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.

Flower buds (and later fruit) are typically produced at every other node on new growth near branch tips of jojoba,

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.

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 (MS_{E}) in a
regular analysis of variance by separating out the variance components (s_{2})
according to the following formula

(MS_{cr} = mean square of clone by replicate; MS_{E} = mean square of the error term;
MS_{c} = mean square of clones; n_{r} = number of replicates; n_{obs} = number of
observations.)

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
acid_{4+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.

Last update September 12, 1997 aw