Table of Contents
Ravetta, D.A. and D.A. Palzkill. 1993. Variation and
broad sense heritability of branching frequency of jojoba. p. 358-359. In: J.
Janick and J.E. Simon (eds.), New crops. Wiley, New York.
Variation and Broad Sense Heritability of Branching Frequency of Jojoba
Damian A. Ravetta and David A. Palzkill
- RESULTS AND DISCUSSION
- Fig. 1
Flower buds (and later fruit) are typically produced at every other node on new
growth near branch tips of jojoba, Simmondsia chinensis (Link) Schneid,
Buxaceae (Gentry 1958). Because of this, the number of nodes produced puts an
upper limit on the number of flowers, fruit, and seed that a plant can produce.
Casual observation of many plants and clones suggested that, in general, highly
branched plants have more flowers and are more productive, and indicated that
this could be a useful trait to select for in a breeding program. To begin to
test this, variability of this trait must be quanified to obtain an estimate of
Since the variance of a non-segregating population (i.e. cloned plants) must be
environmental, such populations have been used to estimate the environmental
component of the total observed variance (Falconer 1990). Once the
environmental component is known, the genetic variation can be calculated by
subtracting environmental variance from the total phenotypic variance observed.
The genetic variance calculated this way includes not only additive variance,
but also dominance, interaction, and epistatic components. The relationship
between genetic variance and total phenotypic variance is, then broad sense
heritability. The objectives of this work were to document the natural
variation in branching frequency within 58 jojoba clones and to calculate broad
sense heritability using the observed variability for branching frequency.
To evaluate the effects of branching frequency on flower bud production, a
survey of 58 jojoba clones growing in a production field near Hyder, Arizona
was conducted during the summer 1989. The number of nodes, number of branches
(tips) and the number of flowers were measured on three branches per plant and
three plants per clone. The length of each branch was fixed by marking on each
major branch the tenth node from the tip. All the tips, nodes, and flowers
above that mark were counted. In a sampling done on a wide range of jojoba
clones with different branching habits, ten nodes was found to be the minimum
length of a branch needed to give an accurate portrayal of branching frequency
of a complete plant.
The same population of jojoba clones was used to calculate broad sense
heritability (H) for branching related traits. Genetic variance for the number
of tips per branch, the number of nodes per branch and the relationship tips to
nodes was derived from the mean squares of clones (MSc) and error (MSE) in a
regular analysis of variance by separating out the variance components (s2)
according to the following formula
The results of the survey of 58 jojoba clones illustrate the relationship
between branching frequency and flower bud production (Fig. 1). The number of
flower buds along the main stem of 10 nodes was not only correlated with the
number of nodes per branch but also with the amount of branching along the
stem. The relationship between the number of nodes and flowers is illustrated
in Fig. 1a, where line A illustrates the regression for all 58 clones (three
plants of each clone and three branches/plant). As the number of nodes in a
branch segment increases, there is a linear increase in the number of flowers.
The slope of 0.49 reflects that on average there is one flower at every other
node. Line B shows the regression for three selected clones that have an
average of about one flower per node (a slope of 0.93). Thus, the number of
flowers increases as the number of nodes increases.
(MScr = mean square of clone by replicate; MSE = mean square of the error term;
MSc = mean square of clones; nr = number of replicates; nobs = number of
A positive relationship also exists between the amount of branching (number of
tips) along the stem segment and the number of nodes (Fig. 1b). Clones with
more branching showed an increase in nodes. As a consequence of the
relationship illustrated in Fig. 1a and 1b, the amount of branching (number of
tips) was also correlated with the number of flowers per branch (Fig. 1c). We
conclude that an increase in branching frequency (number of branch tips/number
of nodes) would likely increase node production (everything else remaining
constant), and if the ratio of flower buds to nodes remains constant, then the
number of flower buds would be increased.
Calculated broad sense heritability was estimated to be 0.36 for the number of
tips per branch, 0.19 for the number of nodes per branch, and 0.84 for the tip
to node ratio.
The low heritability estimates for number of nodes produced by a particular
branch indicates high influence of many conditions which affect growth. The
number of tips per branch is less influenced by the environment, although it
has been shown that the dormancy observed in lateral buds can be overcome with
the external application of plant growth regulators (Ravetta and Palzkill 1990;
Ravetta 1990). Increases in the number of tips per plant 17 months after
treatment application of up to 120% have been observed with applications of
6-benzyladenine and Promalin (a combination of 6-benzyladenine and gibberellic
acid4+7). The use of gibberellic acid produced an increase of more than 150%
probably as a consequence of a change in the plant's architecture. The ratio of
tips to number of nodes is little influenced by environmental factors and this
is borne out by results of plant growth regulators experiments. In conclusion,
selection for branching frequency, which is related to flower bud production
and presumably yield, should be effective.
- Falconer, D.S. 1990. Introduction to quantitative genetics. 3rd ed. Longman
Scientific and Technical. p. 125-141.
- Gentry, H.S. 1958. The natural history of jojoba (Simmondsia
chinensis) and its cultural aspects. Econ. Bot. 12:261-295.
- Ravetta, D.A. and D.A. Palzkill. 1990. Effect of growth regulators and
pinching on branching frequency and flower bud production of jojoba. Proc. 8th
Int. Conf. Jojoba. Asuncion, Paraguay, June 17-22 1990.
- Ravetta, D.A. 1990. Branching in jojoba (Simmondsia chinensis):
natural variation and effects of plant growth regulators and pruning. MS
Thesis, Univ. of Arizona, Tucson.
Fig. 1. Relationship between number of nodes, number of tips, and
number of flowers for 58 jojoba clones growing at Hyder, AZ. Counts were done
on three branches of equal length per plant, and three plants per clone. Each
branch had 10 nodes along the main stem axis. (a) Regression for number of
nodes and number of flowers , line A for the 58 clones, line B for three
selected clones with an average of 0.93 flowers/node; s = slope of regression
line. (b) Regression for number of tips and number of nodes. (c) Regression
for number of tips and number of flowers.
Last update September 12, 1997