Plant Parasitic Nematodes Fact Sheet

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plant parasitic nematodes fact sheet

2009 southern and western REGION Managing cereal cyst and root lesion nematodes Root lesion nematode (RLN, Pratylenchus species) and cereal cyst nematode (CCN, Heterodera avenae) are significant pests that feed on the roots of crop plants and cause yield loss.

KEY POINTS Management of RLN and CCN ■ CCN has one life cycle per season whereas RLN is polycyclic with in winter crops three to five generations per year. ■ CCN hosts are restricted to ■ As a general rule, well-managed rotations with resistant or non-host break crops cereals and grasses whereas the are vital. Avoid consecutive host crops to limit populations. RLN host range is broader and ■ Choose varieties with high resistance ratings, which result in fewer nematodes includes cereals, oilseeds, grain remaining in the soil to infect subsequent crops. legumes, pastures and broad leaf and grass weeds. ■ Reducing RLN and CCN can lead to higher yields in following cereal crops. ■ A number of different RLN ■ Healthy soils and good nutrition can, to some extent, ameliorate RLN and CCN species are present, including damage through good crop establishment, and healthier plants recover more Pratylenchus neglectus, thornei, readily from infestation. penetrans and teres. ■ N ematode type and species will ■ Observe crop roots to monitor development of symptoms. affect choice of management ■ Weeds can host parasitic nematodes and control of host weed species and crop practices, particularly rotation volunteers is important. options.

Table 1: Reaction of major crop and pasture species to Pratylenchus neglectus, P. teres and P. penetrans P. neglectus P. teres * P. penetrans * SUSCEPTIBLE MODERATELY SUSCEPTIBLE RESISTANT SUSCEPTIBLE SUSCEPTIBLE Wheat Barley Field Pea Wheat Wheat Canola Oat Narrow-leafed lupin Barley Oat Chickpea Medic Faba and Narbon bean Oat Field pea Mustard Durum wheat Lentil Canola Faba bean Biserulla Common vetch Lathyrus Narrow-leafed lupin Trigonella Triticale Chickpea Rye Durum wheat Safflower Triticale Clover and Lotus MODERATELY SUSCEPTIBLE MODERATELY SUSCEPTIBLE Legume pastures** Narrow-leafed lupin Barley Field pea Canola Triticale

*Information for P. teres and P. penetrans is based on samples received by AGWEST Plant Laboratories for diagnosis, combined with data from preliminary field and glasshouse trials. ** Clover, Bitter vetch, Yellow serradella, French serradella, Sulla and Lotus. Source: VA Vanstone, DAFWA.

About the root lesion nematode

Pratylenchus spp. are microscopic P. penetrans is rare in WA but can Pastures vary in their susceptibility worm-like organisms less than cause severe damage to some crops. to RLN and under some pastures, one-millimetre in length which feed nematode levels could increase and on root tissues. More than one RLN species can be become damaging to subsequent found in the roots of an individual cereals. Pastures should therefore be P. neglectus is the dominant RLN crop, although one species usually monitored for RLN as other crops are, species in all regions. In WA, at least dominates. as well as considering their place in the 60 per cent of cropping paddocks rotation for RLN management. French Species identification is important to are infested with one or more of the and Yellow serradella, lotus and sulla help management as some varieties, Pratylenchus species. In about 40 per varieties tested to date are resistant crops and plant types have different cent of cases the nematode is at levels to P. neglectus, whereas clovers and resistance or susceptibility to different capable of causing crop damage and medics can be more susceptible. yield loss of five to 15 per cent. members of the Pratylenchus family. For example field pea, lupin and faba Intensive cropping of susceptible crops P. thornei is found in South Australia, bean are resistant to P. neglectus but – particularly wheat – will lead to an Victoria, Queensland and NSW. This are susceptible to P. penetrans. Canola increase in nematode levels. Rotations species occurs rarely in Western is more susceptible to P. neglectus are the key to limiting nematode Australia. than P. thornei (see Table 1). multiplication and reducing future crop damage. P. teres and P. penetrans have both Although there is no truly resistant been identified in WA and research is variety of wheat, there is sufficient Several studies have shown the extent underway to learn more about these variation in susceptibility that variety of yield loss attributed to P. neglectus species and the rotations that will limit selection in rotations can be a useful or P. thornei is directly related to the their populations in cropping soils. tool in managing the impact of RLN. population density present at sowing. Forty per cent of RLN identified in WA is P. neglectus; 10 per cent Oat and barley varieties range from All species of RLN have a wide host P. teres and 10 per cent mixed species. moderately resistant to moderately range. susceptible to P. neglectus.

