Avocado Genotypes Research Articles

Biochemical and morphological characteristics of avocado genotypes in Kerala

Presently, in India, avocado cultivation is limited and scattered in southern and north eastern region of India. Many avocado genotypes are available in Kerala, which vary widely in terms of biochemical and morphological attributes. In the present study, 27 accessions (Acc.) were collected from different parts of Kerala, including high-altitude areas and plains. Wide variability in biochemical and morphological traits was observed among accessions collected from different locations. Acc. 11 had the highest vitamin C and Acc. 15 had highest protein content. The highest fat content was recorded in Acc. 7, while the highest oleic acid was recorded in Acc. 10. Acc. 25 reported the highest flavonoid and calcium content. Genotypes collected from Wayanad recorded comparatively higher values for vitamin C, phenols, potassium and crude fibre content. Protein, total fat and calcium contents were comparatively higher in genotypes collected from Idukki. Accessions 7, 10, 11, 12, 14, 15 and 25 could be selected for future conservation, popularization and commercial cultivation based on their biochemical and morphological quality attributes.

Variação sazonal do teor de nutrientes em folhas de abacateiros dos genótipos Geada, Fortuna e Quintal

Abstract Avocado is an important fruit for fresh consumption and as raw material for several industries. In order to obtain good productivity and fruit quality, adequate plant nutrition is essential. However, information on the relationship between time of year, phenology and nutritional status of plants of different genotypes is difficult to compare, as most data are obtained from plants of different ages, planted in soils with different fertility levels, different management strategies and most cultivated under edaphoclimatic conditions different from those of Brazil. This study evaluated the seasonal nutrient content variation of avocado leaves, genotypic differences, the relationship with phenological stages and the periods of greater nutrient content stability in ‘Fortuna’, ‘Geada’ and ‘Quintal’ avocado genotypes cultivated in the municipality of Jardinópolis-SP, Brazil. All plants aged 30 years, were randomly planted within the same area and submitted to the same cultural treatments and management. Nutrient contents are more stable during the flowering phase (July to September) and in the final phase of fruit formation (February to March). In most of the cycle, ‘Geada’ plants have lower S, P and Zn levels compared to ‘Fortuna’ and ‘Quintal’ genotypes. ‘Fortuna’ genotype has higher Ca, Mg and Mn levels than the others at the time of fruit harvest (April to June). In the budding phase of the three genotypes (October), increase in N, P, K, S, Cu, Zn contents and decrease in Ca, Mg and Mn contents were observed.

Genotypic Variation in Physico-Chemical Properties of Avocado at Dailekh

This study was conducted to analyze the physical and chemical properties of the fruits in 16 avocado genotypes in 2020. Fruits were harvested at physiological maturity stage from seed propagated plants and analyzed their physical (fruit weight, fruit length, fruit diameter, pulp weight, pulp/fruit ratio, and seed/fruit ratio) and chemical properties (moisture content, reducing sugar, total soluble solids, crude protein, total ash, phosphorous, iron, calcium, crude fat and crude fiber). The analysis of one-way variance of the data revealed highly significant variation in physico-chemical properties among avocado genotypes. Genotypes HRSDAV05, HRSDAV07, HRSDAV06 and HRDAV03 displayed the lowest seed/fruit ratio of 10.0, 13.5, 14.6 and 16.8%, respectively. Total soluble solid (TSS) content was the highest in HRSDAV08 (6.7 °Brix), HRSDAV03 (6.0 °Brix), HRSDAV07 (6.0 °Brix) and HRSDAV012 (6.0 °Brix). Crude protein was the highest in HRSDAV07 (19.2%), HRSDAV09 (17.8%) and HRSDAV014 (17.4%). HRSDAV03 and HRSDAV012 had the highest total ash content of 6.4% and 5.1%, respectively. Phosphorus content was the highest in HRSDAV03 (235.2 mg/100 g), but iron content was the highest in HRSDAV07 (2.5 mg/100 g). Crude fat and crude fiber were the highest in HRSDAV013 (63.0%) and HRSDAV03 (48.4%), respectively. The analysis of physico-chemical characters of avocado fruits identified HRSDAV03, HRSDAV05, HRSDAV06, HRSDAV07, HRSDAV08, HRSDAV09 and HRSDAV013 as potential parental genotypes for developing new cultivars.

