J. Japan. Soc. Hort. Sci. 59 (1) ; 29-34 . 1990.
The
Effects
of Several
Photosynthetic
Product,
Rootstocks
and
Kunihisa
Growth
on Photosynthesis,
Distribution
of Young
Mandarin
MORINAGA
and
Fukio
Satsuma
of
Trees
IKEDA
Shikoku National Agricultural Experiment Station, MAFF. Zentsuji, Kagawa-ken 765
Summary
The effects of 14 different rootstocks on leaf photosynthesis, distribution of photosynthetic
product, and growth of one-year-old trees of satsuma mandarin (Citrus unshiu Marc. var.
Sugiyama) were investigated. It was shown that leaves of satsuma mandarin grafted on trifoliate orange strains, such as `Rubidoux', `Pomeroy', and `USDA' showed higher photosynthetic
rates than those on common trifoliate orange (Poncirus trifoliata Raf.) rootstock. However,
`Oba' (Large leaf strain)
, `Barnes', and `sour orange' rootstocks had lower rates. Stomatal
density and ribulose-l,5-bisphosphate carboxylase (RuBPCase) activity in leaves seemed to
be important factors for photosynthetic capacity. Also, the distribution of photosynthetic
product differed among the rootstocks. The greatest value of top-root ratio was measured
in `Rubidoux' trifoliate orange rootstock. Among the trifoliate oranges, tree size on `Rubidoux'
rootstock was greatest and resulted in the highest dry matter production. This was mainly
the result of total photosynthetic capacity of the trees.
been studied.
There is much research on the characteristics of
various rootstocks in relation to enhancement of
fruit quality and the control of tree size, improvement of photosynthetic capacity, and distribution of
photosynthetic product. But, there are very few
studies on the effects of rootstocks on photosynthesis in citrus (19). Therefore, the purpose of the
paper is to clarify the effects of different rootstocks on photosynthetic capacity, distribution of
Introduction
There are many studies of the effects of rootstocks on crop activities. Apparently, selected rootstocks improve physiological functions of crops.
Hozyo and Park studied the effects of rootstock on
photosynthesis (10) and the distribution of photosynthetic product to tuberous roots (11) in grafted sweet potato plants. Takahashi also investigated
the effects of rootstocks on photosynthesis in
young grafted tomato plants (20).
We previously have clarified certain characteristics of photosynthesis by citrus trees in relation to
environmental and intrinsic factors (15, 16). In fruit
tree cultivation, the use of rootstocks can control
tree size and vigor (5, 17). The research of Tukey
(21) is a typical example of such a study. In Japan,
trifoliate. orange is used as a common rootstock in
citrus cultivation. The effects of these rootstocks
on the growth of trees (12), the quality of fruit and
yield (5, 12), water use (4), hormonal balance (18),
and freeze tolerance (3) have been investigated by
many research workers. In citrus, moreover, the
effects of rootstock on alternate bearing (6) and on
activity of vesicular-arbuscular mycorrhiza (9) have
Received
for publication
June
photosynthetic product and growth of satsuma
mandarin trees, with the objective of improving
fruit quality and productivity.
Materials
and Methods
Satsuma mandarin (Citrus unshiu Marc.) scions
were grafted on fourteen 2-year-old rootstocks in
1984. Eight rootstocks of trifoliate orange strains
(Poncirus trifoliata Raf.) were used, `Barnes',
`USDA'
, `Weber-Forset' (W-F), `Pomeroy', `Oba'
(Large leaf strain), `Hiryu' (Flying Dragon),
`Togenashi' (Thornless strain)
, and `Rubidoux'. In
addition, `Shiikuwasha' (Citrus depressa Hayata),
`Cleopatra mandarin' (C. reshni Hort. ex Tanaka),
`sour orange' (C. aurantium L.), `Yuzu' (C. junos
Sieb. ex Tanaka), and `Jagatara' (C. sinensis Osbeck) were also used. Common trifoliate orange
21, 1989.
29
K.
30
MORINAGA
AND
F. IKEDA
was chosen as the standard because it is the major
rootstock in Japan. Photosynthesis of scion leaves,
distribution of photosynthetic product to each organ, and tree growth were investigated in the year
after grafting.
Photosynthesis of single mature leaves on each
of the plants was evaluated using an open gas exchange system (15). Air temperature was 25°C,
relative humidity was 70-80%, intensity of illumination was 80-90klx, and the air flow rate was
2.2-2.6 1/leaf/mm.
For measurements of dark respiration, leaves
were placed in a darkened chamber. Other environmental conditions were the same as for photosynthetic
rate measurements.
The dark
respiration rate was added to the apparent photosynthetic rate to obtain the gross photosynthetic rate.
