Historical Changes and Geographical Differentiations in Harvest Season of Japanese Pear Cultivars (Pyrus serotina Rehder var. culta Rehder)

Abstract

Japanese pear (Pyrus serotina Rehder) is said to be native to Japan. So, the wide genetical variations in harvest season are expected to be observed, and in fact, cultivations and utilizations of late maturing cultivars and those for long storage were recorded in some literatures published in the Edo era (the 18th-19th century). But, nowadays, the narrow periods of fruit supply to the market (about 2.5 months in summer and autumn) and the small number of predominant cultivars (4-5) suggest outwardly that Japanese pear may have the narrow variations. So, to reveal the wide variations in native cultivars and to clarify the historical changes of cultivars from the view point of harvest season, the records of the harvest season on 374 native cultivars and 41 bred ones from four related literatures were evaluated.
A harvest season of native cultivar was recorded as an actual time at its native provenance. Therefore, it should be necessary to modify this season into really genetical one, based on the geographical and phenological difference of the harvest season in each cultivar. The modified harvest season of each native cultivar was indicated as the harvest season of one of 41 indicator cultivars (Table 2), comparing the harvest season with those of indicators at the same provenance (Fig. 1). To express a harvest season numerically, full season was divided into 22 harvest classes(-5.0: earliest maturing, 5.5: latest maturing), which were assorted into threegroups (early maturing: -5.0--1.3, mid maturing: -1.2-2.2, late maturing: 2.3 -5.5). Ranges and distributions of harvest seasons were compared in the histogram of cultivars against these classes among three historically divided groups, A, B and C (see the foot note in Table 5) and among nine province groups of native cultivars (Table 1) classified according to their provenances (Fig.3).
Native cultivars indicated the full genetical variations of harvest season from the end of July till the mid of November at the central Japan (Table 2). 43.2 percent of native cultivars were late maturing ones (Fig. 2). Characteristics at the Edo era were a scarcity of early maturing cultivars and an abundance of late maturing ones and those for storage. As compared with the native cultivars, chance seedlings or open pollinated seedlings, found from the late Edo era to Taisho era (1850-1925), showed the higher percentage of early maturing cultivars and the lower percentage of late maturing ones (Fig. 2). The bred ones showed the highest percentage of early maturing ones (Fig. 2). These results suggest that historical changes of cultivars in harvest season are the increase of early maturing cultivars and the decreases of late maturing ones and those for storage, and that the trend of breeding is towards the earliness in harvest season.
The provenances of late and early maturing cultivars were apt to be situated geographically to the specific areas (Fig. 4). Late maturing cultivars were distributed mainly in Kyushu province and to the coast of the Japan Sea. Early maturing cultivars were mainly found in Kanto and Kansai provinces, and were not distributed in Kyushu province, Shikoku province and the north of Toyama prefecture.