What is Allylisothiocyanate?

Allylisothiocyanate (AITC, CAS No.: 57-06-7), also known as horseradish, is a natural compound extracted from cruciferous plants, and its active ingredients are environmental friendly.

Allylisothiocyanate has effective control on soil nematodes, soil-borne pathogens and a variety of pests and diseases on the ground during the growth of vegetables and field crops.

Allylisothiocyanate has been used in many industries, including food flavoring, bactericidal and antibacterial, antiseptic and preservatives, health care and anticancer drugs, as well as soil sterilization and deworming, grain storage, warehouse deworming, antiseptic, building fumigation, and fumigant for phytosanitary treatment.

Result of HLB detection

After test when you see the test drugs tunring into black like on the right in above picture then the leave already infected by HLB.

If the drus showing other colors like yellow, then it’s not infected by HLB, the yellow leaves might caused by lack of elements, or there are some underground pests like nematode which blocks the transportation of nutrients absobed by roots.

Antimicrobial peptides (AMPs)

Antimicrobial peptides (AMPs) are a class of small peptides that widely exist in nature and they are an important part of the innate immune system of different organisms.

AMPs have a wide range of inhibitory effects against bacteria, fungi, parasites and viruses.

The emergence of antibiotic-resistant microorganisms and the increasing of concerns about the use of antibiotics resulted in the development of AMPs, which have a good application prospect in medicine, food, animal husbandry, agriculture and aquaculture.

Classification of antimicrobial peptides.

Source from  https://doi.org/10.3389/fmicb.2020.582779

The Asian citrus psyllid

The Asian citrus psyllid (ACP; Hemiptera: Psyllidae) is a tiny (0.125 inch, 3 mm, in length) mottled brown insect that is about the size of an aphid. The adult psyllid feeds with its head down, almost touching the leaf, and the rest of its body is raised from the surface at a 45-degree angle with its tail end in the air. No other insect pest of citrus positions its body this way while feeding.

Adults typically live one to two months and develop more quickly in warmer weather. Females lay tiny yellow-orange, almond-shaped eggs in the folds of the newly developing, unfurled, soft leaves, called the feather flush. Each female can lay several hundred eggs during her lifespan. Nymph development is limited to the flush or new growth of citrus. Nymphs are typically yellow-orange but can also have a green hue and lay flat on the surface of new feather flush (young instars), edges of leaves, and stems of flush (older instars). Nymphal development slows at 104°F and continual exposure to 3 or more hours per day of 108°F causes nymphal mortality with no development into adults. Similarly, temperature affects ACP dispersal with high temperatures reducing flight.

HLB Disease

An early symptom of HLB in citrus is the yellowing of leaves on an individual limb or in one sector of a tree’s canopy. Leaves that turn yellow from HLB will show an asymmetrical pattern of blotchy yellowing or mottling of the leaf, with patches of green on one side of the leaf and yellow on the other side.

Citrus leaves can turn yellow for many other reasons and often discolor from deficiencies of zinc or other nutrients. However, the pattern of yellowing caused by nutrient deficiencies typically occurs symmetrically (equally on both sides of the midvein), between or along leaf veins.

As the disease progresses, the fruit size becomes smaller, and the juice turns bitter. The fruit may remain partially green, which is why the disease is also called citrus greening. The fruit becomes lopsided, has dark aborted seeds, and tends to drop prematurely.

Chronically infected trees are sparsely foliated with small leaves that point upward, and the trees have extensive twig and limb dieback. Eventually, the tree stops bearing fruit and dies. Fruit and tree health symptoms may not begin to appear for 2 or more years after the bacteria infect a tree.

The vectors of HLB

Huanglongbing has a complex pathosystem (an ecosystem based on parasitism).

There are multiple strains, diverse hosts, several insect vectors, and different environmental conditions that affect the expression and spread of the disease.

Three forms of the disease are known (Asian, African, and American), and these are associated with different species and strains of Liberibactors that are disseminated by different species of citrus psyllid insect vectors. 

The Asian citrus psyllid, Diaphorina citri, is a tiny, mottled brown insect about the size of an aphid. This insect poses a serious threat to California’s citrus trees because it vectors the pathogen that causes huanglongbing disease (HLB).

The Asian citrus psyllid, Diaphorina citri, is a tiny, mottled brown insect about the size of an aphid. This insect poses a serious threat to California’s citrus trees because it vectors the pathogen that causes huanglongbing disease (HLB). This disease is the most serious threat to citrus trees worldwide—including those grown in home gardens and on farms. The psyllid feeds on all varieties of citrus (e.g., oranges, grapefruit, lemons, and mandarins) and several closely related ornamental plants in the family Rutaceae (e.g., calamondin, box orange, Indian curry leaf, and orange jessamine/orange jasmine).

The Asian citrus psyllid (or ACP), damages citrus directly by feeding on newly developed leaves (flush). However, more seriously, the insect is a vector of the bacterium Candidatus Liberibacter asiaticus, associated with the fatal citrus disease HLB, also called citrus greening disease. The psyllid takes the bacteria into its body when it feeds on bacteria-infected plants. The disease spreads when a bacteria-carrying psyllid flies to a healthy plant and injects bacteria into it as it feeds.

HLB can kill a citrus tree in as little as 5 years, and there is no known cure or remedy. All commonly grown citrus varieties are susceptible to the pathogen. The only way to protect trees is to prevent the spread of the HLB pathogen by controlling psyllid populations and destroying any infected trees.

The Asian citrus psyllid is widely distributed throughout Southern California and is becoming more widespread in the Central Valley and further north. The first tree with HLB was found in March 2012 in a home garden in Los Angeles County and a few years later was found in residences in Orange and Riverside Counties. Spread of the disease began to rapidly accelerate in these areas in 2017. Removal of infected trees by the California Department of Food and Agriculture (CDFA) has occurred wherever they have been found.

What is HLB ?

Huanglongbing (HLB) is a major disease of citrus that has caused catastrophic damage to citrus trees worldwide. The disease causes reduced fruit quality and yield, tree decline, and eventual tree death.

Symptoms are variable and can resemble several disorders of citrus. Typical symptoms include:

  • yellow shoots with pale green and yellow flushes;
  • non-symmetrical mottled leaves (shades of yellow and green on either side of the mid-rib);
  • thickened, leathery leaves;
  • enlarged, corky mid-ribs of leaves; and
  • leaves with zinc deficiency symptoms that include upright leaves in relation to the shoot (acute shoot-leaf angles).

Defoliation, fruit drop, and shoot dieback occurs in more advanced stages. Young trees may die soon after infection; whereas older trees may die in seven to nine years after infection.

Fruit symptoms include small, misshaped fruit that are lopsided or asymmetrical and exhibit color inversion from yellow to orange to green on the peduncle side while remaining green on the stylar end. The vascular tissue is brownish at the peduncle side of fruit. Seeds of affected fruit are small, brown, and aborted.