**4. Discussion**

The quantity and type of the resistance of common eggplant CVS with three resistance categories, including antixenosis, antibiosis, and tolerance, were investigated to *Myzus persicae* in the present study. Experiments originated with fourteen eggplant CVS in the screening test to arrange resistant categories. Screening tests save time and increase the accuracy in the main experiments. Based on the obtained results from the screening test, three relatively resistant ('Long-Green', 'Ravaya' and 'Red-Round') and two susceptible CVS ('White-Casper' and 'Pearl-Round') were selected. Singh et al. [36] found that seven eggplant CVS had diverse resistance and susceptibility to *Tetranychus urticae* (Koch). Also, according to the screening tests, 23 CVS of eggplant were classified into four resistant, relatively resistant, relatively susceptible, and susceptible groups against *Leucinodes orbonalis* Guenee [37].

Our results also showed, in general, there was a significant difference in the performance of *M. persicae* among the five tested eggplant CVS. Based on our findings from the screening test, 'Long-Green' was the most resistant cv. to the *M. persicae*, which was

confirmed in all antixenosis, antibiosis, and tolerance experiments. Although there was not significant difference in the antixenosis test between tested CVS after 24 h, *M. persicae* preferred CV. 'White-Casper' and had less host preference over 'Long-Green' and 'Ravaya' CVS after 24 and 48 h. The host preference of *M. persicae*, like other insect pests, varies according to different plant species [38]. The antixenosis resistance of eight potato [38] and seven cabbage CVS [39] were reported to *M. persicae*. Ahmed et al. [39] declared that chemical and olfactory compounds of CVS caused the attraction of aphids to the preferred hosts. Therefore, differences in host preference of insect pests for the plant species CVS could be due to variations in their chemical and morphological parameters. Although our experiments did not investigate the mechanisms of antixenosis and antibiosis, these compounds may be the main factors in susceptible eggplant CVS for attracting *M. persicae*.

The antibiosis resistance of eggplant CVS, measured as significant effects on the growth, survival, and reproduction of *M. persicae*, was also obtained in the present study. It was used to assess variations in the resistance of different CVS of a plant and to predict the population of pests [40–42]. In the present study, the developmental time (d) of *M. persicae* on the cv. 'Long-Green' with a mean of 4.33 d was significantly longer than other CVS. Furthermore, the highest and lowest intrinsic rates of population increase (rm) were seen on the most susceptible CV. 'White-Casper' (0.383 d−<sup>1</sup> for) and the most resistant CV. 'Long-Green' (0.265 <sup>d</sup>−1), respectively. In the study of Ahmed et al. [25], the intrinsic rate of population increase (rm) and the developmental time (d) of *M. persicae* had a significant difference for seven cabbage CVS. Along with antixenosis resistance, the significantly different rm value of *M. persicae* was also documented on six commonly produced potato cultivars by Mottaghinia et al. [43]. In general, the quality of the host plant can be the main reason to prefer different CVS by aphids and an important factor in the antibiosis resistance [44,45].

In the evaluation of the tolerance category, tested eggplant CVS showed significantly different reactions, based on plant growth parameters containing height and fresh and dry weight, after twenty-one days of infestation by *M. persicae*. Some of them, such as 'Long-Green', indicated significant tolerance, whereas some others, such as 'White-Casper', had less ability to compensate for aphid damage. During the genetic-based phenomena tolerance, plants can continue to grow despite the presence of a specific population and damage of the pest [12,21]. The tolerance existed in some eggplant CVS based on significant differences in their growth parameters. The eggplant tolerance was also investigated by Khan and Singh [46], in which 38 genotypes from 192 tested genotypes were tolerant against *L. orbonalis.*

In the present study, significant differences were supposed between resistant mechanisms of fourteen eggplant CVS against *M. persicae*. According to our observations, CV. 'Long-Green', which presented high resistance against *M. persicae*, had a smaller leaf area than others. Several morphological traits, including plant surface trichrome or epidermal tissue stiffness, may influence host acceptance by aphids [47]. For example, morphological characteristics of eight eggplant CVS had significant effects on the preference of silver whitefly, *Bemisia tabaci* (Gennadius) [48]. Therefore, such characteristics may be the reason why *M. persicae* did not prefer CV. 'Long-Green'.
