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HORTSCIENCE 43(3):947–948. 2008.
‘SJM44’ Apple Rootstock
Shahrokh Khanizadeh
2
, Yvon Groleau, Odile Carisse, Vicky Toussaint,
Raymond Granger
1
, and Gilles Rousselle
1
Agriculture and Agri-Food Canada, Horticulture Research and Develop-
ment Centre, 430 Gouin Boulevard, St-Jean-sur-Richelieu, Quebec, Canada
J3B 3E6
Additional index words. Malus ·domestica, fruit breeding, winter hardiness, dwarf, size
controlling, efficiency
Origin
‘SJM44’ (St-Jean Morden 44) is a new
dwarfing rootstock resulting from a cross
made in 1960 between Malus baccata
‘Nertchinsk’ and ‘M.9’ (‘Malling 9’, clonal
selection of Paradis jaune de Metz). It was
developed at the Agriculture and Agri-Food
Canada Horticulture Research and Develop-
ment Center, St-Jean-sur-Richelieu, Quebec.
It produces trees smaller than ‘Malling 26’
(‘M.26’) but larger than ‘Malling 9’ (‘M.9’)
(Table 1). It was released because of its
infrequent burr knots and freedom from root
suckers compared with ‘M.9’ (Table 1), su-
perior hardiness (Khanizadeh et al., 2000),
ease of propagation, and better yield effi-
ciency (Table 2).
‘SJM44’ was among 56 hybrid seedlings
of ‘Nertchinsk’ ·‘M.9’ to which ‘McIntosh
VC309’ was budded in 1971 and planted in
1974 at Frelighsburg, Quebec, where it was
evaluated until 1984 for hardiness, tree size,
and efficiency (Granger et al., 1991) along
with other selected SJP84 and SJM series
(Khanizadeh et al., 2005). ‘SJM44’ was
planted in 1997 in replicated trials in several
plots at the Frelighsburg, Quebec, and
L’Acadie, Quebec, substations and also at
a grower site at Mont-St-Gre´goire, Quebec
(Khanizadeh et al., 2005).
Description of Self-rooted Trees
Own-rooted trees of ‘SJM44’ are very
prolific and began flowering in L’Acadie,
Quebec, around 15 May compared with
‘M.26’, which begin flowering around 23
May based on average date during 1999 to
2004. The color of the buds in full balloon
stage is white with medium pink along the
petal outline; pedicels are green, and flowers
are single with an average 5.7 cm diameter.
Petals are large, overlapped, circular, and
mainly white.
The mature leaves are fairly large with
length between 7.8 and 9.2 cm, width
between 4.5 and 5.5 cm, and a length to
width ratio of 1 : 7. The leaves are dark green,
glossy on the upper side, and pubescent on
the lower side with an outward orientation.
Petioles are between 1.8 and 2.5 cm long, and
the shape of the leaf apex is cuspidate with
serrated margins.
The reddish brown dormant 1-year-old
shoot is 6 mm thick, and the length of
internodes (at the middle third of the shoot)
is 13 mm based on averages of at least four
replicates during the evaluation period.
Shoots have moderate flexibility and numer-
ous small lenticels.
Fruits are small (23 g) with 3.4 to 3.8 cm
diameter, globose, symmetrical, and the rib-
bing is weak (Fig. 1). Fruit crowning is absent
and the eye is large, closed, and the calyx is
persistent with medium to long lobes. The
stalk is very long (3.1 to 4.6 cm) and the stem
cavity is shallow. The skin is smooth and
partially (20% to 50%) covered with flecked,
streaked, and faded pinkish red [Royal Hor-
ticultural Society (RHS) 50B] over a yellow
ground color (RHS, 1995) with very little
russet around the stalk cavity. The lenticels
are small and inconspicuous and the fruit
flesh is yellowish.
Propagation (stool bed)
‘SJM44’ produces four to five shoots per
plant and rooting efficiency (quantity pro-
duced) was better than O.3 but less than
‘M.9’. Average shoot diameter was 5 to 6
mm and lengths of shoots were 62 cm.
‘SJM44’ produces an average of two to four
thorns or secondary branches per shoot.
Diseases and Pests
‘SJM44’ is resistant to woolly apple aphid
(Erisoma lanigerum Hausmann; based on
visual observation since 1974 in stool bed).
It has similar or lower susceptibility to two
races of Erwinia amylovora (Burrill) than
‘M.9’ and ‘M.26’ and is more resistant to four
races of Phytophthora cactorum (Leb. &
Cohn) Schroet. than ‘M.26’ but less resistant
than ‘M.9’ (Carisse and Khanizadeh, 2006)
(Table 3) using the procedure used by Norelli
et al. (2002).
Performance in the Orchard
The performance of ‘SJM44’ using
‘McIntosh Summerland’ as a scion has been
monitored since 1997 in a commercial
orchard located in Mont-St-Gre´goire, Que-
bec. It produces trees larger than ‘M.9’ but
smaller than ‘M.26’ (Table 1). The trees
grafted on ‘SJM44’ have better yield effi-
ciency and produce fewer burr knots and no
suckers compared with ‘M.9’.
Table 1. Burr knots, sucker number, trunk cross-sectional area (TCSA), height, spread, and vigor of
McIntosh Summerland apple trees at Mont-St-Gregoire, Quebec, on ‘SJM44’ in comparison with
‘M.9’ and ‘M.26’ (1997 planting).
