Variation in hatch among pathotypes of the potato cyst nematodes,

0 downloads 0 Views 204KB Size Report
hatch from its egg by host plant root diffusate. This stim- ... in populations of Globodera that would have a reduced ... tilled water and a further 50 ml added.

Nematology, 2009, Vol. 11(5), 749-756

Variation in hatch among pathotypes of the potato cyst nematodes, Globodera rostochiensis and G. pallida, in response to potato root diffusate from Solanum spp. I. Preliminary assessments to establish optimal testing conditions Susan J. T URNER ∗ , Colin C. F LEMING, Brendan P. M ORELAND, and Trevor J.G. M ARTIN Applied Plant Science and Biometrics Division, Agri-Food and Biosciences Institute, 18a Newforge Lane, Belfast BT9 5PX, Northern Ireland, UK Received: 30 June 2008; revised: 7 January 2009 Accepted for publication: 7 January 2009

Summary – Potato cyst nematodes (PCN) hatch in response to the presence of root diffusate produced by host plants. Potato root diffusate (PRD) contains hatching factors that stimulate differential hatch between the two PCN species (Globodera rostochiensis and G. pallida) throughout the growing season. In order to clarify the role of PRD in wild potato clones resistant to PCN, a series of trials established optimal test conditions using a range of PCN populations on a representation of Solanum species (Solanum sanctae-rosae, S. sparsipilum, S. gourlayi, S. acaule, S. oplocense). Dilution tests showed that half strength PRD consistently stimulated highest levels of nematode hatch. PCN populations were treated with PRD collected weekly throughout the trials, mimicking the natural release of chemical stimulants from growing potato roots. Whilst the G. rostochiensis Ro1 population showed no variation in hatch, other populations displayed differences in hatch in the presence of the different Solanum PRD. This may reflect the different coevolutionary histories of nematodes and their Solanum hosts in South America. Keywords – juvenile hatching, wild Solanum sp.

The active part in the life cycle of cyst nematodes begins when the second-stage juvenile (J2) is stimulated to hatch from its egg by host plant root diffusate. This stimulation is very specific in some groups and in the potato cyst nematodes (PCN) is confined to a few members of the Solanaceae family (Franklin, 1940). Previous work has demonstrated that in the absence of potato root diffusate (PRD) about 30% spontaneous hatch of PCN J2 may occur compared with over 80% when a host plant is present (Jones, 1970). Most South American Solanum species are less effective than S. tuberosum ssp. tuberosum L. at stimulating hatch of PCN (Ellenby, 1944, 1945). These original trials included evaluations of hatch of J2 in PRD from over 40 species of Solanum with varying levels of susceptibility and were completed at a time when PCN was considered as one species (Heterodera rostochiensis) and pathotypes within the species had not been described. However, it is highly likely that all tests were undertaken with the pathotype G. rostochiensis Ro1. ∗ Corresponding

More detailed recent studies by Byrne (1997) on comparative hatching behaviour of G. rostochiensis and G. pallida demonstrated differences both between and within species. In addition Evans (1983) showed a range of hatch stimulation of both G. rostochiensis and G. pallida populations from PRD produced by 25 potato cultivars. Both workers demonstrated that a series of dilutions of PRD resulted in a range of PCN hatch. Generally ‘full strength’ PRD did not result in greatest hatch, and dilutions greater than 1 : 16 also showed progressive decline in hatch stimulation. Previous workers have stated that PRD collected under ‘standard’ conditions (Widdowson, 1958) may inhibit optimal PCN hatch, although generally these statements refer to diffusate from cultivated potato clones. The form and biomass of root systems from wild Solanum species varies along with the possibility that optimum stimulation may also vary with a greater range of dilutions. Byrne (1997) suggested that high concentrations of PRD may be indicative of reduced water content in

author, e-mail: [email protected]

© Koninklijke Brill NV, Leiden, 2009 Also available online - www.brill.nl/nemy

DOI:10.1163/156854109X411005 749

S.J. Turner et al.

