Two-leaf Stage Research Articles

Power on! Low-energy electrophysical treatment is an effective new weed control approach.

Environmental concerns are driving the call for adoption of alternative nonchemical weeding approaches. This study aimed to develop and evaluate a novel, precise, low-energy electrophysical treatment weeding systems and to provide new insight into their control mechanism. Two electrophysical treatment systems, based on AC (2.2 kV) and DC (40 kV) energy sources, were developed and evaluated. The impacts of various operational and biological factors on the weed control effectiveness were evaluated. Additionally, thermal images were taken during the treatments to document plant temperature. Treatments via direct leaf contact caused greater damage to Amaranth plants than the stem contact treatments, with 75% and 20% biomass reduction compared to control, respectively. Treatment of early growth stages was favorable over later growth stages, with 100% and 75% biomass reduction for Trifolium pretense plants treated with 0.0125 W h 2 and 4 weeks after seeding, respectively, compared to control. Additionally, the applied energy affected treatment performance, with its impact varying across the growth stages and species; at the two-leaf growth stage, 0.0025 W h treatment was sufficient for plant death. A >40 °C increase in plant temperature was measured during the electrophysical treatment, with the temperature of some plant organs reaching ~70 °C. Results from this study demonstrate the potential use of electrophysical treatment as an effective weed control tool. The low energetic demands in the new systems provide suitable control results when applied at early stages. Temperature increase seemed to be one of the main control factors, yet efficacy was affected by various biological factors.

Phosphate (Pi) uptake and remobilisation within plant in Brassica spp. under different Pi availabilities input

Phosphorus (P) is one of six essential macronutrients in plants to ensure crop growth and productivity. Plants only acquire phosphorus in the form of inorganic phosphate (Pi) known as orthophosphate, mainly in the form of H2PO4 −. The high demand of Pi in fertilisers for agriculture use contributed to environmental pollution. Therefore, it is important to understand the Pi uptake from the soil and remobilisation within the plant to increase P use efficiency (PUE). In this study, the experiments were undertaken to look at the variation of Pi uptake by Brassica spp. under different soil Pi availability. Two soil Pi concentrations, P1 (0 g L−1) and P4 (0.225 g L−1) were selected to represent the low and high Pi treatment, respectively. B. napus plants grown in compost with both high and low Pi treatments were harvested at four different parts of the plant (leaf, stem, flower, and pod silique and seed) at six different growth stages, namely two-leaf stage, four-leaf stage, flowering stage, first flower opens stage, seed filling stage and maturity stage. The results of free Pi concentration in P4 (0.225 g L−1) were significantly higher than P1 (0 g L−1) (P ≤ 0.01). Remobilisation of Pi determined by total P contents of plants treated with P1 and P4 both showed similar trends, increased P contents up to 50% of plant P at harvest 5 (seed stage), and loss of P at leaf, stem and flower tissues during senescence at maturity stage. Under deficiency, leaf Pi concentration which determined the internal Pi redistribution showed Pi was redistributed from source (mature organs) to sink (developing tissues) Pi tissues. These results provide insights on plant nutrient status and can be used for further investigation for crop optimal production under low Pi availability.

Investigation of the expression pattern of Ribonuclease, Cysteine protease, and Glutathione peroxidase genes in response to septoria leaf blotch in bread wheat

One of the most important diseases of wheat is septoria leaf blotch caused by Zymoseptoria tritici. Pathogen-related proteins cause disease resistance in plants. To identify the onset time of wheat defence response against the pathogen, two wheat cultivars of susceptible (Tajan) and resistant (Nogal), were inoculated with spores of Z. tritici in the two-leaf stage. Sampling was performed and expression pattern of Ribonuclease, Cysteineprotease and Glutathione peroxidase-1 genes were analyzed by Real-Time PCR method. The results showed that these genes are good candidates for wheat defense and their expression patterns were different in both susceptible and resistant cultivars.

