Journal of Nuts ():-, ISSN: - Xenia in Almonds: Pollen Source Effect on Characteristics of Some Iranian Late-Blooming Almonds and their self-Incompatibility S. Alizadeh Salteh * , K. Arzani . Department of Horticulture, University of Tabriz, Tabriz, Iran . Faculty of Agriculture, Tarbiat Modares University, Tehran, Iran Received: August Accepted: October Abstract The objective of this experiment was evaluation of self-compatibility and identification, introduction and selection of late flowering genotypes and later as cultivars are very important for Iranian almond industry. This experiment was carried out in order to determine the best pollinizer for two commercial almond cultivars, 'Shahrood ' and 'Shahrood '. Applied pollinizer cultivars were included pollen from 'Shahrood ', 'Genco', 'Tuno', '-' and 'Super-nova' that were applied on 'Sharood ' mother trees, and 'Shahrood ', 'FeilipCeo', 'Tuno', '-' and 'Super-nova'. Results showed no fruit formation in non-pollinated and self-pollinated flowers. Although, results from cross pollination using pollen from other cultivars showed higher fruit set using pollen of 'Genco' for 'Shahrood ' , and '-' for 'Shahrood ' cultivars. Samples were collected using pollinated flowers for further microscopic examinations. Field and microscopic examination of pollen tube growth in the style confirmed above results. The quantitative traits of fruits obtained of some known almond hybrids were assessed in order to evaluation of this phenomenon which known as xenia. The recorded traits were length (L), width (W), thickness (T) of fruits and seeds, and W/L and T/L ratios. Keywords:Almond, Controlled pollination, Pollen tube growth, Self-incompatibility, Xenia. Introduction Almond (Prunus amygdalus Batsch. Rosaceae, n=) is an economically important nut tree particularly in the Mediterranean basin. Due to low chilling requirement and early flowering in spring, almost all of almond cultivars are damaged by delayed spring frost damage. So identification, introduction and selection of late flowering genotypes and later as cultivars are very important for Iranian almond industry. In addition most commercial almond cultivars are self- incompatibility (SI) system (Socias I Company and Alonso, ), resulting in the arrest of pollen tube growth in the middle third of style (De Nettancourt, ) and for a commercial fruit set of or higher, pollinizers are required (Kester and Griggs, ). The effect of self and cross pollination on pollen tube growth and embryo sac development has been studied by Pimienta and Polito (). SI is a property of many plants and in most cases is determined by a single multi allelic locus, the s locus. If the alleles expressed at this locus in the pollen grain both match the corresponding alleles in the pistil, the pollen grain will be recognized as incompatible. In Iran, almond is planted in the cold and semi-cold regions and in out of total provinces. In order to make a crossing in almond, one of the processes followed is emasculating flowers before anthesis (removing stamens, petals and part of the sepals, using the finger-nails or a small pair of scissors) and subsequently pollinating the stigma. Although damages produced in the flower, very acceptable fruit set can be achieved, but usually lower than the fruit set obtained by natural pollination (De Nettancourt, ). In almond, the majority of the important production characters of the tree viz. growth, flowering and fruit characters are quantitatively inherited (Grasselly and Crossa-Raynaud, . Kester et al., () observed high heritability values for nut size, kernal size and weight. Dicenta et al. () worked out the heritability values for different characters by regression and variance component methods which estimate heritability in a broad sense. There are numerous methods that reported results for compatibility or incompatibility tests between and within cultivars including; controlled pollination tests, pollen tube growth tests, pedigree examination, stylarribonuclease detection on isoelectric focusing (IEF) gels and PCR based S-allele. Each of the methods has an advantage and disadvantage but because of estimate of orchard performance by controlled pollination test, it is recommended for determination of the best pollinizers (Ortega and Dicenta. ). * Corresponding author: E-mail: s.alizadeh@tabrizu.ac.ir