تاثير دماهاي مختلف هوا و منطقه ريشه بر رشد و نمو سه گونه يونجه يكساله

Study of the resistance of alfalfa cultivars (Medicago sativa) to alfalfa weevil (Hypera postica Gyll.) attack under water stress conditions

Alfalfa weevil (Hypera postica Gyll.) is one of the major pests of alfalfa in Iran. It has been proven that environmental stresses like a decrease in water and irrigation, may result in the preference and non-preference of pests towards feeding on plants. Water stresses may even result in the decrease or increase of damage to plants. The response of 77 cultivars of alfalfa to water stress were studied in normal irrigation (every 10 days) and water stress (every 30 days irrigation) conditions during 2 years in the field of Tehran University-Karaj. The experiment was conducted as split plot in time in the pattern of randomized complete block design in 4 replications. The first and second replicates were irrigated every 10 days as experiment 1, whereas the third and forth replicates were irrigated every 30 days as experiment 2. Pest infection occurred naturally. Damage percentage was determined through scoring of shoot injuries, then data were recorded for 4 times, 2 times in the first year and 2 times in the second year. Experiment 1 and 2 were pooled as experiment 3. Cultivars and the time of data recording were considered as main or primary and secondary Finally respectively. There was not any difference between resistance of cultivars in experiment 1 and 2, whereas highly significant difference was expressed after pooling of experiments1 and 2. The results from the paired t-test showed that plant cultivars were relatively immune when farm was under water stress. The intensity of damage was decreasing when plants were growing up with age. With regards to the results, it is exteremely recommended that irrigation of alfalfa farms should be restricted to make water stress. This matter causes reduction in the use of pesticide or no usage at all. Since alfalfa plants have usually a low yield of forage in the fist year of seeding only so, this recomendation is useful for second year and following years.