological measurements showed that the lses1 mutant exhibited starch excess in the leaves and an obvious leaf tip withering phenotype as well as high ROS and MDA contents, low chlorophyll content and protective enzyme activities compared to WT. The correlation analyses between protein and mRNA abundance are weak or limited. However, the changes of several important genes related to carbohydrate metabolism and apoptosis at the mRNA and protein levels were consistent. The protein-protein interaction (PPI) network might play accessory roles in promoting premature senescence of lses1 leaves. Comprehensive transcriptomic and proteomic analysis indicated that multiple key genes/proteins related to starch and sugar metabolism, apoptosis and ABA signaling exhibited significant differential expression. Abnormal increase in temporary starch was highly correlated with the expression of starch biosynthesis-related genes, which might be the main factor that causes premature leaf senescence and changes in multiple metabolic levels in leaves of lses1. In addition, four proteins associated with ABA accumulation and signaling, and three CKI potential target proteins related to starch biosynthesis were up-regulated in the lses1 mutant, suggesting that LSES1 may affect temporary starch accumulation and premature leaf senescence through phosphorylation crosstalk ABA signaling and starch anabolic pathways.ConclusionThe current study established the high correlation between the changes in physiological characteristics and mRNA and protein expression profiles in lses1 leaves, and emphasized the positive effect of excessive starch on accelerating premature leaf senescence. The expression patterns of genes/proteins related to starch biosynthesis and ABA signaling were analyzed via transcriptomes and proteomes, which provided a novel direction and research basis for the subsequent exploration of the regulation mechanism of temporary starch and apoptosis via LSES1/OsCKI1 in rice.

Sugars and the speed of life-Metabolic signals that determine plant growth, development and death.

Plant growth and development depend on the availability of carbohydrates synthesised in photosynthesis (source activity) and utilisation of these carbohydrates for growth (sink activity). External conditions, such as temperature, nutrient availability and stress, can affect source as well as sink activity. Optimal utilisation of resources is under circadian clock control. This molecular timekeeper ensures that growth responses are adjusted to different photoperiod and temperature settings by modulating starch accumulation and degradation accordingly. For example, during the night, starch degradation is required to provide sugars for growth. Under favourable growth conditions, high sugar availability stimulates growth and development, resulting in an overall accelerated life cycle of annual plants. Key signalling components include trehalose‐6‐phosphate (Tre6P), which reflects sucrose availability and stimulates growth and branching when the conditions are favourable. Under sink limitation, Tre6P does, however, inhibit night‐time starch degradation. Tre6P interacts with Sucrose‐non‐fermenting1‐Related Kinase1 (SnRK1), a protein kinase that inhibits growth under starvation and stress conditions and delays development (including flowering and senescence). Tre6P inhibits SnRK1 activity, but SnRK1 increases the Tre6P to sucrose ratio under favourable conditions. Alongside Tre6P, Target of Rapamycin (TOR) stimulates processes such as protein synthesis and growth when sugar availability is high. In annual plants, an accelerated life cycle results in early leaf and plant senescence, thus shortening the lifespan. While the availability of carbohydrates in the form of sucrose and other sugars also plays an important role in seasonal life cycle events (phenology) of perennial plants, the sugar signalling pathways in perennials are less well understood.

Analysis of Recognition Performance of Plant Leaf Diseases Based on Machine Vision Techniques

Agriculture is the primary source of income for the majority of the population in Bangladesh. Agriculture is also a big part of the economy of the country. Therefore, it's more necessary to grow our crops and fruits and boost their harvests. Fruits are adored by the people of this country, and farmers love growing fruits. Owing to numerous diseases, both the quality and quantity of fruits are not meeting expectations. Native fruits are contracting many types of new diseases, and the magnitude of the problem is increasing alarmingly. To deal with this issue, quick detection of the disease and correct treatment or recuperation is required. In many cases, locals fail to even detect rare diseases. Thanks to the huge advancement in technology, rare diseases can now be detected with the use of the right technologies. A good plant's growth is dependent on its leaves. Early leaf disease detection can help in keeping the leaves disease-free, as well as the plants and fruits. Our research focuses on identifying litchi leaf diseases by employing sophisticated image processing technologies to ensure the freshness of the leaves. A machine-vision-based technique, i.e., the Convolutional Neural Network (CNN), has been used in this research work. Doi: 10.28991/HEF-2022-03-01-09 Full Text: PDF

