Heterodera schachtii
Heterodera schachtii[2][3] (Beet cyst eelworm, Sugarbeet nematode) is a plant pathogenic nematode. It infects more than 200 different plants including economically important crops such as sugar beets, cabbage, broccoli, and radish. H. schachtii is found worldwide. Affected plants are marked by stunted growth, wilting, yellowing, decreased yields, and death. While there are many methods of control, crop rotation with non-susceptible plants is preferred.
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| Species: | H. schachtii |
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| Heterodera schactii A.Schmidt, (1871) | |
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Discovery
In the early 1800s, "beet fatigue" was used to describe the decreased sugar beet yields which occurred after repeated planting on the same field. At first, this decrease was believed to be the result of nutrient depletion, but in 1859 the botanist H. Schacht discovered nematode cysts on the roots of affected plants and hypothesized that they were responsible for the disease. It wasn't until 1871 that another researcher, Schmidt, created the genus Heterodera, and named the nematode H. schachtii in honor of its discoverer.[4]
Life cycle
Stage 1&2
Stage one is an egg in a soil, and chemicals released from a susceptible host plant’s roots stimulate larvae to exit cysts which are located freely in the soil(J1). Upon exiting the cysts, these larvae move toward the plant's root.
Stage 3
The infective stage of larvae (J2) penetrate the root and travel through cells until they reach the main vascular tissue of the root. They release chemicals from the stylet to destroy the membranes of nearby cells. This pocket of lysed cells is called the syncytium and will be the larva's food source for the rest of its life.
Stage 5
The still attached female is fertilized by an unattached male.
Stage 6
The fertilized mother continues to feed as her eggs develop. The mother eventually dies and her body toughens and becomes a cyst. The 400-500 eggs of the cyst remain sessile until stimulated by plant chemicals (at which point Stage 1 repeats).
Formation of Syncytium
Heterodera schochtii modifies the host root cells and forms a hypermetabolic feeding site which nematodes withdraw nutrients from. It is assumed that this parasite manipulate the production and signaling of the host plant hormone cytokinin to activate cell division. However, the mechanism of how the cytokinin modifies host plant's cells is still unknown. It is thought that syncytium are the result of repeated mitosis since there are multiple enlarged nuclei inside the cells. These feeding sites serve as the nematode’s sole source of nutrients throughout its life cycle for several weeks.[5]
Economic impact
Because H. schachtii decreases crop yields globally, it has a significant economic impact on the agricultural industry. In 1999, H. schachtii was estimated to have cost European countries $90 million in losses for sugar beets alone.[6] A small concentration of nematode can have a significant effect on crop yields. With just 18 eggs/gm of soil, yields of cabbage decreases by 28%.[7] When there are more than 50 eggs/ml of soil, it is unprofitable to grow sugar beets and a crop loss of 5% is expected.[8]
Prevention and control
Identification
Stunted growth and yellowing are early signs of the disease. Infection can be confirmed by the presence of maturing cysts on plants’ roots.
Fumigants
Ethylene dibromide and metham-sodium are effective at controlling the nematode, but economic and environmental concerns generally prevent the use of fumigants as a form of control.
Soil suppressiveness
H. schachtii is susceptible to infection by Verticillium suchlasporium and other fungi. When sugar beets are grown on a virgin field and a given amount of H. schachtii is introduced, beets are most vulnerable during the first several seasons. With the continued presence of the nematode in a field, infectious fungi levels rise, nematode concentrations decrease, and crop production increases.[9] Experiments have attempted to control H. schachtii with fungi, but this method is not as economical as crop rotation.
Crop rotation
Eggs can survive within cysts for 10 or more years. However, ~40% of surviving eggs in a sessile cyst die each year. By growing non-susceptible plants for 2 or 3 years between sugar beet planting, nematode levels can be dramatically reduced. This is the primary method of control used commercially.[10]
References
- Heterodera schactii Archived 2007-10-20 at the Wayback Machine at CAB International
- Heterodera schactii at Nemaplex, University of California
- Heterodera schactii at Knowledge Master
- Schmidt, A (1871). "Ueber den Ruben-Nematoden zeitsdereft fur Rubenzucher". Industrie. 21: 1–19.
- Siddique, S (2015). "A parasitic nematode releases cytokinin that controls cell division and orchestrates feeding site formation in host plants"
- Muller, J (1999). "The Economic Importance of Heterodera schachtii in Europe". Helminthologia. 36 (3): 205–213.
- Abawi, G; Mai (1980). "Effects of Initial Population Densities of heterodera schachtii on Yield of Cabbage and Table Beets in New York State". Phytopathology. 70 (6): 481–485. doi:10.1094/phyto-70-481.
- Muller, J (1999). "The Economic Importance of Heterodera schachtii in Europe". Helminthologia. 36 (3): 205–213.
- Dackman; Carin, Ilan; Chet, Nordbring-Hertz (1989). "Fungal Parasitism of the Cyst Nematode Heterodera schachtii: Infection and Enzymatic Activity". Microbiology Ecology. 62 (3): 201–208. doi:10.1111/j.1574-6968.1989.tb03694.x.
- Burt, O; Ferris (1996). "Sequential Decision Rules for managing Nematodes with Crop Rotations". Journal of Nematology. 28 (4): 457–474. PMID 19277164.