Symptoms caused by nematodes and its management

It gives detail description of symptoms caused by nematodes

1. Symptoms Caused by Nematodes

2. Symptoms are important means of diagnosis. No management practice can be adopted until symptoms caused by the particular nematode are known. Thus, symptomatology is one of the most important aspect of Economic Nematology . Some specific symptoms are sure indication of nematode infestation. Proper identification of these symptoms facilitates the management of a particular nematode pest, keeping in consideration its feeding behaviour and most susceptible stage to be targeted.

3. Visible expression or indication of any infection/disease is called symptom ’. Symptom may also be defined as ‘ the external or internal reactions that occur as a result of infestation by pest/pathogen ’. Significance: Symptoms are important means for diagnosis of a disease and management practices can be undertaken only when the correct information about the disease and its etiology is available.

4. Kinds of Symptoms : Non Specific symptoms like poor growth, stunting and discolouration of foliage in patches and wilting are most often the result of nematode infestation but may also be caused by some organisms other than nematodes, nutritional deficiency or soil effects. Specific symptoms are better means of diagnosis and are produced by root-knot nematode and most of the above ground nematodes like Anguina tritici , Ditylenchus dipsaci , Aphelenchoides spp. etc.

5. Most of the plant parasitic nematodes affect the root portion of plants except Anguina spp., Aphelenchus spp., Aphelenchoides spp., Ditylenchus spp , Rhadinaphelenchus cocophilus and Bursaphelenchus xylophilus . Nematodes suck the sap of the plants with the help of stylet and causes leaf discolouration , stunted growth, reduced leaf size and fruits and lesions on roots, galls, reduced root system and finally wilting.

6. Symptoms of nematode diseases can be classified as I. Symptoms produced by above ground feeding nematodes II. Symptoms produced by below ground feeding nematodes

7. Above Ground Symptoms Important above ground symptoms caused by nematodes are: i . Retarded growth in patches ii. Increased growth (in a few specific cases) iii.Discoloration of foliage iv.Distortion and abnormal growth v. Temporary wilting

8. i . Retarded growth Slow growth and stunting of plants are common non-specific symptoms of nematode attack. However, stunting of plants when occurs in the patches in field, gives an indication of infestation by nematodes due to their uneven distribution in the field . If host crops are grown in continuation, such patches grow in periphery, season after season. Many nematodes like Pratylenchus penetrans and P. pratensis in crops like cherry, fruit trees and seedlings, Heterodera avenae (in wheat and barley), Globodera rostochiensis (in potatoes), Meliodogyne incognita (in many vegetable and ornamental hosts) cause retardation in plant growth.

9. Nematode infested patches in tomato field Patches and stunting in carnation under protected cultivation due to root-knot nematode

10. Stunting and dieback in walnut trees is caused by its primary pathogen Pratylenchus vulnus . Poor growth and stunting of vines as a general syndrome of decline can be attributed to nematode species like Meloidogyne incognita , M. javanica , Pratylenchus vulnus and P. scribneri

11. ii. Increased growth Nematode infestation though more than often causes growth retardation, in a few very specific cases an increase in growth is also recorded. Ditylenchus dipsaci produces multiple crowns in sugar beet and increased tillering in oats (nematode not recorded from India so far).

12. iii. Discoloration of foliage Generally indicative of nutritional deficiency, foliage discoloration is also caused by nematodes, thus making it a non specific symptom. Discoloration due to nematode infestation may range from chlorosis , light yellow to deep red, purple or even black and at it best serves only as an indication of possible nematode attack.

13. However, some nematodes cause very specific symptom of chlorosis on their host plants which confirm their infestation. e.g. Leaf discolouration: The leaf tip become white in rice due to rice white tip nematode, Aphelenchoides besseyi. Yellowing of leaves on Chrysanthemum due to Chrysanthemum foliar nematodes, A. ritzemabosi .

14. Angular spots on chrysanthemum and Bronzing of strawberry leaves White tip of Rice

15. Twisting of leaves and stem : In onion, the basal leaves become twisted when infested with Ditylenchus angustus .

16. Dead or devitalized buds : In case of strawberry plants infected with Aphelenchoides fragariae , the nematodes affect the growing point and kill the plants and result in blind plant.

17. Crinkled or distorted stem and foliage: The wheat seed gall nematode, Anguina tritici infests the growing point as a result distortions in stem and leaves take place.

18. Seed galls : In wheat, Anguina tritici larva enter into the flower primordium and develops into a gall. The nematodes can survive for longer period (even upto 28 years) inside the cockled wheat grain.

19. Necrosis and discolouration : The red ring disease on coconut caused by Rhadinaphelenchus cocophilus . Due to the infestation, red coloured circular area appears in the trunk of the infested palm.

20. iv. Distortion and abnormal growth Nematodes like Ditylenchus spp., Anguina spp. and Aphelenchoides spp. which feed on the aerial parts (mainly leaves, stem and buds) of the plants cause symptoms of distortion ( a  change  to the  original  or  natural   shape  of something) which are generally specific in nature.

21. Distorted rice ears due to Ditylenchus angustus and Aphelenchoide besseyi respectively

22. V. Temporary wilting Wilting though an above ground symptom is a result of root damage caused by the nematodes. The plants attacked by nematodes show a tendency of temporary wilting in hot weather (although enough moisture may be present in soil) and may recover during cooler hours. Wilting is more pronounced on broad leaved plants.

