Hatching in nematodes
M.Sc. IV Semester Nematology
Behaviour and Physiology of nematodes
Inside the egg
In general, at least three requirements must be fulfilled for efficient hatch:
1. the physiological mechanism of the nematode must be operating efficiently;
2. the nematode must be highly mobile; and
3. it has to possess the anatomical requirements for locomotion and
penetration out of the egg
Movements inside the egg enables the nematode to reach a pitch of physiological efficiency at the time it hatches.
The stylet, is necessary for the escape out of the cyst.
The stylet bearing juvenile makes a line of overlapping
punctures with its stylet, forming a slit through it escapes later. ………..
Hatching largely studied in plant parasites with
special reference to cyst nematodes
Egg shell permeability
According to Perry et al. (1982), PRD (Potato root diffusate) increases the permeability of the lipoprotein membrane of the eggshell, allowing the egg to take up water.
Egg shell permeability is affected by a change in calcium ion
concentration, which changes the structural lipids ( lipid globules) PRD changes egg shell permeability and subsequent water uptake by the juvenile leads to hatching
Water uptake by the juvenile also increases oxygen consumption inside the egg.
The changes in egg shell permeability occur during the first 24 h after exposure to PRD, but it takes 3 days for juvenile hatching (eclosion) to take place
Behavioural response
Behavioural sequence leading to hatching
widespread exploration when the juvenile becomes fully mobile inside the egg,
local exploration when only the head of the juvenile is moving while the lip region is pressed to the eggshell,
and the stage when the juvenile cuts its way out of the eggshell with the stylet
After hatching the juvenile takes up more water before it emerges from the cyst
The sequence of events during hatching in Ascaris 1. Changes in eggshell permeability
2. Activation of the larva 3. Eclosion
As a result of permeability change, there is absorption of water and escape of trehalose from the perivitelline fluid into external
medium.
In cyst nematodes the potato root diffusate causes change in
permability and the leakage of trehalose in mediated by Ca++ ions in G. rostochiensis and by Zn++ in H. glycines
In Ascaris the permeability change is Na+ mediated process with Na+ forming a complex with lipid layer
N
Initiation of hatching Process
Sequence of events
Larval movements leading to hatching
Response to hatching agents
The response to hatching has been shown to differ between the two PCN species.
After hatch stimulation, a series of physical and metabolic changes occur in the unhatched juvenile.
The hatching response of PCN cysts to PRD is generally fast. After very short exposure (5 min) the PCN juveniles are triggered to start
substantial hatching from the cyst.
Tests in vitro on G. pallida show that it has a much slower initial rate of hatch compared with G. rostochiensis
Hatching factors
There are three major factors that have an effect on nematode cyst hatching, namely
host root diffusate,
physical conditions before and during juvenile emergence, and hereditary preconditions of the cyst (Manduric, 2004).
The hatching mechanism of PCN has been shown to be stimulated by PRD,
temperature,
oxygen availability, soil type and
soil water content.
Potato root diffusate
Peak production is for a short period in the plant’s life that stimulates juveniles to hatch. Maximum activity of PRD is reached two weeks after planting
Two classes of chemicals have been found in PRD, hatch inhibitors and hatch stimulants. PRD contains at least four to six different hatching agents (chemical stimulants). The inhibitors are produced at an earlier stage than the stimulants, protecting the plant during its most sensitive stage of growth
PRD is highly mobile in soil and induces hatching up to 80 cm
Hatching compound Solanoeclepin A in potatoes is hatching agent for G.
rostochiensis
A hatching factor, glycinoeclepin A, for H. glycines eggs isolated from the roots of kidney beans.
Temperature
Temperature is an important factor in the hatching of PCN.
PCN requires a relative stable temperature regime to hatch: the
optimum hatching temperature in the field is 13.4 C but substantial emergence can be observed at 10 C.
The optimum temperature for G. rostochiensis hatching in vitro is 20 C.
G. pallida is adapted to lower temperatures (16 C)
At the optimum temperature the fastest growth, reproduction, etc.
occur.
At temperatures below and above the optimum, the rates are slower or death occurs.
Soil and water status
Soil structure and soil water status are important factors for maximum hatching of PCN, RKN and all other soil-borne nematodes.
Coarse-textured soils favour hatching and when the water content is at field capacity the maximum hatching occurs.
Drought and water-logging inhibit the hatching of plant parasitic nematodes
Cultivar
A fully susceptible plant allows the nematode to multiply free on the roots while the partially susceptible plant allows less multiplication.
Thus hatching occurs at a greater rate in host plant
For the resistant cultivars or non host plant hatching is lowered
Diffusates from host roots increased hatching of H. glycines in one study while those from nonhosts had no effect
Hatching activity was not found in another study of root diffusates from soybean plants. However, diffusates from the roots of plants such as
potato stimulated hatching of G. pallida eggs, whereas diffusates from mustard roots, a nonhost, inhibited hatching.
Other chemicals
Zinc chloride stimulated more hatching of eggs of the soybean cyst nematode Heterodera glycines than did calcium
Zinc chloride induced little hatching of the G. rostochiensis eggs.
Signals between plants and organisms
Most signals between organisms and their host plant/s are based on phytochemicals from the host plant, but the organism can also release chemicals to the host plant.
Biotic factors
Soil micro-organisms living in the rhizosphere affect hatching.
According to Ryan and Jones (2004), who tested 70 rhizobacterial
isolates, nine of the isolates had a significant effect on hatching. Six of these affected the hatching of G. pallida and three affected G.
rostochiensis.
The PCN attained optimum hatching, 43-100% more hatching, when treated with a potato isolate that had been soaked in PRD for 48 h, while no effect was found when treated with isolate without PRD.
Other related events
•Delayed hatching
•Embryonic arrest in M. naasi
•Diapause
•Often diapause in G. rostochiensis is initiated by signals from the plant during the growing season (Hominick et al. 1985).
•Nematodes develop inside the female and are arrested at J2, after moulting from J1.
•This development has been observed in eggs outside the female (cyst) and the arrest point remains in the J2
DIAPAUSE
Suggested reading (online resources)
doi: 10.1017/S0031182012001874 DOI:
With context to C. elegans