Phenotype, Physiology, and Gene Expression of Barley Seedlings in Response to Nano Zinc Oxide Stress

In recent years, zinc oxide nanoparticles (ZnO NPs) have been widely used as zinc fertilizers and pesticides. The use of ZnO NPs in this way can provide benefits to humans, but also has potential risks. ZnO NPs inevitably enter the environment during their production and use, which affects the ecological environment and crop growth. In order to investigate the phenotype, physiology, and gene expression of barley (Hordeum vulgare L.) seedlings under ZnO NPs stress, the barely cultivars ZJU3 (P21), Golden Promise (GP) and L23 were chosen for study. Different ZnO NPs concentrations were applied to compare the physiological and biochemical indexes of the barley seedlings and the responses of six stress-related genes, when seedlings were cultured to the two-leaf stage through hydroponics. The results showed that the density of brown spots on the leaf surface increased with increasing ZnO NPs concentration. ZnO NPs stress inhibited the root growth of barley seedlings, and P21 was the most sensitive. Furthermore, ZnO NPs stress could stimulate plants to produce a large number of reactive oxygen species (ROS), resulting in an imbalance between the production and removal of ROS and membrane lipid peroxidation in plants. This imbalance inhibited the growth and development of the barley seedlings. With increasing ZnO NPs concentration, the activity of superoxide dismutase was gradually increased, the activity of catalase was progressively decreased, and the contents of malondialdehyde and proline were increased. Compared with the control, among six stress-related genes, the expression levels of five genes were downregulated and one gene was upregulated in the experimental group. This study preliminarily revealed the toxic effect of ZnO NPs on seedlings and the effect on the expression of stress-related resistance genes in different barley varieties.

EVALUATION OF SALINITY STRESS EFFECTS ON CHANGES IN PHOTOSYNTHETIC PIGMENTS, HYDROGEN PEROXIDE AND OSMOLYTES IN SENSITIVE AND TOLERANT CULTIVARS OF WHEAT CROP

Investigation of wheat response to salinity stress can help to better understand the effective defense mechanisms of salinity stress tolerance. For this purpose, biochemical and physiological traits related to salinity tolerance in wheat cultivars were evaluated at Gorgan University of Agricultural Sciences and Natural Resources in 2019. Experimental factors, included two wheat crop cultivars (Sarc and Chinese spring as tolerant and susceptible wheat cultivars, respectively) and sampling time series (zero or control, 24, 48, 72, and 96 h) were examined in a factorial experiment based on a completely randomized design with three replications. Salinity stress was applied with sodium chloride at a concentration of 250 mM to uniform 10-day-old seedlings at the two-leaf stage, followed by sampling of shoot tissue. The studied traits were hydrogen peroxide (H2O2 ), chlorophyll a, chlorophyll b, total chlorophyll, chlorophyllase, carotenoids, proline, and total carbohydrates. Results of analysis of variance (ANOVA) indicated significant effects of genotype, time, and interaction of genotype × time (except H2O2 and total carbohydrates) on all the studied traits. Results of interaction of genotype × time showed although the trend of changes in the studied traits, depending on the type of cultivar and the sampling time were different, but generally, the susceptible Chinese spring cultivar contained higher levels of chlorophyllase and carotenoids than the control time at the end of sampling time and also higher H2O2 levels than the Sarc tolerant cultivar, while the Sarc tolerant cultivar, on the other hand, contained higher levels of chlorophyll a, chlorophyll b, total chlorophyll, and proline than the control time at the end of sampling time and also greater total carbohydrates than the susceptible Chinese spring cultivar. The results confirm the higher capacity of the antioxidant defense system of Sarc tolerant cultivar than the susceptible Chinese spring cultivar. Therefore

Reducing Grain Sorghum (Sorghum bicolor L. Moench) Injury From Postemergence Application of Mesotrione With Dicamba

Weed management in grain sorghum is limited by the number of herbicide options. A two-year (2017-2018) field study was conducted at the Mississippi State University Delta Research and Extension Center, in Stoneville, MS to evaluate the response of grain sorghum to mesotrione application alone or when tank-mixed with dicamba at the two-leaf and four-leaf growth stage of sorghum. Mesotrione was applied at 0.07 and 0.105 kg ai ha-1 alone or was tank-mixed with dicamba at 0.28 kg ae ha-1. Significant injury to grain sorghum from all herbicide treatments was observed compared with the untreated check. Increase in mesotrione application rate increased injury to grain sorghum from 14 to 19% at two-leaf and from 10 to 24% at the four-leaf stage by 4 weeks after application (WAA) in 2017. Adding dicamba to mesotrione reduced grain sorghum injury in both years. At 4-leaf sorghum application stage, mesotrione applied at 0.07 kg ha-1 resulted in greater grain yield than all other herbicide treatments, except mesotrione (0.105 kg ha-1) + NIS in 2017. Our results indicate that adding dicamba to mesotrione safes grain sorghum from injury caused by mesotrione alone.

