Breeding for resistance to soft rot disease in Ornithogalum

Pectobacterium (formerly Erwinia) carotovorum is a plant pathogen that causes soft rot of many important agricultural crops, including Ornithogalum. The absence of effective control against soft rot bacteria causes the flower and bulb growers substantial yearly losses from the disease. Under these circumstances, interspecies breeding between sensitive and relatively resistant species of the same genus would be a viable option. The orange-flowered species Ornithogalum dubium, which is known for its high susceptibility to soft rot disease, was used as a female parent, while the relatively resistant white species Ornithogalum thyrsoides was used as a pollen donor to yield interspecific F₁ hybrid lines. Two F₁ hybrid lines (99/2/32 and 99/2/28) were tested for their relative resistance to the soft rot bacterium P. carotovorum subsp. brasiliense Pcb3. A bacterial colonization study in parental and hybrid lines was followed by measurement of phenolic content in the tissues of the plant lines. Bacterial colonization was significantly reduced compared with the sensitive parent O. dubium. This was accompanied by higher levels of phenolic compounds in the F₁ hybrids compared with O. dubium.