Tocopherol Accumulation and Temporal Expression Analysis of VTE1 and VTE5 Gene Family in Fruit of Two Contrasting Avocado Genotypes.

α-tocopherol is found in high concentrations in avocado fruit mesocarp, however, its accumulation and genetic control during maturation and ripening has not been elucidated. Based in the relevance of VTE1 and VTE5 genes in tocopherol biosynthesis and aiming to determine the association between tocopherol accumulation and expression of tocopherol biosynthetic genes, gene expression of VTE1 and VTE5 were evaluated through the time during three developmental stages: before harvest at 100, 160 and 220days after flowering (DAF) and after harvest (220 DAF + 5) in two contrasting avocado genotypes (San Miguel and AVO40). San Miguel reached the highest levels at 220 DAF, whereas AVO40 increased α-tocopherol only after ripening (220 DAF + 5). A genome-wide search for VTE1 and VTE5 allowed to identify one and three genes, respectively. Both genotypes showed contrasting patterns of gene expression. Interestingly, AVO40 showed a highly positive correlation between α-tocopherol levels and gene expression of VTE1 and all VTE5 variants. On the other hand, San Miguel showed only a positive correlation between α-tocopherol level and VTE1gene expression.

Diversity Analysis in Avocado (Persea americana Mill.) Accessions of Lower Pulney Hills of Tamil Nadu, India

Avocado (Persea americana Mill.) is one of the world's most important subtropical fruit crops. So far, it’s collection, systematic evaluation and utilization studies are limited and this would be perhaps the first systematic study to quantify the variability available. This investigation of genetic diversity would be a first in Tamil Nadu. Morphological diversity in qualitative and quantitative traits of avocado genotypes investigated in this study using the International Plant Genetic Resources Institute descriptors to evaluate twenty accessions. The traits evaluated were related to leaf, flowering, fruit, seed, and yield traits. The 20 genotypes were classified into ten groups using Mahalanobis statistics. PA-56 and PA-68, which differ in terms of characteristics and distance, might provide transgressive segregants upon curing to resistance desirable traits. Principal component analysis was done to assess the qualitative and quantitative characters combination. The total variability defined by the five PCs was 84.14 percent, whereas the variability of the 13 primary components was 99.99 percent. The genotypes that could be chosen based on PC values in each constituent graph that were positive and > 1.0 in each PC and a combination away that would unravel many genetic patterns. Findings of this research will aid in germplasm management, conservation, and breeding strategies.

Physicochemical and bioactive compounds at edible ripeness of eleven varieties of avocado (Persea americana) cultivated in the Andean Region of Peru

SummaryThis work aimed evaluating some physicochemical compounds, hydrophilic (H‐AC) and lipophilic (L‐AC) antioxidant capacity of eleven avocado genotypes grown in the Andes. The results show great variability in physical and chemical properties, dry matter (DM) and lipid contents with ranges of 18.4–39.3% and 10.1–23.2%, respectively. All genotypes had high oleic acid content (50.4–69.9%) and a high unsaturated fatty acid/saturated fatty acid ratio (UFA/SFA, from 3.05 to 6.05), while the unsaponifiable fraction contained mainly β‐sitosterol (140.83–235.51 mg/100 g DM) and α‐tocopherol (17.44–71.29 µg/g DM). Total phenolic compounds (TPC), H‐AC and L‐AC ranged from 0.48 to 0.88 mg EAG/g DM, 5.37 to 14.00 and 1.87 to 6.71 μmol ET/g DM, respectively. Although the genotype influences avocado characteristics, climatic conditions in the Andean region seem to be important for the biosynthesis of metabolites of interest and should be considered in future studies.