The effects of foliar-applied manganese on major cell wall polysaccharide fractions and soluble sugar composition of cucumber leaves

Increasing evidence shows that micronutrients can induce changes in cell wall (CW) properties in plants. A detailed knowledge of these changes will contribute to understand the beneficial and detrimental impacts of trace elements on plant development and defence. In the present work, the influence of foliar spray of manganese (Mn) on the composition of CW polysaccharides and soluble sugars was investigated in cucumber leaves using spectrophotometric and chromatographic techniques. Cucumber seedlings were hydroponically cultured under controlled situations for 21 days. At the two-leaf stage, the above facade of cucumber leaves was fertilized with MnSO4 solutions at various dosages (1.8, 4.5 and 7.2 mM). Results showed that the foliar Mn spray decreased the galacturonic acid (GalA) content, while it increased the degree-of-methyl-esterification (DM) of pectin. The amounts of fucose, arabinose and galactose diminished upon Mn application. The contents of rhamnose and xylose decreased or did not change by Mn treatment. The glucose level enhanced at low concentration of Mn (1.8 mM), but it decreased at medium and high concentrations of Mn (4.5 and 7.2 mM). The increase of mannose content was significant only at medium concentration of Mn. Overall, the amount of total hemicellulose increased at 1.8 mM concentration of Mn, while a decrease was observed at 4.5 and 7.2 mM concentrations of Mn. The cellulose content decreased at low and high concentrations of Mn, although it remained unchanged at medium concentration of Mn. Generally, the total contents of CW polysaccharides increased at low concentration of Mn, but they decreased at the higher concentrations of Mn. Such changes can be important in plant resistance to environmental stresses via reduction of permeability against fungal pathogens and decrease of water loss from tissues under stresses such as drought and salinity.

Hydrogen peroxide is involved in hydrogen sulfide-induced carbon assimilation and photoprotection in cucumber seedlings

Hydrogen sulfide (H2S) and Hydrogen peroxide (H2O2) are two crucial gaseous signaling molecules that participate in various physiological processes and abiotic stresses. However, how the synergy of H2S and H2O2 regulates photosynthesis have rarely been studied. This study aimed to reveal the mechanism underlying the interaction between H2S and H2O2 in plants response to photosynthesis. Cucumber (Cucumis sativus L., ‘Jinyou 35’) seedlings were used as the material and grown in a climate chamber at 26 °C/18 °C with a 600 μmol m−2·s-1 photon flux density (PFD). Sodium hydrosulfide hydrate (NaHS, an H2S donor), H2O2, and their scavengers or inhibitors were applied as foliar sprayed at the two-leaf seedling stage. The result showed that both NaHS and H2O2 increased the CO2 assimilation, which mainly attributed to an increase in the activity and gene expression of photosynthetic enzymes. NaHS and H2O2 also induced photoprotection for both photosystem Ⅱ (PSⅡ) and photosystem Ⅰ (PSⅠ) in cucumber seedlings, by activating the D1 protein repair pathway under chilling stress. Interestingly, 1.0 mM NaHS significantly enhanced the relative gene expression of respiratory burst oxidase homolog (RBOH), which in turn elevated endogenous H2O2 accumulation in cucumber seedlings. However, H2O2 had little effect on gene expression of L-/D-cysteine desulfhydrase (L-/D-CD) and endogenous H2S level. The H2S-induced adaptive response of photosynthesis to chilling stress was suppressed by diphenyleneiodonium (DPI, a H2O2 generation inhibitor) or dimethylthiourea (DMTU, a H2O2 scavenger). These data suggest that NaHS alleviates the negative effects of chilling stress on photosynthesis by improving photosynthetic carbon assimilation, carbon metabolism, and photoprotection for both PSⅡ and PSⅠ in cucumber seedlings. H2O2 may act as a downstream signal in H2S-induced protection of the photosynthetic apparatus in cucumber seedlings under chilling stress.

