Globodera rostochiensis, (Woll.) (Woll.)

Mwangi, James M., Mwangi, Grace N., Finckh, Maria R. & Kiewnick, Sebastian, 2021, Biology, pathotype, and virulence of Globodera rostochiensis populations from Kenya, Journal of Nematology 53 (1), pp. 1-13 : 5-9

Study of G. rostochiensis biology

In the first experiment, G. rostochiensis J2 were found in the roots of potato for all treatments at 14 days after inoculation ( DAI), at 171 DD 6. The mean number recorded did not differ (p>0.05) among cultivars and populations ( Fig. 1 ). A few third-stage juveniles (J3) of G. rostochiensis ‘Ecosse’ were also detected in ‘Désirée’ 14 DAI. G. rostochiensis ‘HAR1’ J3 were detected in the roots of ‘Désirée’ 18 DAI (237 DD 6). At this time, the number of G. rostochiensis ‘Ecosse’ J3 was 36.3% higher in ‘Désirée’ treatment compared to the same cultivar inoculated with G. rostochiensis ‘HAR1’. The number of G. rostochiensis J 2 in the roots varied among treatments (p <0.05) with higher numbers being recorded on ‘Désirée’ (220.0 J3 per root system) and ‘Laura’ (192.3 J3 per root system) inoculated with G. rostochiensis ‘Ecosse’ compared to G. rostochiensis ‘HAR1’. The first J 3 in the roots of the resistant cultivar were detected 23 DAI (302 DD 6). Overall, the number of J3 was higher in the susceptible cultivar inoculated with G. rostochiensis ‘Ecosse’ compared to the rest of the treatments. At 23 DAI fourth-stage juveniles (J4s) were detected in all treatments except for G. rostochiensis ‘HARI’ on ‘Laura’ which appeared on 28 DAI. In total, 28 days and 367 DD 6 were required for the first males and females to emerge from ‘Désirée’. There were 62% more females in ‘Désirée’ inoculated with G. rostochiensis ‘Ecosse’ than with ‘HAR1’. From 35 DAI (463 DD 6), males were detected in the roots of ‘Laura’, for both G. rostochiensis populations, until 63 DAI (840 DD 6) when the numbers diminished. The number of females extracted from the roots increased steadily from 35 DAI (463 DD 6) with more G. rostochiensis ‘Ecosse’ females counted on the susceptible cultivar compared to G. rostochiensis ‘HAR1’ throughout the experiment. However, no females were detected in resistant ‘Laura’ for either populations ( Fig. 1 ). The first brown cyst of G. rostochiensis ‘Ecosse’ was isolated from the soil 49 DAI (646 DD 6) and for G. rostochiensis ‘HAR1’ seven days later at 741 DD 6. The mean numbers of cysts at the end of the experiment were 918 and 705 cysts per root system for G. rostochiensis ‘Ecosse’ and ‘HAR1’, respectively.

The number of developing ‘HAR1’ and ‘Ecosse’ G. rostochiensis recorded in the roots and soil in the repeat experiment were similar in all treatments. However, some developmental stages were detected earlier than in the first experiment. For instance, at 14 DAI, both J2 and J3 were detected in the roots in all treatments ( Fig. 2 ). At this date, the cumulative degree-days were slightly higher (182 DD 6) than in the first experiment. Similarly, G. rostochiensis J4 were detected five days earlier in experiment two (18 DAI at 239 DD 6). The first G. rostochiensis ‘Ecosse’ females were detected in ‘Désirée’ on 23 DAI at 309 DD 6, this was five days earlier than in the first experiment while G. rostochiensis ‘HAR1’ females were detected five days later (28 DAI at 382 DD 6). Only males were detected in the roots of ‘Laura’ and in low numbers. The number of days required to complete the life cycle was similar to the first experiment with cumulated DD 6 of 645 and 736 DD 6 for ‘Ecosse’ and ‘HAR1’, respectively. The average number of cysts at the end of the experiment was 956 and 876 cysts per root system for G. rostochiensis ‘Ecosse’ and ‘HAR1’, respectively.