Quantification of 'Candidatus Phytoplasma prunorum' in apricot trees exhibiting uneven European stone fruit yellows symptoms

This study focused on quantification of 'Candidatus Phytoplasma prunorum' in apricot trees exhibiting uneven symptoms of European stone fruit yellows. For the research, 17 trees showing early leaf bud break in one part of the crown were selected in winter season, and 13 trees showing leafroll in older part of the shoots and no symptoms in younger part of the same shoots were selected in summer season. Absolute quantification of phytoplasmas was performed by real-time PCR in samples collected from asymptomatic and symptomatic parts. The results showed, that phytoplasma could not be always detected in asymptomatic parts, where 2 out of 17 samples from asymptomatic parts from winter season were negative while in summer season 6 out of 13 samples from asymptomatic parts were negative. Comparison of phytoplasma quantities between symptomatic and asymptomatic plant parts then showed significantly higher quantities in symptomatic parts from samples collected in summer season and no quantity difference in samples collected in winter season.

Effect of Early Basal Leaf Removal on Phenolic and Volatile Composition and Sensory Properties of Aglianico Red Wines.

The aim of this work was to study the influence of early basal leaf removal on Aglianico wines produced in the Apulia region (Italy). Three treatments were carried out, where 100% of fruit-zone leaves on the north (DN), south (DS) and on both sides of the canopy (DNS) were removed. A control (CT), where all basal leaves were retained, was also performed. Instrumental (HPLC-DAD-MS and GC-MS) and sensory analysis (QDA) were used to evaluate the treatment effect on the phenolic and volatile compositions and on the sensory descriptors of wines. DNS reached the highest amounts of phenolic compounds, showing a change in the phenolic pattern from flavonols and anthocyanins. Moreover, leaf removal influenced the levels of 37.8% of volatile compounds, quantified by increasing the concentration when early leaf removal was applied on the north side of the canopy (DN), with respect to the south (DS) and both sides (DNS). In the sensory analysis, Aglianico wines were defined by 16 sensory attributes with GM > 30%, where the highest values were reached for defoliation treatments vs. control. In conclusion, early leaf removal treatments allowed us to modulate the phenolic and volatile concentrations of Aglianico wines.

​​Incidence of Collar Rot of Groundnut in Rajasthan and its Management

Background: Groundnut (Arachis hypogaea L.) is an important legume crop of tropical and sub-tropical areas of the world. This crop suffers from several diseases like early leaf spot, late leaf spot, rust, groundnut bud necrosis, peanut clump and collar rot etc. But collar rot caused by Aspergillus niger van Teighem is one of the most important seed and soil borne diseases causing huge economic (40-50 per cent) loss in India and abroad. Methods: A roving survey was conducted to assess the incidence of collar rot in eight major groundnut growing districts of western Rajasthan i.e. Bikaner, Jodhpur, Churu, Jalore, Jaipur, Sikar, Nagaur and Dausa during Kharif 2018. A field experiment was carried out for two consecutive years (2019 and 2020) to manage the disease through altering micro-climate under canopy with six levels of seed rates (80, 85, 90, 95, 100 and 105 kg/ha). Result: Our investigations cleared that this disease is prevalent in all the 200 fields surveyed in eight districts of Rajasthan with 22.99 per cent overall disease incidence which varied from 17.84 to 32.38 per cent with monetary losses. Maximum disease incidence was recorded in Jaipur (28.85%) district while it was lowest in Nagaur district (20.15%). Higher disease reduction (12.97%) with increased pod yield (27.65%) was observed with higher seed rate of 105 kg/ha as compared to standard recommended seed rate (80 kg/ha) as this pathogen is favoured by higher temperature and low soil moisture, dense canopy provides shade that increases humidity under the cropped area and lowers temperature. As a result of this, plant mortality can be compensated by increasing plant population through seed rate, as it modifies the microclimate and generate an environment which is less favourable for developing collar rot disease of groundnut.

