Comparison of different classical and molecular methods to identify superior self-compatible almond (Prunus dulcis Mill.) genotypes and evaluation of their traits Asghar Estaji a , Ali Ebadi a , Akbar Ghorbani b and Roghaie Allabakhsh c a Department of Horticulture, Faculty of Agriculture, Tehran University, Shahabbasy Avenue, Karaj 009826, Iran; b Department of Horticulture, Faculty of Agriculture, Urmia University, Sero Avenue, Urmia 009844, Iran; c Department of Horticulture, Faculty of Agriculture, University of Mohaghegh Ardabili, Daneshgah Avenue, Ardebil 009845, Iran ABSTRACT Almond [Prunus amygdalus Batsch syn. Prunus dulcis (Mill.) D.A.Webb] trees are either self- or cross-incompatible, which results in lower fruit set and yields. Flower bagging, fluorescence microscopy, and polymerase chain reaction (PCR) were used to discriminate between self- compatible genotypes obtained from crosses of the self-incompatible female parents (‘121’ and ‘4’) with the self-compatible male parent (‘Tuono’). This study was performed on 80 almond genotypes. The results of this study showed that, in the first cross (‘121’ × ‘Tuono’), genotypes 5, 11, 13, 14, 17, 20, 27, 29, 31, 35, and 38 were identified as being self-compatible and, in the second cross (‘4’ × ‘Tuono’), genotypes 1, 2, 10, 11, 12, 15, 21, 23, 25, 32, 37, 38, and 40 were found to be self-compatible. There were some promising genotypes based on self-compatibility and nut and kernel characteristics; for example, genotype 40 had the highest mean fruit and kernel weights at 2.9 and 1.3 g, respectively. PCR can be used to identify self-compatible genotypes at the juvenile stage. Flower bagging under favourable climatic conditions not only discriminated between self-compatible almond genotypes, but can also be used to measure fruit set percentages. Flower bagging and fluorescence micro- scopy can be used to determine the level of self-incompatibility. Fluorescence microscopy identified self-incompatible genotypes, even under unfavourable conditions. In general, a combination of all three methods is recommended to increase the accuracy of detecting self- compatible genotypes of almond. ARTICLE HISTORY Accepted 5 October 2015 KEYWORDS Almond; Prunus dulcis; self-compatible; fruit-set Almond [Prunus amygdalus Batsch syn. Prunus dulcis (Mill.) D.A.Webb.] is a self-incompatible species that exhibits gametophytic self-incompat- ibility (GSI). GSI is a widespread mechanism to prevent self-fertilisation in flowering plants and to promote out-crossing (Socias I Company, Kester, & Bradley, 1976). Self-incompatibility is one of the most important limitations on fruit set and crop- ping in almond trees. Most almond cultivars are self- or cross-incompatible (Momenpour, Ebadi, & Imani, 2011). Therefore, in commercial orchards, it is necessary to select and grow at least two cultivars with overlapping flowering times that are recipro- cally cross-compatible (Lopez et al., 2004). Self- compatibility in almond occurs because of the S f allele (Socias I Company & Felipe, 1988) that appears to function as a partial stylar mutant, because no stylar S-RNase has been linked to the S f allele (Boskovic et al., 1999). Identification of self-compatible genotypes is essential in almond breeding programmes (Williams, 1970). GSI is con- trolled by a single polymorphic locus that contains at least two tightly linked genes, one specifically expressed in the pistil and the other in the pollen (Kao & Tsukamoto, 2004). The pistil component codes for an S-RNase responsible for inhibiting pollen-tube growth in the style (Boskovic, Tobutt, Batlle, & Duval, 1997). Several approaches have been used to assess the level of self-compatibility in almond. These include measuring the fruit set percentage after flower bag- ging and self-pollination, measurements of pollen- tube growth and, more recently, identification of the S f allele using polymerase chain reaction (PCR) mar- ker techniques. Each has advantages and limitations (Socias I Company, Fernandez, Kodad, & Alonso, 2010). The first results on self-compatibility in almond were obtained by Almeida and Marques (1949) by measuring fruit set percentages after artifi- cial self-pollination. Self-compatible cultivars permit planting of a single cultivar, even in the absence of pollinating insects (Socias I Company et al., 2010). The first studies on almond pollination were based on fruit set and concluded that the cultivars studied were self-incompatible (Tufts, 1919). Consequently, the first results on almond self-compatibility were CONTACT Asghar Estaji a_estaji@ut.ac.ir THE JOURNAL OF HORTICULTURAL SCIENCE AND BIOTECHNOLOGY, 2016 VOL. 91, NO. 1, 36–42 http://dx.doi.org/10.1080/14620316.2015.1110990 © 2016 Taylor & Francis Downloaded by [5.222.235.41] at 22:20 16 March 2016