Avocado Fruit Size

by Laurie Meadows

August 28 2019

Some avocado fruit are very big. Wild Persea species tend to have fruit that are quite big relative to other wild fruit. But relative to cultivated avocado fruit, wild Persea fruit are quite small.

In turn, ‘normal’ commercial avocados are rather small relative to some of the largest cultivated avocado seedling variants such as the West Indian x Guatemalan cultivars Choquette and Hall. Choquette weighs 850 to 1133 grams, Hall 567 - 850 grams. The Guatemalan cultivars Queen, Dailey, and Dailey 11 reach similar weights. Queen weighs 567 to 850 grams. Dailey, a seedling of Queen, weighs 850 grams, and Dailey 11, also a Queen seedling, weighs 1360 grams or more, with the occasional fruit reaching 2267 grams.

According to Bergh and Lahav (1996) in every selfed progeny set examined, fruit averaged smaller than the parent. In contrast, Israeli breeders saw no such effect (Lahav and Lavi 2013).

Our 30+ year old seedling Hass tree never has more than 20-40 or so fruit, this year same, but bigger fruit, one at 401 grams, even ~ 5 months out from full maturity. A neighbors late hung Hass went over 500 grams, so no records here.

These Avozilla are big. USA Queen >800 gm https://t.co/mPGeGeIMk9

— Laurie Meadows (@Laurie_Meadows) June 30, 2019

Very small fruited seedlings are sometimes found. Bergh & Whitsell (1973) reported an individual within a population of 300 selfed Hass seedlings which had fruit of about 28 grams. The small and large fruit are from 2 different open pollinated Pinkerton seedlings.

Some avo seedlings produce very small fruit. Bergh & Whitsell 1973 paper shows a selfed Hass seedling that bears tiny fruit, less than 28 grams (1 oz) weight!

At the moment the smallest fruited seedling here is about 90 grams, the largest about 500 grams. pic.twitter.com/LUT2JIdksY

— Laurie Meadows (@Laurie_Meadows) August 30, 2021

A 2014 paper by Monforte et al ‘The genetic basis of fruit morphology in horticultural crops: lessons from tomato and melon’ found genes for fruit weight (likely a proxy for size) “co-localized frequently with members of the [Cell Number Regulator/Fruit Weight] CNR/FW2.2 and KLUH/FW3.2 families, as well as co-localizations between [Ovate Family Proteins] OFP family members”. My expansions are [bracketed].

KLUH gene may affect cell division, possibly increasing the number of cell layers in the fruit pericarp, thus affecting ultimate fruit size.

The CLAVATA (CLV) gene in tomato has a signal-receptor complex affecting meristems, wherein a mutation in CLV3 (whose secreted peptide signal binds to the CLV1 receptor) has resulted in larger fruit size in the course of domestication. (Xu et al 2015)

Other genes possibly implicated in regulating cell division are SUN (regulating fruit elongation), and CYP78A (cytochrome P450 of the 78A class).

These gene families were frequently found located on the chromosomes near both OFP family members and areas on the chromosomes associated with fruit shape.

The authors found two genomic regions in melon that had genes affecting fruit weight.

Recent work on the avocado genome has identified some similar regions when compared with tomato (the only genome I bothered to look at – there are others, such as grape, and Arabidopsis in the spreadsheets).

In the following list the first number is the reference number in the first column of the spreadsheet, followed by the function or type of protein, and whether the match between avocado and tomato is partial or complete. There are separate spreadsheets for ‘Mexican‘ and the ‘nodal hybrid’ cultivar Hass.

‘Mexican’ avocado nodal group :

‘Hass’ avocado nodal group hybrid :

Fruit heavier than the current dominant ‘Hass’ cultivar are probably undesirable (heavier fruit may be suitable for the restaurant trade, but not so much for today’s small family size).

In summary, very large avocado fruit may result from over-expression of homologs of some of these genes. Other genes may also be involved in the expression of such genes.

Further reading:
Bergh B. O., and Whitsell R. H. 1973. Self -Pollinated Hass Seedlings.
California Avocado Society 1973 Yearbook, 57: 118 -156

Bergh, B. O. and Lahav, E. 1996. Avocados. In J. Janick and J.N. Moore, eds., Fruit Breeding, vol. I, Tree and Tropical Fruits, pp. 113-166. John Wiley & Sons, New York, NY.

Monforte, A. J., Diaz, A, Caño-Delgado, A. and van der Knaap, E. 2014. The genetic basis of fruit morphology in horticultural crops: lessons from tomato and melon
Journal of Experimental Botany, Vol. 65, No. 16, pp. 4625–4637, 2014  doi:10.1093/jxb/eru017

Rendón-Anaya,M et al. 2019. The avocado genome informs deep angiosperm phylogeny, highlights introgressive hybridization, and reveals pathogen-influenced gene space adaptation.
PNAS August 20, 2019 116 (34) 17081-17089; first published August 6, 2019 https://doi.org/10.1073/pnas.1822129116

Xu, C., Liberatore, K., MacAlister, C. et al. A cascade of arabinosyltransferases controls shoot meristem size in tomato. Nat Genet47, 784–792 (2015) doi:10.1038/ng.3309