Eco-physiological Traits of a New Wine Grape Cultivar (Vitis ficifolia var. ganebu × Vitis vinifera ‘Muscat of Alexandria’) Puspa Raj Poudel and Ryosuke Mochioka Ikuo Kataoka Kagawa University, Faculty of Agriculture Kagawa University University Farm, Showa, Sanuki Faculty of Agriculture, Miki Kagawa 769-2304 Kagawa 761-0795 Japan Japan Keywords: Grape, growing habit, chilling requirement, endo-dormancy period, irrigation, water relations Abstract The level of moisture and chilling largely affect grape yield and quality. In the present study, the growth dynamics of ‘Kadainou R-1’, a new wine grape cultivar derived from two Vitis genotypes i.e. V. ficifolia var. ganebu and V. vin ife r a ‘Muscat of Alexandria’, was determined under three moisture regimes i.e. wet (0-3.1kPa), medium (3.1-15.54kPa) and dry (>15.54kPa). In addition, the chilling requirements of the same cultivar were investigated. The level of irrigation had dramatic effects on both shoot and root growth of ‘Kadainou R-1’ during the course of the experiment. Shoots on vines maintained under wet condition were 128% and 331% longer than those on vines maintained under medium and dry conditions, respectively. Fresh and dry weight of both root and shoots were found highest in wet conditions followed by medium and dry conditions respectively. Period of endo-dormancy was determined forcing single node cuttings in a growth chamber with the temperature kept at 25±1ºC and with a photoperiod of 16 hours. Unlike its parents, ‘Kadainou R-1’ showed shallow dormancy regardless of the chilling time accumulation. INTRODUCTION Several factors affect yield and fruit composition of grapes. Irrigation substantially increases the rate of photosynthesis (Schultz, 1996). Increases of yield by 2- to 5-fold have been reported by Esteban et al. (2001) under irrigated condition. However, larger amounts of available water have negative effect on quality, mainly due to color losses, low sugar content and acidity imbalances (Cifre et al., 2005). Therefore, knowledge of the mechanisms that regulate plant carbon assimilation and partitioning under different water regimes is of great importance in the area of precision agriculture, since these mechanisms play an important role in the regulation of the fragile balance between grape yield and quality. This knowledge will allow the establishment of physiologically based criteria for irrigation. Similar to other deciduous temperate fruit trees, grapevines exhibit dormancy from early fall and resume growth in the following spring. Dormant grapevine buds have a chilling requirement that is satisfied by exposure to low temperatures. The precise temperature and duration of chilling required for optimum bud break of grapevines are species- and cultivar-specific. However, the chilling requirement of grape is generally thought to be less than that of most deciduous fruit species. Grapevine suffering from inadequate winter chilling exhibit delayed and erratic bud break, decreased shoot and cluster counts per vine, and poor uniformity of fruit development. Fruit yield and compo- sition are affected as a result (Dokoozlian et al., 1995). Chilling, calcium cyanamide, bud scale removal (Iwasaki and Weaver, 1977), and garlic preparations (Kubota et al., 2000) can enhance bud burst in grapevines. The objectives of this work were to compare the growing habit of ‘Kadainou R-1’ under different soil moisture regimes and to determine the dormancy pattern of the same cultivar in comparison with its parents. Proc. XXVII IHC-S1 Plant Gen. Resources Ed.-in-Chief: K.E. Hummer 409 Acta Hort. 760, ISHS 2007 MATERIALS AND METHODS Experiment 1: Quantification of Root and Shoot Growth of ‘Kadainou R-1’ under Three Soil Moisture Regimes, i. e. Wet, Medium and Dry Two-year old, own-rooted plants were grown in a 4.5 L transparent plastic box at the University Farm of Kagawa University in Japan. The soil media consisted of sand, soil and compost in 1:2:1 ratio. The potted grapevines were covered with silver plastic film to allow the roots to grow up to the surface of the boxes, and moved to a greenhouse. The moisture status was maintained at 0-3.1, 3.1-15.54 and above 15.54 kPa for wet, medium and dry conditions, respectively. The moisture status was measured by inserting a tension-meter (Takemura Electric Works, Ltd., Tokyo, Japan) into the soil of each pot. Root and shoot growth of three plants per treatment were recorded every two weeks from the time the pots were transferred to the greenhouse. To quantify the root growth, the new roots appeared at the surface of the transparent plastic box were marked each time and length was recorded. At the end of the experiment, the final fresh and dry weights of roots and shoots were measured. For this purpose, roots and shoots were separated and the fresh weight was measured immediately after separation. Dry weight was measured after drying the shoots and