Genotypic Variation in Plant Traits, Chemical Defenses, and Resistance Against Insect Herbivores in Avocado (Persea americana) Across a Domestication Gradient

Domestication promotes divergence between wild and cultivated plants. The “plant domestication-reduced defense” hypothesis proposes that cultivated plants have lower chemical defenses and resistance against herbivores than their wild counterparts. Yet, the effects of domestication on the interactions between perennial crops and insect herbivores have not been well-documented. In this study, we hypothesized that domesticated avocado (Persea americana) has lowered resistance against insect herbivores. To test this hypothesis, we measured variation in plant traits (fruit and seed size, seed germination, and plant growth), chemical defenses (total phenolics), and resistance against two leaf-chewing insect herbivores—a specialist (Copaxa multifenestrata) and a generalist (Spodoptera frugiperda)—among seven avocado genotypes across a domestication gradient: wild (ancestral) genotypes, five (intermediate) landraces (“Blanco,” “Lonjas,” “Vargas,” “Zarcoli,” and “Rodolfo”), and the cultivated (modern) “Hass.” Our results showed that seeds from “Hass” have a lower germination rate and slower growth and have shorter fruits and seeds than the landraces and wild genotypes. “Hass” leaves also had lower amounts of total phenolics than the landraces; however, no differences were found between “Hass” and the wild genotypes. There was no effect of genotype on larval mass gained for both herbivores. However, C. multifenestrata had longer larval longevity on “Hass” and the wild genotypes, whereas S. frugiperda larval longevity showed no differences among genotypes. Moreover, C. multifenestrata inflicted more damage on “Hass,” whereas S. frugiperda inflicted more damage on “Lonjas” than on the other genotypes. In general, bigger fruit and seeds were positively correlated with plant size and phenolic content, and total phenolics were positively correlated with S. frugiperda and negatively correlated with C. multifenestrata larval performance. However, despite the genotypic variation in plant traits, phenolic content, and resistance against two herbivores with different levels of specialization, there was no clear support for the “plant domestication-reduced defense” hypothesis in avocado.

Outcrossing Rate and Genetic Variability in Mexican Race Avocado

The blooming behavior of the avocado Persea americana Mill. is a sophisticated mechanism that prevents effective self-pollination, enables close pollination, and encourages cross-pollination. However, there is no information on outcrossing rate among Mexican race avocado genotypes (P. americana var. drymifolia Schltdl. & Cham.). Therefore, the objective of this study was to assess the outcrossing rate and genetic variability in progenies of Mexican race avocado genotypes by simple sequence repeat (SSR) and intersimple sequence repeat (ISSR) markers. SSR marker analysis showed a considerable genetic differentiation among avocado families [total expected heterozygosity (He) = 0.540], whereas the total heterozygosity value observed (Ho = 0.098) showed the presence of genetic structure per family. The total Nei’s unbiased average heterozygosity (nHe) value found with ISSR markers was 0.482. The results of the analysis of molecular variance (AMOVA) combining both type of markers showed that genetic variation within avocado families was 58.6%, and among families was 41.6% (P < 0.0001). The outcrossing population rate in P. americana var. drymifolia was 0.774 ± 0.091 (sd), and the ‘Criollo 3’ and ‘Plátano Temprano’ families showed the lowest (–0.083 ± 0.031) and highest (0.814 ± 0.060) outcrossing rates, respectively. Variability in outcrossing rate depends on many factors, including edaphoclimatic, agronomic, and genetic, and needs to be considered to define strategies for the conservation and genetic improvement of outstanding native genotypes. SSR and ISSR markers are useful for estimating genetic variability within and among families of avocado, as well as for determining the outcrossing rates among closely related individuals and with a rather small sample size.