the soil and may act as a survival mechanism by limiting hatch into an unsuitable soil environment. He also demonstrated production of Hatch Inhibitors (HI) e.g., solasodine glycoside and Hatching Factor Stimulants (HS) e.g., alpha-solanine and alpha-chaconine at different stages of the host plant’s maturity. Further work has shown that PRD from non-cultivated potato clones differ in their ability to stimulate PCN hatch (e.g., Turner & Stone, 1981). Solanum tuberosum ssp. andigena PRD stimulated hatch of Ro1 J2 almost as much as PRD susceptible S. tuberosum ssp. tuberosum clones, whilst PRD from resistant S. vernei plants induced only a small hatch. Byrne (1997) showed differences between each of five wild potato species in their ability to stimulate hatch, and the hatch was less than that induced by potato cultivars. The co-evolution of potato species and Globodera within the Andean system has resulted in nematode gene pools that contain a wide spectrum of virulence genes. One aspect of the co-evolutionary process that has not been investigated widely is the evolution of differential responses to hatching stimuli from many host species in the region. Globodera have evolved to respond to host diffusates to ensure J2 maximise their hatch only when host roots are available for invasion. Many species of invertebrates use environmental cues to synchronise hatch with conditions favourable for growth, feeding and reproduction. As insurance against loss of an entire generation through some environmental catastrophe, a proportion of eggs remains unhatched and thus serves as a reserve for the population. It would be expected then that different Globodera populations would exhibit varying levels of hatch when responding to a particular root diffusate. However, this is not the only possible evolutionary strategy. It might be expected that co-evolution would also result in populations of Globodera that would have a reduced hatching response to diffusates from hosts that have developed resistance to specific Globodera gene pools. The presence of barriers to gene flow within the Andean region is likely to have accentuated this process. Thus, prior to movement of Solanum clones and Globodera populations by man, Globodera populations, which exhibited different hatching responses, may have been common in the region. Screening of potato germplasm collections against specific PCN pathotypes by Huaman (1978), Van Soest et al. (1983) and Turner (1989) has identified resistance from a broad range of South American potato species, although the mechanisms of such resistance had been studied in only a few clones. The present study uses seven 750

clones, identified by Turner (1989) from the Commonwealth Potato Collection (CPC) as being resistant to specific PCN pathotypes, for a series of initial assessments in order to clarify optimal test conditions before progressing into more detailed studies with an extensive range of PCN-resistant potato clones. These studies were aimed at providing material for breeding programmes, in particular, clones that may be of benefit for trap-cropping strategies. PCN populations display a range of hatch responses under various test conditions. In order to clarify this variation in greater detail, eight G. pallida populations from Europe and South America were evaluated for further study with PRD collected from a range of CPC clones and the PCN susceptible cv. Désirée.

Materials and methods H ATCH OF GLOBODERA PALLIDA POPULATIONS IN DIFFUSATE FROM CV. D ÉSIRÉE Twenty sprouted tubers of cv. Désirée were planted singly in 12.5 cm diam. pots containing standard John Innes compost. PRD was collected after 6 weeks (Widdowson, 1958) i.e., watering was stopped 24 h before collection of the diffusate. Each pot was saturated with distilled water and a further 50 ml added. The solution draining from the pot was collected and passed through the pot twice more. PRD was collected, bulked, filtered and stored in dark glass bottles at 4◦ C. Prior to use, all PRD solutions were diluted to half strength with distilled water (Turner & Stone, 1981). Eight G. pallida populations, representing a wide geographical distribution, were chosen to clarify their inherent differences in rate and amount of hatch (Table 1). All populations had been maintained as glasshouse cultures in pots planted with susceptible cvs Désirée or Pentland Crown for approximately 10 years. Fifteen cysts of each population were counted into watch glasses (three-fold replication), soaked in distilled water for 7 days and any emerging J2 were counted. The cysts were kept at 20◦ C throughout the experiment, within the optimum temperature range for hatching (Parrot & Berry, 1976). A volume (5 ml) of half strength PRD was added to each watch glass containing cysts and counts made at 7-day intervals for a further 6 weeks. The diffusate was replaced after each count with fresh solution stored at 4◦ C. After 6 weeks the J2 remaining within the cysts were counted and total percentage hatch achieved during the test period was calculated. Nematology

Variation in hatch among potato cyst nematodes

Table 1. Mean percentage hatch (log transformed data in brackets) and origin of eight Globodera pallida populations. Population

Pathotype

Origin

B B4 Cadishead F6 Junin E6 E8 Kalle

Pa1 Pa1 Pa2 Pa2/3 Pa2 (P4A) Pa3 Pa3 Pa3

SASA, Scotland AFBI, Northern Ireland RR, England Falkland Islands Peru AFBI, Northern Ireland AFBI, Northern Ireland Germany

Percentage hatch 59.3 (1.763) 52.5 (1.717) 76.9 (1.885) 82.5 (1.916) 78.8 (1.894) 73.0 (1.861) 69.8 (1.844) 79.7 (1.901)

5% LSD = 0.101 (n = 3, 16 d.f.) based on log transformed data. AFBI = Agri-Food and Biosciences Institute; RR = Rothamsted Research; SASA = Scottish Agricultural Science Agency.

