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Angular leaf spot caused by bacteria Pseudomonas syringae pv. lachrymans is a very common cucumber disease, which causes serious yield losses. The objective of this study was to examine the selected cucumber lines regarding their resistance to this pathogen. Twelve cucumber lines bred at the Research Institute of Horticulture were evaluated and compared with the resistant inbred line GY 14 and the susceptible cv. ‘Wisconsin SMR 18’. Plants were inoculated under controlled conditions at cotyledon stage (experiment I) and at leaves stage (experiment II) with the highly aggressive strain of P. s. pv. lachrymans BO 1537. Dis-ease severity was scored 8 days after inoculation using a nine-point rating scale (9 – no symptoms or a few pin-point lesions; 1 – damage up to 100% of leaves). Distribution of plants across severity classes and low variation coefficient indi-cate that all evaluated cucumber lines showed rather good uniformity in their re-spective degrees of resistance to this pathogen. All the materials tested presented lower disease severity in cotyledons stage than in leaves stage. It was also noted that greater differentiation among the lines in regard to their resistance to the bacteria was observed in the leaves stage. Two lines PW 2 and PW 7 exhibited the highest resistance against P. s. pv. lachrymans and can serve as a useful source of this trait in future breeding efforts.
The interplay of plant resistance mechanisms and bacterial pathogenicity is very complex. This applies also to the interaction that takes place between the pathogen Pseudomonas syringae pv. lachrymans (Smith et Bryan) and the cucumber (Cucumis sativus L.) as its host plant. Research on P. syringae pv. lachrymans has led to the discovery of specific factors produced during pathogenesis, i.e. toxins or enzymes. Similarly, studies on cucumber have identified the specific types of plant resistance expressed, namely Systemic Acquired Resistance (SAR) or Induced Systemic Resistance (ISR). This paper presents a summary of the current state of knowledge about this particular host-pathogen interaction, with reference to general information about interactions of P. syringae pathovars with host plants.
The study aimed to examine resistance of 14 cucumber double haploid (DH) lines obtained from Izyd F₁ and Frykas F₁ varieties to angular leaf spot. The DH lines are valuable, homozygous breeding material. The DH lines were tested in laboratory conditions with the use of one, highly virulent Pseudomonas syringae pv. lachrymans strain. The inoculum concentration used was equal to 10⁷ CFU. Plants were scored for resistance in comparison to resistant (GY 14 line) and susceptible (B line) standards, as well as in comparison to Izyd F₁ and Frykas F₁ varieties. Seven days after inoculation the plants were scored by nine degree rating scale, where 1 means total susceptibility and 9 means the total resistance. Data were statistically processed using one-way analysis of variance. 70% of the tested DH lines showed higher resistance level to angular leaf spot than the resistant standard - GY 14 line, and were scored in rating scale above 6. These lines did not show any chlorotic lesions, whereas the necrotic lesions were found on 10-20% of leaf area. The most valuable were I 502, I 504, I 506/2, I 18/1, and I 321 lines obtained from Izyd F₁ variety, which were scored at 7-8 in rating scale; only tiny necrotic lesions without halo were visible on the leaf surface of these lines. The results showed the higher resistance to angular leaf spot in DH lines as compared with Izyd F₁ and Frykas F₁ varieties.
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