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Diagnosis, Biology, and Management of Root-Knot and Lesion Nematodes on Potato

George S. Abawi, John W. Ludwig, and Beth K. Gugino

Dept. of Plant Pathology and Plant-Microbe Biology,

NYSAES, Cornell University, Geneva, NY 14456

March 2008

The northern root-knot (Meloidogyne hapla) and the lesion (principally, Pratylenchus penetrans) nematodes are widespread on potatoes and many other agronomic crops grown in New York State. At high populations, these nematodes are capable of causing a significant reduction in marketable yield of potato and other more susceptible crops such as carrot, lettuce, and onion. In addition, they cause damage even at low populations by interacting with other pathogens resulting in highly damaging disease complexes such as Early Dying of Potato caused by the interaction between the lesion nematode and the Verticillium-wilt fungus. Both nematodes are more damaging in sandy (light-textured) soils and also in poor quality soils that are compacted, poorly drained, weedy and have low organic matter. The host range of the root-knot and lesion nematodes has been reported to exceed 550 and 400 host species, respectively. Both nematodes infect and reproduce well in the roots of most vegetable and forage legume crops typically included in the rotation with potatoes. However, one major difference in the host range of these nematodes is that all grain crops are non-hosts to the northern root-knot nematode (only root-knot species found in NYS), but they are good hosts to the lesion nematode.

Root-Knot Nematode: In early spring, second stage juveniles of this nematode hatch from surviving eggs in the soil and search for young potato roots. They tend to penetrate roots just behind the root apex and then establish permanent feeding sites in the xylem parenchyma of the vascular tissues. They form giant cells which continue to provide nutrients to the nematodes as they enlarge and molt (3 times) before reaching maturity. The mature female deposits up to 1000 or more eggs in an egg sac of gelatinous materials which can be observed attached to the protruding posterior end of females on the root surface. The root cells around the feeding site are also induced to enlarge and extensively divide thus forming galls (Figure 1). The latter are the diagnostic symptoms that are found only on the fine potato roots. Above-ground symptoms on heavily infected potatoes are those of general stunting, uneven growth which can result in smaller tubers. These non-diagnostic symptoms often contribute to under estimating the occurrence and damage of this nematode on potatoes. Under experimental conditions in field microplots, we have shown that controlling the root-knot nematode with the nematicide Vydate resulted in a significant increase in tuber weight of the cv. ‘Monona’ (Table 1A). However, only limited information is available on root-galling severity and damage of this nematode to potatoes in New York. Thus, the reproduction of M. hapla on 12 commercial varieties of potatoes was evaluated in pasteurized soil infested with 10-eggs/cc soil in a greenhouse test in Geneva, NY. All the varieties included in the test were susceptible and showed extensive root-galling symptoms on the fine fibrous roots, but they differed in their degree of susceptibility. For example, the reproduction factor of this nematode on Reba and Chieftain was 32, but it was 57 and 95 on Katadin and Yukon Gold, respectively (Table 2).

Figure 1. Root-galling (left) and lesion symptoms (right) on potato from infection by root-knot and lesion nematodes, respectively.
nematode galling nematode lesions

Lesion nematode:  This nematode is a migratory endoparasite, because it feeds and reproduces in and/or outside plant roots. Both sexes are required for reproduction and mature females deposit single eggs in the root or soil around the roots. The first molt occurs in the egg and the hatched second-stage juvenile molts three times between feeding before becoming mature. All stages of lesion nematode can penetrate roots and move from cell to cell in the root cortex by rupturing cells mechanically and by secreting hydrolytic enzymes. Again, above-ground symptoms on infected potatoes are not diagnostic, but include poor growth, stunting, chlorosis, wilting and/or delayed maturity. Symptoms on the roots might include poor root development, root pruning, discoloration and general lack of fine fibrous roots. At early infection stages, brown to black narrow lesions may be visible on the roots (Figure 1).  Yield losses can be significant when populations of this nematode are high. In Canada , marketable yield of potato in an experimental trial was reduced by 35% at a soil population of 6000 lesion nematodes/kg soil. In a field trial in New York, marketable yield of potato was increased and lesion nematodes in soil were decreased by the application of Vydate, although these differences were not statistically significant (Table 1B). In addition, it is well documented in the literature that in the presence of Verticillium dahliae and only a low number of lesion nematodes per 100 cc soils is required to increase the severity of Early Dying and synergistically reduce the marketable yield of potato.  Tolerance to the lesion nematode in potato germplasm has been previously reported in New York and elsewhere, but also the existence of distinct intraspecific variants of P. penetrans that reproduce differentially on various breeding lines and varieties.