23. II. Symptoms produced by below ground feeding nematodes The nematodes infest and feed on the root portion and exhibit symptoms on below ground plant parts as well as on the above ground plants parts and they are classified as A. Above ground symptoms B. Below ground symptoms

24. A. Above ground symptoms 1 . Stunting : Reduced plant growth, and the plants can not able to withstand adverse conditions. Patches of stunted plants appears in the field. ( eg .) in potato due to Globodera rostochiensis , in maize due to Heterodera zeae & Pratylenchus zeae and in wheat by Heterodera avenae . 2 . Discolouration of foliage : Patchy yellow appearance in coffee due to Pratylenchus coffeae , G. rostochiensis infested potato plants show light green foliage. Tylenchulus semipenetrans induce fine mottling on the leaves of orange and lemon trees . 3 . Wilting : Wilting due to Meloidogyne spp. i.e. in hot weather the root-knot nematodes infected plants tend to droop or wilt even in the presence of enough moisture in the soil. Severe damage to the root system due to nematode infestation leads to wilting of plants.

25. Stunting

26. Globodera rostochiensis Stunting

27. Potato cyst nematode

28. Root galls or Root-knots : The abnormal galling or swelling of the roots is a specific diagnostic symptom of nematode infestation. Meloidogyne spp. produce characteristic galls on the roots and host plants. The size and number of galls vary from species to species and host to host. It is due to hypertrophy & hyperplasia. Plants like cotton and carnation show small galls, while very large galls are produced on cucurbits which may coalesce with each other in a way that the entire root looks swollen and deformed. Extensive galling is often observed on crops like tomato, okra, brinjal etc . B. Below ground symptoms

29. Nacobbus batatiformis ---on beet- larger galls. Ditylenchus radicicola ---small galls on the roots of oats, barley, rye, wheat and some grasses. Hemicycliophora arenaria and M. indica induce galling on lemon roots Xiphinema diversicaudatum --galls on roses. Longidorus spp. induce galls on roots of marigold.

30. Extensive galling of okra roots and Heavily galled cucurbit roots

31. Reduced root system: Coarse root (With root but without lateral roots caused by Belonolaimus longicaudatus on corn. Stubby roots (The lateral roots produce excessive rootlets caused by Trichodorus christie on corn ) Stubby roots Coarse root

32. Root lesions: Necrotic lesions are often visible on the roots of plants infested by Pratylenchus spp. Radopholus similes causes similar symptoms on citrus. In banana, R. similes produce lesions which girdle the roots at a later stage, the trees tend to be uprooted. Root lesion

33. Toppling Disease – Burrowing nematodes causes ‘toppling’ of banana plant. Banana roots are so severely affected that they cannot hold the tree upright. once the extra weight of the developing fruit is added and the whole plant topples down.

34. Lodging banana plants suffering from Toppling Disease caused by the burrowing nematode

35. Progressive development of root rot symptoms (from left to right) by the burrowing nematode, Radopholus similis , in banana roots

36. The most dramatic disease symptom in banana plantations is the uprooting (toppling) of plants . Burrowing nematode feeding destroys anchor roots and makes plants susceptible to toppling, especially when fruiting or during strong winds. Burrowing nematode, Radopholus similis , in banana

37. Necrotic feeder roots (arrows) caused by R. similis . (Photo by F. Brooks)

38. Root rots: When nematodes enter the fleshy structure, they initiate the injury leading to the extensive tissue destruction. Through the decayed tissue, the other plant pathogens like bacteria or fungi may attack and as a result rot is produced. The potato rot nematode Ditylenchus destructor is involved in this type of injury (so far not reported from India).

39. Root proliferation: Increase in the root growth or excessive branching due to nematode infestation. The infested plant root produced excessive root hair at the point of nematode infestation. Trichodorus christei , Nacobbus spp., Heterodera spp. Meloidogyne hapla and Pratylenchus spp. etc.

40. Root curling : Eg . Ditylenchus spp., Xiphinema spp . Root surface necrosis : eg ., Trichodorus semipenetrans Cluster of sprouts on tubers: e.g., Ditylenchus dipsaci

41. Tunnels: Feeding on cortex region and produced tunnels eg . Rhadinaphelenchus cocophilus on coconut and produced Red ring disease of coconut. Red colored ring on coconut trunk

42. Pearly disease of pigeonpea :- Immature whitish females of cyst nematode are found attached with the roots of pigeonpea . It is known as pearly disease of pigeonpea . Eg , H. cajani . Dirty root:- In banana, castor, pigeonpea , due to infection of Rotylenchulus reniformis , soil particles adhere to the gelatinous matrix of egg masses, which are not removed by washing the roots, thus giving dirty appearance of roots. Beard shape:- The root tip, after attacked by stunt nematodes comes out large number of branches from point of infection , these branches in turn again infected and branches again .This condition is known as beard shape. At feeding point root is cut off, so stop the nutrient movement , so many secondary & tertiary roots comes out from cut end eg . Tylenchorhynchus vulgaris

43. Cysts on Roots: Cyst nematodes do not cause major malformations or lesions on roots. However, their ‘pearly’ white swollen cysts (dead females) are often observed adhering to the root which can be seen easily by careful examination of roots with a magnifying glass.