E FFECT OF ROOT DIFFUSATE DILUTION ON PCN HATCH

In order to determine the root diffusate dilution that would stimulate optimal hatch in subsequent experiments, diffusates from six potato clones from the Commonwealth Potato Collection were tested at a range of dilutions (Table 2). Together with cv. Désirée as a susceptible control the possible effect on hatch of other soil factors was also tested using water percolated through pot soil. The effects of PRD were tested on three replications of cysts from each of the six pathotypes of PCN; population Ro1 (A1), Pa1 (B4) and Pa3 (E6) originated from Northern Ireland, Ro3 (Dutch C) from The Netherlands, Ro5 (Harmerz) from Germany, and P5A (Otuzco) from Peru. The protocol for determining hatch was as described above, except that cysts were pre-soaked in distilled water for 4 days. After final counts, unhatched J2 were assessed by crushing the cysts and recording the remaining eggs and J2. E FFECT OF SIMULATING POTATO ROOT DIFFUSATE PRODUCTION ON PCN HATCH The same combination of PRD source, plus the additional clone CPC 2777b, S. oplocense, and PCN populations for the dilution experiment above were used to assess the effect of collecting diffusate over a 6-week interval (Table 3). An additional comparison was established with distilled water. The diffusate was used immediately, rather than collected at weeks 3 and 4 combined, and used as a stock solution. This aimed to mimic any changes in PRD produced by the plant throughout its maturation. The PRD was used at half strength following the results from the previous dilution experiment. All methods of assessment of hatch of J2 were as for the dilution experiment. Vol. 11(5), 2009

S TATISTICAL ANALYSIS All statistical analyses were carried out using Statistica for Windows (StatSoft, Tulsa, OK, USA). As the hatching data did not initially conform to the assumptions required by ANOVA, subsequent analyses were performed on logtransformed data which met the criteria of the analysis.

Results H ATCH OF GLOBODERA PALLIDA POPULATIONS IN DIFFUSATE FROM CV. D ÉSIRÉE The hatch of each of the eight populations of G. pallida is presented as a percentage of the total potential hatch (Table 1). Hatching from the Northern Ireland Pa1 population was significantly lower (P < 0.05) than the other nematode populations. No significant differences in hatching were apparent between the Pa2 and Pa3 populations. The hatch shown by all PCN populations were considered acceptable for further evaluations with other sources of PRD. E FFECT OF ROOT DIFFUSATE DILUTION ON PCN HATCH

Table 2 shows the percentage hatch stimulated by PRD from each potato genotype for six PRD dilutions and six PCN pathotypes. For all genotypes, undiluted and half strength PRD dilution generally stimulated maximum hatch. On the basis of these results all further tests were standardised using half strength solution as the common PRD dilution. A further assessment of the hatching potential of half strength PRD solutions (expressed as a percentage of 751

S.J. Turner et al.

Table 2. Effect of dilution of soil water and root diffusate from cv. Désirée and six Solanum clones on hatch from Globodera rostochiensis (pathotypes Ro1, Ro3, Ro5) and G. pallida (pathotypes Pa1, Pa3, P5a) (expressed as the mean percentage hatch of cyst contents with log transformed data in parentheses). Diffusate

PRD dilution Full

1:4

1:8

1 : 16

1 : 64

Désirée (susceptible control) (LSD = 0.281) Ro1 84 (1.921) 87 (1.939) Ro3 18 (1.222) 19 (1.326) Ro5 52 (1.699) 42 (1.632)

88 (1.943) 13 (0.949) 62 (1.757)

89 (1.946) 33 (1.506) 52 (1.689)

79 (1.896) 24 (1.239) 66 (1.783)

72 (1.861) 17 (1.275) 68 (1.818)

84 (1.920) 92 (1.964) 43 (1.614)

86 (1.923) 94 (1.975) 30 (1.482)

85 (1.927) 95 (1.976) 33 (1.441)

83 (1.920) 97 (1.987) 41 (1.605)

