Huanglongbing (yellow dragon disease), previously known as citrus greening disease, is one of the worst diseases of citrus trees worldwide. It is caused by the bacterial disease Candidatus Liberibacter asiaticus that spreads through the tree canopy, causing decline and then death of the tree.
There is no cure – the only way to stop the disease is to destroy all infected trees and replace them.
The disease huanglongbing originated from China, with its vectors from Asia (Asiatic citrus psyllid) and Africa (African citrus psyllid). Depending on the species, the disease and its vectors can now be found throughout:
North, Central and South America
South East Asia, including Indonesia and East Timor
Papua New Guinea.
The islands of Torres Strait provide a potential pathway for the movement of serious pests into Australia, such as huanglongbing and the Asian citrus psyllid, present in countries to our north.
How to identify Huanglongbing (Candidatus Liberibacter asiaticus)
Everyone needs to keep an eye out for symptoms of huanglongbing.
Huanglongbing is spread by the movement of infected plants and plant propagative material and by sap sucking insects. These insects – the Asiatic citrus psyllid (Diaphorina citri) and African citrus psyllid (Trioza erytreae) – are not present in Australia and are of major concern due to their ability to spread huanglongbing.
Adults of the Asiatic citrus psyllid are 3-4 millimeters long with brown markings on the wings. When feeding on the veins of the young leaves, they adopt a ‘head-down, tail-up’ position.
Juvenile psyllids are yellow and commonly found feeding on young, soft shoots.
The African citrus psyllid is similar but larger with a light brown-grey body and black head, and large transparent forewings.
Huanglongbing causes yellowing of citrus plant leaves and in some instances deformed, sour and bitter fruit.
Symptoms on leaves are subtle and hard to pick but one key sign is a blotchy yellowing that is not symmetrical or mirrored on both sides of the leaf.
Later, new young leaves are small, upright and yellow, with green bands around the veins.
In well-managed orchards, a yellowing that spreads slowly over the tree and through an orchard is an easily seen sign. The spreading yellowing effect can be especially hard to see in neglected backyard citrus trees growing in poor soils.
Infected trees have a blotchy yellowing that is not symmetrical or mirrored on both sides of the leaf Source: DAWR
Fruit from infected trees can be misshapen or lopsided, and when cut lengthwise, the arrangement of internal tissues may be irregular Source: DAWR
Methylation Vegetable oil can improve the spreading area, adhesion and permeability of droplets on the surface of the crop, and promote the absorption and conduction in crop.
Besides, the methylated vegetable oil can prevent the liquid droplets from drying too fast, thereby enhancing the absorption of droplets through pores and the stratum corneum, and enhances efficacy for herbicides.
Tea Saponin, a glycoside compound extracted from camellia tea seeds, is excellent natural nonionic active surfactant. It can be widely used in pesticide, cultivation, textile, daily chemicals, arthitectural field, medical field and so on.
Tea saponin is triterpenoid saponin, it tastes bitter and spicy. It stimulates mucous membrane of nose to lead to sneeze. The pure product is fine white column-shape crystalloid with strong moisture absorption ability. It presents apparent acidity to methyl red. It’s easy to be dissolved in water, water-contained methanol, water-contained ethanol, glacial acetic acid, acetic anhydride and pyridine etc. Its melting point: 224.
Chemical name : N,N’-Dimethylolurea
Formula : C3H8N2O3
Molecular Weight : 120.1
CAS No. : 140-95-4
Dimethylolurea is used to treat textiles and wood, and is mixed with fillers for use in molding adhesives. And used in disinfectants and other biocidal products, as an in-can preservative, as a preservative for liquid-cooling and processing systems, and as a slimicide. Dimethylolurea is also used as a preservative in metal-working fluids, as a developer of photographic film, and as a cleaning agent and disinfectant.
Tomato plants (Lycopersicum esculentum Mill) grown under tropical field conditions were treated with an alkaline seaweed extract made from Ascophyllum nodosum (ASWE).
Two field experiments and one greenhouse experiment were conducted to evaluate methods of application, dosage of application, and the impact of each on plant growth parameters and on the quality and yield of fruit.
Field experiment 1 included 0.2 % ASWE spray, 0.2 % ASWE root drench, fungicide spray and combinations of the above. Plants foliar-sprayed with 0.2 % ASWE had significantly increased plant height (10 %) and plant fruit yield (51 %) when compared to control plants. Similar results were observed for ASWE spray alternated with fungicide or with ASWE root drench. Field experiment 2 included 0.5 % ASWE spray, fungicide spray and ASWE spray alternated with fungicide. The higher concentration of ASWE resulted in a significant increase in plant height (37 %) and plant fruit yield (63 %) compared to control plants. The third experiment under greenhouse conditions also showed that 0.5 % ASWE spray caused a significant increase in plant height (20 %) and plant fruit yield (54 %) compared to control plants.
In the greenhouse, ASWE-treated plants had larger root systems and increased concentrations of minerals in the shoots. Fruit from plants treated with ASWE showed significant increases in quality attributes including, size, colour, firmness, total soluble solids, ascorbic acid levels and mineral levels.
Overall, the use of ASWE resulted in clear improvements in tomato fruit yield and quality under tropical growing conditions.
The‘Christmas Rose’grape is a type of the late-maturing cultivars which is widely planted in China. It is favored by consumers because of its delicate flesh，resistance to storage and transportation，and high quality. However，in some areas，the coloration of the‘Christmas Rose’grape was not very good because of high temperature and humidity，which affected its internal and external qualities. In recent years，researchers found that jasmonates，which widely exist in plants，could improve coloration of fruit by promoting the accumulation of anthocyanin. This study is to explain the effect of different concentrations of exogenous prohydrojasmon(PDJ)，methyl jasmonate(MeJA) on the coloration and quality of the‘Christmas Rose’grape so as to provide some theoretical evidence to improve coloration and quality of this grape berry.
