“Floral Primordia Necrosis” Incidence in Mixed Buds of Japanese Pear (Pyrus pyrifolia (Burm.) Nakai var. culta) ‘Housui’ Grown under Mild Winter Conditions and the Possible Relation with Water Dynamics

Abstract

The effects of global warming have been observed in several crops as changes in temperature-dependent processes, such as dormancy in perennial fruit trees. We exposed potted Japanese pear 'Housui' plants to 600 chilling hours (CH) below 7.2°C, which is below the theoretical requirement. Such low chilling accumulation was initiated at different times (three treatments) and carried out during four consecutive seasons in order to observe the influence of these factors on the incidence and severity of floral primordia necrosis, water dynamics, phenological, and morphological changes during dormancy in lateral mixed buds, which is comprised of vegetative and reproductive primordia, obtained from the current season's shoots. The submitted amount of chilling temperatures brought about the release of dormancy stage, regardless of seasonal variations in the duration to accumulate 600 CH, but caused a remarkable increase of floral primordia necrosis and a great increase in the number of floral primordia as a consequence of the development of new inflorescences; however, these morphological changes did not increased number of opened flowers because of the progression of floral primordia necrosis. Consecutive seasons of mild winter conditions anticipated the incidence of floral primordia necrosis. The results obtained from magnetic resonance imaging in the buds of plants subjected to low chilling accumulation showed low water mobility and water content especially in scales compared to plants grown under natural conditions. In contrast, increased water mobility and relative content were observed in specific portions of the bud base in treated buds, which was more accentuated in the mixed buds of plants grown for several seasons under mild winter conditions. Moreover, abnormal functional water movement inside dormant mixed buds might result in the necrosis of floral primordia, giving way to the development of new inflorescences.

Study of the Consequences of Global Warming in Water Dynamics During Dormancy Phase in Temperate Zone Fruit Crops

“…The data presented suggest that MRI techniques can be an useful non-destructive and rapid analysis tool of internal anatomical details of tissues or organs, the spatial distribution of water, dynamics and mobility of water (Yamamoto et al, 2010a). Japanese pear plants grown under conditions of sufficient chilling accumulation showed a gradual increase in T2 values in the whole bud, indicating a conversion from bound to free water (Fig.…”

“…After four consecutive seasons of mild winters (CS), buds showed also variations on primordia size especially during heating accumulation (600 CH and 4000 GDH). (Yamamoto et al, 2010a).…”

“…Reduced number of opened flowers, variations on length of pedicels, and differences on flowering stage were observed in buds of plants grown under mild winter conditions. (Yamamoto et al, 2010a).…”

“…Another consequence of low chilling accumulation during dormancy stage is a prolonged and poorly synchronized flowering, which results in poor uniformity of fruit size at harvest (Yamamoto, 2010). Nishimoto et al (1995) cited the value of 750 chilling hours as the requirement in 'Housui' buds, but the amount of 600 hours below 7.2 o C (80% of requirement) brought about the release from endodormancy stage (Yamamoto et al, 2010a). According to Yamamoto (2010), however, abnormalities on floral primordia (partial or total necrosis) and eventual development of new inflorescences, during dormancy progression ( Fig.…”

“…seedlings were detected by acoustic emission coupled with magnetic resonance microscopy, respectively. NMR and MRI has been used to provide details during cold acclimatization and/or dormancy stage control in organs and tissues of several species, such as in dogwoods (Burke et al, 1974), Norway spruces (de Fay et al, 2000), tulip bulbs (Kamenetsky et al, 2003;Van der Toorn et al, 2000b), hybrid poplars (Kalcsits et al, 2009), blueberries (Parmentier et al, 1998;Rowland et al, 1992), grapes (Fennell & Line, 2001;Gardea et al, 1994), peaches (Erez et al, 1998;Sugiura et al, 1995;Yooyongwech et al, 2008b), Japanese pears (Yamamoto et al, 2010a), apples Liu et al, 1993;Millard et al, 1993;Snaar & Van As, 1992), among others.…”