Cork spot disorder has affected the fruit of Asian pear since the 1990s and has become serious in recent years with increasingly affected cultivars and areas. The commodity value of affected fruit is greatly decreased, resulting in severe economic losses. Cork spot disorder of pear fruit is a physiological disorder, and the factors responsible are relatively complex. Research on the cause of cork spot disorder is still at an early stage and, thus, further investigations are needed to elucidate the underlying mechanism of the disorder. In this review, current knowledge of the factors associated with the incidence of cork spot disorder in Asian pear fruit is summarized, including fruit growth and development, fruit nutrient status, and environmental factors. Potential preventive measures and priorities for future research are outlined.

Asian pear plays an important role in the world pear industry, accounting for over 70% of world total production volume. Commercial Asian pear production relies on four major pear cultivar groups, Japanese pear (JP), Chinese white pear (CWP), Chinese sand pear (CSP), and Ussurian pear (UP), but their origins remain controversial. We estimated the genetic diversity levels and structures in a large sample of existing local cultivars to investigate the origins of Asian pears using twenty-five genome-covering nuclear microsatellite (simple sequence repeats, nSSR) markers and two non-coding chloroplast DNA (cpDNA) regions (trnL-trnF and accD-psaI). High levels of genetic diversity were detected for both nSSRs (HE = 0.744) and cpDNAs (Hd = 0.792). The major variation was found within geographic populations of cultivated pear groups, demonstrating a close relationship among cultivar groups. CSPs showed a greater genetic diversity than CWPs and JPs, and lowest levels of genetic differentiation were detected among them. Phylogeographical analyses indicated that the CSP, CWP, and JP were derived from the same progenitor of Pyrus pyrifolia in China. A dissemination route of cultivated P. pyrifolia estimated by approximate Bayesian computation suggested that cultivated P. pyrifolia from the Middle Yangtze River Valley area contributed the major genetic resources to the cultivars, excluding those of southwestern China. Three major genetic groups of cultivated Pyrus pyrifolia were revealed using nSSRs and a Bayesian statistical inference: (a) JPs; (b) cultivars from South-Central China northward to northeastern China, covering the main pear production area in China; (c) cultivars from southwestern China to southeastern China, including Yunnan, Guizhou, Guangdong, Guangxi, and Fujian Provinces. This reflected the synergistic effects of ecogeographical factors and human selection during cultivar spread and improvement. The analyses indicated that UP cultivars might be originated from the interspecific hybridization of wild Pyrus ussuriensis with cultivated Pyrus pyrifolia. The combination of uniparental DNA sequences and nuclear markers give us a better understanding of origins and genetic relationships for Asian pear groups and will be beneficial for the future improvement of Asian pear cultivars.

Asian pear (Pyrus bretschneideri) is one of the most important fruit crops in the world, and its growth and productivity are frequently affected by abiotic stresses. Calcineurin B-like interacting protein kinases (CIPKs) as caladium-sensor protein kinases interact with Ca(2+)-binding CBLs to extensively mediate abiotic stress responses in plants. Although the pear genome sequence has been released, little information is available about the CIPK genes in pear, especially in response to salt and osmotic stresses. In this study, we systematically identified 28 CIPK family members from the sequenced pear genome and analyzed their organization, phylogeny, gene structure, protein motif, and synteny duplication divergences. Most duplicated PbCIPKs underwent purifying selection, and their evolutionary divergences accompanied with the pear whole genome duplication. We also investigated stress -responsive expression patterns and co-expression networks of CIPK family under salt and osmotic stresses, and the distribution of stress-related cis-regulatory elements in promoter regions. Our results suggest that most PbCIPKs could play important roles in the abiotic stress responses. Some PbCIPKs, such as PbCIPK22, -19, -18, -15, -8, and -6 can serve as core regulators in response to salt and osmotic stresses based on co-expression networks of PbCIPKs. Some sets of genes that were involved in response to salt did not overlap with those in response to osmotic responses, suggesting the sub-functionalization of CIPK genes in stress responses. This study revealed some candidate genes that play roles in early responses to salt and osmotic stress for further characterization of abiotic stress responses medicated by CIPKs in pear.