Evaluation of bean cultivars resistance to two spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae) under field conditions

Two-spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae) is one of the most important damaging pests to bean farms. In order to reduce these damages, farmers are forced to spray their fields several times. One of the best methods to reduce pest damages is using of resistant cultivars. In addition to tolerance to the pests and reduction of spraying and consequently reduction of environmental pollutions, this method can also have benenefit of higher yield. In this research,bean cultivars resistance to two- spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae) in field conditions evaluated.

In order to study and evaluate resistance of eight cultivars (including: Sadri, Shokufa, Akhtar, Khomein, Dorsa, Kusha, Darakhshan and Pak) and two lines (21191 and 31169) of bean to two-spotted spider mite during two successive farming years of 2015 and 2016. An experiment was conducted in the form of split plots design in time, in National Research Bean Center of Khomein city. This experiment was performed by observational method with leaves’, stems’, pods’ and bushes infestation to two-spotted spider mite and comparing them with the control and the evaluation of their yields. The statistical population included 10 genotypes of bean. This experiment was carried out in four replications in a field with a size of 23 × 26 m in a split plot arrangement based on a randomized complete block design. Ten genotypes were tested against two-spotted spider mite on leaf, stem, pods, plant, and their grain yield by spray treatment. In each plot, 30 samples were prepared. The data were analyzed by SAS software. The comparison of the mean of infestation of the cultivars and the sampling time by Duncan's test and the comparison of the mean yield by Tukey HSD test was performed.

Infestation in the stems of bean began in two consecutive years on 12 August every year and peaked on the 22 of August. The highest amount of stem infestation in two years was related to Darakhshan cultivar and Dorsa and Line 21191 had the least infestation in this regard. Infestation in pods of beans began in year 2015 on 26th of August and in 2016 year on the 21st of August. But in two consecutive years, the peak of pod infestation was on 16th of September. Darakhshan, Sadri, Khomein cultivars were identified as susceptible cultivars to the mite and the cultivars Dorsa, Kusha and Line 21191 as more resistant cultivars in this regard. Beginning of infestation in bushes in both years was 20 September and the peak of them occurred on 30 September. Results showed that the amount of infestation of experimental cultivars and lines to two-spotted spider mite was significantly different. These differences were related to the beginning of infestation and yield. Means comparison showed that Darakhshan, Akhtar and Khomein were sensitive to the pest but line 21191 and Kusha cultivar as chiti bean cultivars, Dorsa as a White bean cultivar, and line 31169 as a Red bean have more resistance to two-spotted spider mite and have acceptable yield in comparison with other experimental cultivars. The combined analysis of the data two yearly showed that the effect of year on the grain yield was significant, which was probably due to the uneven atmospheric rainfall, exposure to light, or under the influence of environmental stresses over two years. Also, the interaction of year and cultivar was not significant that it is showed the same response of the cultivars to the pest in the two years of the experiment.

In general, the results of the present study showed that Dorsa, Kusha and line of 21191, as compared to Darakhshan, Chiti of Khomein, showed more resistance to the populations of two-spotted spider mite in field conditions that the most important causes of these results cases such as genotype, vegetation type and date of mite infestation can be attributed. Therefore, in order to prevent continuous spraying in bean fields and to obtain optimum yield, it is recommended that the line 21191 (introduced in 2016 as Ghaffar cultivar) and Dorsa and Kusha cultivars to be used. Also, Dorsa cultivar as white bean cultivar, line 21191 (Ghaffar cultivar) as chiti’s bean, and line 31169 (which was introduced as Yaghut ​​cultivar in 2016) as a red bean, resistant cultivars to two-spotted spider mite was designated in this study. So this research can be very helpful and efficient for improving yield and reducing the use of pesticides in the bean fields.