Fatty acid and volatile organic compound profiling of avocado germplasm grown under East-Central Florida conditions

Worldwide avocado consumption is growing due to potential health benefits. Most research has been focused on ‘Hass’, which does not perform well in Florida. Fatty acids and volatile organic compounds (VOCs) were evaluated in 14 avocado genotypes grown in East-Central Florida conditions and compared to ‘Hass’. Two saturated and five unsaturated fatty acids were detected. Total oil content (TOC) was 11–25%, with 58.2–71.5% unsaturated fatty acids (UFA). ‘FL Hass’ contained 20% TOC, near the average for genotypes tested, but with a low UFA of 61.9%. ‘PA-6206’ (a ‘Hass’ x ‘Bacon’ seedling) and ‘35707’ (a ‘Catalina’ seedling) had higher TOC and UFA than other genotypes, while the mostly West Indian types such as ‘Simmonds’, ‘Day’, ‘Pflume’ and ‘Miguel’ had low TOC. Detected VOCs were acetaldehyde, hexanal, (E)-2-hexenal, limonene, α-cubebene, α-copaene, and β-caryophyllene. Most genotypes contained most of the VOCs. ‘Monroe’ lacked C6 aldehydes, and ‘Pflume’, ‘Bernecker-43’, ‘Lula’ and ‘35707’ lacked some or all sesquiterpenes.

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

Because of the low availability of avocado rootstocks with resistance to Phytophthora cinnamomi, it is necessary to search for genotypes that offer resistance and that could be used as commercial rootstocks. The objective of this study was to select progeny from the genotypes of Mexican race avocado plants that are resistant to P. cinnamomi. Seedlings from 12 avocado genotypes were placed in containers inoculated with a mycelial suspension of P. cinnamomi. Signs of disease in the upper part of the seedlings were registered every 3 days for 8 weeks using a visual scale of damage severity. The χ2 test (P < 0.009) showed significant differences among the genotypes evaluated, with ‘Todo el Año’ being the most resistant, as demonstrated by its rating of 70% asymptomatic seedlings, followed by ‘Plátano’ with 40%. The most susceptible genotypes were ‘María Elena’, ‘Silvestre’, and ‘Hass’, with 100% mortality. Seedling inoculation facilitated the detection of resistance to P. cinnamomi. ‘Todo el Año’ showed resistance toward P. cinnamomi. Therefore, individuals of its offspring could be recommended for use as rootstocks after confirming their resistance with a second evaluation, as well as performing tests in multiple localities to demonstrate their productive behavior after grafting.

Rosellinia necatrix infection induces differential gene expression between tolerant and susceptible avocado rootstocks.

Rosellinia necatrix is the causal agent of avocado white root rot (WRR). Control of this soil-borne disease is difficult, and the use of tolerant rootstocks may present an effective method to lessen its impact. To date, no studies on the molecular mechanisms regulating the avocado plant response towards this pathogen have been undertaken. To shed light on the mechanisms underpinning disease susceptibility and tolerance, molecular analysis of the gene’s response in two avocado rootstocks with a contrasting disease reaction was assessed. Gene expression profiles against R. necatrix were carried out in the susceptible ‘Dusa’ and the tolerant selection BG83 avocado genotypes by micro-array analysis. In ‘Dusa’, the early response was mainly related to redox processes and cell-wall degradation activities, all becoming enhanced after disease progression affected photosynthetic capacity, whereas tolerance to R. necatrix in BG83 relied on the induction of protease inhibitors and their negative regulators, as well as genes related to tolerance to salt and osmotic stress such as aspartic peptidase domain-containing proteins and gdsl esterase lipase proteins. In addition, three protease inhibitors were identified, glu protease, trypsin and endopeptidase inhibitors, which were highly overexpressed in the tolerant genotype when compared to susceptible ‘Dusa’, after infection with R. necatrix, reaching fold change values of 52, 19 and 38, respectively. The contrasting results between ‘Dusa’ and BG83 provide new insights into the different mechanisms involved in avocado tolerance to Phytophthora cinnamomi and R. necatrix, which are consistent with their biotrophic and necrotrophic lifestyles, respectively. The differential induction of genes involved in salt and osmotic stress in BG83 could indicate that R. necatrix penetration into the roots is associated with osmotic effects, suggesting that BG83’s tolerance to R. necatrix is related to the ability to withstand osmotic imbalance. In addition, the high expression of protease inhibitors in tolerant BG83 compared to susceptible ‘Dusa’ after infection with the pathogen suggests the important role that these proteins may play in the defence of avocado rootstocks against R. necatrix.

