Cucurbit Genetics Cooperative Report 10:10-11 (article 9) 1987
Inheritance of Opposite Leaf Arrangement in Cucumis
sativus L.
R. W. Robinson
Horticultural Sciences Department, New York State Agricultural Experiment
Station, Geneva, NY 14456
Cucumber plants normally have alternate leaves, with a single leaf per
node at 180° angle from leaves at adjacent nodes. The Lemon cultivar
is heterogeneous for leaf arrangement, with some plants having alternate
leaves and others two opposite leaves per node, borne at 90° angle from
the pair of leaves at the next node. In a population of 930 'Lemon' plants,
17% had opposite leaves.
Opposite leaf arrangement is unstable. All plants with opposite leaves
at the first nodes of their main stem eventually convert to alternate leaf
arrangement. The number of nodes with opposite leaves on 18 opposite-leaved
'Lemon' plants varied from one to ten, with a mean of 5.4. The change from
opposite to alternate leaf arrangement is usually abrupt, with all nodes
on the main stem above the point of transition having alternate leaves and
those below opposite leaves. Occasionally, a plant has a node with a single
leaf between nodes with opposite leaves. Internodes are often longer after
the change from opposite to alternate leaf arrangement.
Opposite-leaved plants do not breed true for that trait. Progeny of over
100 self-pollinated 'Lemon' plants with opposite leaves all segregated for
alternate vs. opposite leaf arrangement.
Opposite leaf arrangement is recessive. All F1 plants of alternate
x opposite or the reciprocal cross had alternate leaves.
There is no evidence of a cytoplasmic factor being involved in the inheritance
of opposite leaf arrangement; similar ratios were obtained in the F2 generation of reciprocal crosses between alternate- and opposite-leaved
plants. The proportion of seedlings with opposite leaves was significantly
less than 25% in each of 26 F2 populations. The combined segregation
ratio was 875 alternate to 86 opposite.
Tkachenko (1) concluded that at least three genes are required to produce
opposite leaves. An alternate explanation is that inheritance is simple,
but the single recessive gene has incomplete penetrance. Evidence agreeing
with, though not conclusively proving the latter hypothesis, was obtained
when linkage was detected between opposite leaf arrangement and two genes
known to be on the same chromosome. Genes of 'Lemon' for sex expression (m) and five fruit locules (l) are linked (2), and were associated
with opposite leaves in segregating generations. In coupling phase F2 populations there were 302 alternate +: 51 alternate m: 31 opposite
+: 22 opposite m (contingency X2 = 22.9, p > .001)
and 139 alternate +: 29 alternate l: 21 opposite +: 19 opposite l plants (contingency X2 = 16.6, p > .001). It is suggested
that the gene for opposite leaves that is linked with m and l be given the symbol opp.
Literature Cited
- Tkachenko, N.N. 1935. Preliminary results of a genetic investigation
of the cucumber, Cucumis sativus L. Bull. Appl. Pl. Breed.
Ser. 2, 9:311-356.
- Youngner, V.B. 1952. A study of the inheritance of several characters
in the cucumber. PhD. Thesis. Univ. Minnesota, St. Paul.
