Mandarin Plants Research Articles

Экологические условия и лимитирующие факторы возделывания мандарина (Citrus reticulata Blan. var. unshiu Tan.) в субтропиках черноморского побережья России

Abstract. The main environmental factors determining the optimal conditions for the growth of the main species of the genus Citrus on the example of mandarin (Citrus reticulata Blan. var. unshiu Tan.) and limiting factors of environmental impact on plants are considered. The most informative sources in this case are: temperature (minimum, average, maximum) and the amount of precipitation). The study of weather conditions of five growing seasons (2019-2023) revealed the main environmental factors that expose early-maturing (Kawano-Wase) and late-maturing (Unshiu) citrus varieties in the subtropical zone of Russia to waterthermal stresses. The likelihood of devastating frosts (-5 °C for lemon and -12 °C for mandarin and orange) pose a threat to citrus farming in this region. The relationship between precipitation and HTC is shown. The correlation coefficient is statistically significant r = 0.98. The connection is strong and direct. The largest number of temperature stressors (seven) has been established in 2020, 2022, and 2023. At the same time, the maximum temperature reached from 26.9 °C – 2.10.2022, to 35.9 °C – 6.08.2023. Frosts were not critical, the minimum temperature reached -7.2 °C (09.02.2020) and -4.3 °C (23.12.2021). The last frost – -2.4 °C was observed late on March 18, 2022, but was no longer dangerous for plants. The lack of precipitation creates a stressful situation along with the temperature. 2020 was the most critical year due to the values of this indicator. Precipitation was distributed: 25 mm in June, 11 mm in August and 30 mm in September, that is only 66 mm (19 %) with a norm of 341 mm. Water deficiency affects the growth, generative processes and metabolism of mandarin plants. Mandarin plants exposed to stress exhibit adaptive responses to stressors regardless of the biological characteristics of low-growing (Kawano-Wase) or strong-growing (Unshiu) plants varieties. Keywords: vegetation, environment, stress, adverse effects, temperature

Chemical Quality Parameters of Mandarin (Citrus reticulata Blanco.) Fruits Influenced by different Organic Sources

A field experiment was carried out during the year 2021-22 and 2022-23 on 12 years old mandarin plants at the Instructional Farm, Department of Fruit Science, College of Horticulture and Forestry, Jhalawar. The experiment was consisting of 21 treatments of different organic source of NPK viz., vermicompost, cotton fortified vermicompost, neem cake, cotton cake, mustard cake and bio fertilizers such as PSB and VAM with three levels of recommendation dose of fertilizers. The experiment was laid out in randomized block design with three replications. Among different treatments, treatment T9 (75 % RDF + 10 kg Vermicompost + 7.5 kg Neem cake + 50 g PSB) was found best with regards to maximum pooled TSS (11.74 0B), reducing sugar (6.30%) non-reducing sugar (2.62%), total sugar (8.92%) per cent, sugar/acid ratio (14.40), ascorbic acid (53.08mg/100g) and juice (46.57%). Therefore, based on two years experimentation, use of organic source of nutrients with bio-fertilizers favoured biochemical compounds of Nagpur Mandarin fruits.

First report of Phytopythium vexans causing gummosis and root rot of Khasi Mandarin (Citrus reticulata Blanco) in north eastern states of India.

