Can Oecophylla smaragdina be used to suppress incidence of CVPD in citrus orchards in Indonesia?

Citrus vein phloem degeneration (CVPD) is the Indonesian name for the Asian form of the devastating and incurable citrus disease known internationally as huánglóngbìng. It is associated with a phloem-limited pathogen, 'Candidatus Liberibacter asiaticus' (CLas) and transmitted by the Asiatic citrus psyllid (ACP), Diaphorina citri. ACP originated in South Asia but was first observed on citrus in 1900 in Java to where it may have been introduced decades earlier on lemon or lime seedlings brought from South Asia to reduce the incidence of scurvy among European sailors and in colonial settlements. CLas appears to have been introduced to the Pasar Minggu area of Jakarta in the 1940s from southern China, after it was introduced to Guangzhou, directly or indirectly, from South Asia in the late 1920s-early 1930s. Minimising incidence of the disease relies on planting pathogen-free trees, removal of infected trees, and unstainable use of synthetic pesticides that do not prevent spread of the disease. Parasitoids and predators of ACP are killed by the pesticides. Evidence from China and Viátnam suggests that effective management of the disease may be feasible if the weaver ant (semut rangrang), Oecophylla smaragdina, is deployed, cultivated, and managed in orchards

A methodology to estimate net proton : phosphorus co-adsorption ratios for acidic soils

Despite extensive research, the behaviour of the key nutrient element, phosphorus (P), in soil is not yet fully understood. This study focussed on the outstanding issue of the co-adsorption of protons (H+ ) and P by soils. We developed a congruent set of measures to determine the net H+ :P co-adsorption ratio and tested it on goethite, for which a ratio of 1.6:1 had been estimated under CO2-free conditions for additions of NaH2PO4. Under our conditions, and using additions of KH2PO4, the net H+ :P co-adsorption ratio was estimated to be 1.44:1, i.e., in passable agreement with the published value. Application of the protocol to acidic soils resulted in a net H+ :P co-adsorption ratio of 1.92:1, and substitution of H3PO4 for KH2PO4 gave a ratio of 1.96:1. These ratios for soils differ significantly from that for goethite. The soils for which we estimated net H+ :P co-adsorption ratios had a wide range of properties and two had received previous applications of P fertiliser (Ca(H2PO4)2), which does not appear to have affected the net H+ :P co-adsorption ratios. The H+ :P co-adsorption ratio method could benefit from refinement, and further study is required to explore how these findings may apply to commercial P fertilisers under field conditions

Detection of phytoplasma in citrus orchards of Pakistan

Citrus fruits are one of the major export commodities of Pakistan. However, being such an important crop citrus is affected by a number of destructive diseases and phytoplasmal disease is one of them. In Pakistan no significant research has been conducted on phytoplasmal diseases of citrus. Therefore, present study was conducted to confirm the presence of phytoplasmal particles in diseased samples of citrus from Sahiwal, Pakpattan, Multan and Khaenwal districts the most important citrus growing areas of Pakistan. For this purpose DNA was extracted from leaf samples collected from the three districts and single (O-MLO) and nested PCR were applied to detect phytoplasmal particles. With O-MLO primers a 558bp fragment was amplified from 16S rRNA phytoplasmal gene and 1.2kb phytoplasmal DNA fragment was amplified with nested PCR. The results revealed the presence of citrus phytoplasma in Southern Punjab region of Pakistan. In order to confirm the alternate hosts of citrus phytoplasma as well as the insect vectors involved in the transmission of the disease, weeds as well as insects were collected from citrus orchards for molecular detection of phytoplasma and their analysis are is in progress

Comparison of biochemical, anatomical, morphological, and physiological responses to salinity stress in wheat and barley genotypes deferring in salinity tolerance

A greenhouse hydroponic experiment was performed using salt-tolerant (cv. Suntop) and -sensitive (Sunmate) wheat cultivars and a salt-tolerant barley cv. CM72 to evaluate how cultivar and species differ in response to salinity stress. Results showed that wheat cv. Suntop performed high tolerance to salinity, being similar tolerance to salinity with CM72, compared with cv. Sunmate. Similar to CM72, Suntop recorded less salinity induced increase in malondialdehyde (MDA) accumulation and less reduction in plant height, net photosynthetic rate (Pn), chlorophyll content, and biomass than in sensitive wheat cv. Sunmate. Significant time-course and cultivar-dependent changes were observed in the activities of antioxidant enzymes such as superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR) in roots and leaves after salinity treatment. Higher activities were found in CM72 and Suntop compared to Sunmate. Furthermore, a clear modification was observed in leaf and root ultrastructure after NaCl treatment with more obvious changes in the sensitive wheat cv. Sunmate, rather than in CM72 and Suntop. Although differences were observed between CM72 and Suntop in the growth and biochemical traits assessed and modified by salt stress, the differences were negligible in comparison with the general response to the salt stress of sensitive wheat cv. Sunmate. In addition, salinity stress induced an increase in the Na+ and Na+/K+ ratio but a reduction in K+ concentrations, most prominently in Sunmate and followed by Suntop and CM72

