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    • Abstract: In: M. L. Arpaia and R. Hofshi (eds.), Proceedings of Avocado Brainstorming. Session I. Plant Breed-ing and Genetics. Pages 9-11. October 27-28, 1999. Riverside, CA. Hofshi Foundation.http://www.avocadosource.com.

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In: M. L. Arpaia and R. Hofshi (eds.), Proceedings of Avocado Brainstorming. Session I. Plant Breed-
ing and Genetics. Pages 9-11. October 27-28, 1999. Riverside, CA. Hofshi Foundation.
http://www.avocadosource.com.
WHY DO WE NEED CONTINUED EFFORTS IN AVOCADO SCION
AND ROOTSTOCK IMPROVEMENT
Mary Lu Arpaia
Dept. of Botany and Plant Sciences, University of California, Riverside
The California avocado industry is dominated by a single variety, ‘Hass’. Although this va-
riety has some excellent attributes such as good eating quality, relatively high yields under
favorable conditions and reliable postharvest attributes the variety is also has a number of
problems. Some of these problems include small fruit size (especially as the tree ages);
intolerance to extreme climactic conditions, alternate bearing and sensitivity to certain in-
sect pests (greenhouse thrips, Persea mite and avocado thrips). The introduction of more
reliably producing varieties should help to stabilize production swings. Consistently heavier
yields per acre can lower production costs per pound. The biodiversity resulting from a
multi-variety industry should slow the spread of diseases and pests like Persea mite, avo-
cado thrips and others that may well appear in the future. Two new avocado cultivars,
‘Lamb Hass’ and ‘Sir Prize’ have been recently patented and released by the University of
California. The ‘Lamb Hass’ in particular shows promise as a new variety for the California
industry. The tree has an upright growth habit, possibly conducive to high density plantings
and/or intensive canopy management. It has also demonstrated some apparent tolerance
to the Persea mite. The fruit is ‘Hass’-like in appearance and matures later in the season
than ‘Hass’. We know less about the ‘Sir Prize’, but this cultivar may show potential as an
alternative to the ‘Zutano’ for San Joaquin Valley growers. Additionally, several of other
potentially interesting selections: ‘Nobel’ (BL 667), ‘GEM’, ‘Harvest’, ‘Marvel’, ‘5-552’, ‘5-
186’, ‘OA184’ and ‘BL312’ have been identified. Much more information needs to be col-
lected on these selections; however, all these selections show some sort of improved char-
acteristic over the ‘Hass’. One interesting sidelight to these new selections is the possible
utility of these varieties as pollenizers for ‘Hass’. The efficiency of these new selections as
pollen donors to the ‘Hass’ will be evaluated by Dr. Clegg’s lab at UCR (Clegg et al., 1998).
Other avocado producing countries are now actively searching for improved varieties
(Bergh and Lahav, 1996; Bijzet et al., 1997a, 1997b; Lahav and Lavi, 200_; Sippel et al.,
1997a, 1997b; A. Blumenfeld and E. Lahav, Volcani Research Institute, Israel, personal
communication). Many of these countries have used material from the California avocado
breeding project to build their plant improvement program. As we move ahead in looking
for improved plant material, it is critically important to maintain open ties with researchers
developing new cultivars so that we may introduce this material into California for evalua-
tion under our conditions. We also need to re-examine older plant material in California for
potential development of both regional and national niche markets. We should not be
blinded by the mentality that only “black” sells, but rather that we could market any cultivar
as long as it has desirable and reliable quality. The success of the CA deciduous fruit in-
dustry which markets literally hundreds of varieties in a span of only 16 weeks should serve
as a reminder that we can also market multiple varieties.