Development of prediction equations for early blight leaf spot on tomato under different fungicides treatments

Field experiment was conducted during 2008-09 and 2009-10 to study the influence of different weather factors on the development of early blight on tomato caused by Alternaria solani (Ell. and Mart.) under six different fungicidal treatments and also to compare the two transformation models viz. Logit and Gompertz through which the disease progress curve move over time. Here, different prediction equationswere developed for each fungicide treatment separately through step down multiple regression analysis which showed that different meteorological factors having different influence on disease severity and these were done after Logistic and Gompertz transformation of the realized observed value of the disease severity (expressed as AUDPC).Results revealed that among the six fungicides tested Mancozeb was superior in controlling the disease severity with the lowest (AUDPC: 97.34 and 95.74) for the two experimental years respectively. Linearization of area under disease progress curve (AUDPC) following the two models (Logit and Gompit) showed that Gompit fit better than Logit for the prediction of early blight disease severity and this was confirmed by the low standard error estimate value of Gompertz. The co-efficient of determination value (R2) showed thatvariation in disease severity can be explained up to 77 percent (with an exception 85percent in case of Mancozeb application in 2009-10) in Logistic as well as 88 percent in Gompertz with combined effect of the weather variables included in the present study. Among the seven meteorological factors considered only average temperature,RH and total rainfall were found to act positively and significantly,whereas, bright sunshine hours were found to have negative significant effect on early blight disease severity on tomato. These situations were observed in both the transformation models but vary with in the treatments and with in the years.

Identification of maize leaf diseases by using the SKPSNet-50 convolutional neural network model

Maize leaf disease is the main factor that affects the yield and quality of maize. Early diagnosis and control of maize leaf diseases help ensure maize yield and quality. However, early maize leaf diseases show small spots and irregular shapes in natural scene images, resulting in current models having difficulty identifying maize leaf diseases accurately. This study proposes a SKPSNet-50 convolutional neural network model to realize the accurate identification of maize leaf diseases in natural scene images. The proposed model replaces the 3 × 3 convolution kernel in the backbone network ResNet-50 with Select Kernel–Point–Swish_B (SKPS), which is an improved building block of the selected kernel (SK) unit, and replaces the ReLU activation function with the Swish_B activation function to improve the feature extraction capability of diseased leaves with small spots and irregular shapes. In addition, this study adopts the combined focal loss function to guide the parameter adjustment of the model to solve the problem of data imbalance. Experimental results show that compared with classic machine learning models (such as BP neural network and support vector machine) and deep neural network models (such as AlexNet, VGG16, ResNet-50, SENet-50, SKNet-50 and GhostNet), the proposed model is more effective in the identification of maize leaf diseases in natural scene images, with an average identification accuracy of 92.9%, which is about 6% higher than that of the SKNet-50 model.