Role of ethylene on various ripening pathways and on the development of sensory quality of Charentais cantaloupe melons

Charentais melons (Cucumis melo L., var cantalupensis Naud.) in which ethylene biosynthesis has been suppressed by an antisense ACC oxidase gene have been used to better understand the role of ethylene in the regulation of the ripening process of climacteric fruit and on the development of sensory qualities. We have shown that a number of biochemical and molecular processes associated with the ripening of climacteric fruit are ethylene-independent. In some cases, such as softening of the flesh, the same pathway comprises both ethylene-dependent and -independent components. The various ethylene-dependent events exhibit differential sensitivity to ethylene. The threshold level for degreening of the rind is 1 ppm, while 2.5 ppm are required to trigger the ethylene-dependent component of the softening process. The saturating level of ethylene for all these events is less than 5 ppm, which is by far lower than the internal ethylene concentrations found in the fruit at the climacteric peak (around 100 ppm). Detachment of the fruit influences the development of respiratory climacteric. Fruit remaining attached to the vine, although producing higher levels of ethylene, exhibit a reduced climacteric rise in respiration as compared to detached fruit. The response of antisense ACO fruit to exogenous ethylene in terms of respiration is higher in detached than in attached fruit. Ethylene-suppressed melons show a severe reduction of aroma volatiles production, particularly in ester production. In the biosynthetic pathway of aliphatic esters, the dehydrogenation of fatty acids and aldehydes appears to be ethylene-dependent. In contrast, alcohol acetylation comprises ethylene-dependent and ethylene-independent components, probably corresponding to differentially regulated alcohol acetyl transferases. In terms of sensory quality, these data show that the extension of shelf-life through the inhibition of ethylene production has some beneficial effects on texture and sugar accumulation but is detrimental for the generation of aroma

Comparative transcriptomic analysis of plum fruit treated with 1-MCP

Microarray technology has allowed the large scale transcriptomic analysis of fruit ripening. The μPEACH1.0 microarray containing 4,806 probes corresponding to genes expressed in peach fruit tissues has been used in a heterologous fashion in two studies of plums ripening behavior. Gene expression of different cultivars of plums treated with the ethylene antagonist, 1-methylcyclopropene (1-MCP) and stored for short periods at room temperature or for longer periods of cold storage was examined. In the first study, mature fruit of a suppressed ethylene climacteric cultivar 'Shiro' and a cultivar characterized by a typical increase of ethylene production during ripening ('Santa Rosa') were harvested and incubated for 24h in air (control) or 1-MCP and allowed to ripen at room temperature. Different levels of transcripts of genes implicated in cell wall metabolism, hormone (ethylene and auxin) regulation, stress and defense, and in the transcription/translation machinery, as well as others involved with ripening were identified. In the second study, the effects of 1-MCP on gene expression in relation to the development of chilling injury (CI) in the climacteric cultivars 'Ruby Red' (RR) and 'October Sun' (OS) and 'Zee Lady' peaches (ZP) were analyzed. The fruit were treated for 24h at room temperature with 1-MCP prior to storage at 0°C. For RR, there was no significant effect of 1-MCP on the level of CI symptoms, while 1-MCP significantly reduced CI symptoms in OS fruit and an increase of CI in treated ZP fruit. Microarray analysis showed that immediately following treatment, 186, 134 and 56 genes were differentially expressed between the control and 1-MCP-treated fruit of these cultivars, respectively: after 4 weeks cold storage, 311, 52 and 224 genes for RR, OS and ZP, respectively, were differentially expressed between control and treated fruit. Thus, for OS, the number of differentially expressed genes reduced during storage while the number increased in RR and ZP. Comparisons of the data suggest that the transcript profile is altered by 1-MCP more in plums than peaches. These studies, carried out within an international collaborative network, will increase our understanding of the regulation of pathways involved in plum fruit ripening and in metabolic processes related to storage and shelf lif

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 CLas1 mandarin seedlings

Susceptibility of Diaphorina citri to irradiation with UV-A and UV-B and the applicability of the Bunsen–Roscoe reciprocity law

