DETERMINING THE RELATIONSHIP BETWEEN VIRULENCE AND AGGRESSIVENESS IN PLASMOPARA HALSTEDII: RESULTS

RESULTS

ANALYSIS OF AGGRESSIVENESS CRITERIA

There were significant differences between P. halstedii isolates for all aggressiveness criteria (Table 2). Percentage infection ranged between 93.2% for isolate MIL 002 and 99.8% for isolate DU 1767. Latent period ranged between 8.09 days for isolate DU 1842 and 11.29 days for isolate DU 1734. Sporulation density varied three fold: 5.02×105 zoosporangia were produced by cotyledons for isolate DU 1915 and 16.72×105 for isolate DU 1842. Hypocotyl length varied from 27.5 mm for isolate DU1915 to 40.7 mm for isolate DU1943. Results shown in Table 2 indicate that the progeny isolate DU 1842 was the most aggressive among the isolates tested with an index of aggressiveness of 6.3; followed by progeny isolate DU 1767 with an index of aggressiveness of 5.9; parental isolate MIL 001 with an index of aggressiveness of 4.9, and progeny isolate DU 1734 with an index of aggressiveness of 4.5. The parental isolate MIL 002 and the two progeny isolates DU 1734 and DU 1915 were the least aggressive, recording the mean value for index of aggressiveness of 1.9.

Table 2: Aggressiveness between Plasmopara halstedii parental and progeny isolates measured on the sunflower inbred line FU

Isolates Percentageinfection(%)a Latent period (days)b Sporulation density (105 zoosporangia per cotyledon) c Hypocotyl length (mm) d Index ofaggressiveness
Parental isolate MIL 001 96.0 9.22 14.32 30.7 4.9
(race 100)Progeny isolate DU 1842 99.1 8.09 16.72 32.4 6.3
(race 300)Progeny isolate DU 1943 99.3 8.42 13.53 40.7 4.5
(race 314)Progeny isolate DU 1767 99.8 8.25 14.10 29.0 5.9
(race 304) Parental isolate MIL 002 93.2 10.80 7.03 28.7 2.1
(race 710) Progeny isolate DU 1915 95.2 11.06 5.02 27.5 1.61.9
(race 714)Progenyisolate 96.4 11.29 6.31 27.9
DU 1734 (race 704) P= 0.00001 VC= 4.52% P= 0.0 VC=6.01% P= 0.0 VC=21.86% P= 0.0 VC=10.01%

a number replications = 3, 60 plants per replication, b number replications = 3, 10 plants per replication, c number replication = 2, 18 counts per replication, d number replication =3, 10 plants per replication (Sakr 2009, Sakr et al. 2011). Probability (P), Variation Coefficient (VC), index of aggressiveness = (percentage infection x sporulation density) / (latent period x reduction of hypocotyl length).

MOLECULAR ANALYSIS

The combination of 12-EST derived markers revealed five multilocus genotypes (MLG) among seven P. halstedii isolates (Table 3). Parental isolates MIL 001 and MIL 002 were different for all genomic markers excepting Pha54. Furthermore, isolates MIL 001, DU 1842 and DU 1767 shared the same genetic background. The Neighbour-joining tree showed that isolates DU 1915, DU 1734 and DU 1943 had an intermediary genetic position between parental isolates MIL 001 and MIL 002 (Figure 1).

Table 3: Multilocus genotypes (MLG) characterized using 12 EST-derived genomic markers on the isolates of Plasmopara halstedii

Isolates EST-derived markers
Pha6 Pha39 Pha42 Pha43 Pha54 Pha56 Pha74 Pha79 Pha82 Pha99 Pha106 Pha120
MIL 001 2/2 2/2 1/1 1/1 1/1 1/1 1/1 3/3 2/2 2/2 1/1 2/2
DU 1767 2/2 2/2 1/1 1/1 1/1 1/1 1/1 3/3 2/2 2/2 1/1 2/2
DU 1842 2/2 2/2 1/1 1/1 1/1 1/1 1/1 3/3 2/2 2/2 1/1 2/2
DU 1943 1/1 2/2 1/1 2/2 1/1 2/2 2/2 3/3 2/2 1/1 2/2 1/1
DU 1734 2/2 2/2 2/2 1/1 1/1 1/1 2/2 3/3 1/1 1/1 2/2 1/1
DU 1915 1/1 2/2 1/2 1/1 1/1 1/1 1/1 3/3 2/2 1/1 2/2 1/1
MIL 002 1/1 1/1 2/2 2/2 1/1 2/2 2/2 1/1 1/1 1/1 2/2 1/1

Fig1Determining The Relationship_decrypted
Figure 1: Phylogenetic tree according to Neighbour-joining analysis of 12 EST-derived markers. Figures on branches indicate bootstrap values (10.000 replicates)

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