Influence of plant growth regulators on vegetative growth, sex expression and yield of summer bottle gourd

Field experiments on bottle gourd variety ‘BARI Lau -4’ were conducted at the Plant Physiology field of Horticulture Research Center, Bangladesh Agricultural Research Institute, Gazipur during two consecutive summer seasons of 2015 and 2016 to investigate the effect of plant growth regulators on growth, sex expression, yield and yield components of the crop. The experiment consisted of different concentrations of Gibberellic acid (GA3), Naphthalene acetic acid (NAA), Maleic hydrazide (MH) and single concentration of cycocel (CCC) viz., GA3 @ 10 ppm, GA3 @ 30 ppm, NAA @100 ppm, NAA @ 150 ppm, MH @ 50 ppm, MH @ 150 ppm and CCC @ 500 ppm along with distilled water considered as control. All growth regulators were sprayed to the seedlings at two-leaf stage and 4 days after the first spray. Growth regulator treatments had significant effect on primary branches/plant, node number of 1st male and female flower appearance, number of days to 1st male and female flower appearance, number of male and female flowers, sex ratio (male:female flower) number of fruits/plant, individual fruit weight and fruit yield. Spraying of MH @ 150 ppm gave the highest primary branches/plant (17.0 and 18.0 in first and 2nd year, respectively) and induced maximum female flowers (37.3 and 40.0 in first and 2nd year, respectively) at lower nodes followed by CCC @ 500 ppm (36.3) in the first year and MH @ 50 ppm (40.0) in the 2nd year. Application of MH @ 150 ppm caused early appearance of female flowers on the nearest node (from bottom). Application of MH @ 150 ppm gave the lower number of male flowers (81.7 and 96.0 in first and 2nd year, respectively) and the highest number of female flowers/plant, thereby producing lower male:female sex ratio (2.2 and 2.5 in first and 2nd year, respectively) and the maximum number of fruits/plant (12.0 and 14.0 in first and 2nd year, respectively). The maximum fruit weight/plant was obtained from the application of MH @ 150 ppm (29.3 and 35.8 in first and 2nd year, respectively) followed by CCC @ 500 ppm (26.0 in the 1st year and 29.0 in 2nd year). The highest fruit yield per hectare was recorded significantly with the application of MH @ 150 ppm (97.6 t/ha and 89.6 t/ha in first and 2nd year, respectively) closely followed by CCC @ 500 ppm (88.5 t/ha in 2015) and GA3 @ 30 ppm (75.3 t/ha in 2016), as compared to other treatments. The highest mean yield over the years was also recorded at MH @ 150 ppm (93.6 t/ha) followed by CCC @ 150 ppm (80.6 t/ha) and GA3 30 (74.1). Application of MH @ 150 ppm gave the maximum gross return and net return with the highest BCR of 5.24 followed by CCC 500 ppm (4.15) and GA3 30 ppm (3.86).
 Bangladesh J. Agril. Res. 44(4): 577-590, December 2019

Identification of a Locus Conferring Dominant Susceptibility to Pyrenophora tritici-repentis in Barley

The fungus Pyrenophora tritici-repentis (Ptr) causes tan spot, a destructive foliar disease of wheat worldwide. The pathogen produces several necrotrophic effectors, which induce necrosis or chlorosis on susceptible wheat lines. Multiple races of Ptr have been identified, based on their ability to produce one or more of these effectors. Ptr has a wide host range of cereal and non-cereal grasses, but is known to cause damage only on wheat. Previously, we showed that Ptr can interact specifically with cultivated barley (Hordeum vulgare ssp. vulgare), and that the necrotrophic effector Ptr ToxB induces mild chlorosis in a highly selective manner when infiltrated into certain barley genotypes. In the present study, a barley doubled-haploid (DH) population was evaluated for reaction to Ptr race 5, a Ptr ToxB-producer. Then a comprehensive genetic map composed of 381 single nucleotide polymorphism (SNP) markers was used to map the locus conditioning this chlorosis. The F1 seedlings, and 92 DH lines derived from a cross between the resistant Japanese malting barley cultivar Haruna Nijo and the susceptible wild barley (H. vulgare ssp. spontaneum) OUH602 were inoculated with a conidial suspension of Ptr race 5 isolate at the two-leaf stage. The seedlings were monitored daily for symptoms and assessed for chlorosis development on the second leaf, 6 days after inoculation. All tested F1 seedlings exhibited chlorosis symptoms similar to the susceptible parent, and the DH lines segregated 1:1 for susceptible:resistant phenotypes, indicating the involvement of a single locus. Marker-trait linkage analysis based on interval mapping identified a single locus on the distal region of the short arm of chromosome 2H. We designate this locus Susceptibility to P. tritici-repentis1 (Spr1). The region encompassing this locus has 99 high confidence gene models, including membrane receptor-like kinases (RLKs), intracellular nucleotide-binding, leucine-rich repeat receptors (NLRs), and ankyrin-repeat proteins (ANKs). This shows the involvement of a dominant locus conferring susceptibility to Ptr in barley. Further work using high-resolution mapping and transgenic complementation will be required to identify the underlying gene.