78 (1.895) 97 (1.987) 33 (1.495)

74 (1.875) 89 (1.945) 26 (1.415)

Soil water (LSD = 0.453) Ro1 2 (0.319) Ro3 1 (0.080) Ro5 1 (0.079)

8 (0.928) 5 (0.475) 1 (0.064)

19 (1.226) 5 (0.651) 2 (0.425)

12 (0.986) 2 (0.342) 2 (0.310)

14 (1.100) 13 (1.089) 4 (0.444)

16 (1.106) 13 (1.107) 1 (0.079)

Pa1 Pa3 P5A

9 (0.906) 7 (0.826) 2 (0.277)

12 (1.099) 5 (0.453) 3 (0.446)

23 (1.254) 2 (0.322) 2 (0.342)

16 (1.094) 1 (0.111) 1 (0.089)

20 (1.233) 2 (0.339) 3 (0.426)

Solanum sanctae-rosae 3269B (LSD = 0.439) Ro1 77 (1.889) 61 (1.774) Ro3 20 (1.246) 14 (1.178) Ro5 55 (1.397) 20 (1.295)

37 (1.577) 20 (1.180) 24 (1.295)

21 (1.327) 4 (0.571) 18 (1.327)

16 (1.195) 5 (0.713) 9 (0.850)

12 (1.124) 6 (0.824) 5 (0.731)

Pa1 Pa3 P5A

14 (1.115) 39 (1.590) 16 (1.236)

7 (0.684) 21 (1.230) 13 (0.990)

5 (0.622) 11 (1.041) 13 (1.108)

2 (0.285) 5 (0.656) 6 (0.755)

1 (0.082) 2 (0.293) 3 (0.491)

Solanum sanctae-rosae 3779A (LSD = 0.289) Ro1 98 (1.992) 97 (1.986) 18 (1.224) Ro3 32 (1.313) Ro5 48 (1.621) 37 (1.565)

97 (1.988) 41 (1.615) 14 (1.140)

90 (1.953) 17 (1.213) 34 (1.524)

69 (1.841) 21 (1.344) 8 (0.854)

39 (1.596) 9 (0.869) 4 (0.626)

Pa1 Pa3 P5A

90 (1.956) 95 (1.978) 36 (1.548)

91 (1.959) 95 (1.976) 44 (1.636)

88 (1.944) 87 (1.930) 33 (1.523)

62 (1.794) 77 (1.888) 7 (0.862)

35 (1.531) 35 (1.538) 7 (0.797)

Solanum sparsipilum 3562B (LSD = 0.442) Ro1 78 (1.894) 57 (1.729) Ro3 18 (1.228) 22 (1.355) Ro5 42 (1.643) 27 (1.467)

50 (1.694) 16 (1.188) 25 (1.391)

40 (1.611) 8 (0.854) 20 (1.300)

22 (1.340) 8 (0.806) 5 (0.615)

15 (1.213) 4 (0.363) 3 (0.334)

Pa1 Pa3 P5A

29 (1.464) 53 (1.714) 7 (0.828)

19 (1.277) 40 (1.608) 4 (0.527)

6 (0.790) 23 (1.337) 4 (0.577)

3 (0.495) 11 (1.008) 4 (0.627)

2 (0.182) 33 (1.339) 3 (0.243)

Solanum sparsipilum 5874A (LSD = 0.409) Ro1 84 (1.927) 87 (1.940) Ro3 19 (0.959) 20 (1.160) Ro5 32 (1.461) 32 (1.443)

81 (1.908) 12 (0.990) 21 (1.225)

46 (1.662) 12 (1.082) 33 (1.500)

61 (1.780) 12 (0.900) 6 (0.762)

48 (1.686) 10 (0.968) 10 (0.916)

Pa1 Pa3 P5A

11 (1.042) 12 (1.065) 4 (0.487)

7 (0.854) 9 (0.935) 2 (0.375)

2 (0.367) 5 (0.662) 2 (0.280)

12 (1.066) 3 (0.459) 4 (0.650)

Pa1 Pa3 P5A

752

4 (0.647) 5 (0.708) 1 (0.083)

31 (1.436) 53 (1.722) 15 (1.063)

79 (1.897) 88 (1.940) 31 (1.475)

53 (1.718) 62 (1.795) 6 (0.799)

24 (1.370) 42 (1.618) 5 (0.650)