Management Options:  The most effective management for root-knot and lesion nematodes requires an integrated approach that focuses on preventing soil populations from reaching damaging threshold levels and the implementation of control options on an as-needed basis. Nematode population density at planting time determines the severity of infection and potential yield losses, if any. Thus, it is advisable to submit representative soil samples from the target field to a nematode laboratory for analysis (nematode identification and population assessment) or to conduct the recently developed on-farm, visual soil bioassays with lettuce and soybean (see the write-up by Gugino and Abawi in this proceeding).

Chemical Control. Pre-plant soil fumigation with Vapam or Telone C-17 is still available in New York and is highly effective when applied under good soil and weather conditions. Good control of these nematodes has been obtained with Vydate C-LV, which is currently registered on potato as a foliar spray. Soil applications of Vydate for the control of these nematodes on potato in upstate NY is currently been considered by DuPont.

Rotation and Cover Crops use. The use of grain crops (corn, wheat, rye, barley, oat, sudangrass) as rotation and/or cover crops are highly effective in reducing population and damage of the root-knot nematode, but unfortunately not the lesion nematode. Thus, it is challenging when both the root-knot and the lesion nematode are present in the same field. In addition, legume crops (alfalfa, clover, soybean, vetch,) are all good hosts to both nematodes. Furthermore, weed management should be an important component of controlling these nematodes, as several weeds (purslane, plantain, dandelion, catnip, mallow, chickweed, mustard, bindweed, etc.) are maintenance hosts to these nematodes, especially the root-knot nematode. However, it is known that green manures of sudangrass hybrids, sorghum-sudan hybrids, and various cruciferous plants incorporated into warm soil act as bio-fumigants in reducing populations of both nematodes.

Other Control Options.  Summer fallow and flooding, various organic amendments and a number of biological products are reported to reduce populations of these nematodes and will be discussed briefly.

Table 1. Evaluation of Vydate C-LV applications on the yield of potatoes cv. ‘Monona’ grown in infested mineral soil in microplots (A) and in a commercial field naturally infested with root-knot nematode in 2003.

A.  Treatment

Yield per microplot

 

Nematodes/ 100cc soil

 

Root-galling severity (1-9)

Number

Weight (lb)

 

Root-knot

Free-living

 

Untreated

63

8.2

   

1353

 

820

 

5.6

Vydate C-LV broadcast

66

10.0

   

60

 

500

 

3.8

Vydate C-LV foliar

82

14.4

   

587

 

487

 

2.4

LSD (P = 0.05)

 8

1.8

 

643

 

328

 

1.9

B.  Treatment

Yield per microplot

 

Nematodes/ 100cc soil

 

Root-galling severity (1-9)

Number

Weight (lb)

 

Root-knot

Lesion

 

No Vydate

253

46.6

   

40

 

1600

   

1.0

Vydate C-LV foliar

295

54.2

   

0

 

144

   

1.0

LSD (P = 0.05)

 66

14.3

   

61

 

1336

   

ns

Table 2. Reaction of potato varieties to Northern root-knot nematode (M. hapla) in a greenhouse trial, 2003.

Variety

Reps

Root-galling severity (1-9)

Eggs/ plant

Eggs/g root

RF = Pf/Pi a

Alleghany

1

7.0

718080

35200

72

Andover

2

7.0

632760

39600

63

Reba

5

7.0

322140

12960

32

Monona

4

7.0

643920

33900

64

Genesee

4

7.0

358355

14850

36

Keuka

5

6.6

391236

25400

39

Marcy

2

6.5

620100

39600

62

Katahdin

5

6.4

570540

17880

57

Yukon Gold

2

6.0

946340

44200

95

Atlantic

5

5.4

560008

30240

56

Chieftain

5

4.4

317820

15264

32

LSD (P = 0.05)

 

1.7

458498

26042

46

a Reproductive factor (RF) is a measure of the final population divided by the initial nematode population.

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