Populations of Diaphorina citri decline with elevation and, in a study in Bhutan, were rarely found above 1200 m ASL. The impact of ultraviolet (UV) radiation, particularly UV-B, on immature stages of the psyllid was proposed as limiting factor. As no studies have been undertaken on the influences of UV radiation on the development of D. citri, we examined the effects of UV-A and UVB on different stadia of the psyllid. In addition, compliance with the Bunsen–Roscoe reciprocity law was examined. Irradiation with UV-A marginally reduced egg hatch and the survival times of emerging nymphs. Early instar nymphs were little affected by this waveband, but the survival of adults was reduced at the higher doses used. With UV-B, egg hatch and the survival times of early and late instar nymphs declined in proportion to UV-B dose. A dose of 57.6 kJ m−2 d−1 reduced the survival time of only adult females. Female fecundity was reduced at high UV-A and UV-B doses but increased at low doses. The Bunsen–Roscoe law held true for eggs and early instar nymphs for different durations and irradiances of UV-B. Eggs and nymphs had ED50 values for UV-B lower than the daily fluxes of this wavelength experienced worldwide. Thus, UV-B could be a factor causing the psyllid to be scarce at high elevations

Mechanistic insights into potassium‐conferred drought stress tolerance in cultivated and Tibetan wild barley : differential osmoregulation, nutrient retention, secondary metabolism and antioxidative defense capacity

Keeping the significance of potassium (K) nutrition in focus, this study explores the genotypic responses of two wild Tibetan barley genotypes (drought tolerant XZ5 and drought sensitive XZ54) and one drought tolerant barley cv. Tadmor, under the exposure of polyethylene glycol‐induced drought stress. The results revealed that drought and K deprivation attenuated overall plant growth in all the tested genotypes; however, XZ5 was least affected due to its ability to retain K in its tissues which could be attributed to the smallest reductions of photosynthetic parameters, relative chlorophyll contents and the lowest Na+/K+ ratios in all treatments. Our results also indicate that higher H+/K+‐ATPase activity (enhancement of 1.6 and 1.3‐fold for shoot; 1.4 and 2.5‐fold for root), higher shoot K+ (2 and 2.3‐fold) and Ca2+ content (1.5 and 1.7‐fold), better maintenance of turgor pressure by osmolyte accumulation and enhanced antioxidative performance to scavenge ROS, ultimately suppress lipid peroxidation (in shoots: 4% and 35%; in roots 4% and 20% less) and bestow higher tolerance to XZ5 against drought stress in comparison with Tadmor and XZ54, respectively. Conclusively, this study adds further evidence to support the concept that Tibetan wild barley genotypes that utilize K efficiently could serve as a valuable genetic resource for the provision of genes for improved K metabolism in addition to those for combating drought stress, thereby enabling the development of elite barley lines better tolerant of abiotic stresses

Effects of Mineral Oils on Host Selection Behavior of Diaphorina Citri

Response of Diaphorina citri Kuwayama (Hemiptera: Psyllidae) on citrus leaves treated with horticultural and agricultural mineral oil (HMO & AMO) was evaluated under laboratory condition in choice and non-choice trials. Combination of HMO and AMO at concentration of 0 up to 2% was applied to citrus leaves. Mineral oil applications significantly reduced the proportion of D. citri stayed on citrus leaves for feeding with the proposed mechanisms: 1) oils covered leaves thus hampered it for releasing volatile compounds, 2) oil film preventing the direct contact of tarsus or palpus to leaf surfaces, and 3) the volatile compounds produced by mineral oils also blended with plant volatiles in the atmosphere and reduced the probability of olfactory receptors capturing the olfactory cues for locating the feeding site. Mineral oils also increased the mortality of D. citri due to the refusion for feeding on the treated citrus leaves. The effect of AMO was more prominent than HMO. Tanggapan Diaphorina citri Kuwayama (Hemiptera: Psyllidae) pada daun jeruk yang diperlakukan dengan minyak mineral (HMO dan AMO) dievaluasi dengan metode pilihan maupun tanpa pilihan di laboratorium. Kombinasi antara HMO dan AMO pada konsentrasi 0% sampai dengan 2% diaplikasikan pada daun jeruk. Minyak mineral secara nyata menurunkan proporsi D. citri hinggap untuk makan pada daun jeruk, yang mungkin disebabkan oleh mekanisme: 1) minyak melapisi daun sehingga tidak mampu melepaskan senyawa volatil, 2) lapisan minyak menghalangi kontak langsung antara tarsus atau palpus pada permukaan daun, dan 3) senyawa volatil dari minyak bercampur dengan volatil tanaman di udara sehingga menurunkan probabilitas reseptor olfaktori menangkap sinyal penanda lokasi inang. Minyak mineral juga meningkatkan mortalitas, akibat dari penolakan makan pada daun jeruk yang diperlakukan. Pengaruh AMO lebih besar dari pada HMO