RLN Above and below ground: (Right) Symptoms of RLN on cereal root systems. Note discolouration of roots and reduction in lateral root growth. (Far right) Patchiness, stunting and yellowing of cereal infested with RLN.

photoS: VA Vanstone, DAFWA The symptoms Above-ground symptoms are often nutrient deficiencies. Depending on chickpea can be severely stunted and indistinct and a poor diagnostic the extent of damage and the growing reduced in number. indicator. The first signs are poor conditions, affected plants may partly emergence and establishment, recover if the rate of new root growth The root cortex (or outer root layer) is stunting, cereals tiller poorly and exceeds the rate at which nematodes damaged and may disintegrate. plants may wilt despite moist soil. damage the roots. Diagnosis is difficult and can only Symptoms of nematode damage can To gain the full picture, an examination be confirmed with laboratory testing, be confused with, or exacerbated particularly to identify the species by, nutrient deficiencies. Nematodes of what is going on under the ground is needed. Primary and secondary as all RLN species cause identical, are usually distributed unevenly symptoms. across a paddock, resulting in roots of cereals will show a general irregular crop growth. browning and discolouration and there will be fewer, shorter laterals When roots are damaged by RLN, branching from the main roots. the plants become less efficient in Chickpea roots can show distinct dark taking up water and nutrients, and in brown-orange lesions at early stages tolerating stresses such as drought or of infection and the lateral roots of PAGE 3

The life cycle of RLN Management of RLN When a pasture is included in the cropping rotation, weeds strongly RLN is a migratory plant parasitic The most important management tool influence nematode populations at the nematodes, meaning they migrate is good rotations. In heavily infested end of the pasture phase. freely between roots and soil providing paddocks break crops should be grown the soil is moist. The life cycle of for one or two years to decrease the Manage volunteer susceptible crop RLN begins after the opening rains in population. Resistant varieties should plants that can harbour nematodes. autumn. Juvenile and adult nematodes be selected for the following years. rehydrate, become active and invade Nematodes cannot move great plant roots where they feed and Adequate nutrition (especially nitrogen, distances unaided. However, they multiply as they move through the root. phosphorus (P) and zinc) normally can be spread by surface water, and allows plants to better tolerate plant in soil adhering to vehicles and farm Individual eggs are laid within the root parasitic nematodes, although this does machinery. In uninfested areas, good from which juvenile nematodes hatch, not necessarily lead to lower nematode hygiene should be adopted. They can grow to adults and lay eggs. There reproduction. Field trials in areas also be spread in dust when they are in may be three to five cycles within the infested with P. neglectus have shown a dehydrated state over summer. plant host each season. As plants and yield losses for intolerant wheat ranged soil dry out in late spring, RLN enters a from 12 to 33 per cent when minimal dehydrated state called anhydrobiosis levels of P were applied but losses were and can survive high soil temperatures reduced to only five per cent with a high Cultivation and desiccation over summer. (50 kilograms per hectare) rate of P. Since RLN is vulnerable to death As nematodes feed and multiply, Weeds can play an important role through soil disturbance while in lesions and/or sections of brown in the increase or persistence of its dehydrated state, mechanical discolouration are formed on the plant nematodes in cropping soils. Thus, disturbance through tillage has been root. Other symptoms include the poor control of susceptible weeds considered as a method of reducing reduction in the number and size of compromises the use of crop rotations nematode populations. However, tillage lateral roots and root hairs. for RLN management. of dry soil is not an option in southern or western Australian farming systems Wild oat, barley grass, brome grass as this would expose the soil to wind and wild radish are susceptible to erosion and also result in the loss of P. neglectus. valuable soil moisture.

FIGURE 1 ROOT LESION NEMATODE Nematode invading Root system of root healthy plant cortex

Adults Nematodes penetrate roots directly

Larvae and adults Some nematodes Invaded IV Stage attack roots leave the lesion tissues larvae and attack other turn 4th roots molt brown III Stage larvae Reduced root 3rd system and lesions molt on roots of infected II Stage plant larvae 2nd Nematode reproduces molt and migrates within the root II Stage Nematode leaves larvae decaying roots and attacks new roots 1st I Stage molt larvae Young roots may be Eggs girdled and their Eggs are laid or distal portions killed released in soil Invaded cortical tissues collapse and break down

Source: Agrios GN, Plant pathology 4th edition. Academic Press: New York and London, 1997. PAGE 4

