عنوان مقاله [English]
Introduction: Plant resistance to insect pests as a method of pest control in the context of IPM has a greater potential than any other method of pest suppression. Development of crop varieties resistant to insect pests and diseases has been the major research thrust at ICRISAT (International Crops Research Institute for the Semi-Arid Tropics) for sustainable crop production. The most attractive feature of host plant resistance (HPR) is the simplest seed-based technology for which farmers do not need any extra skills concerning the application, and any additional cash investments. Sugar beet root aphid Pemphigus fuscicornis Koch (Hem.: Aphididae) is one of the most important pests of sugar beet, Beta vulgaris L. in many countries. Variability in response to root aphids by commercial varieties is demonstrated by Campbell and Hutchison (1995). Sugar beet variety trials in the western plains region have shown that sugar beet varieties vary greatly in the level of resistance to sugar beet root aphid feeding. Correlative data from these trials in Nebraska, Wyoming and Colorado indicate that varieties being susceptible to root aphids had the yield reductions as much as 30% compared to those varieties with a high level of resistance. Cultivars resistant to root aphid, Pemphigus spp. have been highly successful and the resistance has been stable for more than 30 years in Texas or other areas. Several seed companies have had trouble developing resistant cultivars and even those companies with resistant parental lines required an evaluation of new hybrids.
Materials and Methods: In this research that was carried out during 2010- 2011, the responses of Pemphigus fuscicornis to 12 sugar beet genotypes (19610, OtypeA37.1, Simin2, 19584, Jit13, Polyrave, OtypeA1, Shirin, Zarghan, OtypeC2, Chinock, Branco) were examined under the laboratory conditions. The sugar beet seeds were planted in the field, and plants were grown to 6 true leaf stages, then were transplanted into a peat-vermiculite mix (50:50) in pots. Four young adult aphids were placed in the root mass before placement into the pot. The plants were irrigated weekly and the incubator was set at 20±2ºC and 16 h in the artificial light. Sixty days after root infestation, the aphid populations were evaluated by floating aphids out of the root mass in 20-cm diameter bowls and they were classified as adults and nymphs based on the presence of the sub-genital plate as an indicator of maturity. Therefore, all count data were transformed by log (x+1) before the analysis. Statistical analyses were performed using SAS statistical software (SAS Institute Inc, Version 9.1) and means comparison of treatments were done by Tukey's tests.
Results and Discussion: Sugar beet variety trials in the laboratory conditions have shown that sugar beet varieties vary significantly in the level of resistance to P. fuscicornis feeding. There was a significant difference among aphid population densities with regard to different host plant varieties (F=10.56, df=11, 43., P=0.0001). Out of 12 genotypes, line 19610 was highly susceptible, OtypeA37.1 and Simin2 were susceptible, 19584, Jit13, Polyrave and OtypeA1 were moderately susceptible, Zarghan, Shirin and OtypeC2 were moderately resistance and Chincko and Branco were resistance to P. fuscicornis at laboratory condition. Also, the effect of root aphid infestation on the sugar content of plant showed that, P. fuscicornis significantly decreased the sugar content (F=42.05, df=3, P=0.0001) in Doreti variety at field conditions. So, more than 15 percent of infestation to root aphid at harvest time significantly decreased the sugar content.
Conclusions: Based of the present results, it is concluded that planting of resistant varieties (Chincko and Branco) or moderately resistant varieties (Zarghan, Shirin and OtypeC2) will have a significant effect on reducing the aphid damage in this area. However, it is recommended that these varieties to be examined under greenhouse or field conditions. In this research, screening for resistance has been carried out under laboratory conditions. Laboratory tests are useful to confirm the resistance observed under field conditions. Procedures for infestation and evaluation of resistance under field, greenhouse or laboratory conditions using artificial infestation need to be standardized to breed for plant resistance to this pest. Insecticides have been unsuccessful for controlling root aphid, P. fuscicornis and for chemical control to be effective, a soil drench or systemic action through the sugarbeet plant may be necessary.