First Report of Spot Blotch of Barley Caused by Cochliobolus sativus in Morocco

Barley (Hordeum vulgare L.) is grown on ∼2 million hectares in Morocco (av. 1.2 t/ha), with ∼70% under semiarid conditions (FAO 2017). Historically, net form net blotch (NFNB) (Pyrenophora teres f. teres [Ptt]) and spot form net blotch (SFNB) (P. teres f. maculata [Ptm]) have predominated in Morocco, causing up to 29% yield losses (El Yousfi and Ezzahiri 2002). Often, barley spot blotch (SB) caused by Cochliobolus sativus (anamorph: Bipolaris sorokiniana [Sacc.] Shoem.) is misdiagnosed as SFNB. Disease surveys were conducted in six regions (Abda, Rommani, Choiya, Dokhala, Gharb, and Rahamna) in 2015 (54 fields) and 2018 (49 fields) at heading stage and covered three cultivars (Annoucer, Rabat 071, and Arig 08) representing 34, 41, and 25% of fields, respectively. Leaf samples (∼10) from three plants per field were collected. From each site, a representative sample with SFNB symptoms (20 leaf segments, 1-cm² pieces) was used for isolation. Samples were surface sterilized with 50% ethanol for 30 s and 5% bleach for 60 s, followed by rinsing in sterile deionized water twice for 5 min. Samples were dried between two layers of sterile filter paper, followed by incubation on PDA under 12 h light/dark at 22 ± 1°C. After 4 to 5 days, dark brown elliptical conidia of 60 to 120 × 12 to 20 µm with 5 to 9 septa per cell were observed. Cultures sporulated profusely with light to dark gray or brown cottony mass with wavy colony margins (Kumar et al. 2002). Based on morphology, isolates were identified as C. sativus. Of 103 samples, C. sativus was recovered from 11 (11%), and 92 samples were Ptt (40%) and Ptm (50%). To test pathogenicity of the SB isolates, two SB differential genotypes (NDB5883 and Bowman) were used as checks, along with three cultivars (Rabat 071, Annoucer, and Oussama). Seeds (∼4 to 5 per genotype per replicate) were sown in three replications in peat moss with 14-14-14 NPK; seedlings were raised in a growth chamber with 16 h light/8 h dark at 20 ± 1°C. To produce inoculum, lyophilized agar plugs of monoconidial SB isolates were incubated on V8PDA in the dark for 4 to 5 days at 22 ± 1°C, followed by 22 ± 1°C with 12 h light/dark for 7 to 8 days. V8PDA plates were flooded with 5 to 10 ml of sterile distilled water, and the conidia were harvested followed by filtration with a double layer of cheese cloth. Spore density was adjusted to 5,000 conidia/ml supplemented with surfactant (0.01% Tween 20). Seedlings at the two-leaf stage (∼14 days old) were inoculated with the two isolates independently until runoff and incubated at 100% RH at 20 ± 1°C in the dark for 24 h. Seedlings were transferred to a greenhouse with 16 h light/8 h dark at 20 ± 1°C. After 10 days, the seedlings were scored on a 0 to 9 scale (Fetch and Steffenson 1999). All infected seedlings produced lesions as described by Kumar et al. (2002) and Fetch and Steffenson (1999). The experiment was carried out twice to confirm the repeatability of SB symptoms. To satisfy Koch’s postulates, leaf tissue from infected seedlings of all genotypes for both SB isolates was surface sterilized and incubated on PDA as described above. Monoconidial cultures were induced for sporulation on V8PDA; upon inoculation, similar symptoms were observed, confirming SB. Both SB isolates were grown in Fries medium, and genomic DNA was isolated (Benslimane et al. 2013). PCR with ITS1-F/ITS2-R produced a single band of ∼500 bp and was subjected to DNA sequencing from both ends. Homology-based BLASTN searches using sequences from both SB isolates produced 100% identity (E-value 0) to 98 GenBank accessions of SB partial sequence of small and large subunit rRNA, complete sequence of ITS1, 5.8S rRNA gene, and ITS2 (MK676001, MK905507, MH864698). Conidia and colony morphology, symptomology, Koch’s postulates, and DNA sequencing corroborate C. sativus (perfect stage) causing SB in barley. The queried sequences were deposited in GenBank as MN444781, 82, 84, and 85. This is the first report of SB in Morocco. This has implications for future barley breeding and cultivation under dry areas, as SB so far has been a disease of hot and humid conditions of South Asia.