The trial was conducted at the experimental farm of the Zheng⁃zhou Fruit Research Institute，CAAS，on uniform 6- year- old‘Christmas Rose’grapevines. All treatments were applied in three replications and arranged in a complete randomized block design，with a single grapevine for each replication. Two different concentrations (10 mg·L– 1，50 mg·L– 1) of prohydrojasmon，methyl jasmonate were respectively applied to the‘Christmas Rose’grape berries. The aqueous solutions of both treatments and control involved 0.1% Tween-80 and 1% ethanol. The experimental grape berries were sprayed uniformly with aqueous solution twice at the beginning of veraison and 7 days later after the first application. After the first treatment，samples were taken every 10 days until the fruit was ripe when the seeds were completely brown and the soluble solids content no longer increased. A total of 40 single berries from the top，middle and bottom parts of randomly selected 10 grape bunches were picked and brought to the laboratory for analysis. The coloration of the grape berry was measured by a Minolta colorimeter and expressed as the L value (the fruit surface light brightness)，a value (color component of red and green)，b value (color component of yellow and blue) and CIRG value (color index of red grape). Anthocyanin content in the skin extraction was measured by the pH differential method. The contents of chlorophyll a and chlorophyll b in the skin extraction were tested according to the Arnon’s method. The soluble solids content of the fruit was measured by a PR-101 refractometer. The titratable acid in the grape juice was titrated by 0.1 mol·L– 1 NaOH according to the Gao’s method. The total phenolics，and flavonoids in the skin extraction were determined respectively according to the Jia and Meyer’s method. The pedicel endurable pulling force and berry endurable pressing force were measured by a Digital Push & Pull Tester. In addition，the berry weight，berry length，berry diameter，and the content of vitamin C were also determined. All analyses were performed using Excel and SPSS software.
During the ripening period of the grapes that were treated or not treated，the Lvalue，and bvalue decreased，while the avalue，and CIRG value increased，the brightness of the grape skin declined and the coloration of the grape skin was transformed from green to red. The grape berries treated with PDJ，and MeJA had a higher a value，CIRG value and a lower L value，b value than the control. The highest a value，CIRG value and the lowest L value，b value were found in the grapes treated with 50 mg·L-1 PDJ. At harvest，the CIRG value of 50 mg·L-1 PDJ-，MeJA- treated grapes reached 4.61 and 4.50 respectively while the CIRG value of the untreated grapes was only 4.04. During the ripening period of the grapes，the anthocyanin content rose gradually，in contrast to chlorophyll a and chlorophyll b which declined gradually in the grape skin. The content of anthocyanin in the grape skin treated with PDJ，and MeJA was obviously higher than the control. The 50 mg·L-1 PDJ，and MeJA treated grapes presented a higher an⁃ thocyanin content than the 10 mg·L-1 PDJ，and MeJA- treated grapes. The PDJ treatment had a better effect than the MeJA treatment under the same concentration on increasing the content of anthocyanin. At harvest，the anthocyanin content in the grape skin treated with 50 mg·L-1 PDJ，and 50 mg·L-1 MeJA was respectively 31.2%，and 20.0% higher than the control. The content of chlorophyll a and chlorophyll b in the grape skins treated with PDJ，and MeJA were lower compared with the control. The PDJ，and MeJA treatments promoted the synthesis of anthocyanin while enhanced the degradation of chlorophyll a and chlorophyll b，and the coloration of the grape berry improved. The 50 mg·L– 1 PDJ treatment performed best in improving the coloration of the grape berries among all of the treatments. During the period of maturation，the soluble solids content of grapes treated with PDJ，and MeJA were obviously higher compared with the grapes that were untreated. The 50 mg·L-1 PDJ，and MeJA treatments were more effective in increasing the content of soluble solids than the 10 mg·L-1 PDJ，and MeJA treatments. There were no obvious differences between the treated and untreated grapes on the titratable acid content. The application of PDJ，and MeJA promoted the accumulation of total phenolics，and flavonoids in the skin at harvest，and total phenolics in the skin treated with 50 mg·L-1 PDJ，and MeJA were respectively 36.4%，and 29.0% higher than the control. The application of PDJ，and MeJA significantly enhanced the content of vitamin C in the fruit，however，the berry weight，berry length and berry diameter were not influenced. The grape treated with PDJ，and MeJA had a higher nutritional quality，in addition，the PDJ，and MeJA treatment did not have a negative effect on fruit yield. The pedicel endurable pulling force and berry endurablepressing force were not influenced by the PDJ，and MeJA treatment. The phenomenon of berry drop did not happen in the treated grapes. There was no difference between the treated and untreated grapes on resistance to storage and transportation.
Two different concentrations of exogenous PDJ，and MeJA improved coloration and quality of the‘Christmas Rose’grape berry compared with the control. Under the same concentration，the PDJ treatment had a better effect than the MeJA treatment on improving coloration and the quality of grapes; the 50 mg·L-1 PDJ，and MeJA treatment showed a better effect than the 10 mg·L-1 PDJ，and MeJA treatment. Among all of the treatments，the 50 mg·L-1 PDJ treatment was the most effective in improving the coloration and quality of grapes in the trial.
By SUN Xiaowen，GAO Dengtao，WEI Zhifeng，GUO Jingnan*，CAO Meng （Zhengzhou Fruit Research Institute，CAAS，Zhengzhou 450009，Henan，China）