About the cereal cyst nematode

Only one race of CCN, Heterodera Although the majority of barley varieties CCN infested paddocks (regions) in avenae, occurs in Australia and it are tolerant to CCN, they can still be southern Australia are now relatively causes cereal crop damage in Western susceptible. Although the tolerant rare following the widespread adoption Australia, South Australia, Southern barley crop will not be affected by the of rotations using resistant cereals and NSW and Victoria. nematodes, they can still reproduce non-host crops. if that crop is susceptible, leaving It affects wheat, barley, oat and triticale high populations in the soil to infect a If CCN is present at moderate to high varieties and can cause yield loss of subsequent crop. levels growers need to implement up to 80 per cent in intolerant varieties. rotations using tolerant and resistant Barley varieties are tolerant, whereas If CCN is a problem, the best choice cereals and non-host crops for at least wheat, and particularly oat, range is to grow a cereal variety that is both two years and then monitor nematode significantly from moderately tolerant to resistant and tolerant to the nematode. levels before considering the use of very intolerant depending on the variety. susceptible varieties. The symptoms

The symptoms of CCN infection are year, can be thought of as four stages invade host plants. Each nematode readily recognised. Above-ground, beginning as an over summering stage sets up a feeding site called a syncytia. patches of yellowed and stunted as a brown cyst containing 200 to 300 Female nematodes remain feeding plants can be observed. Planting a eggs. Only 70-80 per cent of eggs in the root and gradually swell in the susceptible crop in successive years hatch in the first year, regardless of process of producing eggs. will result in these patches becoming conditions, leaving some in reserve larger with time. Below-ground, wheat for the second year which will infect a The eggs are retained inside the body and barley roots will be ‘knotted’, future host crop if planted. which eventually bursts through to the and oat roots appear ‘ropey’ and outside of the root. The white female swollen. Development of root systems The brown cyst develops from the can then be seen on the outside of the is retarded and shallow. In spring, the swollen body of the female nematode roots as a small cyst about the size characteristic pinhead-sized ‘white as the crop matures in the previous late of a pinhead and visible to the naked females’ can be seen, particularly on spring. Each cyst is approximately one eye. Resistant plants may have a susceptible plants, with the naked eye millimetre in diameter and is covered small number of white females present if roots are carefully dug and washed with a hard, brown outer casing which whereas susceptible plants may have free of soil. enables the eggs to survive in soil over large numbers where CCN is present in the hot dry Australian summer. a paddock. CCN is a sedentary plant-parasitic nematode which means after invasion After opening rains (April-June), The female nematode dies as the crop of the host it sets up a fixed feeding and when soil temperatures drop ripens and forms a brown cyst that site within the plant root. The life cycle to 15 degrees C or below, juvenile hardens and remains in the soil until of CCN, which has one generation per nematodes hatch from the cyst and the next season to complete the cycle.

Resistant and tolerant Resistant and intolerant Variety ratings for nematodes Varieties are rated according to their tolerance or intolerance and their susceptibility or resistance to nematodes. The mechanisms of resistance and tolerance are different and need to be treated as such. ■ Intolerance means the crop yields poorly when attacked. ■ Susceptibility means nematode numbers increase during the cropping season. ■ Tolerance and intolerance ratings indicate the effect nematodes will have on Susceptible and tolerant Susceptible and intolerant the yield of the current crop. ■ Resistance/susceptibility ratings indicate so u rce : sardi the effect the crop variety will have on reproduction of the nematodes, and hence the possible effect on the next crop via the nematode population remaining in the soil to infect the next crop. Pictured are four combinations of ratings for nematodes. Tolerance/intolerance = the effect on the yield of the current crop, Resistance/susceptibility = the effect on building nematode numbers and the carryover to next year’s crop. PAGE 5

Management of CCN

CCN is easy to manage which is services to check CCN levels is carry-over of cysts and eggs into the evidenced by the widespread reduction encouraged. Less than five eggs per following season. The widespread in paddock CCN levels that has taken gram of soil can produce yield loss for adoption of no-till farming systems, place since the introduction of resistant intolerant cereals. along with the associated increase in varieties and extension of management row spacing, has probably played a strategies. CCN is much easier to If susceptible cereal varieties are role in reducing losses from CCN. manage than RLN because of the continually used in a rotation CCN can greater range of resistant and non-host cause ongoing significant yield losses. Testing crops available. Soil testing can help ascertain the risk. If cases of CCN or RLN infestation CCN only feeds on cereals and other are suspected, growers are advised Break crops must be maintained free to check the roots of the host crops. grasses. Wild oats are susceptible of wild oats and susceptible cereal so will multiply the CCN population, Carefully digging up, then simply volunteers. The benefit of a two-year washing the soil from the roots of an but other grasses are resistant and break should be regarded as temporary produce low levels of CCN. infected plant can sometimes reveal because the nematode population evidence of infestation in the roots The use of CCN-resistant cereals and rises quickly when susceptible cereals which warrants laboratory analysis. non-host crops such as pulses and are returned to the system. The Testing services are available around oilseeds in rotation is the required solution is not instant and it can take Australia and growers are advised management strategy. Where CCN several years to reduce high levels. to contact their local agricultural levels are moderate to high the best department for advice. choice is two years of resistant and Cultivation tolerant cereal or non-host crops. Cultivation exacerbates CCN damage, The most profitable option will often probably because it spreads cysts and be chosen, but growers should also hatched nematodes and/or facilitates be mindful of management of other the movement of nematodes to roots diseases and weeds when making by lowering soil bulk density. these choices to produce longer-term profits. While two years is generally In contrast, there is less root damage accepted to reduce CCN to low levels, under reduced tillage. Since there exceptions do occur. Monitoring are also fewer white females on roots paddocks and the use of diagnostic in non-till situations, there is less