Pathogenic variability of a Uruguayan population of Bipolaris sorokiniana in barley suggests a mix of quantitative and qualitative interactions

Race-specific and race-non-specific interactions with barley have been previously reported for Bipolaris sorokiniana. The aims of the study were to characterize a Uruguayan population of B. sorokiniana, to determine the nature of the interactions, and to identify a set of the most informative barley genotypes to characterize the pathogen. Infection responses of 322 single-spore isolates of B. sorokiniana collected from 2001 to 2010 were assessed for their interaction with 35 barley genotypes after inoculation at the two-leaf stage under controlled conditions on a 1–9 scale. After removal of the most redundant isolates, the interactions of 147 isolates were analyzed with Hierarchical Clustering on Principal Components, resulting in eight clusters of barley genotypes and seven clusters of B. sorokiniana isolates. A set of 12 potential differential barley genotypes grouped into 11 clusters that interacted in a partially specific but also in a quantitatively variable manner with the 147 isolates. Despite some clear isolate-specific interactions, the predominately quantitative interactions found make it unlikely that a universal differential set could be used to monitor diversity worldwide.

Bioherbicidal activity of terpenes and phenylpropenes against Echinochloa crus-galli

This study was undertaken to evaluate the herbicidal activity of twelve natural compounds belonging to monoterpenes, phenylpropenes, and sesquiterpenes against Echinochloa crus-galli under laboratory and glasshouse conditions. Experiments were conducted to determine the impact of different concentrations (0.5, 1, 2, 4 and 8 mM) of these compounds on the seed germination and root and shoot growth of barnyard grass. trans-Cinnamaldehyde, eugenol, and thymol caused the highest impact on barnyard grass reducing its seed germination and shoot growth. p-Cymene (EC50 = 0.22 mM) and trans-cinnamaldehyde (EC50 = 0.34 mM) were the most potent compounds in limiting the root growth of the E. crus-galli. In a post-emergent experiment, thymol, trans-cinnamaldehyde, eugenol, farnesol, and nerolidol significantly reduced the shoot growth, fresh and dry weight of two-leaf stage barnyard grass after 2 days of the foliar treatment with the concentrations of 0.5, 1.0 and 2.0%. These compounds induced severe visible injury symptoms where trans-cinnamaldehyde, eugenol, farnesol and nerolidol showed a complete weed control at 1.0 and 2.0%. These compounds were successfully formulated as emulsifiable concentrates and showed higher herbicidal activities against barnyard grass. Altogether, our data showed that trans-cinnamaldehyde, eugenol, thymol, farnesol, and nerolidol can be developed as novel bioherbicides for managing E. crus-galli.