Khasi mandarin (Citrus reticulata Blanco) is the most economically important crop among the citrus growing region in the north-eastern India (Singh et al. 2016). An extensive survey was conducted to identify the causal agent of citrus root rot and gummosis in north eastern states (Meghalaya, Tripura, Manipur, Arunachal Pradesh, Sikkim, Nagaland and Assam) of India during October 2021-23. The gummosis disease incidence ranged from 5 to 95 % in 10 to 25 years old Khasi mandarin plants showing relatively more chronic symptoms on mature trees. Yellowing and dropping of leaves, twigs die back, gum oozing from infected bark and loss of feeder roots were the typical symptoms of the disease. Infected bark tissue and young lemon leaf baits in rhizosphere soil were plated on corn meal agar medium supplemented with pimaricin (10 µg/ml), ampicillin (250 µg/ml), rifamycin (10 µg/ml) and 300µg/ml carbendazim and incubated at 26℃. Fifty isolates were purified and maintained on Carrot agar medium. These isolates showed similar cultural and morphological characteristics. Two representative isolates from Arunachal Pradesh (AP21 and AP26) were selected for further experiments and deposited to Indian Type culture collection (ITCC), New Delhi with accession no. 9156 and 9157 respectively. The colonies were fast growing, showing rosette pattern along with whitish blooming mycelium appearance with no visual sporulation at the surface. The hyphae were coenocytic with initially right-angled branching. Sporangia were globose or sub globose and papillated. Oogonia were smooth and globose (16.29-21.09 µm) in diameter. Antheridia were irregular, cylindrical and broadly attached to oogonia. Empty sporangia were also observed. Multilocus phylogenetic analysis using internal transcribed spacer region (Das et al. 2011), β tubulin (Blair et al. 2008) and Cytochrome oxidase II gene (Noireung et al. 2020) showed that these isolates formed a stable clade with Phytopythium vexans (CBS119.80) sequence retrieved from NCBI database. BLAST analysis showed that ITS sequence of AP21 (OQ372986) and AP26 (OQ381083) had >99 % identity with P. vexans isolate NS-3 (ON533631). Further, BLAST analysis of β tubulin (AP21 OQ446053, AP26 OR405377) and Cox II gene (AP21 OQ473414, AP26 OR552422) sequences showed that our Indian isolates showed >99 % similarity with P. vexans voucher strain CBS119.80. To fulfil Koch's postulates, Khasi mandarin (Citrus reticulata) seedlings were inoculated by adding 100 ml zoospore suspension of P. vexans (1x105 spores/ml) in sterilized soil (Thao et al. 2020). The experiment was carried out in triplicate. Yellowing of leaves and leaf drop were observed 7 days post inoculation while 30 days post inoculation, treated plants started showing symptoms of root rot, including mild root decay. No symptoms were observed in control treatment. The pathogen was reisolated from symptomatic roots and confirmed through colony and sporangium morphology. Recently, it was reported that P. vexans is associated with apple and pear decline in the Saiss plain of Morocco (Jabiri et al. 2021), root rot on mandarin in Thailand (Noireung et al. 2020) and on Durian in Vietnam (Thao et al. 2020). As per our knowledge, this is the first report of P. vexans causing root rot and gummosis in Khasi mandarin from north eastern states of India. This finding is significantly important for the development of a successful disease management strategy in India.

Water productivity associated to the planting system in young Nadorcott mandarin plants

The main goal of citriculture in Uruguay is to increase yield, quality, and improve sustainability and efficiency of natural resources. Today, it is not possible to conceive an efficient citrus production system without the use of irrigation technologies. The aim of this work was to evaluate the irrigation water efficiency and growth conditions of different plantation systems focused on speeding up production and the improvement of water use efficiency. An experiment was installed in Nadorcott mandarin with two planting densities (909 and 1220 pl. ha-1), and three plantation designs: ridges covered with white plastic cloth; uncovered ridges, and flat planting at ground level. At the end of the evaluation period, the volume of the trees planted in the covered ridges doubled those in the flat (1 m3). The trees on the flat design consistently produced fewer fruits and lower yield than those on ridges. Covered ridge showed the best performance. Soil water content remained higher and soil temperature lower in covered ridges. Overall, trees planted on ridges with or without plastic mulch allowed a better water use efficiency, and the lower soil temperature promoted a better environment for tree growth.