Generation of composite Persea americana (Mill.) (avocado) plants: A proof-of-concept-study.

Avocado (Persea americana (Mill.)), an important commercial fruit, is severely affected by Phytophthora Root Rot in areas where the pathogen is prevalent. However, advances in molecular research are hindered by the lack of a high-throughput transient transformation system in this non-model plant. In this study, a proof-of-concept is demonstrated by the successful application of Agrobacterium rhizogenes-mediated plant transformation to produce composite avocado plants. Two ex vitro strategies were assessed on two avocado genotypes (Itzamna and A0.74): In the first approach, 8-week-old etiolated seedlings were scarred with a sterile hacksaw blade at the base of the shoot, and in the second, inch-long incisions were made at the base of the shoot (20-week-old non-etiolated plants) with a sterile blade to remove the cortical tissue. The scarred/wounded shoot surfaces were treated with A. rhizogenes strains (K599 or ARqua1) transformed with or without binary plant transformation vectors pRedRootII (DsRed1 marker), pBYR2e1-GFP (GFP- green fluorescence protein marker) or pBINUbiGUSint (GUS- beta-glucuronidase marker) with and without rooting hormone (Dip 'N' Grow) application. The treated shoot regions were air-layered with sterile moist cocopeat to induce root formation. Results showed that hormone application significantly increased root induction, while Agrobacterium-only treatments resulted in very few roots. Combination treatments of hormone+Agrobacterium (-/+ plasmids) showed no significant difference. Only the ARqua1(+plasmid):A0.74 combination resulted in root transformants, with hormone+ARqua1(+pBINUbiGUSint) being the most effective treatment with ~17 and 25% composite plants resulting from strategy-1 and strategy-2, respectively. GUS- and GFP-expressing roots accounted for less than 4 and ~11%, respectively, of the total roots/treatment/avocado genotype. The average number of transgenic roots on the composite plants was less than one per plant in all treatments. PCR and Southern analysis further confirmed the transgenic nature of the roots expressing the screenable marker genes. Transgenic roots showed hyper-branching compared to the wild-type roots but this had no impact on Phytophthora cinnamomi infection. There was no difference in pathogen load 7-days-post inoculation between transformed and control roots. Strategy-2 involving A0.74:ARqua1 combination was the best ex vitro approach in producing composite avocado plants. The approach followed in this proof-of-concept study needs further optimisation involving multiple avocado genotypes and A. rhizogenes strains to achieve enhanced root transformation efficiencies, which would then serve as an effective high-throughput tool in the functional screening of host and pathogen genes to improve our understanding of the avocado-P. cinnamomi interaction.

Avocado oil characteristics of Mexican creole genotypes

Mexico is a major avocado producer and exporter, mainly the Hass variety, while the Mexican creole genotypes remain unexplored. We investigated the physicochemical characteristics, phenolics, and bioactivity of oils from six different Mexican avocado genotypes to increase their consumption and utilization. Oil content varied significantly among Mexican genotypes and increased linearly with dry matter content. Oils from Mexican creole genotypes varied significantly in UV absorbance and generally exhibited low secondary oxidation. Avocado oil displayed two intense fluorescence peaks at 675 and 720 nm (chlorophyll concentration) and two broad bands centered at 465 and 510 nm (oxidation products). The antioxidant activity of avocado oils was independent of total phenolic content and influenced the anti‐inflammatory (COX) activity and selectivity. Three thermal structural transitions occurred in avocado oils between −30 and 20°C. Thermal oxidation by differential scanning calorimetry (DSC) revealed that avocado oils from Mexican genotypes exhibited higher thermal stability than those of Hass. Multivariate data analysis performed on 18 oil characteristics using principal component and cluster analysis demonstrates that fluorescence emission was the major factor segregating Mexican avocado genotypes. Mexican creole avocado is an important beneficial resource for the diversity of its oil quality compared to Hass variety.Practical applications: Mexican creole avocado oil exhibited superior distinctive physicochemical characteristics than Hass avocado variety. The fluorescence emission can be considered as the predictive attribute to characterize and identify the oil quality and distinguish creole avocado genotypes. Avocado oil from creole genotypes could be an important option to add value to these crop resources, ignored by their delicate post‐harvest management. Cold press avocado oil from creole genotypes provides a distinctive regional origin denomination of gourmet oil, enabling to break its confines by post‐harvest management, simultaneously conserving the huge genetic diversity of this valuable crop.Mexican creole avocado oils exhibit superior physicochemical characteristics than Hass. Fluorescence emission effectively segregates avocado oil quality by genotypes.

