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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.
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.
Downy mildew, caused by the Oomycete pathogen Pseudoperonospora cubensis, is one of the most destructive diseases of cucumber (Cucumis sativus L.) and muskmelon (C. melo L.). Although the process of pathogenesis is well understood, there are few disease control options available. The development and deployment of resistant cultivars is generally considered to be the best approach to control downy mildew. The recently completed sequencing of the cucumber genome provides a great opportunity for reliable and thorough study of the sequence and function of resistance genes in the Cucurbitaceae, which will help us to understand the resistance mechanisms and metabolic pathways activated by these genes. It can be anticipated that, in the near future, we will have more information about the genetic bases of resistance to downy mildew in Cucumis, which will facilitate efforts to breed for resistance to this pathogen.
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