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Avocado (Persea americana) cultivars were assayed for phosphoglucose isomerase (PGI) isozymes using starch gel electrophoresis. Three PGI genes were identified: one monomorphic locus, Pgi-I, coding for the plastid isozyme and two independently assorting loci, Pgi-2 and Pgi-3, coding for the cytosolic isozymes. The genetic analysis was based on comparisons of PGI zymograms from somatic and pollen tissue and on Mendelian analysis of progeny from selfed trees. The isozymic variability for PGI can be used for cultivar identification and for differentiating between hybrid and selfed progeny in avocado breeding.

The effects of various pollen parents on outcrossing rates, yield, and fruit and seed weights were studied in a `Fuerte' avocado (Persea americana Mill.). Isozyme analysis was used to identify the pollen parent of mature fruits. Cotyledons were assayed for five polymorphic enzyme systems: alcohol dehydrogenase, leucine aminopeptidase, malate dehydrogenase, phosphoglucomutase, and triosephosphate isomerase. When sampling of fruits was done to a height of 2 m, percent of hybrids produced by `Teague' and `Topa-Topa' pollenizers was in the range of 30% to 40%. With `Teague' as the pollenizer, `Fuerte' yield increased by 30% in trees adjacent to the pollenizer. With `Tops-Tops' as pollenizer, the yield was increased by 40% for trees adjacent to and at a distance from the pollenizer. `Ettinger' trees planted at a distance of 30 to 50 m from `Fuerte' were found to be the pollen parent of 2% to 14% of the progeny, thus supporting our previous conclusion regarding the high potency of `Ettinger' as a pollen parent. `Tops-Tops', `Teague', and `Ettinger' significantly increased fruit and seed weights of crossed compared with selfed `Fuerte' fruits.

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Outcrossing rate in a solid block of ‘Hass’ avocado (Persea americana Mill) was determined 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), for which evidence concerning the genetic control of the latter is presented. Almost all ‘Hass’ mature fruits were found to have resulted from cross-pollination. Among the potential pollen donors—‘Hass’, ‘Ettinger’, and ‘Reed’—‘Ettinger’ excelled, producing almost all of the hybrid fruits.