First report of damage from apple rust mite, Aculus schlechtendali in Iran (Short report)

Fruit russeting is one of the important symptoms affecting marketing of apple (Malus × domestica Borkh.) fruits. The study had been conducted in Semirom region, Iran, in 2019 showed that one of casuals of fruit russeting is stemend russeting caused by yeastlike fungi Aureobasidium sp. (Heidarian et al., 2020). Easterbrook and Fuller (1986) reported apple rust mite, Aculus schelchtendali Nalepa (Acari: Eriophyidae) as a causative of russeting on apple fruits. In some orchards of Semirom region, in addition to two common cultivars (Red Delicious and Golden Delicious), several other cultivars (including GolabeIsfahan, GolabeKohanz, Miracle, Granny Smith and Fuji) were also cultivated. Miracle is one of the apple cultivars was recently introduced to the country and its cultivation area has been increased. This cultivar has export value and a high marketability due to its desirable color. During the study on the causative agents of fruit russeting in 2017 and 2018, some rusted fruits of Miracle cultivar were found, with similar symptoms to apple rust mite. Infested leaf and fruit samples were collected, and their microscopic slides were prepared in the laboratory after clearing the mites. To check possible infestation of different apple cultivars to the mite, their leaf and fruit samples were collected and compared with the typical symptoms of its damage. Specimens of the mite were identified by the third author as Aculus schlechtendali Nalepa (Acari: Eriophyidae). In Iran, apple rust mite was reported firstly by Sadeghi Nameghi (1995) from Mashhad on apple leaves. However, this is the first report of the mite as the causing agent of fruit russeting in Iran. Examination of the infested fruits showed that the damage appears as russeting around the calyx which gradually covers the entire surface of the fruit to varying degrees. Moreover, feeding of the mite on underside of the leaves causes browning of the leaves in summer (Figure 1). Generally, damage intensity and fruit russeting from apple rust mite is related to population density of the mite, cultivar and plant age (Easterbrook and Fuller, 1986). In the present study, damage of apple rust mite was found only on Miracle cultivar. Regarding increasing of cultivation area of this cultivar in some apple orchards around the country, it is necessary to be careful for possible increase of population density of apple rust mite, because the mite, in addition to direct damage, could reduce marketability of the cultivar, due to the occurrence of fruit russeting.