Melting-flesh peaches produce large amounts of ethylene, resulting in rapid fruit softening at the late-ripening stage. In contrast, stony hard peaches do not soften and produce little ethylene. The indole-3-acetic acid (IAA) level in stony hard peaches is low at the late-ripening stage, resulting in low ethylene production and inhibition of fruit softening. To elucidate the mechanism of low IAA concentration in stony hard peaches, endogenous levels of IAA and IAA intermediates or metabolites were analysed by ultra-performance liquid chromatography-tandem mass spectrometry. Although the IAA level was low, the indole-3-pyruvic acid (IPyA) level was high in stony hard peaches at the ripening stage. These results indicate that YUCCA activity is reduced in ripening stony hard peaches. The expression of one of the YUCCA isogenes in peach, PpYUC11, was suppressed in ripening stony hard peaches. Furthermore, an insertion of a transposon-like sequence was found upstream of the PpYUC11 gene in the 5'-flanking region. Analyses of the segregation ratio of the stony hard phenotype and genotype in F1 progenies indicated that the transposon-inserted allele of PpYUC11, hd-t, correlated with the stony hard phenotype. On the basis of the above findings, we propose that the IPyA pathway (YUCCA pathway) is the main auxin biosynthetic pathway in ripening peaches of 'Akatsuki' and 'Manami' cultivars. Because IAA is not supplied from storage forms, IAAde novo synthesis via the IPyA pathway (YUCCA pathway) in mesocarp tissues is responsible for auxin generation to support fruit softening, and its disruption can lead to the stony hard phenotype.

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Peach (Prunus persica) shoots were artificially inoculated with stone fruit bacterial spot bacteria (Xanthomonas arboricola pv. pruni) to evaluate varietal differences in peach genetic resources for their susceptibility to this disease. Current shoots of cultivars/selections were wounded, a bacterial suspension was injected by a syringe attached to multiple needles, and lesion length was measured a few months later. Inoculation was carried out in May, June and July with two concentrations of bacterial suspension: 10 6 cfu·mL −1 or 10 8 cfu·mL −1 . Although the effect of inoculation time was not significant and the effect of inoculum concentration was significant, inoculation in June at a concentration of 10 8 cfu·mL −1 was the most suitable treatment. Among 69 cultivars/selections tested, there was no immune cultivar, however; there were varietal differences in susceptibility to bacterial spot. 'Nishiki' and 'Mochizuki', two cultivars for canning use, 'Chimarrita', a Brazilian cultivar, and 'Tsukikagami', a table peach cultivar, were relatively resistant and may be useful sources for breeding aimed at disease resistance.

A major goal of peach breeding programs in Japan is to develop cultivars with lower chilling requirements than the leading cultivars. Low-chill cultivars can be grown in subtropical as well as temperate regions. We investigated the chilling requirements (chill units; CU), heat requirements (growing degree hours; GDH), and blooming dates of 7 leading Japanese peach cultivars, 3 subtropical low-chill cultivars, and a promising new selection, Momo Tsukuba 127. In general, the CU of the 7 leading cultivars were higher than those of the 3 subtropical cultivars and Momo Tsukuba 127. The chilling and heat requirements were determined for the 3 leading high-chill cultivars ('Akatsuki', 'Hikawahakuhou', and 'Kawanakajimahakutou'), the low-chill cultivar 'Okinawa 1', and Momo Tsukuba 127 during 4 seasons at a single location. The CU for 'Okinawa 1' and Momo Tsukuba 127 were significantly lower than those of the three high-chill cultivars. Because Momo Tsukuba 127 had lower chilling requirements than the 7 leading peach cultivars but higher chilling requirements than the subtropical cultivars, we classified this new selection as a mid-chill variety. We used the CU and GDH, along with local temperature data, to estimate the blooming dates of 4 cultivars and the new selection during 11 seasons at one location. Regression analyses showed high correlations between the calculated and actual blooming dates. We also compared calculated and actual blooming dates for the 3 leading cultivars and Momo Tsukuba 127 at between17 and 21 locations per genotype. A total of 25 locations were used, and these were widely spread over the temperate zones of Japan. The correlations between the calculated and actual blooming dates were close to 1:1. Our results indicated that our CU and GDH values, along with actual temperature data, could be used to reliably estimate the blooming dates of the genotypes. Because of its lower chilling requirements, the new selection, Momo Tsukuba 127, bloomed 7 or more days earlier than the leading peach cultivars in this study.