Classification Method of Plug Seedlings Based on Transfer Learning

The classification of plug seedlings is important work in the replanting process. This paper proposed a classification method for plug seedlings based on transfer learning. Firstly, by extracting and graying the interest region of the original image acquired, a regional grayscale cumulative distribution curve is obtained. Calculating the number of peak points of the curve to identify the plug tray specification is then done. Secondly, the transfer learning method based on convolutional neural network is used to construct the classification model of plug seedlings. According to the growth characteristics of the seedlings, 2286 seedlings samples were collected to train the model at the two-leaf and one-heart stages. Finally, the image of the interest region is divided into cell images according to the specification of the plug tray, and the cell images are put into the classification model, thereby classifying the qualified seedling, the unqualified seedling and the lack of seedling. After testing, the identification method of the tray specification has an average accuracy of 100% for the three specifications (50 cells, 72 cells, 105 cells) of the 20-day and 25-day pepper seedlings. Seedling classification models based on the transfer learning method of four different convolutional neural networks (Alexnet, Inception-v3, Resnet-18, VGG16) are constructed and tested. The classification accuracy of the VGG16-based classification model is the best, which is 95.50%, the Alexnet-based classification model has the shortest training time, which is 6 min and 8 s. This research has certain theoretical reference significance for intelligent replanting classification work.

Evaluation of Different Inoculation Methods for Screening of Sclerotinia rot and Phytophthora blight in Perilla Germplasm

Sclerotinia rot and Phytophthora blight are devastating diseases of perilla that can cause huge loss of perilla production. Screening disease resistant genetic resources is necessary to develop disease-resistant cultivars and conduct related research. The objective of this study was to find suitable inoculation methods for screening of Sclerotinia rot and Phytophthora blight in perilla germplasm. Three different inoculation methods [i.e., detached leaf (agar plug placed on start point of vein, 1/3 point of leaf vein & front side, back side), stem tip, and soil drenching] with three-growth stages (two, four & six-leaf stage) at two different temperatures (20 & 25°C) were assayed for their effectiveness for screening using IT 229019 & Sang-yeop perilla germplasm. Based on disease lesion, 20°C in two-leaf stage with detached leaf method (start point of vein) was found to be an efficient method for screening of Sclerotinia rot whereas 25°C in two-leaf stage with stem tip was an effective method for screening of Phytophthora blight in perilla germplasm. However, stem tip method was laborious as it required more time. Therefore, detached leaf method (start point of vein & back side) was a simple and rapid method that could be preferably used for screening of Sclerotinia rot and Phytophthora blight in perilla germplasm.

Influence of Oilseed Rape Seed Treatment with Imidacloprid on Survival, Feeding Behavior, and Detoxifying Enzymes of Mustard Aphid, Lipaphis erysimi.

Imidacloprid application, as a seed coating agent on oilseed rape, is recommended to control mustard aphid, Lipaphis erysimi (Kaltenbach) (Hemiptera: Aphididae). In this study, responses of L. erysimi were investigated, including survival, feeding behavior, and detoxifying enzymes, on the oilseed rape seedlings grown from seeds coated with imidacloprid at rates of 6, 12, or 18 g active ingredient (a.i.)/kg seed. The results showed that the aphids’ survival rate, together with that of the progeny of the survivors, on the seed-treated seedlings significantly decreased. This indicates that the aphid population in fields can be suppressed effectively. The electrical penetration graph (EPG) technique was used to record aphid feeding behaviors on two-, four-, and six-leaf stages of oilseed rape seedlings that had been seed-coated with imidacloprid, and individual responses were revealed during the aphid feeding behavior. On the plants at the two-leaf stage, aphid feeding behaviors were influenced, showing decreased frequency of stylet penetration into the leaf (probe) or into the mesophyll cells (potential drops, pds for short), and shortened duration of stylet event in the leaf (probe) or in the phloem. On the plants at the four- and six-leaf stages, these impacts of imidacloprid were weakened; however, the saliva secretion duration in phloem was shortened to less than 5 min in all imidacloprid treatments. The activity of mixed-function oxidase in aphids maintained on the treated seedlings with imidacloprid was elevated. In conclusion, imidacloprid could be used as a seed coating agent for aphid control, but chemical resistance in aphids should not be ignored.

