Pollen Parent Effect on Outcrossing Rate in ‘Hass’ and ‘Fuerte’ Avocado Plots during Fruit Development

Abstract

Outcrossing rates in ‘Hass’ and Fuerte’ avocado ( Persea americana Mill.) blocks were determined during fruit development using the isozyme systems of malate dehydrogenase (MDH, EC 1.1.1.37), leucine aminopeptidase (LAP, EC 3.4.11.1), and triosephosphate isomerase (TPI, EC 5.3.1.1) as genetic markers. Abscission of avocado fruitlets was selective and was greatly influenced by the pollen parent. Thus, in ‘Hass’ trees subjected to crosspollination by ‘Ettinger’ and ‘Fuerte’, the population of ‘Hass’ fruitlets 1 month after fruit set consisted mainly of ‘Hass’ selfs; however, during fruit development, the rate of ‘Hass’ selfs decreased and the rate of ‘Hass’ hybrid fruitlets produced by ‘Ettinger’ and ‘Fuerte’ increased. By the end of fruit abscission, the surviving mature ‘Hass’ fruits were mostly ‘Ettinger’ hybrids. The ‘Hass’ fruit yield was found to correlate significantly with the rate of outcrossing with ‘Ettinger’. When ‘Ettinger’ served as a pollen parent for ‘Fuerte’, the outcrossing rate in trees adjacent to ‘Ettinger’ was about 40%, which shows that cross-pollination among avocado cultivars of the same flowering group can be substantial at close proximity. The outcrossing rate in ‘Fuerte’ diminished with increasing distance from ‘Ettinger’, but no effect on yield was observed.