Exploring the antagonist potential of indigenous Trichoderma spp., Bacillus, and Pseudomonas against Phytophthora palmivora of Soe mandarin in East Nusa Tenggara, Indonesia

Phytophthora palmivora-induced root and basal stem rot pose a significant threat to the survival of Soe mandarin plants in East Nusa Tenggara Province, Indonesia. We isolated four Trichoderma species, five Bacillus, and 13 Pseudomonas isolates from the rhizosphere of healthy Soe mandarin. This study pursued two main objectives: (a) assessing the inhibitory capabilities of indigenous Trichoderma spp., Bacillus, and Pseudomonas towards P. palmivora in vitro, and (b) investigating the combined efficacy of Trichoderma spp., Bacillus, and Pseudomonas in controlling P. palmivora in a pot trial. Results revealed that four Trichoderma species (T. asperellum, T. hamatum, T. harzianum, and T. viride) significantly inhibited the growth of P. palmivora. Notably, T. asperellum exhibited the highest inhibition, at 84.31%, followed closely by T. harzianum (84.11%), T. viride (83.67%), and T. hamatum (80.28%). Bacillus and Pseudomonas exhibited varying levels of inhibition to P. palmivora growth in vitro, with the most substantial inhibition observed in Bacillus 1, followed by Pseudomonas 6. In the subsequent pot trial, the application of Trichoderma, Bacillus, or Pseudomonas, either individually or in combination, significantly increased the height increment and reduced the disease incidence caused by P. palmivora in Soe mandarin seedlings.

DRIS standards for identifying yield-limiting nutrients in Khasi Mandarin and their relationship with fruit yield on acidic soil of the eastern Himalayas, India

Mandarin fruits are the most widely grown citrus fruits in the world, particularly in the eastern Himalayas of India, which is the primary center of citrus diversity. Diagnosing potential nutritional imbalances using leaf tissue analysis is a mandatory practice for a higher yield. Regarding the nutritional diagnosis of Khasi mandarin plants, particularly in the acidic soil of the hilly ecology of the Eastern Himalayas, India, there is currently no information available. Therefore, the present study was conducted to identify nutrient constraints, establish leaf-based diagnostic recommended and integrated system (DRIS) norms, and determine nutrients’ relationship with fruit yields in 144 orchards. The result showed that the DRIS indices predicted a nutritional optimum value for Khasi mandarin: 2.26–2.83% N, 0.11–0.16% P, 1.86–2.07% K, 1.85–2.12% Ca, 0.33–0.48% Mg, 170.10–225.10 mg kg−1 Fe, 74.03–83.43 mg kg−1 Mn, 1.24–2.45 mg kg−1 Cu, and 19.84–21.28 mg kg−1 Zn. The DRIS norms identified the nutrients Zn, P, Ca, K, N, and Mg as deficient to low levels (14.15→2.14), while Fe, Mn, and Cu were at high to excessive levels (5.50→18.25). The nutritional balance index had a significantly negative relationship with the fruit yield. Leaf nutrient concentrations of N (0.909**), P (0.827**), K (0.867**), Zn (0.833**), Ca (0.827**), and Mg (0.592**) had a significant positive correlation with fruit yield. The finding will facilitate the correct interpretation of leaf nutrient analysis, and the norms developed will enable a precise intervention through nutrient management for higher yields in mandarin citrus.

Differential impact of plant-based selenium nanoparticles on physio-biochemical properties, antioxidant defense system and protein regulation in fruits of huanglongbing-infected 'Kinnow' mandarin plants.

Huanglongbing disease (HLB) is the most severe citrus disease destroying Citrus reticulata L. 'Kinnow', the most commonly grown mandarin in Pakistan. It is caused by Candidatus Liberibacter bacterial species and it spreads through the sucking Asian citrus psyllid insect. The current study was designed to investigate the potential impact of plant extract mediated selenium nanoparticles (SeNPs) on antioxidant defense system, fruit quality and protein regulation in the fruits of HLB-infected 'Kinnow' mandarin plants. Garlic cloves extract was used as reducing and capping agent for the synthesis of SeNPs. Various concentrations of SeNPs (25, 50, 75, and 100 mg L-1) were exogeneously applied to HLB-positive citrus plants. SeNPs at the concentration of 75 mg L-1 affected positively fruit physio-biochemical parameters, e.g., peel thickness, peel weight, fruit weight, fruit diameter, total soluble solids, juice volume, ascorbic acid content and reduced total acidity. Furthermore, SeNPs also enhanced the amounts of total protein and total sugar as well as elevated antioxidant enzymes, e.g., superoxide dismutase, peroxidases, and catalases. Non-enzymatic antioxidant content, e.g., total phenolic and total flavonoids, was also elevated. Proteomics analysis revealed that exposure to SeNPs at the concentration of 75 mg·L-1 significantly altered in HLB infected mandarin fruting plants the expression of proteins associated with transcription, protection, cell wall biogenesis, cell wall organization, reproduction, stamen formation, embryo development, inflorescence development, as well as translation and response to oxidative stress. Our results revealed that foliar application of SeNPs influences the protein contents positively, therefore ameliorating fruit physio-biochemical quality by boosting antioxidant defense systems of HLB-infected 'Kinnow' mandarin plants.