Exploring genetic variation, oil and α-tocopherol content in avocado (Persea americana) from northwestern Mexico

The Hass cultivar of avocado is the most widely grown commercial cultivar in Mexico. Unfortunately, this cultivar is poorly adapted to the Mexican low-lands with hot dry climates characteristic of northwestern Mexico. Other well-adapted avocado accessions are available for these regions, but their nutritional traits and genetic diversity have yet to be explored. In this study, we analyze oil content, (α-tocopherol) and genetic variation among five local varieties from northwest Mexico that grow in high temperatures regimes in unfertilized soils and without any agronomic management. We report significant phenotypic variability in oil and α-tocopherol components in different accessions of avocado as determined by HPLC. Interestingly, we find higher α-tocopherol content (45.02–50.66 μg/g of fresh pulp) in some local avocados compared to Hass (32.28 μg/g of fresh pulp). The analyzed accessions represent a moderately polymorphic set of genotypes as measured by microsatellite (10 alleles by locus) and SNP (1 SNP every 164.4 bp) analysis of the VTE3 and VTE4 genes, implied in the biosynthesis of tocopherols. SNP data allowed also identifying differences between the local varieties and controls (Hass and the Mexican race accession). The variation observed at the genetic, morphologic and nutritional levels provide significant new information that may be valuable in selecting and developing avocado genotypes adapted to high-temperature environments.

Nondestructive Detection of White Root Rot Disease in Avocado Rootstocks by Leaf Chlorophyll Fluorescence.

White root rot (WRR) disease caused by Rosellinia necatrix is one of the most important threats affecting avocado orchards in temperate regions. In this study, we monitored the progression of WRR disease at the leaf and root levels by the combination of nondestructive chlorophyll fluorescence measurements and confocal laser-scanning microscopy on avocado genotypes susceptible to R. necatrix. Leaf photochemistry was affected at early stages of disease development prior to the appearance of aboveground symptoms, made evident as significant decreases in the trapping efficiency of photosystem-II (Fv'/Fm') and in the steady-state of chlorophyll fluorescence yield (Fs) normalized to the minimal fluorescence yield (F0) (Fs/F0). Decreases in Fv'/Fm' and Fs/F0 were associated with different degrees of fungal penetration, primarily in the lateral roots but not in areas next to the main root collar. Aboveground symptoms were observed only when the fungus reached the root collar. Leaf physiology was also tracked in a tolerant genotype where no changes were observed during disease progression despite the presence of the fungus in the root system. These results highlight the usefulness of this technique for the early detection of fungal infection and the rapid removal of highly susceptible genotypes in rootstock avocado-breeding programs.

Histological and anatomical responses in avocado, Persea americana, induced by the vascular wilt pathogen, Raffaelea lauricola

Raffaelea lauricola causes laurel wilt of avocado, Persea americana. Host × pathogen interactions were examined with light and scanning electron microscopy. The susceptible avocado cultivar ‘Simmonds’ was inoculated and examined 5 cm above the inoculation site 3, 7, 14, 21, and 42 days after inoculation (dai). No external symptoms were observed at 3 and 7 dai, and there were no anatomical differences when compared with the mock-inoculated plants. By 14 dai, external symptoms were present and dark discoloration had developed in sapwood. Tylose development increased significantly by 14 dai, and was positivity correlated with disease severity (P < 0.05). By 14 dai, gels formed in xylem vessels, fibers, and adjacent parenchyma cells; they were associated with xylem blockage and composed of phenols, pectin, and lipids, as suggested by, respectively, toluidine blue O, ruthenium red, and Sudan III stains. With a chitin-specific stain, fluorescein-conjugated wheat germ agglutinin, infrequent mycelia, and conidia of R. lauricola were visualized within xylem lumena and fibers, regardless of sample date. Understanding how avocado responds to the presence of this pathogen could assist the development of laurel wilt-resistant avocado genotypes and inform efforts to manage this disease with other measures.