Extraction and assay of ribulose-l,5-bisphosphate
carboxylase (RuBPCase) were carried out as
described by Yamashita (22) modified from
Friedrich and Huffaker's method (8). Leaves (0.5 g
fr wt) were ground under low temperature with
0.1 g of PVP and 4 ml of 0.2 M TRIS-HC1 buffer
(pH 8.0), containing 10 mM 2-mercaptoethanol.
The homogenates were centrifuged at 30,000 x g
for 10 min, after which the supernatant fractions
were used for assay of RuBPCase activity. RuBPCase activity was measured by incubating 10µl of
a leaf extract at 25°C for 2 min with 10 µmol of
TRIS (pH 8.0), 1 µmol 2-mercaptoethanol, 1 µmol
MgCl2, 2 µmol NaH14CO3 (1 µCi), and 0.2 µmol
RuBP in a final volume of 220 µl. The reaction
was terminated by transferring duplicate 50µl portions of the reaction mixture to counting vials containing
50µl of 10 % trichloroacetic
acid.
Radioactivity was counted in ACS II with a liquid
scintillation spectrometer.
Stomatal density was measured from replicas using S.U.M.P. (Suzuki's Universal Macro Printing)
method. The degree of green in leaves was measured with a colorimeter as Hunter's `a' value.
Results
Rootstocks had significant effects on photosynthesis of satsuma mandarin scion leaves.
Phtosynthetic capacity of trees on `Rubidoux',
`Pomeroy'
, and `USDA' rootstocks increased over
10 % in comparison with those on common trifoliate orange rootstock. On the contrary, pho-
Fig . 1.
Relationship
mata
in different
mandarin
Fig.
2.
satsuma
rootstock
to density
combinations
of sto-
of satsuma
trees.
Relationship
matter
of photosynthesis
weight
of photosynthesis
in different
mandarin
rootstock
of tree
to total dry
combinations
of
trees.
tosynthesis of scion leaves on `Barnes', `Jagatara',
and `sour orange' rootstocks decreased. Especially in sour orange rootstock, photosynthesis was
reduced by 50 % when compared to common
trifoliate orange rootstock (Fig. 1).
The density of stomata showed a positive correlation with photosynthesis (Fig. 1). Leaves on
`Rubidoux' rootstock had the highest density of
stomata.
Total photosynthetic capacity of entire trees also
showed a high positive correlation with total dry
matter weight (Fig. 2).
Rootstocks had no significant effect on the
EFFECTS
OF ROOTSTOCKS
ON PHOTOSYNTHESIS
degree of green in scion leaves (Fig. 3).
RuBPCase activity was positively correlated with
photosynthesis (Fig. 4).
Growth of trees on different rootstocks was considerably influenced by rootstock variety. Trees on
`Rubidoux' rootstock grew most vigorously
, and total dry matter per tree was 92.8 g on the average
in `Rubidoux' trifoliate. With `Togenashi' rootstock, the weight was 33.3 g, in large leaf rootstock the weight was 44.0 g, and in common
trifoliate orange rootstock total dry weight was
69.8 g. Trees on `Rubidoux' trifoliate rootstock
Fig
3.
Relationship
of leaf green
of photosynthesis
of leaf
1.
The
MANDARIN
Fig.
to degree
4.
Relationship
of ribulose-1,5-bisphosphote
ylase activity
to photosynthesis
rootstocks
of satsuma mandarin
effects
of different
31
TREES
grew three times as much as those on `Togenashi'
rootstock (Table 1).
The distribution of photosynthetic product was
also influenced. Trees on `Togenashi' and `sour
orange'
rootstocks,
which showed
graftincompatibility, had a high distribution ratio to
roots. But, trees on `Rubidoux' and `Shiikuwasha'
rootstocks which showed vigorous growth had a
lower distribution ratio to roots (Table 1).
color.
Table
OF SATSUMA
rootstocks
on growth
of satsuma
mandarin
with
tree.
trees.
five
carboxdifferent
K. MORINAGA
32
Discussion
Photosynthesis of scion leaves grafted on various
rootstocks varied in comparison with those on
common trifoliate orange. Since photosynthesis had
a significant positive correlation with stomatal density, this was considered to be one of the most important factors affecting photosynthetic capacity.
Beakbane and Majumder (2) also showed that rootstocks influenced the density of stomata in scion
leaves, and growth was closely related to the density of stomata. Therefore, the density of stomata might be an index related to photosynthesis of
scions. The scion leaves on 'sour orange' rootstock
had the lowest photosynthesis. This was highly
correlated with low density of stomata of leaves,
but graft-incompatibility
may also be a factor
decreasing photosynthetic capacity in this scionrootstock combination.
The extent of green color in leaves (i.e., chlorophyll content) had no correlation with photosynthetic rate. Other factors, other than chlorophyll
content, influenced photosynthesis to a greater
extent.
Photosythetic capacity of scion leaves showed a
positive correlation with RuBPCase activity. Consequently, enzymic activity influenced photosynthesis. RuBPCase activity is also correlated with
photosynthetic capacity in other crops (14).