Discovery of Brassica Yellows Virus and Porcine Reproductive and Respiratory Syndrome Virus in Diaphorina citri and Changes in Virome Due to Infection with 'Ca. L. asiaticus'.

Detection of new viruses or new virus hosts is essential for the protection of economically important agroecosystems and human health. Increasingly, metatranscriptomic data are being used to facilitate this process. Such data were obtained from adult Asian citrus psyllids (ACP) (Diaphorina citri Kuwayama) that fed solely on mandarin (Citrus ×aurantium L.) plants grafted with buds infected with 'Candidatus Liberibacter asiaticus' (CLas), a phloem-limited bacterium associated with the severe Asian variant of huanglongbing (HLB), the most destructive disease of citrus. Brassica yellows virus (BrYV), the causative agent of yellowing or leafroll symptoms in brassicaceous plants, and its associated RNA (named as BrYVaRNA) were detected in ACP. In addition, the porcine reproductive and respiratory syndrome virus (PRRSV), which affects pigs and is economically important to pig production, was also found in ACP. These viruses were not detected in insects feeding on plants grafted with CLas-free buds. Changes in the concentrations of insect-specific viruses within the psyllid were caused by coinfection with CLas. IMPORTANCE The cross transmission of pathogenic viruses between different farming systems or plant communities is a major threat to plants and animals and, potentially, human health. The use of metagenomics is an effective approach to discover viruses and vectors. Here, we collected buds from the CLas-infected and CLas-free mandarin (Citrus ×aurantium L. [Rutaceae: Aurantioideae: Aurantieae]) trees from a commercial orchard and grafted them onto CLas-free mandarin plants under laboratory conditions. Through metatranscriptome sequencing, we first identified the Asian citrus psyllids feeding on plants grafted with CLas-infected buds carried the plant pathogen, brassica yellows virus and its associated RNA, and the swine pathogen, porcine reproductive and respiratory syndrome virus. These discoveries indicate that both viruses can be transmitted by grafting and acquired by ACP from CLas+ mandarin seedlings.

Phytomediated Silver Nanoparticles (AgNPs) Embellish Antioxidant Defense System, Ameliorating HLB-Diseased 'Kinnow' Mandarin Plants.

Citrus production is harmed worldwide by yellow dragon disease, also known as Huanglongbing (HLB), or citrus greening. As a result, it has negative effects and a significant impact on the agro-industrial sector. There is still no viable biocompatible treatment for Huanglongbing, despite enormous efforts to combat this disease and decrease its detrimental effects on citrus production. Nowadays, green-synthesized nanoparticles are gaining attention for their use in controlling various crop diseases. This research is the first scientific approach to examine the potential of phylogenic silver nanoparticles (AgNPs) to restore the health of Huanglongbing-diseased 'Kinnow' mandarin plants in a biocompatible manner. AgNPs were synthesized using Moringa oleifera as a reducing, capping, and stabilizing agent and characterized using different characterization techniques, i.e., UV-visible spectroscopy with a maximum average peak at 418 nm, scanning electron microscopy (SEM) with a size of 74 nm, and energy-dispersive spectroscopy (EDX), which confirmed the presence of silver ions along with different elements, and Fourier transform infrared spectroscopy served to confirm different functional groups of elements. Exogenously, AgNPs at various concentrations, i.e., 25, 50, 75, and 100 mgL-1, were applied against Huanglongbing-diseased plants to evaluate the physiological, biochemical, and fruit parameters. The findings of the current study revealed that 75 mgL-1 AgNPs were most effective in boosting the plants' physiological profiles, i.e., chl a, chl b, total chl, carotenoid content, MSI, and RWC up to 92.87%, 93.36%, 66.72%, 80.95%, 59.61%, and 79.55%, respectively; biochemical parameters, i.e., 75 mgL-1 concentration decreased the proline content by up to 40.98%, and increased the SSC, SOD, POD, CAT, TPC, and TFC content by 74.75%, 72.86%, 93.76%, 76.41%, 73.98%, and 92.85%, respectively; and fruit parameters, i.e., 75 mgL-1 concentration increased the average fruit weight, peel diameter, peel weight, juice weight, rag weight, juice pH, total soluble solids, and total sugarby up to 90.78%, 8.65%, 68.06%, 84.74%, 74.66%, 52.58%, 72.94%, and 69.69%, respectively. These findings enable us to develop the AgNP formulation as a potential citrus Huanglongbing disease management method.

