Development of a detached leaf procedure to evaluate susceptibility to Plum pox virus infection by the green peach aphid (Myzus persicae (Sulzer)) in peach

Figures & data

Fig. 1 Addition of aphids to PPV-infected plum leaves positioned over detached peach leaves on a gel bed. Peach leaves were incubated 2 weeks in a containment room before being tested by DRT-PCR for PPV infection.

Table 1. Percentage infection of peach seedlings and detached peach leaves following manual serial aphid transmission of PPV from infected plum leaves.

		Seedlings		Detached leaves
Trial	Host	Samples (n)	% infection	Samples (n)	% infection
1	Peach	20	55	10	20
2	Peach	22	45	10	20
3	Peach	34	36	12	25
4	Peach	21	24	25	17
5	Peach	30	25	7	29
6	Peach	47	15	12	25
		x ± sd:	33.3 ± 14.9		21.5 ± 3.4

Six replicated trials inoculating either peach seedlings or detached peach leaves. Fifty aphids were used for each inoculation. Means and standard deviations were determined using the means of the six trials. The two means are not significantly different based on Welch’s test (P = 0.1529 at α = 0.05, n = 6).

Table 2. Comparison of PPV infection rates of detached leaves by the manual serial aphid transfer method and the leaf overlay method.

Manual transfer method				Leaf overlay method
Trial	Host	Samples (n)	% Infection	Trial	Host	Samples (n)	% Infection
1	Peach	10	20	1	Peach	16	25
2	Peach	34	15	2	Peach	20	15
3	Peach	34	20	3	Peach	5	25
4	Peach	56	11	4	Peach	27	37
5	Peach	10	28	5	Peach	30	23
6	Peach	15	15	6	Peach	42	22
		x ± sd:	18.2 ± 5.9				24.5 ± 7.1

Six replicated trials comparing efficacy of the inoculation methods. Twenty-five aphids were used for each inoculation. Means and standard deviations were determined using the means of the six trials. The two means are not significantly different based on Welch’s test (P = 0.1288 at α = 0.05, n = 6).

Table 3. Percentage infection of detached peach leaves influenced by the number of aphids applied to infected plum leaf segments overlaid on the peach leaves.

			% Infection
Trial	Host	Samples (n)	50 aphids	25 aphids
1	Peach	27	37	8
2	Peach	12	41	17
3	Peach	30	23	23
4	Peach	10	20	30
5	Peach	10	40	30
6	Peach	10	10	10
		x ± sd:	28.5 ± 12.7	19.7 ± 9.6

Mean and standard deviation was determined using the means of the six trials. The two means are not significantly different based on Welch’s test (P = 0.2071 at α = 0.05, n = 6).

Table 4. Effect of pre- and post-incubation temperatures on PPV multiplication in peach leaves collected from the field during the growing season.

Temperature	Pre % Transmission*	Post % Transmission*
Control	9.86 ± 0.98 a	9.10 ± 1.27 a
4°C	10.86 ± 1.22 a	9.69 ± 0.44 a
10°C	10.86 ± 1.22 a	10.47 ± 0.67 a
20°C	7.20 ± 3.11 a	7.80 ± 0.28 a
	**Chi-square = 13.2473 (3 df);	**Chi-square = 9.0982 (3 df);
	P = 0.0041;	P = 0.0280;
	Contingency Coefficient = 0.0934	Contingency Coefficient = 0.0776

* Transmission (%) followed by different letters within each assay indicates significant differences (P ≤ 0.05) according to Chi-square test and Fisher exact test when the expected values were lower than 5.

** Contingency Coefficient measures the association between the two variables, values closer to 1 indicate higher degree of association between the variables.