Investigating the presence of diapause in Kenya G. rostochiensis populations

The G. rostochiensis Kenyan populations tested were able to reproduce without diapause ( Fig. 3 ). The Rf values varied significantly among generations for ‘RIR’ and ‘KIN1’, but not the other four populations. In the two former populations, reproduction of the 2nd second generation was higher ( p <0.05) than the 3rd generation. The overall reproduction in the 2nd generation ranged from Rf =9.5 ± 2 in ‘TGN’ to Rf= 26.5± 3 in ‘RIR’ ( Fig. 3 ). In the 4th generation, the lowest Rf was recorded for ‘HAR1’ (Rf= 6.4±1) while ‘KIN1’ had the highest (Rf= 19.3±4).

When G. rostochiensis ‘HARI’ was incubated in PRD for a period of 10 weeks, up to 68% of the 1st generation cysts hatched, compared to 14% hatch in water. The hatching rate was lower in the subsequent generations with 55 and 44%, respectively ( Fig. 4 ). Hatching in water was less than 2% in the 3rd and the 4th generation cysts.

Testing the pathotype of G. rostochiensis from Kenya

Globodera rostochiensis ‘HAR1’ and ‘Ecosse’ had a high Rf on susceptible ‘Désirée’ ( Table 1 ). There was no cyst produced on S. tuberosum cv. ‘Laura’ and S. vernei , 65.346.19 (Rf =0), the two clones were therefore resistant to the two populations.

The Rf value on S. vernei , 58.1642.4 was <1 for both populations. Equally, both G. rostochiensis populations had a low Rf on S. vernei , 62.33.3. Only G. rostochiensis ‘HAR1’ had a Rf of more than one (Rf =1.1) on S. kurtzianum , 60.21.19 ( Table 1 ).

Virulence assessment of G. rostochiensis from Kenya

The Rf value varied between the G. rostochiensis populations ‘Ecosse’, ‘HAR2’, ‘KIN1’, and ‘TGN’. In addition, the populations had a higher Rf in experiment 1 compared to experiment 2 ( Table 2 ). Reproduction of the four populations on in vitro cultivar ‘Désirée’ ranged from an Rf of 14.75 to 37.27 in experiment 1 compared with Rf value of 3.53 to 19.92 in experiment 2. There was no significant difference in Rf among the populations, on ‘Désirée’, except for G. rostochiensis ‘HAR2’ in experiment 1 and G. rostochiensis ‘KIN1’ in experiment 2, which had significantly lower Rfs ( p <0.05) than other populations. All G. rostochiensis populations had significantly lower reproduction ( p <0.05) on the potato cultivars ‘Rossini’, ‘Caruso’, ‘Amanda’, and ‘Laura’ with an Rf<1 compared to ‘Désirée’, ‘Connect’, and ‘Performer’ in both experiments ( Table 2 ).

The G. rostochiensis population ‘HAR2’ had the lowest reproduction on ‘Connect’ in the first experiment compared to the other G. rostochiensis populations with Rf values ranging from 21.8 to 31.7 ( Table 2 ). In the second experiment, all G. rostochiensis populations had a similar Rf value on ‘Connect’ except G. rostochiensis ‘KIN1’ that was significantly ( p <0.05) lower. On ‘Performer’, G. rostochiensis populations ‘Ecosse’, ‘HAR1’, and ‘KIN1’ had similar reproduction, while ‘TGN’ had the lowest reproduction in experiment 1. The relative reproduction of all populations on ‘Performer’ was low (Rf≤1) in experiment 2 ( Table 2 ).

