Ethylene and expansin biosynthesis related genes polymorphism in local apple (Malus domestica Borkh.) cultivars from VIR Collection of plant genetic resources

At Pushkin and Pavlovsk Laboratories of the N.I. Vavilov All-Russian Institute of Plant Genetic Resources (VIR) a diverse collec tion of local apple cultivars is maintained. Some of the cultivars are widely used in breeding programs for their ecological plasticity, increased adaptation to abiotic stress and disease resistance, still there have been no large-scale studies of these local cultivars for fruit storage ability. Fruit softening during storage is an important problem for apple production. Retention of desirable firmness after prolonged storage is one of the key requirements for new apple cultivars. Expansin and ethy lene biosynthesis related genes are known to be involved in control of fruit softening in apple, and gene specific molecular markers have been reported. In this study the polymorphism and allelic configuration of ethylene and expansin biosynthesis related genes Md-ACS1, Md-ACO1 and Md-Exp7 involved in control of fruit softening in 87 local apple cultivars from VIR Collection of Plant Genetic Resources were analyzed. PCR markers Md-ACS1, Md-ACO1 and SSR-marker Md-Exp7 were used in the study. The allele frequencies in the collection generally coincided with the data from previous studies. Md-ACS1 allele 2 associated with reduced ethylene production was found only in three local cultivars, while all the studied local cultivars were heterozygous for the Md-ACO1 locus, as well as most modern Russian apple cultivars. Half of the studied local cultivars were heterozygous for Md-Exp7 (198 : 202). Thirteen local cultivars with rare Md-Exp7 alleles (206, 210 and 212) were detected. No association was found between the Md-Exp7 genotype and the cultivars’ maturation time. The obtained results can be used for additional evaluation of the cultivars’ potential for breeding.

The calculation of recombination frequencies in crosses of allogamous plant species with applications to linkage mapping

SummaryThe recombination frequency (r) between two loci defined by conventional or molecular markers can be estimated by solving proper Maximum Likelihood equations. These are based on expected and observed marker class frequencies in the progeny of a cross, and are specific for each allelic configuration of the parents(1). In a cross between two diploid parents up to four different alleles, besides a null allele, can be detected at one locus. This defines in each parent, considering a locus A, nine basic allelic configurations based on two allelic marker fragments(Ai/Aj), one single marker allele and a null allele (Ai/AO), or just null alleles (AO/AO). With respect to two loci the consideration of all possible diploid allelic configurations in the parents of a cross allows the detection of 21 different expected marker class distributions producing estimates of r in the progeny. General formulas for calculating the ML equations and the corresponding information functions have been developed for the 21 marker class distributions. Simplified formulas have been also derived and the relative efficiency of the information functions compared. As expected, in the majority of cases, allelic marker configurations give more precise estimates of linkage values than single marker configurations. A method for the construction of linkage maps based on two point estimates, linkage subgroups and allelic bridges is presented. The method is an improvementon an original proposal by Ritter et al.(1990).

ON THE DIVERGENCE OF ALLELES IN NESTED SUBSAMPLES FROM FINITE POPULATIONS

ABSTRACT Within-population variation at the DNA level will rarely be studied by sequencing of loci of randomly chosen individuals. Instead, individuals will usually be chosen for sequencing based on some knowledge of their genotype. Data collected in this way require new sampling theory. Motivated by these observations, we have examined the sampling properties of a finite population model with two mutation processes and with no selection or recombination. One mutation process generates new alleles according to an infinite-alleles model, and the other generates polymorphisms at sites according to an infinite-sites model. A sample of n genes is considered. The stationary distribution of the number of segregating sites in a subsample from one of the allelic classes in the sample conditional on the allelic configuration of the sample is studied. A recursive scheme is developed to compute the moments of this distribution, and it is shown that the distribution is functionally independent of the number of additional alleles in the sample and their respective frequencies in the sample. For the case in which the sample contains only two alleles, the distribution of the number of segregating sites in a subsample containing both alleles conditional on the sample frequencies of the alleles is studied. The results are applied to the analysis of DNA sequences of two alleles found at the Adh locus of Drosophila melanogaster. No significant departure from the neutral model is detected.