roots in an oven at 70RC for 3 days. Experiment 2: Comparison of Bud Break Patterns of ‘Kadainou R-1’ and Parent Lines To observe the bud break aptitude along the dormant period, single node cuttings (approx.15 cm length) of ‘Kadainou R-1’ and its parents V. ficifolia var. ganebu (Ryuukyuuganebu) and V. vinifera ‘Muscat of Alexandria’ (‘Muscat of Alexandria’) were collected from mature vines at the University Farm vineyards of Kagawa University in Sanuki City, Kagawa, Japan on the first day of every month from September 2004 to February 2005, regardless of the chilling hours accumulated. The temperature was monitored by a thermo-recorder (Real time thermo recorder, Ota Keiki Seisakusho Co., Ltd., Japan) in a ventilated case placed at the vineyards. Total chilling hour (<7°C) accumulated in each month are presented in Table 1. The collected cuttings were planted in a tray (35 cm x 25 cm x 8 cm) containing Kanuma soil (Kumeya Co., Ltd., Japan). Irrigation was provided at three-day intervals. The planted cuttings were kept in a growth chamber with a 16-hour photoperiod at 25±1RC. The light source was provided by cool white fluorescent tubes supplying 30 µmol m-2 s-1. The percentage of bud break was recorded after 4 weeks of inducing the cuttings in growth chamber. Bud break was defined as stage 05 as described by Eichorn and Lorenz (1977) when green tissue beneath the bud scales was first visible. Each treatment was replicated three times and the experimental unit consisted of 10 cuttings. RESULTS AND DISCUSSION Growth Habit The level of irrigation had dramatic effect on both shoot and root growth of ‘Kadainou R-1’ during the course of the experiment. The effect of different soil moisture regimes on shoot growth of ‘Kadainou R-1’ vines is presented in Fig. 1. Shoots on vines maintained in wet conditions were 128% and 331% longer than those on vines maintained in medium and dry conditions, respectively. Similarly, shoots on vines maintained in medium conditions were 259% longer than those maintained in dry conditions. Shoot growth rate was highest in the first week of July but decreased steadily and practically stopped by mid August in vines maintained in wet condition. Vines maintained under medium and dry conditions had the highest shoot growth rate at mid- and the end of September, respectively. Compared to the other two treatments, shoot growth rate of vines under dry conditions was very low but growth persisted until the end of the measurement period. 410 The effect of different moisture regimes on root growth of ‘Kadainou R-1’ vines is presented on Fig. 2. Roots on vines maintained in wet conditions were 152% and 351% longer than those on vines maintained in medium and dry conditions, respectively. Similarly, vines maintained in medium conditions had 230% longer roots than those maintained under dry condition. The highest root growth rate in wet conditions (170.81mm) coincided with the maximum shoot growth rate; both shoot and root growth showed almost the same trend. In medium condition, the highest root growth (95.47 mm) rate period occurred slightly earlier than that of shoot growth. Unlike in wet and medium conditions, root growth rate in dry condition was highest in the second week of June but showed a decreasing trend onwards to mid-September when no root growth was observed (Fig. 2). Fresh/dry weight ratios of shoots in wet, medium and dry conditions were 3.45, 4.10 and 3.73, respectively (Fig. 3). Similarly, the fresh/dry weight ratios of roots in wet, medium and dry conditions were 3.73, 5.28 and 5.10, respectively (Fig. 3). The stomatal closure is the first process occurring in the leaves in response to drought (Cifre et al., 2005). A close, curvilinear correlation between stomatal conductance and net photosynthesis has been described in grapevines. Drought also induces non- stomatal limitations to photosynthesis (Naor and Bravdo, 1997). Moreover, Kriedemann and Smart (1971) also reported that the soil water deficit reduces photosynthesis. These factors may explain the difference in growth of grapevines under different soil moisture regimes. There was a marked difference between fresh and dry weight ratios of shoots and roots under different moisture regimes. Soil water deficits have been reported to yield poor vegetative growth coinciding with smaller berry size and lower total acidity (Pieri et al., 1995). Seasonal Changes on Bud Break ‘Kadainou R-1’ showed the deepest endo-dormancy in December having the lowest bud burst percentage of 13.33 %. Ryuukyuuganebu did not show any rest period since the bud burst was always above 70 % in all months. ‘Muscat of Alexandria’ underwent endo-dormancy during the months of November and December, resuming bud break in January after receiving a certain number of chilling hours (Fig. 4). The mechanism of bud break is not well understood and previous studies have reported conflicting information.