Jerusalem Artichoke as a Strategic Crop for Solving Food Problems

Jerusalem artichoke is a staple for the raw material base of healthy food, beverages, feed, medicine, and fuel, in addition to being the source of its herbage and tubers. The choice of conditions for cultivating a variety depends on the purpose or direction for the crop and the products obtained from it. This research involved laboratory and on-farm studies of 16 Jerusalem artichoke varieties of different maturity groups cultivated on sod-podzolic sandy loam soils to determine their suitability for further use in feed production. The list of varieties in question is presented in this work. The gross yield of tubers obtained from varieties with early leaf wilting was 33.1–51.1 t/ha, whereas that from varieties with late leaf wilting was 14.4–43.9 t/ha. The total yield of Jerusalem artichoke raw biomass was 36.8–98.1 t/ha. Moreover, early varieties had a dominant mass of tubers in the total feed value structure (68%), whereas herbage mass (59%) prevailed in the total feed value structure of varieties with late leaf wilting. The highest total solids in tubers (25.0–26.4%) were found in varieties Korenevskiy, Novost VIRa, and Blank Brekos; whereas high inulin content was found in varieties Dieticheskiy, Kaluzhskiy, Korenevskiy, Nakhodka, Novost VIRa, and Blank Brekos. The aggregate feed value amounted to 37.0–103.4 thousand MJ/ha of metabolized energy; this exceeded energy production costs on properly selected varieties by two- to three-fold. The data obtained can be useful for growers in the introduction and evaluation of Jerusalem artichoke varieties to be cultivated for further usage and processing, including fodder purposes.

Phytoplasma Infection Blocks Starch Breakdown and Triggers Chloroplast Degradation, Leading to Premature Leaf Senescence, Sucrose Reallocation, and Spatiotemporal Redistribution of Phytohormones.

Witches’-broom (WB, excessive initiation, and outgrowth of axillary buds) is one of the remarkable symptoms in plants caused by phytoplasmas, minute wall-less intracellular bacteria. In healthy plants, axillary bud initiation and outgrowth are regulated by an intricate interplay of nutrients (such as sugars), hormones, and environmental factors. However, how these factors are involved in the induction of WB by phytoplasma is poorly understood. We postulated that the WB symptom is a manifestation of the pathologically induced redistribution of sugar and phytohormones. Employing potato purple top phytoplasma and its alternative host tomato (Solanum lycopersicum), sugar metabolism and transportation, and the spatiotemporal distribution of phytohormones were investigated. A transmission electron microscopy (TEM) analysis revealed that starch breakdown was inhibited, resulting in the degradation of damaged chloroplasts, and in turn, premature leaf senescence. In the infected source leaves, two marker genes encoding asparagine synthetase (Sl-ASN) and trehalose-6-phosphate synthase (Sl-TPS) that induce early leaf senescence were significantly up-regulated. However, the key gibberellin biosynthesis gene that encodes ent-kaurene synthase (Sl-KS) was suppressed. The assessment of sugar content in various infected tissues (mature leaves, stems, roots, and leaf axils) indicated that sucrose transportation through phloem was impeded, leading to sucrose reallocation into the leaf axils. Excessive callose deposition and the resulting reduction in sieve pore size revealed by aniline blue staining and TEM provided additional evidence to support impaired sugar transport. In addition, a spatiotemporal distribution study of cytokinin and auxin using reporter lines detected a cytokinin signal in leaf axils where the axillary buds initiated. However, the auxin responsive signal was rarely present in such leaf axils, but at the tips of the newly elongated buds. These results suggested that redistributed sucrose as well as cytokinin in leaf axils triggered the axillary bud initiation, and auxin played a role in the bud elongation. The expression profiles of genes encoding squamosa promoter-binding proteins (Sl-SBP1), and BRANCHED1 (Sl-BRC1a and Sl-BRC1b) that control axillary bud release, as determined by quantitative reverse transcription (qRT)-PCR, indicated their roles in WB induction. However, their interactions with sugars and cytokinins require further study. Our findings provide a comprehensive insight into the mechanisms by which phytoplasmas induce WB along with leaf chlorosis, little leaf, and stunted growth.

English

Early and late leaf spots caused by Cercospora arachidicola and Phaeoisariopsis personata respectively, are the most widespread peanut fungal diseases in West Africa. These diseases lead to notable crop losses in the rural area. In the recent decades, chemical fungicides are used to fight against crop losses, but these chemical substances cause big damages to the environment including the animals and human beings. Thus, the biological control is encouraged by scientific community and all government because it is well known to be safety and cost effective. For this reason, we investigated on the effectiveness of Lecanicillium lecanii on leaf spots of peanut in Burkina Faso. To do so, spore suspensions (106 spores / ml) from four strains of L. lecanii was used in vitro. The results revealed that L. lecanii 4181 inhibited the pathogen conidia germination up to 87%, as well as elongation germ tube with highest rate of 56%. Compared to the distilled water control, the severity scores vary between 5.7 and 8, but our results showed a notable decrease of score from 2.3 and 4.7. From our findings, the treatments with L. lecanii spore suspensions on peanut leaves significantly reduced the severity of leaf spots and may be potentially used to promote organic farming in West Africa. Key words: Foliar diseases, biological control, peanut, agriculture.