Phytophthora root rot continues to spread, with no fully satisfactory control measures avail-
able. Even if more effective fungicidal treatments are developed, concerns regarding their
cost and the eventual development of fungal resistance still favor improved rootstock ge-
9
netic tolerance. There has been extensive research conducted by the University of Califor-
nia to identify rootstocks which are tolerant to Phytophthora cinnamomi and P. citricola, but
little evaluation of the horticultural attributes of these selections have been made. Part of
this research program is designed to assess the horticultural attributes of promising clonal
rootstocks. The results from this study will help to provide guidelines for distinguishing be-
tween avocado clonal rootstocks beyond the criteria of disease resistance (Arpaia et al.,
1991; Barrientos-Priego et al., 1991; Ben-Ya’acov et al., 1991; Oster and Arpaia, 1991;
Mickelbart and Arpaia, 200_).
We also need to be constantly vigilant for new rootstock material which may be more toler-
ant to environmental stresses, such as salinity, drought stress and which may be dwarfing.
In California we are actively pursuing collaborative ties with Dr. Crowley (UCR, Dept. of Soil
and Environmental Sciences), Dr. A. Ben-Ya’acov (Emeritus, Volcani Institute, Israel), Dr.
Miriam Zilberstaine (Volcani Institute, Israel) and Dr. Grant Thorp (Hort Research, New
Zealand) in order to maximize the genetic material available for testing.
The genus Persea and its near relatives are largely indigenous to Central and South Amer-
ica. Much of the germplasm in the wild is threatened by deforestation and land develop-
ment. An integral component of any plant improvement program should be the preserva-
tion of the genetic resources for the species, genus and family. Dr. Scora over the last few
years has successfully moved a large portion of the Persea germplasm collection at the UC
South Coast REC to a non-Phytophthora infested section of the Center. Funding is needed
to maintain and expand this collection as well as maintaining cooperative ties with other in-
ternational researchers committed to germplasm conservation (Barrientos-Priego et al.,
1991; Ben-Ya’acov et al., 1991a, 1991c, 1991d; Bowman and Scora, 1991; Smith, 1992).
Finally, all the information gathered in plant improvement needs to be disseminated back to
the source of this research funding, namely the California avocado grower. Information
generated in this effort is disseminated through grower meetings, UC Cooperative Exten-
sion publications (Subtropical Fruit News), CAC, trade and California Avocado Society pub-
lications and a UC Avocado Improvement Home Page (www.ucavo.ucr.edu).
REFERENCES
The following 2 references are the most current and thorough review of the subject of avo-
cado improvement available. Both include extensive literature reviews.
Bergh, B.O. and E. Lahav. 1996. Avocados. In: J. Janick and J.N. Moore (eds.), Fruit
Breeding, Volume I: Tree and Tropical Fruits. John Wiley & Sons, Inc. N. Y. pp: 113 -
166.
Lahav, E. and U. Lavi. 200_. Genetics and Breeding. In: A.W. Whiley and B. Schaeffer
(eds.), The Avocado. CAB Intl. (In press).
Listed below are selected references referring to avocado crop improvement and evaluation
that are not listed in the literature cited section of the above review.
Arpaia, M.L., G.S. Bender, and G.W. Witney. 1991. Avocado clonal rootstock trial. In: C.J.
Lovatt (ed.) World Avocado Congress II Proceedings. April 21 – 26, 1991. Orange, CA
pp: 305 – 310.
Barrientos-Priego, A.F., S. Sanchez-Colin, J.J. Aguilar-Melchor, and A. Lopez-Jimenez.
1991a. Selection of Avocado dwarfing rootstocks. In: C.J. Lovatt (ed.) World Avocado
Congress II Proceedings. April 21 – 26, 1991. Orange, CA pp: 515 – 520.
10
Barrientos-Priego, A.F., M.W. Borys, E. Escamilla-Prado, A. Ben-Ya’acov, E. de La Cruz
Torres, and L. Lopez-Lopez. 1991b. A study of Avocado germplasm resources, 1988 –
1990. IV. Findings in the Mexican Gulf Region. In: C.J. Lovatt (ed.) World Avocado
Congress II Proceedings. April 21 – 26, 1991. Orange, CA pp: 551 – 558.
