Outcrossing between ‘Bacon’ Pollinizers and Adjacent ‘Hass’ Avocado Trees and the Description of Two New Lethal Mutants

Abstract

<jats:p>Avocado (<jats:italic>Persea americana</jats:italic> Mill.) has an unusual flowering mechanism, diurnally synchronous protogynous dichogamy, that promotes crosspollination among avocado genotypes. In commercial groves, which usually contain pollinizer rows adjacent to the more desirable commercial cultivars, the rate of outcrossing has been measured with variable results. Using microsatellite markers, we estimated outcrossing in a commercial California ‘Hass’ avocado orchard with adjacent ‘Bacon’ pollinizers. Seedlings grown from mature harvested fruit of both cultivars were genotyped with five fully informative microsatellite markers and their parentage determined. Among the 919 seedlings of ‘Hass’, 688 (75%) were hybrids with ‘Bacon’; the remaining 231 (25%) seedlings were selfs of ‘Hass’. Among the 850 seedlings of ‘Bacon’, 382 (45%) were hybrids with ‘Hass’ and the remaining 468 (55%) seedlings were selfs of ‘Bacon’. The high outcrossing rate observed in the ‘Hass’ seedlings was expected, because adjacent rows of opposite flowering types (A versus B) are expected to outcross. However, the high selfing rate in ‘Bacon’ was unexpected. A previous study in Florida using the cultivars ‘Simmonds’ and ‘Tonnage’ demonstrated differences in outcrossing rates between complementary flowering type cultivars. In both Florida and California, the A type parents (‘Hass’ and ‘Simmonds’) had similar outcrossing rates (≈75%); however, the B type parents (‘Bacon’ and ‘Tonnage”) had highly skewed outcrossing rates of 45% and 96%, respectively. Two new avocado lethal mutants were discovered among the selfed seedlings of ‘Hass’ and ‘Bacon’. These were labeled “spindly” and “gnarly” and are similar in phenotype to mutants described in <jats:italic>Arabidopsis</jats:italic> and other crop species.</jats:p>

Postharvest and Sensory Evaluation of Selected ‘Hass’ × ‘Bacon’ and ‘Bacon’ × ‘Hass’ Avocado Hybrids Grown in East-Central Florida

“…Fruit were collected from selected trees that were among 350 unique 'Hass' · 'Bacon' and 'Bacon' · 'Hass' hybrid trees planted at the USHL-ARS, Fort Pierce, FL, in 2008 on double row beds in Riviera fine sand soil type. Trees originated from seeds collected from a commercial orchard in California by Dr. Raymond Schnell (SHRS-ARS, Miami), and molecular marker analysis confirmed which seedlings were true 'Hass'-'Bacon' hybrids before planting (Schnell et al, 2009). The trees were sprayed with horticultural oil and copper (CS-2005; Magna-Bon II, LLC, Okeechobee, FL), received foliar fertilization with a 20N-10P-20K soluble fertilizer every 2 weeks as part of a regular maintenance regimen, and received annual granular dry fertilizer (12N-2P-14K) at 226-270 kg · ha -1 .…”

Screening Progenies of Mexican Race Avocado Genotypes for Resistance to Phytophthora cinnamomi Rands

“…It has been assumed that Persea americana demonstrates outcross pollination as a result of its floral dichogamy. However, different studies have shown that a high rate of self-pollination in avocado may be possible (Borrone et al, 2008;Garner et al, 2008;Kobayashi et al, 2000;Schnell et al, 2009). The differences in the resistance levels presented among the genotypes are a result of not only the high genetic variability found in individuals coming from the seed as a result of open pollination (Andrade-Hoyos et al, 2015), but also the level of pathogenicity presented by P. cinnamomi (Ochoa-Fuentes et al, 2015) and the interaction between these in an environment beneficial to disease development.…”

Outcrossing Rate and Genetic Variability in Mexican Race Avocado

“…Molecular markers in avocado have been used to assess genetic diversity among and within racial groups (Boza et al, 2018;Cuiris-P erez et al, 2009;Gross-German and Viruel, 2013), in phylogenetic studies (Ashworth and Clegg, 2003;Reyes-Alem an et al, 2013), and in construct linkage maps ; to identify quantitative trait loci (Sharon et al, 1998), and in outcrossing studies (Alcaraz and Hormaza, 2011;Borrone et al, 2008;Chen et al, 2007;Garner et al, 2008;Kobayashi et al, 2000;Schnell et al, 2009;Violi et al, 2009). Outcrossing rate studies based on molecular markers have been done in different plant species such as Brassica carinata A. Braun (Teklewold et al, 2013), Foeniculum vulgare Mill.…”

“…In avocado, most outcrossing studies have been done in cultivars such as Hass, Bacon, Zutano, and others (Kobayashi et al, 2000;Schnell et al, 2009) to detect potential donors of pollen and to calculate the correlation between outcrossing and yield (Kobayashi et al, 2000), to determine the incidence and effectiveness of self-and cross-pollinated avocado fruit (Davenport et al, 2006), and to assess the relation among outcrossing rate with yield and alternate bearing (Garner et al, 2008). In addition, the outcrossing rate has been used to assess the proportion of progeny resulting from parents with complementary blooming (Borrone et al, 2008;Violi et al, 2009) and to determine whether an outcrossed progeny is more tolerant to Phytophthora root rot than a self-pollination progeny ).…”