1:2

20 (1.292) 28 (1.440) 4 (0.653)

Nematology

Variation in hatch among potato cyst nematodes

Table 2. (Continued). Diffusate

PRD dilution Full

1:4

1:8

1 : 16

1 : 64

Solanum gourlayi 2480E LSD = 0.379) Ro1 45 (1.640) 44 (1.635) Ro3 13 (1.078) 13 (0.579) Ro5 24 (1.360) 12 (1.089)

32 (1.450) 4 (0.600) 7 (0.841)

19 (1.293) 4 (0.510) 4 (0.572)

12 (1.066) 1 (0.030) 4 (0.615)

10 (1.003) 5 (0.642) 6 (0.710)

13 (1.095) 30 (1.472)

9 (1.001) 19 (1.287)

6 (0.734) 5 (0.730)

3 (0.327) 4 (0.606)

3 (0.375) 3 (0.389)

Solanum acaule 3923C (LSD = 0.375) Ro1 32 (1.634) 58 (1.635) Ro3 33 (1.078) 17 (0.579) Ro5 24 (1.360) 20 (1.089)

47 (1.450) 20 (0.600) 21 (0.841)

38 (1.293) 10 (0.510) 8 (0.572)

42 (1.538) 6 (0.705) 4 (0.615)

30 (1.400) 6 (0.642) 10 (0.710)

Pa1 Pa3 P5A

14 (1.001) 14 (1.287) 5 (0.389)

13 (0.734) 12 (0.730) 4 (0.162)

9 (1.003) 7 (0.606) 8 (0.812)

7 (0.605) 3 (0.389) 9 (0.792)

Pa1 Pa3 P5A

26 (1.398) 34 (1.519)

36 (1.398) 26 (1.519) 10 (0.716)

1:2

18 (1.095) 24 (1.472) 10 (0.596)

For each genotype the 5% LSD (n = 3, 72 d.f.) based on log transformed data is indicated.

the hatch of J2 stimulated by PRD from cv. Désirée) demonstrated differences between pathotypes and clones (Fig. 1). Hatch stimulation of the Ro1 population was consistent between the test clones and similar to levels in the control. The percentage hatch of the Ro3 population (with the exception of S. acaule 3923c PRD) and P5A was lower than the control, whilst the Ro5 population (with the exception of S. sparsipilum 5874a PRD) was higher than the control. The Pa1 population displayed the most consistently high level of hatch, whilst Pa3 showed greatest variation across all test clones. Solanum acaule 3923a and S. sanctae-rosae 3779a produced the greatest stimulation of hatch with all the PCN populations, whilst S. sparsipilum 5874a produced the lowest. E FFECT OF SIMULATING POTATO ROOT DIFFUSATE PRODUCTION ON PCN HATCH Comparisons of the percentage hatch induced by test clones and between PCN populations, revealed significant differences (P < 0.05) in hatch stimulation (Table 3). Hatch in distilled water was consistently low, particularly with G. pallida and G. rostochiensis Ro5. Greater hatch occurred with the G. rostochiensis Ro1 population, but this was still less than 50%. Hatch in water precirculated through the soil medium were generally similar, with the exception of population Pa1, which showed significantly greater hatch. Vol. 11(5), 2009

For the susceptible control (cv. Désirée) PCN hatch was greater than that obtained with the water controls, with the exception of Pa1 with ‘soil water’. Pathotypes Ro1, Pa1 and Pa3 produced greater than 50% hatch, whilst there was less than 50% hatch from Ro3, Ro5 and P5A. For the Solanum test clones, variable results were obtained, both between test clones and populations within clones. Within Solanum species, S. sanctae-rosae (3269b vs 3779a) showed similar hatching trends, whilst S. sparsipilum (3562b vs 5874a) exhibited more differences. Overall, greatest hatch was obtained using S. sanctaerosae 3779a diffusate, and lowest hatch using diffusate from S. sparsipilum 5874a.

Discussion Evaluating PCN hatch stimulation by PRD has been studied from the 1940s (Ellenby, 1944; Widdowson, 1958). Since then a greater appreciation of PCN species, pathotypes and virulence has developed (Kort et al., 1978), together with a wider range of PCN-resistant clones from wild potato species (Turner, 1989). Prior to an extensive study into the contribution of PRD to PCN resistance in Solanum spp. clones, this reassessment of testing conditions has clarified optimal procedures. Some differences in potential hatch were shown between populations and pathotypes within G. pallida but 753

S.J. Turner et al.

