Editing Avocado (section)

===Breeding===
[[File:Seedless Avocado in Mexico.jpg|thumb|upright|A seedless avocado, or cuke, growing next to two regular Ettinger avocados]]

The species is only partially able to [[self-pollination|self-pollinate]] because of [[Sequential hermaphroditism|dichogamy]] in its flowering. This limitation, added to the long juvenile period, makes the species difficult to breed. Most cultivars are propagated by [[grafting]], having originated from random seedling plants or minor [[mutation]]s derived from cultivars. Modern breeding programs tend to use isolation plots where the chances of cross-[[pollination]] are reduced. That is the case for programs at the [[University of California, Riverside]], as well as the [[Agricultural research In Israel#Agricultural Research Organization (ARO)|Volcani Centre]] and the Instituto de Investigaciones Agropecuarias in Chile.

The avocado is unusual in that the timing of the male and female flower phases differs among cultivars. The two flowering types are A and B. A-cultivar flowers open as female on the morning of the first day and close in late morning or early afternoon. Then they open as male in the afternoon of the second day. B varieties open as female on the afternoon of the first day, close in late afternoon and reopen as male the following morning.
* A cultivars: 'Hass', 'Gwen', 'Lamb Hass', 'Pinkerton', 'Reed'
* B cultivars: 'Fuerte', 'Sharwil', 'Zutano', 'Bacon', 'Ettinger', 'Sir Prize', 'Walter Hole'<ref>{{cite web|url = http://ceventura.ucdavis.edu/Agriculture265/Avocado_Handbook.htm|title = Agriculture Handbook|publisher = [[University of California]]|access-date = 29 December 2007|year = 2007|archive-url = https://web.archive.org/web/20071217095028/http://ceventura.ucdavis.edu/Agriculture265/Avocado_Handbook.htm|archive-date = 17 December 2007}}</ref><ref>{{cite web|url = http://edis.ifas.ufl.edu/MG213|title = Avocado Growing in the Florida Home Landscape|publisher = [[University of Florida]]|first = JH|last = Crane|author2=Balerdi CF|author3=Maguire I|access-date = 29 December 2007|date = 1 August 2007| archive-url= https://web.archive.org/web/20080113011328/http://edis.ifas.ufl.edu/MG213| archive-date= 13 January 2008 | url-status= live}}</ref>

Certain cultivars, such as the 'Hass', have a tendency to bear well only in alternate years. After a season with a low yield, due to factors such as cold (which the avocado does not tolerate well), the trees tend to produce abundantly the next season. In addition, due to environmental circumstances during some years, seedless avocados may appear on the trees.<ref>{{cite web|url=http://www.soilzone.com/Library/Crops/Avocado/Phenology/Avocado%20fruit%20growth.pdf|title=Development of Seeded and Seedless Avocado Fruit|work=Agricultural Research Organization, Volcani Center, Bet-Dagan, Israel|author1=Blumenfeld, Amos|author2=Gazit, Shmuel|access-date=21 September 2010|archive-url=https://web.archive.org/web/20140125180713/http://soilzone.com/Library/Crops/Avocado/Phenology/Avocado%20fruit%20growth.pdf|archive-date=25 January 2014}}</ref> Known in the avocado industry as "cukes", they are usually discarded commercially due to their small size.<ref>{{cite journal|url=http://www.avocadosource.com/CAS_Yearbooks/CAS_33_1948/CAS_1948_PG_113-116.pdf|journal=California Avocado Society 1948 Yearbook|author1=Stewart, W.S. |author2=Smoyer, K.M. |author3=Puffer, R.E. |title=Progress Report on Effects of Plant Growth Regulator Sprays on Avocados|access-date=21 September 2010|volume=33|pages=113–116}}</ref>