The impact of climate change on mandarin production in Dumtoed Chewa Chiwog under Samtse Dzongkhag

Climate change which refers to a long-term shift in temperature, precipitation, wind patterns, and other elements of the Earth's climate system has a significant impact on agricultural practices across the world. Climate change has caused a notable impact on Bhutan, an agriculturally reliant nation, particularly affecting the production of mandarin, a crucial cash crop in the southern regions of the country. The study explored the impact of climate change on mandarin production in Dumtoed Chewa Chiwog under Samtse Dzongkhag. Employing the mixed methods research approach the study explored community perception of the impact of climate change on mandarin production, identified the impact of climate change on the production of mandarin, and explored the adaptations to reduce the impact of climate change on mandarin production in their locality. The study revealed that farmers are increasingly vulnerable to climate change. Erratic rainfall, rise in temperature, storms, drying soil moisture, and the emergence of new diseases and pests attributed to climate change have declined both the quality and quantity of their mandarin production, ultimately resulting in decreased income levels for farmers. While local indigenous practices have proven effective in safeguarding mandarin plants, there is a need to strengthen the resilience of mandarin cultivators against the influence of climate change. This can be achieved through policy support, raising awareness, and the provision of training.

Condition of mandarin plants (Citrus reticulata var. unshiu Tan.) upon treatment using physiologically active substances

Тhe humid subtropics of the Russian Federation constitute a conditionally suitable area for cultivating citrus crops. In recent years, low winter temperatures have been observed with increasing frequency, leading to the subfreezing of seedlings and delayed vegetation, as well as the death of plants. In addition, prolonged dry periods in summer have been recorded, contributing to a fall of leaves and fruits. One promising approach involves agricultural methods, such as the treatment of plants with regulatory and stress-protective agrochemicals. In this article, the water regime and the improvement of plant health under the influence of a number of growth regulators having a stimulating and stress-protecting effect are considered. Тhis research has been carried out at the Federal Research Centre “Subtropical Science Centre of RAS” since 2019. Тhe positive influence of such agents on the functional state of mandarin leaves was determined; the leaf health was higher (2.0–2.8 units) in the varieties treated with siliplant than that in the control (1.4-1.9 units); lower values of water deficiency (1.1-12.1 % against 13.2-15.8 % in the control) and lower content of accumulated dry matter (37-43 g against 38.5-43.8 g in the control) were noted in the same experiment. Тhe plants treated with a growth regulator yielded fruits of a higher mass (44.8-48.2 g against 41.3 g in the control). Тhe obtained data will help to develop efficient means for regulating the functional state of plants under stressful conditions.

Zinc fertigation studies in Nagpur mandarin (Citrus reticulata) grown on black clay soil