Despite the variability in the reproduction of the four populations between the two experiments, the Rs values of the cultivars to the G. rostochiensis populations did not differ ( Table 3 ). The potato cultivars, ‘Rossini’, ‘Caruso’, ‘Amanda’, and ‘Laura’ had an Rs value of less than 1% and therefore were ranked as highly resistant (score=9) according to EPPO (2006). ‘Connect’ was ranked as highly susceptible (score= 1-2) to all populations tested ( Table 3 ). The Rs of ‘Performer’ to the G. rostochiensis populations ranged from 5 to 17%. The cultivar had an Rs of 6 for G. rostochiensis populations ‘Ecosse’, ‘HAR1’, and ‘TGN’ and a score of 4 for ‘KIN1’ ( Table 3 ).

Reproduction of G. rostochiensis ‘HAR1’ and ‘Ecosse’ was very low on ‘Albatros’, ‘Belana’, ‘Ribera’, ‘Amado’, ‘Seresta’, and ‘Papageno’ with an Rf<1 and Rs of less than 1% based on experiments with tuber derived potatoes ( Table 4 ). The six cultivars scored = 9 in resistance. Reproduction of both G. rostochiensis populations on ‘Désirée’ was high but not different ( p > 0.05), although ‘HAR1’ had higher Rf of 56.6 compared to ‘Ecosse’ Rf of 51.1 ( Table 4 ).

Figures

Figure 1: Figure showing the mean number of different developmental stages of GlOBOdeRa ROSTOChienSiS, ‘HAR1’ and ‘Ecosse’ populations in resistant cv. ‘Laura’ and susceptible cv. ‘Désirée’ in the glasshouse during the first experiment.

Figure 2: Figure showing the mean number of different developmental stages of GlOBOdeRa ROSTOChienSiS, of ‘HAR1’ and ‘Ecosse’ populations in resistant cv. ‘Laura’ and susceptible cv. ‘Désirée’ in the glasshouse in the second experiment.

Figure 3: Mean reproduction factor (±SE) of six populations of GlOBOdeRa ROSTOChienSiS from Kenya on the susceptible cultivar ‘Désirée’ for three successive generations without diapause. Vertical bars show the standard error of the mean (n = 6). Means within a population with the same small letter are not significantly different (P>0.05).

Figure 4: Percentage hatch of GlOBOdeRa ROSTOChienSiS ‘HAR1’ population in PRD for three successive generations of cysts without diapause. Vertical bars are mean percentage±standard error (n=4).

Tables

Table 1. The reproduction factor (Rf) of GLOBODeRa ROSTOCHIeNSIS populations ‘HAR1’ and ‘Ecosse’ on six differential potato clonesa.

		Population		Statusc
Potato clones	Resistanceb	‘HAR1’	‘Ecosse’	‘HAR1’	‘Ecosse’
S. tuberosum cv. ‘Désirée’	None	61.4	46.6	+	+
S. tuberosum cv. ‘Laura’	Ro1,4	0.0	0.0	–	–
S. kurtzianum , 60.21.19	Ro1,2	1.1	0.4	+	–
S. vernei , 58.1642.4	Ro1,2,3	0.1	0.1	–	–
S. vernei , 62.33.3	Ro1,2,3,4	3.2	2.4	+	+
S. vernei , 65.346.19	Ro1,2,3,4,5	0.0	0.0	–	–

Notes: aThe table shows the reproduction factor of ‘HAR1’ population from Kenya and ‘Ecosse’ reference population on six differential potato clones according to Kort et al. (1977). Data are means of two experiments (n = 10); bRo 1, 2, 3, 4, and 5 refers to the five pathotypes of R. rostochiensis according to Kort et al. (2077); c (+) indicates a reproduction factor (Rf> 1.0 (susceptible), and (−) indicates a Rf <1.0 (resistant).

Table 2. Response of seven potato cultivars to four populations of GLOBODeRa ROSTOCHIeNSIS under greenhouse conditions.