Ben-Ya’acov, A., G. Bufler, A. Barrientos-Priego, E. de La Cruz Torres, and L. Lopez-
Lopez. 1991a. A study of Avocado germplasm resources, 1988 – 1990. I. General de-
scription of the international project and its findings. In: C.J. Lovatt (ed.) World Avocado
Congress II Proceedings. April 21 – 26, 1991. Orange, CA pp: 535 – 542.
Ben-Ya’acov, A., E. Michelson, M. Zilberstaine, Z. Barkan, and I. Sela. 1991b. Selection of
clonal avocado rootstocks in Israel for high productivity under different soil conditions.
In: C.J. Lovatt (ed.) World Avocado Congress II Proceedings. April 21 – 26, 1991. Or-
ange, CA pp: 521 - 526.
Ben-Ya’acov, A., L. Lopez-Lopez, E. de La Cruz Torres, and A.F. Barrientos-Priego.
1991c. A study of Avocado germplasm resources, 1988 – 1990. II. Findings from the
central part of Mexico. In: C.J. Lovatt (ed.) World Avocado Congress II Proceedings.
April 21 – 26, 1991. Orange, CA pp: 543 – 544.
Ben-Ya’acov, A., M. Zilberstaine, and I. Sela. 1991d. A study of Avocado germplasm re-
sources, 1988 – 1990. V. The evaluation of the collected material for horticultural pur-
poses. In: C.J. Lovatt (ed.) World Avocado Congress II Proceedings. April 21 – 26,
1991. Orange, CA pp: 559 – 562.
Bijzet, Z., B. Snijder, and A.D. Sippel. 1997a. Cultivars and selections in the Phase I
breeding selection programme. S. A. Avocado Growers’ Assn. Yrbk. 20: 24 – 26.
Bijzet, Z., S.P. Van Vuuren, and L. Schroeder. 1997b. Progress with local selections in the
quest for a more tolerant/resistance avocado rootstock than Duke 7. S. A. Avocado
Growers’ Assn. Yrbk. 20: 17 – 23.
Bowman, K.D. and R.W. Scora. 1991. The necessity of avocado germplasm resources.
In: C.J. Lovatt (ed.) World Avocado Congress II Proceedings. April 21 – 26, 1991. Or-
ange, CA pp: 531 – 534.
Clegg, M.T., M. Kobayashi and L. Francis. 1998. Outcrossing in Avocado: Is there a rela-
tionship to fruit yield? Subtropical Fruit News. 6(1): 24 – 28.
Menge, J.A., F.B. Guillemet, S. Campbell, E. Johnson, and E. Pond. 1991. The perform-
ance of rootstocks tolerant to root rot caused by Phytophthora cinnamomi under field
conditions in southern California. In: C.J. Lovatt (ed.) World Avocado Congress II Pro-
ceedings. April 21 – 26, 1991. Orange, CA pp: 53 – 59.
Mickelbart, M.V. and M.L. Arpaia. 200__. Effects of salinity on growth, ion concentrations
and water relations of ‘Hass’ avocado (Persea americana L.) trees propagated on three
rootstocks. J. Am. Soc. Hort. Sci. (Submitted).
Oster, J.D. and M.L. Arpaia. 1991. ‘Hass’ avocado response to salinity as influenced by
clonal rootstocks. In: C.J. Lovatt (ed.) World Avocado Congress II Proceedings. April
21 – 26, 1991. Orange, CA pp: 209 – 214.
Sippel, A.D., B. Snijder, J. Werksman, and Z. Bijzet. 1997a. Performance of rootstock cul-
tivars in the avocado Phase II evaluation programme: 1996. S. A. Avocado Growers’
Assn. Yrbk. 20: 28 – 29.
Sippel, A.D., B. Snijder, J. Werksman, and Z. Bijzet. 1997b. Cultivar and selection Per-
formance in the Avocado Phase II evaluation programme: 1996. S. A. Avocado Grow-
ers’ Assn. Yrbk. 20: 30 – 34.
Smith, N.J.H., J.T. Williams, D.L. Plucknett, and J.P. Talbot. 1992. Tropical forests and
their crops. Comstock Publishing Associates. Ithaca, N.Y.
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