A field experiment was conducted for four seasons (2013–17) on 12-year-old bearing Nagpur mandarin (Citrus reticulata Blanco) plants budded on rough lemon rootstock (Citrus jambhiri Lush) at ICAR-Central Citrus Research Institute, Nagpur, Maharashtra. Six zinc-based treatments, viz. S100 as soil application of ZnSO4 (100 g/plant), S200 as soil application of ZnSO4 (200 g/plant), S300 as soil application of ZnSO4 (300 g/plant, F100 as fertigation of ZnSO4 (100 g/plant), F200 as fertigation of ZnSO4 (200 g/plant) and F300 as fertigation of ZnSO4 (300 g/plant) with uniform doses of macronutrients (450 g N + 150 g P2O5 + 150 K2O/tree/year) were evaluated in a randomized block design (RBD) with four replications on a smectite rich alkaline black clay soil. Significantly higher concentration of Zn in index leaves was observed with fertigation treatments than soil application treatments with regard to fruit yield and quality. The fruit yield was observed significantly lower with soil application of ZnSO4 (11.5–13.95 tonnes/ha with S100-S300) than fertigation treatments (15.6–16.4 tonnes/ha with F100-F300). The fruit quality parameters were observed much higher with F200 followed by F300. On the other hand, the lowest acidity (0.82%) and higher TSS to acidity ratio (11.52) were observed with F200. Hence, the treatment F200, split through 4 pulses at 40 days interval from anthesis to the fruit development stage proved highly efficient for quality production of Nagpur mandarin in central India.

Real-Time Assessment of Mandarin Crop Water Stress Index.

The use of plant-based indicators and other conventional means to detect the level of water stress in crops may be challenging, due to their difficulties in automation, their arduousness, and their time-consuming nature. Non-contact and non-destructive sensing methods can be used to detect the level of water stress in plants continuously and to provide automatic sensing and controls. This research aimed at determining the viability, efficiency, and swiftness in employing the commercial Workswell WIRIS Agro R infrared camera (WWARIC) in monitoring water stress and scheduling appropriate irrigation regimes in mandarin plants. The experiment used a four-by-three randomized complete block design with 80–100% FC water treatment as full field capacity and three deficit irrigation treatments at 70–75% FC, 60–65% FC, and 50–55% FC. Air temperature, canopy temperature, and vapor pressure deficits were measured and employed to deduce the empirical crop water stress index, using the Idso approach (CWSI(Idso)) as well as baseline equations to calculate non-water stress and water stressed conditions. The relative leaf water content (RLWC) of mandarin plants was also determined for the growing season. From the experiment, CWSI(Idso) and CWSI were estimated using the Workswell Wiris Agro R infrared camera (CWSIW) and showed a high correlation (R2 = 0.75 at p < 0.05) in assessing the extent of water stress in mandarin plants. The results also showed that at an altitude of 12 m above the mandarin canopy, the WWARIC was able to identify water stress using three modes (empirical, differential, and theoretical). The WWARIC’s color map feature, presented in real time, makes the camera a suitable device, as there is no need for complex computations or expert advice before determining the extent of the stress the crops are subjected to. The results prove that this novel use of the WWARIC demonstrated sufficient precision, swiftness, and intelligibility in the real-time detection of the mandarin water stress index and, accordingly, assisted in scheduling irrigation.

The level of chlorophyll fluorescence in mandarin plants during non-root treatments with growth regulators

The level of chlorophyll fluorescence in mandarin plants during non-root treatments with growth regulators

Phytogenic Selenium Nanoparticles Elicited the Physiological, Biochemical, and Antioxidant Defense System Amelioration of Huanglongbing-Infected 'Kinnow' Mandarin Plants.