FIGURE 2 CEREAL CYST NEMATODE II Stage larvae in eggs inside brown cyst overwintering in soil Male Female lays leaves eggs in Female begins root gelatinous to produce II Stage mass Root Female eggs larvae surface cyst filled emerge with eggs from Syncytia begin to degenerate still attached eggs to root

Adult nematodes Females at various stages of development II Stage larvae attached to root emerge from cyst II Stage larvae free in 4th molt soil IV Stage larvae 3rd molt 2nd molt

Syncytia of male begins to degenerate II Stage larvae CCN cause roots to be retarded attack young roots and shallow. Infected wheat and II Stage male and female larvae II Stage larvae invades root barley roots will appear knotted feeding on syncytia and causes formation of syncytia and oats appear ‘ropey’ and Source: GN Agrios, Plant Pathology, 4th edition, Academic Press, 1997. swollen. PAGE 6

Frequently asked questions Q. Why is my resistant cereal Currently, no nematicides are Q: Does timing of sowing help? showing CCN root damage? registered for use on broadacre crops There is limited information on the in Australia. Resistant cereals sown into a affect of time of sowing on the yield paddock with CCN will be attacked Q: Is CCN ever likely to be a loss to intolerant crops in the presence and penetrated at a similar rate as a major problem in Australian of RLN. Trials in the northern region susceptible variety causing the same farming again? have shown later sown wheat crops damage. Resistant cereals act by can be more severely affected than suppressing the development of CCN Yes. In SA and Victoria, the those sown early. In Victoria, sowing in the root so very few can mature and widespread adoption of resistant in mid July compared with late May cause multiplication whereas the CCN cereal varieties and non-host rotations resulted in 60 per cent lower yield for in the root of a susceptible variety will has significantly reduced the problem. an intolerant wheat variety, and 10 per mature to produce large numbers of However, if susceptible varieties are cent lower yield for a tolerant variety CCN white females. grown in continuous rotation, CCN where there was a high population of levels could easily increase again. P. thornei. Q. Can I spray for CCN or RLN? Although CCN is less widespread in WA than in SA or Victoria, many Q: Could P. teres and P. penetrans Nematicides provide significant Western Australian cereal varieties spread to other states? improvements in grain yield when are susceptible to CCN. Intensive applied to nematode-infested plots, P. teres has only been identified in cultivation of susceptible cereals can but are no longer used commercially in crops in WA and is not known to occur lead to significant increase in CCN Australia. They are not recommended in other regions of Australia. In fact, levels. So it is not a major problem because of their cost and inherent P. teres is uncommon on broadacre at the moment but could be again if mammalian toxicity, and also because crops anywhere in the world. precautions are not taken, much the rotational crops are available for P. penetrans does occur in other same way some human diseases nematode management. If they were states, although it is generally known could increase if inoculation programs used commercially, it is likely their as a horticultural pest. were to stop. efficacy would be poor, particularly in situations where the nematode occurs at depth.

Useful resources:

■ Dr Vivien Vanstone, DAFWA (08) 9368 3141 Email [email protected] ■ John Lewis, SARDI (08) 8303 9394 Email [email protected] ■ PreDicta B™ – a soil analysis service delivered by accredited agronomists which can detect P. neglectus, P. thornei and CCN. This test is not currently able to detect P. teres and P. penetrans, so results need to be interpreted with caution, particularly for Western Australia. Contact your local agronomist or to locate your nearest supplier, email your contact details and location to: [email protected] ■ Growing season tests can be carried out on affected plants and associated soil through state departments ■ Testing laboratories WA (08) 9368 3721 or [email protected] SA (08) 8303 9360, VIC (03) 5362 2111 ■ Cereal Root and Crown Diseases (2000), Hugh Wallwork, GRDC and SARDI ■ DAFWA Bulletins www.agric.wa.gov.au ■ For variety ratings see state crop variety and disease guides published annually

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Acknowledgements: Dr Vivian Vanstone, DAFWA; John Lewis, SARDI. produced by