Cultivar	‘Ecosse’	‘HAR2’	‘KIN1’	‘TGN’
Experiment 1
‘Désirée’	28.43 d ± 12.0 a, A	14.73 ± 9.6 a, B	24.97 ± 10.5 a, A	37.27 ± 22.7 a, A
‘Connect’	31.70 ± 9.3 a, A	18.43 ± 5.2 a, B	30.84 ± 15.3 a, A	21.80 ± 9.4 a, A
‘Performer’	2.37 ± 1.3 b, A	1.74 ± 1.3 bA, B	2.45 ± 1.9 b,AB	1.18 ± 0.9 b, B
‘Rossini’	0.02 ± 0.1 c	0.00 ± 0.0 c	0.00 ± 0.0 c	0.01 ± 0.0 c
‘Caruso’	0.02 ± 0.1 c	0.00 ± 0.0 c	0.00 ± 0.0 c	0.02 ± 0.1 c
‘Amanda’	0.00 ± 0.0 c	0.01 ± 0.0 c	0.02 ± 0.1 c	0.05 ± 0.1 c
‘ Laura’e	0.00 ± 0.0	0.00 ± 0.0	0.00 ± 0.0	0.00 ± 0.0
Experiment 2
‘Désirée’	10.07 ± 1.5a, A	8.11 ± 1.5a, A	3.53 ± 0.3a, B	12.92 ± 0.8a, A
‘Connect’	7.47 ± 1.1 a, A	13.31 ± 1.9 a, A	2.42 ± 0.3 a, B	12.25 ± 2.7 a, A
‘Performer’	0.53 ± 0.1 b,AB	0.35 ± 0.1 b, B	0.85 ± 0.2 b, A	1.00 ± 0.3 b, A
‘Rossini’	0.00 ± 0.0 c	0.00 ± 0.0 c	0.04 ± 0.1 c	0.01 ± 0.0 c
‘Caruso’	0.00 ± 0.0 c	0.08 ± 0.3 c	0.00 ± 0.0 c	0.02 ± 0.1 c
‘Amanda’	0.00 ± 0.0 c	0.00 ± 0.0 c	0.00 ± 0.0 c	0.05 ± 0.0 c
‘ Laura’e	0.00 ± 0.0	0.00 ± 0.0	0.00 ± 0.0	0.00 ± 0.0

Notes: dReproduction factor (Rf) ± SE. Data are means of two experiments (n = 10). Means of Rf within the same column in each experiment followed with similar lowercase letters are not significantly different ( p > 0.05). Similarly, means of Rf within the same row in each experiment followed with similar capital letters are not significantly different ( p > 0.05); e Reproduction on cv. ‘Laura’ was tested using eye-plugs due to lack of in vitro plants of this cultivar.

Table 3. Mean relative susceptibility (Rs %) of six potato cultivars to four G. ROSTOCHIeNSIS populations: ‘Ecosse’, ‘HAR2’, ‘KIN1’, and ‘TGN’a.

	‘ Ecosse’		‘HAR2’		‘ KIN1’		‘TGN’
Cultivar	Rs (%) a	Score	Rs (%)	Score	Rs (%)	Score	Rs (%)	Score
‘Connect’	92.9	2	144.6	1	96.1	2	76.7	2
‘Performer’	6.8	6	8.1	6	17.0	4	5.5	6
‘Rossini’	0.1	9	0.0	9	0.6	9	0.1	9
‘Caruso’	0.1	9	0.5	9	0.0	9	0.2	9
‘Amanda’	0.0	9	0.1	9	0.1	9	0.3	9
‘ Laura’b	0.0	9	0.0	9	0.0	9	0.0	9

Notes: The table shows percentage relative susceptibility (Rs) and the resistance ranking of seven potato cultivars. Data are from two experiments with ten replications per experiment. aRs (%)= Pf/ Pf×100 test cultivar standard susceptible control cultivar and the resistance level (score) determined using the EPPO score scale (1 (>100), 2 (50.1-100%), 3 (25.1-50%), 4 (15.1-25%), 5 (10.1-15%), 6 (5.1-10%), 7 (3.1-5%), 8 (1.1-3%), 9 (≤1%)), where 9 represent the highest level of resistance and 1 represent the least resistant; bReproduction on cv. ‘Laura’ was tested using eye-plugs due to lack of in vitro plants of this cultivar.