Antibiosis Resistance Of Promising Apple Rootstocks To Woolly Aphid [(Eriosoma lanigerum (Hausm.)] under Environmental Conditions of Karaj in Iran

The woolly aphid [Eriosoma lanigerum (Hausm.)] is an important pest of apple trees. This research was conducted to evaluate the antibiosis resistance of promising apple rootstocks to this pest during 2019 to 2021. Ten selected rootstocks developed from hybridization and open pollination of two local apple varieties, Azaish Isfahan and Morabaei Mashhad, as the female parents and commercial apple rootstocks including M9, M27, B9 were selected as the male parents. The number of aphid colonies in the root, crown, stem and branch was evaluated. Antibiosis resistance indices including, population growth rate, antibiosis, population age structure, cumulative aphid day, exploitable ecological potential and survival were calculated. The data were analyzed in by complete randomized block design and means were compared with Tukey's test. Principal component analysis order to identify unobservable combined factors affecting the resistance mechanism based on indices. Observable values were calculated and cluster analysis method used to group the rootstocks based on the degree of susceptibility. Based on the results of this research, four apple rootstocks named Azop(285), AZ × M9(185), Azop(286) and Azop(386) were the most susceptible and M9op3 was the most resistant to woolly aphid.  Average of population growth rate, antibiosis, age population structure, Aphid day, exploitation ecological potential. and survival indices were 23.90, 0.03, 0.06, 381.46, 801.9, 9.09 and 150.00, respectively. Resistance to apple wooly aphid should be taken into consideration in apple breeding programs and orchard management for sustainable apple production.

Woolly apple Aphid [(Eriosoma lanigerum (Hausm.)], feed on the bark and roots of the apple tree, weakens it and reduces the growth of the tree organs (Yang et al., 2023). Various apple rootstocks have rich genetic resources of resistance to the woolly apple aphid that enables the development of resistant apple cultivars (Moinina et al., 2018). There is always need to develop and release new resistant cultivars to woolly aphid biotypes (Han and Korban, 2010). Antibiosis is a type of plant resistance that includes at least one plant characteristic that affects the biological indices of the pest (Le Roux et al., 2014). This research was carried out to evaluate the level of antibisis resistance in promising apple rootstocks against woolly aphid and to determine morphological characteristics of apple rootstocks related to this type of resistance.
 

This research was conducted in the collection orchard of the temperate fruits research center in Kamalshahr of Karaj in Iran during 2019 to 2021. Ten apple rootstocks were selected from the promising progenies developed from hybridization and open pollination of two local apple varieties including Azaish Isfahan and Morabaei Mashhad as female parents and commercial apple rootstocks including M9, M27, B9 as male parents in the apple rootstocks development programs in temperate fruits research center, Horticultural Sciences Research Institute, Karaj, Iran. Samples of apple woolly aphid colonies were taken, every two weeks, from the beginning of April to mid-November. The root, crown, trunk and branch sections of apple rootstocks were evaluated. Antibiosis resistance indices including bloomber (R), population growth rate (MRCR), antibiosis (ABI), population age structure (PASI), cumulative aphid day (CAD), ecological expolitation potential (EEP) and survival (St) were calculated. Vegetative growth traits of apple rootstocks were measured and recorded. Analysis of variance of data was performed as randomized complete block design and means were compared using Tukey test. Factor analysis was used to identify the unobservable combined factors. Cluster analysis was used to group the apple rootstocks, and canonical discriminatnt function analysis (LDA) was used to evaluate the accuracy of clustering of apple rootstocks using IBM SPSS Statistics 27.0.1.0 software.
 

Cophenetic correlation coefficients between the Euclidean distance matrix and the dendrogram output matrix obtained from cluster analysis was equal to 0.83 which indicated the acceptable grouping of apple rootstocks using antibibiosis resistance indices. Four apple rootstocks; Azop(285), AZ × M9(185), Azop(286) and Azop(386) were the most susceptible rootstocks to woolly aphid. Average bloomber, population growth rate, antibiosis, population age structure, cumulative day aphid, ecological exploitation potential and survival were 23.90, 0.03, 0.06, 381.46, 9.801, 9.09 and 150, respectively. Comparison of demographic parameters including population age structure index and seasonal index of effective aphid day showed that these indices affect the dynamics of aphid population on apple rootstocks. The minimum value of blumber index in the resistant rootstock, M9op(387), was 0.76 and the maximum in the susceptible rootstock Azop(285) was 34.16.
The average root length had the greatest effect on the variation in the relative establishment rate of apple wolly aphid (Latifian et al., 2023). These authors reported that this trait had significant effect on the bloomber and ecological exploitation potential indices. The relation between this trait and bloomber and ecological exploitation potential indices was negative, and with increase in root length the bloomber and ecological exploitation potential decreased, therefore, the antibiosis resistance level in the apple rootstocks increased. Antibiosis resistance to woolly aphid is a valuable finding and should be taken into consideration in apple breeding programs and apple orchard management for sustainable apple production.