Modeling seasonal branch carbon dynamics in pistachio as a function of crop load

A simplified model for the prediction of carbon balance was developed to elucidate the seasonal trend of sink-source relationships in bearing and non-bearing pistachio (Pistacia vera L.) branches. Seasonal changes in growth rate of vegetative (leaf and shoot) and reproductive (infructescence) organs were monitored in branches of mature rainfed pistachio trees during the entire growing season (April–September). Simulations from the model were used to gain understanding of the implications of crop load on branch carbon (C) depletion and alternate bearing.Results showed that the pistachio branch was energetically able to sustain up to two infructescences (∼28 fruits) having a slightly positive carbon budget (2.6 g of C) at the end of the season. A branch with 4 infructescences (∼56 fruits) ended the season with a very negative carbon budget (-14.1 g of C) suggesting the implication of resource mobilization during heavy crop load.The simulations with the model allowed the identification of two energetically critical periods for pistachio, both characterized by a decreasing trend of the carbon budget. The first is at the beginning of the season, from leaf out until 35/40 days after full bloom (DAFB), when leaves are still not source of carbon, and the branch energetic need is largely satisfied by the remobilization of carbon from the reserves accumulated the previous year and stored through the winter. The second critical period is at the end of the season for bearing branches, at ∼100 DAFB, when a strong reduction in leaf area due to early leaf senescence and drop coincides with high carbon request for kernel growth. Overall, results demonstrate that the branch carbon budget model is a valid tool to study bearing dynamics in tree species and can help to develop physiologically-based management strategies for achieving increased and more constant productions in pistachio orchard systems.

Cluster-Zone Leaf Removal and GA3 Application at Early Flowering Reduce Bunch Compactness and Yield per Vine in Vitis vinifera cv. Pinot Gris

Compact bunches have been often associated with higher susceptibility to Botrytis cinerea and therefore reduction in berry quality in grapevine. The objective of this study was to evaluate three management methods (early leaf removal, gibberellic acid, and their combination) for reducing bunch compactness in Vitis vinifera cv. Pinot gris trained in two different training systems with contrasting vigor (Guyot and pergola). Treatments were applied at BBCH 62 or BBCH 65 and yield components, total soluble solids, fruit set, and bunch compactness parameters were evaluated. Both treatments individually reduced berry number, mean bunches weight and bunches compactness as well as yield per vine when compared to control-untreated vines. However, no major differences were observed when both the treatments were applied in combination for Guyot or pergola although a higher reduction in yield was detected for Guyot and a significant increase in total soluble solids was observed in pergola. Our study suggests that intense leaf removal and gibberellic acid applied at early flowering can help reducing bunch compactness in Pinot gris and showing it in two training systems. In particular, leaf removal represents a valuable alternative to plant growth regulators (i.e., gibberellic acid) as applicable in organic viticulture.

Transcriptomic, Metabolomic and Ionomic Analyses Reveal Early Modulation of Leaf Mineral Content in Brassica napus under Mild or Severe Drought.