Attraction and Electroantennogram Responses of Male Mediterranean Fruit Fly to Volatile Chemicals from Persea, Litchi and Ficus Wood

Trimedlure is the most effective male-targeted lure for the Mediterranean fruit fly, Ceratitis capitata (Wiedemann). A similar response is elicited by plant substances that contain α-copaene, a naturally-occurring sesquiterpene. α-Copaene is a complex, highly-volatile, widely-distributed plant compound, and male C. capitata respond to material from both hosts (e.g., Litchi chinensis) and non-hosts (e.g., Ficus benjamina) that contain α-copaene. Avocado, Persea americana, recently was found to contain varying amounts of α-copaene in the bark and underlying cambial tissue. Short-range attraction bioassays and electroantennography (EAG) were used to quantify responses of sterile male C. capitata to samples of rasped wood from four avocado genotypes, L. chinensis, and F. benjamina. Gas chromatography-mass spectral (GC-MS) analysis was used to identify and quantify the major sesquiterpenes. Attraction and EAG amplitude were correlated, with L. chinensis eliciting the highest and F. benjamina the lowest responses. Responses to the avocado genotypes were intermediate, but varied among the four types. GC-MS identified 13 sesquiterpenes, including α-copaene, from all samples. Amounts of α-copaene in volatile collections from samples (3 g) ranged from 11.8 μg in L. chinensis to 0.09 μg in F. benjamina, which correlated with short-range attraction and EAG response. α-Copaene ranged from 8.0 to 0.8 μg in the avocado genotypes, but attraction and EAG responses were not correlated with the amount of α-copaene. Differences in enantiomeric structure of the α-copaene in the different genotypes and/or presence of additional sesquiterpenes may be responsible for the variation in male response. EAG responses were correlated with the amount of several other sesquiterpenes including α-humulene, and this compound elicited a strong antennal response when tested alone.

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

Avocado (Persea americana 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 Arabidopsis and other crop species.

Selection of potential pollinizers for ‘Hass’ avocado based on flowering time and male–female overlapping

Avocado production is dependent on the singular synchronous protogynous dichogamy of the species that promotes outcrossing. With the objective of selecting potential pollinizer avocado genotypes for ‘Hass’, the most important avocado cultivar worldwide, we have monitored during two consecutive years the flowering phenology of 27 avocado genotypes in South-eastern Spain. The average length of the flowering season was 45 days ranging from 18 days for ‘Harvest’ to 50 days for ‘Fuerte’. The earliest genotypes to flower were ‘Fuerte’ and ‘Shepard’ that started blooming during the third week of March. The latest genotypes to flower were ‘Colin V-33’, ‘Adi’, ‘OA184’ and ‘Harvest’, which started blooming in the second week of April. ‘Hass’ blooming lasted 30 days, from the first week of April until the second week of May. Since a good pollinizer must present not only an overlapping in the flowering season but also an overlapping in sexual stages with the pollinated cultivar, a group of 12 genotypes (‘Hass’, ‘Fuerte’ and 10 genotypes producing ‘Hass-like’ fruit with good overlapping in the flowering season with ‘Hass’) was studied with more detail determining daily the stages of male and female overlapping every 2 h. Results herein indicate that ‘Marvel’ and ‘Nobel’ showed a high sexual overlapping with ‘Hass’. Taking into account the flowering phenology, the overlapping in sexual stages and the fruit set obtained with hand-pollinated flowers in the field, those two genotypes could be an interesting alternative to the current use of ‘Fuerte’ as pollinizer for ‘Hass’ in South-eastern Spain.