Table 3. Percentage hatch (log transformed data in brackets) of six populations of potato cyst nematodes, Globodera rostochiensis (pathotypes Ro1, Ro3, Ro5) and G. pallida (pathotypes Pa1, Pa3, P5a), in potato root diffusate from eight Solanum genotypes. Hatch in distilled water and water passed through soil are also presented. Solanum genotype or treatment Water hatch Soil water hatch S. sanctae-rosae 3269b S. sanctae-rosae 3779a S. sparsipilum 3562b S. sparsipilum 5874a S. gourlayi 2480e S. acaule 3923c S. oplocense 3777b S. tuberosum Désirée

Ro1 44.7 (1.645) 59.4 (1.769) 85.2 (1.929) 85.8 (1.933) 84.2 (1.820) 77.2 (1.887) 66.7 (1.923) 78.3 (1.892) 84.7 (1.927) 79.0 (1.897)

Ro3 23.9 (1.189) 9.9 (0.892) 30.7 (1.486) 37.5 (1.550) 14.3 (1.412) 21.2 (1.287) 26.2 (1.418) 41.6 (1.568) 23.8 (1.364) 40.5 (1.602)

Ro5 3.6 (0.511) 5.6 (0.740) 38.6 (1.543) 29.7 (1.376) 31.5 (1.579) 11.4 (1.057) 40.6 (1.474) 43.7 (1.639) 38.5 (1.546) 20.6 (1.288)

Pa1 2.0 (0.274) 60.0 (1.772) 74.7 (1.873) 81.6 (1.911) 79.3 (1.698) 68.9 (1.835) 51.9 (1.899) 83.0 (1.919) 84.9 (1.925) 52.5 (1.717)

Pa3 1.8 (0.258) 13.2 (1.121) 67.8 (1.831) 97.2 (1.988) 73.1 (1.742) 50.9 (1.685) 56.4 (1.861) 69.6 (1.838) 87.1 (1.936) 63.2 (1.799)

P5A 1.9 (0.269) 5.6 (0.725) 35.6 (1.516) 52.9 (1.716) 16.2 (1.146) 13.3 (1.124) 14.4 (1.202) 37.1 (1.566) 36.4 (1.546) 14.1 (1.148)

5% LSD = 0.285 (n = 3, 120 d.f.) based on log transformed data.

this was due to the hatch of a Pa1 population being lower than the Pa2/3 populations. However, it is essential to establish good viability of all populations to be used prior to

any biological studies, and to present results as a percentage of hatch related to a control PRD of known high hatch stimulation and tested on the same PCN population.

Fig. 1. Effect of half strength potato root diffusate from six Solanum genotypes on the hatch of six populations of potato cyst nematodes Globodera rostochiensis (pathotypes Ro1, Ro3, Ro5) and G. pallida (pathotypes Pa1, Pa3, P5a), expressed as a percentage of the hatch in diffusate from cv. Désirée. Error bars represent standard errors of the mean. 754

Nematology

Variation in hatch among potato cyst nematodes

Potato root structure varies within and between wild and cultivated potato clones. Therefore, it is reasonable to assume that the production of PRD at their root tips also varies and, along with it, stimulation of PCN hatch. This is confirmed from studies into the effect of PRD on hatch of J2. Prior to these studies, PRD was usually collected 3-6 weeks after planting, depending on plant growth, and then stored for future use. It is known that the chemical composition of PRD varies throughout the growing season, stimulating preferential hatch of G. rostochiensis and G. pallida as the potato plant matures. PRD composition may vary as well among populations within each of the two nematode species (Byrne et al., 2001). To obtain optimum hatch, the PRD to be used for hatch and resistance studies should be collected and used weekly, beginning 3 weeks after planting tubers, to mimic the actual stimulation throughout the plants growing season. All clones studied can be assumed to have co-evolved with potato cyst nematodes in regions of South America where G. rostochiensis was the dominant species (Evans et al., 1975). Analysis of hatch from the six PCN populations in half strength diffusate from the six South American Solanum species showed little evidence of PCN species differences between the clones (Fig. 1). The G. rostochiensis Ro1 population responded consistently across all clones tested, averaging over 70% hatch. This confirmed that all clones were producing diffusate able to stimulate PCN hatch, and validated that in further specific comparisons any differences measured were due to clone effect rather than root structural differences. An initial assessment of hatch by test clones and between a range of PCN populations did reveal that important differences can exist, both within and between Solanum clones. The six PCN populations divided into two groups for their overall hatch. Pathotypes Ro1, Ro5, Pa1 and Pa3 showed significantly greater hatch compared with Ro3 and P5A. The former group were originally Northern Ireland or German field populations, whilst the latter had been collected in The Netherlands and South America. The significance of this is not clear since all populations had been maintained for several years in quarantine glasshouse facilities, and all tests undertaken in a controlled laboratory environment. Pathotypes Pa3 and P5A are considered to be equivalent by both of the two current International Pathotype Schemes (Canto-Saenz et al., 1978; Kort et al., Vol. 11(5), 2009