Barden and Ferree (1) reported that rootstocks
of apple trees did not influence photosynthesis of
scion leaves. In citrus trees, however, rootstocks
did influence photosynthesis of scions. It was assumed that an increase or decrease in photosynthesis was related to morphological factors, such as
stomata! density, or to biochemical factors such as
RuBPCase activity.
Trees on `Rubidoux' rootstock grew most
vigorously. But, trees on `Pomeroy' and `W-F'
rootstocks which had photosynthetic rates similar
to those on `Rubidoux' rootstock showed less
growth than those on `Rubidoux' rootstock. It is
suggested that this is due to high differentiation of
leaves having high photosynthesis on `Rubidoux'
rootstock. Trees on `Rubidoux' rootstock had more
leaves with high photosynthesis and a larger total
leaf area. As a result, the trees produced more total photosynthetic product per tree than those on
other rootstocks. Photosynthetic capacity was an
excellent prediction parameter for selection of su-
ANDF. IKEDA
perior rootstocks.
In some rootstock studies of citrus (5,17), trees
on `Rubidoux' rootstock grew more vigorously and
had a higher yield/canopy volume among trifoliate
orange rootstocks. These data agreed with the
present results. It is desirable to combine the scion
with rootstock which differentiates more leaves
having high photosynthetic rates.
As mentioned in results, different rootstocks influenced the distribution of photosynthetic product.
The ratio of top-root (T-R) dry matter was the
greatest on `Rubidoux' rootstock, 1.17. The ratio
in common trifoliate orange rootstock was 0.67,
and in `Togenashi' rootstock, 0.39. The cause of
this difference is not clear from these experiments,
but it is supposed that the sink-source relationship
(13) in trees is affected by changing rootstocks.
The function of the root as a sink decreases with
growth of roots on rootstocks having a high T-R
ratio, consequently the sink function of the top
part increases relatively. Since trees having a high
T-R ratio have a higher top part and less root, the
root is considered to have high physiological functions and activities. Accordingly, it is suggested
that rootstocks influence the distribution of photosynthetic product. Syvertsen and Graham (19)
showed that hydraulic conductivity of roots was
positively correlated with CO2 exchange rates of
leaves in citrus. Thus, the functions and activities
of roots also influence photosynthetic capacity and
distribution of trees.
It is clear that differences among rootstocks influence phtosynthetic rates and hence growth and
distribution of photosynthetic products. Consequently, the effect on photosynthesis and distribution of photosynthetic product in trees should be
considered as an important selection factor for
rootstocks.
In this study, the relationship between rootstock
and fruit set was not investigated since one-yearold trees were used. Thus, this relationship should
be studied in the future.
Acknowledgment
The authors express their sincere thanks to Prof.
Irwin P. Ting, University of California, Riverside,
Department of Botany and Plant Sciences, for his
critical reading of the manuscript.
EFFECTS
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K. MORINAGA
34
AND
F. IKEDA
異 な る台木 に おけ る カ ン キツ若 木 の光 合 成,分 配 お よび樹 体 生 育 の 相 違
森 永 邦 久 ・池 田 富喜 夫
四 国農業 試験 場765香
摘
ウ ン シ ュ ウ ミカ ンの 若 木 を用 い,14種
類 の 台 木 を変
え た場 合 の 光 合 成 速 度 の 差 異 な ら び に 樹 体 の 生 育 や 分
配 率 の 変 化 を検 討 し そ の 差 異 の 原 因 に つ い て考 察 し た.
台 木 に よ る 光 合 成 の 差 異 を み る と,普 通 系 カ ラ タ チ
川県善 通寺 市
要
と共 に,リ
ブ ロー ス ー1.5一二 燐 酸 カ ル ボ キ シ ラー ゼ 活 性
な ど 生 化 学 的 要 因 の 差 異 が 考 え られ た.
ま た 台 木 を変 え る こ とに よ り樹 体 の 生 育 は か な り異
な り,`ル ビ ドー'台 が 最 も 旺 盛 な 生 育 を示 し た.こ
れ
と比 較 して 向 上 し た 台 木 は,`ポ メ ロ イ',`USDA',`ル
は 高 い 光 合 成 能 力 を持 つ 葉 が 多 く分 化 し,樹 体 の 総 光
ビ ドー'な ど で あ っ た.逆 に 低 下 し た 台 木 は,`大 葉',
`バー ネ ス'
,`サ ワー オ レ ン ジ'な どで あ っ た.光 合 成 能
合 成 量 が 高 くな っ た こ とに よ る と考 え ら れ た.さ
力 の 変 化 の 原 因 は,気
孔 密 度 の 変 化 な どの 形 態 的 要 因
らに
各 器 官 へ の 光 合 成 産 物 の 分 配 率 も台 木 に よ り相 違 し,
`ル ビ ドー'台 で はT -R比
が最 も高か っ た
.