While it is generally acknowledged that drought is one of the main abiotic factors affecting plant growth, how mineral nutrition is specifically and negatively affected by water deficit has received very little attention, other than being analyzed as a consequence of reduced growth. Therefore, Brassica napus plants were subjected to a gradual onset of water deficits (mild, severe, or severe extended), and leaves were analyzed at the ionomic, transcriptomic and metabolic levels. The number of Differentially Expressed Genes (DEGs) and of the most differentially accumulated metabolites increased from mild (525 DEGs, 57 metabolites) to severe (5454 DEGs, 78 metabolites) and severe extended (9346 DEGs, 95 metabolites) water deficit. Gene ontology enrichment analysis of the 11,747 DEGs identified revealed that ion transport was one of the most significant processes affected, even under mild water deficit, and this was also confirmed by the shift in ionomic composition (mostly micronutrients with a strong decrease in Mo, Fe, Zn, and Mn in leaves) that occurred well before growth reduction. The metabolomic data and most of the transcriptomic data suggested that well-known early leaf responses to drought such as phytohormone metabolism (ABA and JA), proline accumulation, and oxidative stress defense were induced later than repression of genes related to nutrient transport.

Seasonal changes in nitrate assimilation of boreal woody species: importance of the leaf-expansion period

Key messageNitrate served as an important nitrogen source for dominant deciduous tree species, especially during their leaf expansion period, even in boreal forests, where nitrate availability was assumed to be low.Temporal changes in leaf nitrate assimilation with leaf growth were intensively investigated in boreal tree species to demonstrate the contribution of nitrate as a N source and to determine temporal changes in the contribution of nitrate during leaf ontogeny. Leaf area, mass, nitrate reductase activity (NRA), N concentration, and δ15N were repeatedly measured in developing leaves of naturally grown Alnus crispa, Betula neoalaskana, and Populus tremuloides during their leaf expansion period. Alnus crispa and B. neoalaskana showed distinct peaks in NRA during leaf expansion, whereas P. tremuloides did not. The highest peak in NRA occurred for A. crispa, whereas it had low NRA during the summer. Peak NRA in B. neoalaskana was lower than that of A. crispa (p < 0.01, ANOVA), although it showed higher NRA during summer (p < 0.01, ANOVA). All species showed clear decrease in N concentration through the leaf expansion period, but total N content per leaf increased. Only the N-fixing species A. crispa showed a rapid change in δ15N during the leaf expansion, and the decline indicated the changes in N source during the leaf development. The results indicate leaves of target species assimilated nitrate during the leaf expansion period, consuming immense energy, although leaves were considered a carbon sink during the early leaf expansion period. We suggest the early onset of leaf growth due to climate warming could influence plant nutrition via asynchrony between supply and demand for energy during spring.

Mycosphaerella arachidis (early leaf spot of groundnut)

Mycosphaerella arachidis (early leaf spot of groundnut)

Target of rapamycin (TOR) regulates the response to low nitrogen stress via autophagy and hormone pathways in Malus hupehensis.

Target of rapamycin (TOR) is a highly conserved master regulator in eukaryotes; it regulates cell proliferation and growth by integrating different signals. However, little is known about the function of TOR in perennial woody plants. Different concentrations of AZD8055 (an inhibitor of TOR) were used in this study to investigate the role of TOR in the response to low nitrogen (N) stress in the wild apple species Malus hupehensis. Low N stress inhibited the growth of M. hupehensis plants, and 1 μM AZD alleviated this effect. Plants supplied with 1 μM AZD had higher photosynthetic capacity, which promoted the accumulation of biomass, as well as higher contents of N and anthocyanins and lower content of starch. Exogenous application of 1 μM AZD also promoted the development of the root system. Plants supplied with at least 5 μM AZD displayed early leaf senescence. RNA-seq analysis indicated that TOR altered the expression of genes related to the low N stress response, such as genes involved in photosystem, starch metabolism, autophagy, and hormone metabolism. Further analysis revealed altered autophagy in plants supplied with AZD under low N stress; the metabolism of plant hormones also changed following AZD supplementation. In sum, our findings revealed that appropriate inhibition of TOR activated autophagy and jasmonic acid signaling in M. hupehensis, which allowed plants to cope with low N stress. Severe TOR inhibition resulted in the excessive accumulation of salicylic acid, which probably led to programmed cell death in M. hupehensis.