Citrus greening or huanglongbing (HLB) is commonly known as yellow dragon disease and affects citrus production worldwide. Therefore, it has a significant impact on and deleterious effects in the agro-industrial sector. Significant efforts have been made to combat this disease and mitigate its destructive impact on citrus production, but still, there is no effective biocompatible treatment available to control HLB disorder. This study is considered the first biocompatible approach to evaluate the potential of phytogenic selenium nanoparticles (SeNPs) to improve the health of HLB-infected ‘Kinnow’ mandarin plants. Polymerase chain reactions (PCRs) with specific primers were used to detect HLB disease in ‘Kinnow’ mandarin plants, and PCR products were sequenced to identify Candidatus Liberibacter asiaticus (CLas), and accession numbers for CLas1 and CLas2, MZ851933 and MZ851934, respectively, were obtained. SeNPs were synthesized by using Allium sativum L. clove extract as a reducing, capping, and stabilizing agent and various techniques such as UV-visible spectrophotometry, energy dispersive X-rays, scanning electron microscopy (SEM), Fourier transformed infrared spectroscopy (FTIR), and X-ray diffraction analysis (XRD) were used to confirm the biogenesis of SeNPs. Different concentrations of SeNPs (25, 50, 75, and 100 mg L−1) were exogenously applied to HLB-infected ‘Kinnow’ mandarin plants and obtained spectacular results. The obtained results from the current study proved that 75 mg L−1 of SeNPs was most effective to improve the chlorophyll, carotenoids, relative water content (RWC), membrane stability index (MSI), total soluble sugar (TSS), superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), total flavonoid content (TFC), and total phenolic content (TPC) and significant decrease was observed in hydrogen peroxide (H2O2), malondialdehyde (MDA), and proline (PRO) contents of HLB-infected ‘Kinnow’ mandarin plants as compared to untreated diseased citrus plants. In conclusion, these results allow us to synthesize the SeNPs formulation as a promising management strategy to treat the HLB disease in citrus plants.

Diversity and Phylogenetic Analysis of Phytophthora Species Infecting Coorg Mandarin

Coorg mandarin is a particular type of mandarin grown in Western Ghats' high humid tropical region. The crop is cultivated in multiple cropping systems of pepper and coffee plantations in Karnataka, Tamil Nadu, and the Kerala states of India. The crop is attacked by a number of diseases. Among them, Phytophthora is a century-old disease causing a major threat to Coorg mandarin cultivation and production in Southern states of India. A systematic random survey was conducted to collect Phytophthora infected samples from the seeds and grafted Coorg mandarin plants in 184 orchards located in different parts of Karnataka. A total of 111 Phytophthora isolates were isolated and characterized from infected plant roots (59) and soil (52) infected Coorg Mandarin samples collected in different orchards. Based on the pathogenicity parameter, only 45 out of 111 Phytophthora isolates were selected, and the ITS region was amplified by PCR using ITS primers and sequenced. Based on the ITS sequence pairwise identity score, 45 Phytophthora isolates were assembled into three groups. The type I group of P. palmivora isolates showed the highest nucleotide identity of 88.5 to 90.8% with P.palmivora (JX198562). In contrast, the type II group of P. palmivora isolates showed nucleotide identity of 93.6 to 99 % with P.palmivora (KF010299) infecting different citrus species, and the type III group of P.nicotianae isolates showed maximum nucleotide identity of more than 93% with P.nicotianae (KJ549640) infecting different citrus species.

Large Scale Cultivation of Bacillus velezensis CE 100 and Effect of Its Culture on Control of Citrus Melanose Caused by Diaporthe citri

Diaporthe citri is an important fungal pathogen which causes melanose in various citrus growing regions of the world. In our study, control of D. citri was performed by using effective biocontrol agent, Bacillus velezensis CE 100. Mycelial growth of D. citri was highly restricted by strain CE 100 in dual culture plates. Our study demonstrates large-scale inoculation of strain CE 100 in non-sterilized PB medium. In addition, bacterial culture filtrate (BCF) of strain CE 100 from the large-scale culture showed better growth inhibition of D. citri than those from small-scale culture in the laboratory. Moreover, microscopic observation revealed that hyphal morphology of the pathogen was significantly affected by BCF, probably because of various cell-wall degrading enzymes and metabolites produced by strain CE 100. In addition, 50% BCF of strain CE 100 inhibited D. citri conidial germination by over 80%. Treatments, applied by foliar spray with fungicide and strain CE 100 culture, significantly lowered melanose disease incidence more than did control. The results of this study indicate that large-scale culture of strain CE 100 was effective for control of D. citri by means of adequate active metabolites and cells. Therefore, we demonstrate biocontrol applicability of B. velezensis CE 100 on control of citrus melanose by developing a low-cost PB medium using affordable large-scale fermenter. Effect of different treatments on melanose disease incidence on leaves of mandarin plants at 20 days after inoculation with D. citri. Statistical comparison between treatments was done by least significant difference (LSD) test at p < 0.05 level. Means with the same letter are not significantly different from each other. *Con- Control, CE 100- Treatment with B. velezensis CE 100 culture, F- Treatment with fungicide

