Evaluating the Effect of the Rootstock on the Resistance of Some Grafted Pear Cultivars to the Fire Blight Disease

Abstract

IntroductionPear (Pyrus communis L.) is a cold-climate fruit tree belonging to the Rosaceae family, and it is native to Western Asia and Eastern Europe. Fire blight disease is caused by the gram-negative bacterium Erwinia amylovora, and it is considered one of the most damaging and harmful diseases in pome fruit trees in cold and temperate regions worldwide. The most sensitive plant organ in pome fruit trees to this disease is flowers. Fire blight disease has five important stages, from initial infection to the final death of the tree trunk. These five stages include blossom blight, fruit blight, leaf blight, main branches, and trunk blight, and finally, root blight. The first and most important stage of pathogenicity in fire blight disease begins in early spring under high humidity, causing the burning and death of the flower. Materials and MethodsThe Rootstock used in this experiment were Dargazi and Pyrodwarf, and the cultivars studied were Koshia and Dargazi. The experiment was conducted in two conditions, orchard and greenhouse. In the orchard, a factorial experiment was carried out in a completely randomized block design with five repetitions. The factors studied were Rootstocks (Dargazi and Pyrodwarf) and cultivars (Koshia and Dargazi). In the greenhouse, a factorial experiment was carried out in a completely randomized design with three repetitions. The factors studied were Rootstocks (Dargazi and Pyrodwarf) and cultivars (Dargazi and Kosha). Gardner scale was used to measure the severity of fire blight infection. In addition, the levels of sucrose, sorbitol, and pH in leaf tissue were measured. The sucrose content in the leaf tissue of Koshia/Pyrodwarf Rootstock increased from day 0 to 6 and reached its highest level (10%) on the 6th day, then decreased to 5% on the 12th day. In the Dargazi/Pyrodwarf base, sucrose levels increased from day 0 to 6 and reached its highest level (8%) on the 6th day, then decreased to 5% on the 12th day. In the Dargazi/Dargazi base, sucrose levels increased from day 0 to 6 and reached its highest level (7%) on the 6th day, then decreased to 4% on the 12th day. The sorbitol content in the leaf tissue of Koshia/Pyrodwarf base increased from day 0 to 6 and reached its highest level (2%) on the 6th day, then decreased to 1% on the 12th day. In the Dargazi/Pyrodwarf Rootstock, sorbitol levels increased from day 0 to 6 and reached its highest level (1.5%) on the 6th day, then decreased to 1% on the 12th day. In the Dargazi/Dargazi Rootstock, sorbitol levels increased from day 0 to 6 and reached its highest level (1%) on the 6th day, then decreased to 0.5% on the 12th day. On the other hand, the pH of the leaf tissue in the Dargazi/Pyrodwarf base remained constant at 6.2 from day 0 to 12 and increased to 7.4 on the 12th day. Results and DiscussionThe rootstock used in this experiment were Dargazi and Pyrodwarf, and the cultivars studied were Koshia and Dargazi. The experiment was conducted in two conditions, orchard and greenhouse. In the orchard, a factorial experiment was carried out in a completely randomized block design with five repetitions. The factors studied were rootstocks (Dargazi and Pyrodwarf) and cultivars (Koshia and Dargazi). In the greenhouse, a factorial experiment was carried out in a completely randomized design with three repetitions. The factors studied were Rootstocks (Dargazi and Pyrodwarf) and cultivars (Dargazi and Koshia). Gardner scale was used to measure the severity of fire blight infection. In addition, the levels of sucrose, sorbitol, and pH in leaf tissue were measured. The sucrose content in the leaf tissue of Koshia/Pyrodwarf Rootstocks increased from day 0 to 6 and reached its highest level (10%) on the 6th day, then decreased to 5% on the 12th day. In the Dargazi/Pyrodwarf Rootstock, sucrose levels increased from day 0 to 6 and reached its highest level (8%) on the 6th day, then decreased to 5% on the 12th day. In the Dargazi/Dargazi Rootstock, sucrose levels increased from day 0 to 6 and reached its highest level (7%) on the 6th day, then decreased to 4% on the 12th day. The sorbitol content in the leaf tissue of Koshia/Pyrodwarf Rootstock increased from day 0 to 6 and reached its highest level (2%) on the 6th day, then decreased to 1% on the 12th day. In the Dargazi/Pyrodwarf Rootstock, sorbitol levels increased from day 0 to 6 and reached its highest level (1.5%) on the 6th day, then decreased to 1% on the 12th day. In the Dargazi/Dargazi Rootstock, sorbitol levels increased from day 0 to 6 and reached its highest level (1%) on the 6th day, then decreased to 0.5% on the 12th day. On the other hand, the pH of the leaf tissue in the Dargazi/Pyrodwarf Rootstock remained constant at 6.2 from day 0 to 12 and increased to 7.4 on the 12th day. The collected data from both orchard and greenhouse experiments were analyzed to determine the effects of Rootstock and cultivar on fire blight resistance. ConclusionThe results showed that the combination of Koshia/Dargaz had higher resistance to fire blight compared to Koshia/Pyrodwarf. Additionally, the pH and carbohydrate content in the leaf tissue of the rootstock affected the growth and proliferation of fire blight bacteria. This study demonstrated varying levels of resistance to fire blight among the studied combinations, indicating significant potential for breeding and improving pear resistance to this disease. The Dargazi cultivar exhibited very high resistance to fire blight in both orchard and greenhouse conditions. Overall, the resistance of the Dargazi rootstock contributed to the resistance of the sensitive Koshia cultivar.

Keywords

• cultivar
• fire blight disease
• gardner scale
• rootstock
• usda system