Genotype
Burr
knots
z
2004
Suckers (no.)
1999–2003
TCSA
(cm
y
) 2004
Ht (cm)
2004
Spread
(cm) 2004
Relative
vigor 2004
x
SJM44 0.5 0.0 29.8 350 360 128
M26 1.7 0.0 40.8 367 357 150
M9 2.0 2.3 18.2 267 283 100
LSD
0.05
1.5 5.8 11.0 65 75 17
z
Burr knots on a scale of 0 to 5: 0 = no burr knots; 5 = aerial section of rootstock is covered with burr knots.
y
Circumference (mm): 25 cm above the graft union.
x
Relative vigor to M9 (circ. ‘SJM44’/circ. of ‘M.9’)*100.
LSD = least significant difference.
Table 2. Precocity, cumulative yield (1999–2004), yield efficiency, and average fruit size of McIntosh
Summerland apple trees at Mont-St-Gregoire, Quebec, on ‘SJM44’ in comparison with ‘M.9’ and
‘M.26’ (1997 planting).
Genotype
Yield (kg)
z
Yield
efficiency
y
Fruit size
(g) 2004
x
1999 2000 2001 2002 2003 2004 1999–2004
SJM44 0.3 5.5 20.3 31.4 84.9 48.7 190.9 6.7 123
M26 0.6 3.8 12.1 32.1 44.8 44.7 138.1 3.3 146
M9 0.5 6.7 10.5 25.5 21.0 39.4 103.7 5.8 135
LSD
0.05
1.3 4.8 11.5 14.4 77.8 25.6 72.2 3.2 31
z
Yield (kg) = includes weight of fallen, harvested, and sampled apples.
y
Yield efficiency (kgcm
2
) = (cumulative yield 1999 to 2004/trunk cross-sectional area 2004).
x
Size (g): average fruit size obtained from a randomly selected sample of 25 fruits.
LSD = least significant difference.
Received for publication 2 Nov. 2007. Accepted
for publication 18 Feb. 2008.
Agriculture and Agri-Food Canada, St-Jean-sur-
Richelieu, Contribution No. 335/2008.04.01R.
1
Retired Research Scientists.
2
To whom reprint requests should be addressed;
e-mail khanizadehs@agr.gc.ca
HORTSCIENCE VOL. 43(3) JUNE 2008 947
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tsp/horts/163067/02646
Availability
A Canadian Plant Breeder’s Right (PBR)
has been issued (PBR certificate number
2906) and limited quantities of indexed bud-
wood are available for research purposes
(universities and research centers) from
Canadian Food Inspection Agency, Shahrokh
Khanizadeh (for North America) or Meiosis
(http://www.meiosis.co.uk) for Europe fol-
lowing a written request. Interested nurseries
may inquire about ‘‘nonexclusive licenses’’
directly from Agriculture and Agri-Food
Canada, office of technology transfer.
Literature Cited
Carisse, O. and S. Khanizadeh. 2006. Relative
resistance of newly released apple rootstocks
to Phytophtora cactorum. Can. J. Plant Sci.
86:199–204.
Granger, R.L., G.L. Rousselle, M. Meheriuk, and
H.A. Quamme. 1991. Promising winter hardy
apple rootstocks from a breeding program at
Morden, Manitoba. Fruit Var. J. 45:185–187.
Khanizadeh, S., Y. Groleau, R. Granger, J. Cousineau,
and G.L. Rousselle. 2000. New hardy rootstocks
from the Quebec apple breeding program. Acta
Hort. 538:719–721.
Khanizadeh, S., Y. Groleau, A. Levasseur, R.
Granger, G.L. Rousselle, and C. Davidson.
2005. Development and evaluation of St Jean-
Morden apple rootstock series. HortScience
40:521–522.
Norelli, J.L., H.S. Aldwinckle, H.T. Holleran, T.L.
Robinson, and W.C. Johnson. 2002. Resistance
of ‘Geneva’ apple rootstocks to Erwinia amy-
lovora when grown as potted plants and
orchard trees. Acta Hort. 590:359–362.
Royal Horticultural Society (RHS). 1995. Royal
Horticultural Society colour chart. Royal Hor-
ticultural Society, London, UK.
Table 3. Relative susceptibility of ‘SJM44’ rootstock compared with ‘M.26’ and ‘M.9’ based the length of
necrosis on excised apple rootstocks inoculated with four isolates of Phytophthora cactorum and two
races of Erwinia amylovora.
Rootstocks
Race of Phytophthora cactorum
z
Race of Erwinia amylovora
y
PC04-01 PC04-02 PC04-03 PC04-04 ST998 ST1585
M.26 34.67 41.48 36.28 29.18 63.17 66.40
M.9 17.17 20.21 17.04 13.70 81.70 94.82
SJM44 25.70 29.70 28.24 22.72 76.40 60.00
LSD
x
2.28 5.61 5.56 4.29 29.31 20.74
z
Length (mm) of necrosis induced by Phytophthora cactorum isolates.
y
Percentage of the shoot length with necrotic lesions after inoculation (Norelli et al., 2002).
x
LSD = least significant difference at the 0.05 level.
Data collected from Carisse and Khanizadeh (2006), and http://www.cyberfruit.info/apple/apple-
rootstocks/pdf/disease-susceptibility.pdf.
Fig. 1. Fruit of ‘SJM44’ rootstocks (fruits are 3.4 to
3.8 cm in diameter).
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