Plant-feeding may explain why the generalist predator Euseius stipulatus does better on less defended citrus plants but Tetranychus-specialists Neoseiulus californicus and Phytoseiulus persimilis do not

The generalist predator Euseius stipulatus (Athias-Henriot) and the Tetranychidae-specialist predators Neoseiulus californicus (McGregor) and Phytoseiulus persimilis Athias-Henriot play a key role in the regulation of Tetranychus urticae Koch in Spanish citrus orchards. Previous studies have shown that sour orange (Citrus aurantium L.) and Cleopatra mandarin (Citrus reshni hort. ex Tan.) display extreme resistance and susceptibility to T. urticae, respectively. When offered a choice between these two genotypes infested by T. urticae, E. stipulatus preferred Cleopatra mandarin, whereas the specialists did not show any preference. The present study was undertaken to check whether these preferences could be related to the feeding of E. stipulatus on the host plant and/or to differences in prey feeding on the two plants. Our results demonstrate that E. stipulatus is a zoophytophagous mite, which can engage in direct plant feeding in sour orange and Cleopatra mandarin, whereas neither N. californicus nor P. persimilis do so. Whereas Cleopatra mandarin provided a higher-quality prey/feeding substrate for E. stipulatus, which may be related to its phytophagy, no differences were observed for the two specialists. As higher constitutive and faster inducible defense against T. urticae in sour orange relative to Cleopatra mandarin plants result in sour orange supporting lower T. urticae densities and plant damage, our results demonstrate that pest regulation by specialist natural enemies may be more effective when prey feed on better defended plants.

Optimization of the adaptive mechanism of subtropical crops under the influence of innovative forms of fertilizers

The research is aimed at developing effective ways to regulate the functional state of plants under stress. It is shown that the functional state of tea and mandarin plants is more favorable under the influence of growth regulators (humic and amino acids, metabolites of mold fungi are used as biologically active substances). In the variants with foliar treatments, there is an increase in bound water (up to 54.8-54.9%); activation of assimilant synthesis, more active formation of proline and ascorbic acid in tea leaves. There was an increase in the number of carotenoids (up to 1.78 mg / g) and active synthesis of ascorbic acid in mandarin leaves during stressful periods; the value of the viability index increased (up to 5.19 – 5.33 units) in accordance with the control (4.37 umits). The developed specific surface density of the leaf provides greater productivity of mandarin plants. The optimal functional state of the plants led to an increase in the crop productivity of tea leaves (22.88-32.22 c/ha compared to the control-22.04-26.88 c/ha) and mandarin fruits (6.83 kg/tree compared to the control – 3.80 kg / tree). The use of innovative forms of fertilizers and plant growth regulators should become the main element of the technology of cultivation of subtropical crops, optimizing the adaptive potential, regulating the effective productivity of plants and their quality indicators.

Impact of exogenous growth regulators on growth and photosynthetic activity in dwarf mandarin plants (Citrus unshiu Marc.)

The impact of synthetic regulators on the growth and development of mandarin plants was investigated. It was shown that the exposure of plants to growth regulators had no effect on leaf chlorophyll content. Non-root application of nanoelicitor and siliplant synthetic regulators elevated the carotenoid content to 2.69-3.11 mg/g (control, water: 2.57 mg/g) and stimulated protective response. The total chlorophyll- carotenoid ratio in plants treated with nanoelicitor (4.29 mg/g) and siliplant (4.12 mg/g) was less than in the control, reflecting the degree of plant adaptation to adverse conditions in the growing season. Exposure to growth regulators improved photosynthetic activity and overall functionality. Chlorophyll fluorescence assays were used to evaluate photosynthetic activity coefficient as falling within a range of 0.54-0.57, which exceeded the control by 1.2-fold. Nanoelicitor was shown to induce active shooting and reduce fruit shedding. Compared to the control, growth regulators increased the retained fruit value by 1.5-1.9-fold and improved plantation productivity. Phytoregulators have shown promise in both improving the functional condition and reducing preharvest shedding in dwarf mandarin plants.