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We report the accurate determination of the allelic configurations of a total of eight new citrus tetraploid hybrids by means of SSR analysis, coupled with capillary electrophoresis, and PCR based dosage effects. Tetraploid hybrids were spontaneously obtained from different interploid crosses (2x × 4x) between diploid ‘Femminello’ lemon and the allotetraploid somatic hybrid (2 n = 4x = 36) ‘Key’ lime + ‘Valencia’ orange, and between diploid ‘Wilking’ and ‘Fortune’ mandarins and an autotetraploid ‘Dancy’ mandarin (2 n = 4x = 36). To understand the opportunity to employ them in further backcross programs, the cytological mechanisms underlying their ploidy level were unambiguously determined using six SSR primers. PCR conditions were optimized and skewness in template/product ratios were verified. Tetraploid allelic configurations were determined from PCR based dosage effects using electropherogram peak heights to estimate the copy number per allele. In all the tetraploid hybrids we found out that diploginy (2 n eggs) has occurred, contributing the extra haploid genome in the tetraploids. According to the marker genotypes, it was further inferred that the 2 n eggs in ‘Femminello’ lemon resulted from first division restitution (FDR), while in ‘Wilking’ and ‘Fortune’ mandarins 2 n eggs occurred in second division restitution (SDR). These new genotypes, with their improved genetic female background, can be therefore considered very valuable in our citrus genetic improvement program as pollen donors in backcrosses suitable to eliminate negative traits. [ABSTRACT FROM AUTHOR]

A collection of 18 accessions of sour orange (Citrus aurantium L.) coming from Sicily and other countries was investigated by two polymerase chain reaction (PCR)-based DNA marker technologies. Ten inter-simple sequence repeat (ISSR) primers and fifteen randomly amplified polymorphic DNA (RAPD) primers were used to identify and to evaluate the genetic variability and relationship of accessions. A total of 111 ISSR and 145 RAPD amplified fragments were used to estimate the Dice's coefficient of similarity for cluster analysis using a unweighted pair-group method using an arithmetic averaging (UPGMA) algorithm. The genetic relationships identified using ISSR and RAPD markers were highly concordant, such that the correlation between ISSR and RAPD genetic distance (GD) estimates was r = 0.93. The ISSR and RAPD analysis of 18 sour orange accessions found a high grade of genetic diversity in foreign accessions, while a low variability was detected in local accessions. Sicilian accessions could be grouped in two distinct clusters, including indistinctly plants from three origin regions. Some markers could be linked to the different growing areas. The ISSR and RAPD molecular reference system seems to be suitable for a fine identification of tightly related plants and the obtained results can form the basis for future setting up of Citrus rootstock genetic improvement projects. [ABSTRACT FROM AUTHOR]