Estación Experimental Agropecuaria INTA La Consulta Laboratorio de Análisis de Semillas “José Crnko” [ISTA Member ARDL0200]
Jorge G. Valdez
Relationship between germination, Fusarium incidence and pathogenicity in onion seed samples. Jorge G. Valdez & Pablo Caligiore Gei Laboratorio de Análisis de Semillas “José Crnko”. INTA La Consulta, Ex ruta 40 Km 96, Mendoza, Argentina. Email:
[email protected]
INTRODUCTION
RESULTS and DISCUSSION
Fusarium is a common inhabitant of onion growing regions and therefore it is also commonly presented in onion seeds. One of the objectives of the seed health tests is to explain the low level results obtained with standard germination. Also, many fungi can be observed at the end of a germination analysis (Figure 1) which asks the question how germination was affected because of them? In onion seed samples, most of the fungi present at the end of the germination period, looks like Fusarium spp. colonies.
Germination percentages ranged from 23 to 97 (x =83.8; s = 14.4) .
The objective of this study is compare the relationship of onion germination with the presence of Fusarium seed borne and their pathogenicity.
Infection in samples ranged from 0 to 56% (x =6.72; s = 9.41). Pathogenity ranged from 0 to 88% (x= 43.2; s= 23.3). Pathogenicity was sorted in six groups to obtain different classes (Table 1). Fusarium proliferatum was the main fungi isolated (86.7%), followed by F. oxysporum (6.7%) and F. verticillioides (6.7%, not pathogenic). There was not significant correlation between variables, which produced no association in the PCA biplot (74% of explanation of the model, Figure 2). Correlations among dead seeds and abnormal plantlets with ISS or pathogenicity were 0.09; 0.02; 0.20 and 0.14 showing clearly the lack of significant correlations. According to our results, germination in onion is not affected by Fusarium. CPA Germination, Infected seeds and Pathogenicity of Fusarium isolates 2,0
1,0 tg2
G12 tm2
0,0
D
tg1
G6
Infected Seed in Samples
CP 2 18%
ta2
A
-1,0
60 50 40
-2,0
30 PatDegree
-3,0
Pat
20 10 R² = 0,004
ISS
ISS
-4,0
-5,0
0 0
-3,0
-2,0
-1,0
0,0
1,0
2,0
20
3,0
4,0
40
5,0
60
80
6,0
100
120
7,0
8,0
CP 1 56%
Figure 1. Fusarium spp developed on dead seeds at the end of a germination standard analysis.
MATERIALS and METHODS
Fig. 2. Biplot of PCA relative to germination variables (G6, G12, D, A), Infected seeds in sample (ISS) and pathogenicity (Pat) of Fusarium isolates. Incrusted: Infected seeds in samples plotted against germination percentage.
• Sixty samples of onion seed obtained from local producers of San Juan and Mendoza provinces, in the central west part of Argentina. • Germination data were obtained, using ISTA Rules (4 replicates of 100 seeds/TP/20 ± 2 °C/6, 12 d). The following variables were recorded: G6 (normal plantlets obtained after six days); G12 (final normal plantlets); A (abnormal plantlets at the end of the assay); D (dead seeds at the end of the assay). • Percentage of Infected Seeds in Sample (ISS) was recorded by DFB. • Isolates were obtained from emerging colonies, three per sample. • Pathogenicity (Pat) was tested in pots with 150 g of sterile sand and 25 seeds of onion cv Valcatorce INTA. Two plugs (5 mm diameter) of PDA of fresh colonies were used as inoculum. • Identification of more aggressive isolates were made by micromorphology.
Table 1:. Number of isolates of Fusarium species distributed into 6 pathogenicity classes (PC)
Species Fusarium spp. F. oxysporum F. proliferatum F. verticillioides Total
PC 0 PC 1 PC 2 PC 3 PC 4 PC 5 Total 21 2 1 24
28 4
19 1 2
32
22
3
1
26
1 23
2
29
24
3
72 2 59 1 134
Pathogenicity classes were defined by percentage of dead plants (DP) on sand. PC 5, >85 % DP; PC 4, >70 % DP; PC 3, > 55 % DP; PC 2, > 40 % DP; PC 1, > 25 % DP; PC 0, > 0 % DP
• Principal Component Analysis (PCA) was run to analyse correlations between variables. This work was presented at 7th ISTA Seed Health Symposium Edinburgh, 12-14 June 2014 Session 1 #5.