1978). Both showed the same pattern of relative hatch between clones, although hatch from Pa3 was consistently higher. Within the two groups, S. sanctae-rosae 3779a PRD stimulated highest hatch with these two populations. This would support suggestions by Byrne et al. (2001) that PCN genotypes behave differently in their hatching responses to PRD from wild potato species. These results set the basis for further in depth studies using a wider range of wild Solanum species with varying levels of PCN resistance. This will help clarify clone vs pathotype interactions and assist in examining the inheritance of hatching factors.

Acknowledgements This work was funded by the Agri-Food and Biosciences Institute. We wish to thank all staff within the Nematology Section, Applied Plant Science Division, for their varied contributions within this investigation.

References B YRNE, J. (1997). Comparative hatching behaviour of Globodera rostochiensis and Globodera pallida. Ph.D. Thesis, Department of Plant Science, University College, Cork, Ireland, 302 pp. B YRNE, J.T., M ATHER, N.J. & J ONES, P.W. (2001). Comparative responses of Globodera rostochiensis and G. pallida to hatching chemicals. Journal of Nematology 33, 195-202. C ANTO S AENZ, M. & DE S CURRAH, M.M. (1978). Races of the potato cyst nematode in the Andean region and a new system of classification. Nematologica 23 (1977), 340-349. E LLENBY, C. (1944). Standardization of root excretions for immunity trials on the potato root eelworm. Nature 154, 363364. E LLENBY, C. (1945). Susceptibility of South American tuberforming species of Solanum to the potato-root eelworm Heterodera rostochiensis Wollenweber. European Journal of Experimental Agriculture 13, 158-168. E VANS, K. (1983). Hatching of potato cyst nematodes in root diffusates collected from twenty-five potato cultivars. Crop Protection 2, 97-103. E VANS, K., F RANCO, J. & DE S CURRAH, M.M. (1975). Distribution of species of potato cyst-nematodes in South America. Nematologica 21, 365-369. F RANKLIN, M. (1940). On the specific status of the so-called biological strains of Heterodera schachtii Schmidt. Journal of Helminthology 18, 193-208. 755

S.J. Turner et al.

H UAMAN, Z. (1978). CIP Potato Germplasm Collection. Inventory of accessions with resistance to some pests and diseases. Lima, Peru, International Potato Center, 20 pp. J ONES, F.G.W. (1970). The control of the potato cyst-nematode. Journal of the Royal Society of Arts March 1970, 179-199. KORT, J., ROSS, H., RUMPENHORST, H.J. & S TONE, A.R. (1978). An international scheme for identifying and classifying pathotypes of potato cyst nematodes Globodera rostochiensis and G. pallida. Nematologica 23 (1977), 333-339. PARROTT, D.M. & B ERRY, M.M. (1976). Hatching of encysted eggs. Report of Rothamsted Experimental Station for 1975, Part 1, p. 198.

756

T URNER, S.J. (1989). New sources of resistance to potato cyst-nematodes in the Commonwealth Potato Collection. Euphytica 42, 145-153. T URNER, S.J. & S TONE, A.R. (1981). Hatching of potato cyst-nematodes (Globodera rostochiensis, G. pallida) in root diffusates of Solanum vernei hybrids. Nematologica 27, 315318. VAN S OEST, L.J.M., RUMPENHORST, H.J. & H UIJSMAN, C.A. (1983). Resistance to potato cyst-nematodes in tuber-bearing Solanum species and its geographical distribution. Euphytica 32, 65-74. W IDDOWSON, E. (1958). Observations on the collection and storage of potato root diffusate. Nematologica 3, 173-178.

Nematology

Suggest Documents