Fruit development period (FDP), defined as the time between full bloom and maturity, varies greatly in peaches (Prunus persica L. Batsch). It is necessary to develop molecular markers associated with maturity date to extend the harvest season in new peach cultivars. We designed the 260 SSR primer set covering the entire genome of approximately 300 kb to 1 Mb based on P. persica cultivar ‘Mihong’ genome sequence. The SSR markers were used to survey the relationship between the parentages ‘Yumeyong’ and ‘Chiyomaru’ and their offspring cultivars ‘Mihong’, ‘Yumi’, ‘Misshong’ and ‘Soomee’. Male cultivar ‘Chiyomaru and its offspring cultivars ‘Mihong’, Yumi’, and ‘Misshong’ are early and middle maturity cultivars with FDP of 77, 76, 82, and 108 days, respectively, whereas female cultivar ‘Yumyeong’ and its offspring cultivar ‘Soomee’ are late maturity cultivars with FDP of 128 days. Three regions of SSR markers could distinguish between early, middle, and late maturity cultivars. In the early stages of breeding, these markers will be used for marker-assisted selection (MAS) in the parentages ‘Yumyeong’ and ‘Chiyomaru’ and their offspring cultivars.

Prunus persica “Mihong” cultivar is a domesticated white peach that was generated from the crossing between “Yumyeong” and “Chiyomaru” cultivars in the Republic of Korea in 1995. We launched “Mihong” genome sequencing in 2018 and “Mihong” reached to 200 scaffold and 241 Mb sequences using long-read sequencing and Hi-C technology. F₁ populations of ”Kawanakajima Hakuto,” “Mihong,” “Changhowon Hwangdo,” and “Yumi” were developed in NIHHS. These four cultivars were sequenced and assembled using the SOAPdenovo version 2.04. First, we surveyed the SSRs in “Mihong” assembly sequences and extracted the ±300 bp flanking sequences containing SSRs. Second, the assembly sequences of three cultivars were aligned and mapped against “Mihong” ±300 bp flanking sequences using BLASTn (version 2.2.29+). We anticipated the differential length in SSRs among the four cultivars. We sorted the primers with a standard deviation over 4.5 (STEV > 4.5) among the four cultivars. In addition, we surveyed the primers having difference in over 10 bp with “Kawanakajima Hakuto” and “Mihong” for polymorphic markers in the mapping population. All primer pairs were designed to generate amplicons of 150-200 bp in coating SSR regions using primer3 (version 3-2.2.3). We selected 260 SSR markers with a physical distance of average per 1 Mb. These SSR markers accounted for 74% polymorphism in the four genotypes. Finally, a F₁ population of “Kawanakajima Hakuto” and “Mihong” covered 884.5 cM with 465 SNPs and 86 SSRs and this genetic map matched correctly to the HI-C pseudomolecule of P. persica.

The range of peach rootstocks currently available worldwide has increased dramatically in the last few decades. However, peach rootstocks in Republic of Korea still primarily use mainly seeds of different species imported from China. This kind of rootstocks is not ideal for clonal production and uniformity since it is a varietal blend of genotypes with differing physical characteristics. We collected genetic resources of 214 native peaches and determined 156 native peaches for breeding the suitable peach rootstock with easy propagation, uniform growth habit, and the resistance to biotic and abiotic stresses under domestic conditions. ‘PR1’ peach rootstock [Prunus persica (Batsch) L.] was originated from open-pollinated seeds of ‘PHJN0129’ collected in 2001 at Suncheon. ‘PR1’ peach rootstock was preliminarily designated as ‘PH193’ in 2002 and then grafted onto ‘Maotao’ (P. persica) wild peach seedling rootstocks. In Hwasung, three grafted trees were observed from 2005 to 2009 and seen to have the properties of ‘PH193’. In Suwon, one-year- old seedlings were observed from 2010 to 2014 and showed to have the commercial availability of ‘PH193’ when compared with 5 peach rootstocks (Tsukuba No.4, GF677, Nemaguard, Yumyeong, and imported peach seeds from China). ‘PH193’ was finally selected in 2014, owing to its superior seed germination, graft compatibility, resistance to nematodes and crown gall, and low mortality. It was named ‘PR1’ to indicate the first peach rootstock in Republic of Korea and was released for commercial use in 2015. (Grant Number 5896).

FT-IR spectroscopy, combined with multivariate analysis, was used to determine whether 67 different wild and rootstock peach accessions could be discriminated from each other. Genomic DNA was isolated from leaves, and the purified genomic DNA was analyzed by FT-IR spectroscopy in the spectral region from 1800 to 800 cm^-1. FT-IR spectra showed that typical spectral differences existed in the frequency regions of N-H stretching (amide I), C=O stretching vibrations (amide II), and PO₂⁻ ionized asymmetric and symmetric stretching. Principal component analysis (PCA) was able to discriminate three groups. The partial least squares discriminant analysis (PLS-DA) yielded more clear discrimination among the three groups of peach accessions. The FT-IR spectral differences might be directly related to subtle changes in the base functional group and backbone structures of genomic DNA. This technique could provide a research foundation for FT-IR spectral-based rapid diagnosis, selection, and discrimination of peach accessions for rootstock.