Hypocotyl elongation is regulated by supplemental blue and red light in cucumber seedling

Light is fundamental for plants in growth and development, with regulating by integration of photoreceptors, hormones, and transcription factors. In this study, the cucumber seedlings were supplemented with different ratios of red and blue light (1R1B, 2R1B, 1R2B and weak daylight as control), with triggering change of phenotype, and gene expression profiles of CsPHYs and CsCRYs, CsGAs/BRs, and CsPIFs in hypocotyls. The cucumber seedling growth was significantly improved by supplemental light quality as compared with CK, and the seedlings in 2R1B were the stoutest, with obviously shortening hypocotyls, and higher dry weight and seedlings index at two-leaf stage. The gene expression of photoreceptor and hormone, including CsPHYA, CsPHYB, CsCRY1, CsGA20ox1, CsGA20ox2, CsGA3ox1, was significantly up-regulated in hypocotyl under different supplemental light conditions. The cucumber seedlings silenced by pTRV2-PIF4 had an obvious shortened hypocotyl. The expression level of CsCRY1, CsGA20ox1 and CsGA3ox1 was markedly down-regulation, whereas CsPHYA and CsPHYB expression increased observably and CsGA20ox2 expression was not dramatically difference in pTRV2-PIF4-infected seedlings. Thus, cucumber seedlings hypocotyl elongation was regulated by different supplemental light through crosstalk of photoreceptor, GAs, PIFs, and increasing ratio of red light could promote suppression of hypocotyl elongation.

Effects of Melatonin on Growth, Physiology and Gene Expression in Rice Seedlings Under Cadmium Stress

Melatonin (MLT) is a hormonal substance found in many organisms and can improve plant stress resistance. In this study, the japonica rice variety Y32 and indica rice variety NJ6 were cultivated in hydroponics under different concentrations of CdCl2 at the two-leaf stage. The growth, physiological and biochemical responses of the seedlings and the expression of cadmium (Cd)-related genes under exogenous melatonin (MLT) treatment were assessed. The results indicated that Cd stress destroyed the dynamic balance between reactive oxygen species (ROS) production and removal, resulting in ROS accumulation, membrane lipid peroxidation, and impaired growth and development. Following the application of exogenous MLT to rice seedlings, increases in plant biomass including both underground and above-ground areas were observed. MLT also relived the inhibition of superoxide dismutase (SOD) and peroxidase (POD) in a concentration dependent manner in response to Cd stress. Catalase (CAT) activity and malondialdehyde (MDA) expression also decreased following MLT treatment. Amongst the six Cd-related genes assessed, five genes were down-regulated and one was up-regulated in response to MLT treatment. Taken together, these data demonstrate that MLT improves the resilience of rice seedlings at the biochemical, physiological, and molecular levels, and alleviates the damage caused by Cd stress.

Seed size and seedling ontogenetic stage as modulators of damage tolerance after simulated herbivory in a woody exotic species

Herbivory is one of the most important threats that plants face during early stages of development. Previous studies have indicated that seed size and seedling ontogeny strongly influence the response to herbivory at the seedling stage. However, little is known about their interactive effect. We simulated herbivory on seedlings of the exotic Gleditsia triacanthos L. and evaluated the combined effects of seed size and ontogenetic stage at which herbivory occurred on tolerance to herbivory. A greenhouse experiment was performed, with three non-overlapping levels of seed size. Seedlings from each seed size were clipped at two ontogenetic stages (two and five leaves). After three weeks, seedling survival, height, leaf number and dry biomass were measured. Damaged seedlings were not able to reach the size of the undamaged ones. Seedlings from small seeds showed the lowest values in most of the growth variables. Seedlings cut at two-leaf stage showed a higher compensation capacity than those cut at five-leaf stage. Seedlings from large seeds cut at ontogenetic stage I showed the highest compensation capacity in most of the variables. Partly compensating herbivory at this stage may be an advantage for the expansion of this exotic species to new areas.

Bacillus subtilis S37-2와 Pseudomonas sp. GHR1-1을 이용한 토마토 시들음병 방제 효과

The control effect of tomato wilt disease was investigated using the strain developed by Rural Development Administration. As a result, <italic>Bacillus subtilis</italic> S37-2 and <italic>Pseudomonas</italic> sp. GHR1-1 showed an inhibitory effect on mycelial growth and spore germination of <italic>Fusarium oxysporum</italic> f sp. <italic>lycopersici</italic>. The control effects of wilt disease in tomato seedlings showed that the disease severity was lower when the strains were treated in the sowing stage than in the two-leaf stage. In the sowing stage, the control effect of the tomato wilt disease was 94.6% when GHR1-1 was treated, and 87.1% when the GHR1-1 and S37-2 were mixed. These results suggest that the two strains may be used as environmentally friendly microbial agents.