Evaluation of the Resistance of some Commercial Cultivars and Breeding Lines of Wheat, Triticum aestivum L., to the Russian Wheat Aphid, Diuraphis noxia (Mordvilko)

The Russian wheat aphid, Diuraphis noxia (Mordvilko), is an important pest of cereal, particularly wheat (Triticum eastivum L.) and barley (Hordeum vulgare L.) in many countries. It can also be damaging as a vector of plant pathogenic viruses including Barley Yellow Dwarf Virus (BYDV), Barley Mosaic Virus (BMV), and Sugarcane Mosaic Virus (SMV). Also, a yield loss of as much as 60% has been reported in wheat in years of heavy infestation. Utilization of synthetic pesticides is a common method for control of D. noxia, but the continuous application of such chemicals caused several side-effects such as environmental hazards, insect pest resistance and the outbreak of secondary pests. Therefore, other control methods need to be investigated for effective control of the pest. The use of resistant cultivar is an environmentally safe method of insect control and is also less expensive for growers resistance of host plants against herbivore insects may be due to antibiosis. The antibiosis properties of the host plant can reduce the amount of feeding, fecundity and size of the insect. They also can lengthen the development period, and increase the mortality rate. Therefore, the use of plant tolerance for managing D. noxia has received greater emphasis than in other systems. Wheat and triticale lines [×Triti- cosecale Wittmack, a hybrid between wheat and rye (Secale cereale L.)] with tolerant traits or tolerance combined with antibiotic, antixenotic and tolerance traits have been identified.

In the present study, the possibility of existence of resistance in thirty bread wheat genotypes (Tak Ab, Ryzhav, Oohadi, Gaspard, Say Sunz, Alvand, Phishgam, Azadi, Kras Sabalan, Omid, Navid, Sabalan, Mihan, Orum, Zare, SardariHoma, Rasad, Cascogen, Tos, Shahriar, Bezostiya, Azar 2, Bak Kras Roshan, MV17, C-89-7, C-89-12, C-89-15, Zarin and Almot, respectively) and one triticale cultivar that was evaluated at 12th growth stages of the plants. The experiments were carried out in the greenhouse (23±3˚C, 50±10% RH and a photoperiod of 14L: 10D h) and using a completely randomized design. The aphids used in the experiments were provided from the stock colony reared in Department of Plant Protection, University of Mohaghegh Ardebili, (originated from Namin city infested fields). Antixenosis was determined by counting the number of adult aphids attracted to each genotype potted plants at 24, 48 and 72 hours after release. Life tables were constructed based on the method described by Birch (1948) and Meyer et al. (1986). Differences in intrinsic rate of increase (rm) and other life table parameters were estimated by the jackknife method. Before analysis, all data were tested for normality by Kolmogorov-Smirnov method. Statistical differences among means were compared using the Tukey post hoc Honestly Significant Difference (HSD) and Student-Newman- Keuls (SNK) tests at α= 0.05 using the statistical software of SPSS ver. 19.0.

In summary, the analysis of variance of number attracted adult aphids to each genotype indicated that there were no significant differences among genotypes with respect to the number of aphids attracted to them. Antibiosis evaluated in two experiments. In the first experiment, the mean number of aphids among 31 genotypes was significantly lowest on triticale (Juanilo cultivar) (1 aphid) than resistance control (35.2 aphids). In the second experiment, D. noxia intrinsic rate of natural increase (rm) evaluated on four selected genotypes in the first experiment. The highest and lowest rm values were found on Alvand cultivar (0.273 day-1) and Bezostaya cultivar (0.214 day-1), respectively. Intolerance experiment, height and dry weight of seedling between control (no infested plants) and 14 aphids-day infested plants were measured. Proportional dry weight and height changes were significantly different among the genotypes. According to the results obtained in this research, to avoid hazardous chemicals against insect pests of such crops, certain protective or curative procedures could be implied using different non-chemical methods to reduce the pest population and resultant damage. Consequently, our results indicate Kaskogen and Juanilo cultivars had relatively tolerance and antibiotic resistance to Russian wheat aphid, respectively and so it can be used in the IPM of the aphid.

Further experiments under the field conditions will be needed to validate these findings. The study on chemical components of these cultivars which is unsuitable in our lab may further reveal the chemical base of the unsuitability of cultivars Kaskogen and Juanilo.