Avocado Leaf Research Articles

Effects of Persea americana leaf extracts on body weight and liver lipids in rats fed hyperlipidaemic diet

The effects of aqueous and methanolic leaf extracts of Persea americana on body weight and liver lipids in rats were studied. Male albino rats were fed a modified diet containing 0.5% cholesterol and 0.25% cholic acid to provoke hyperlipidaemia. The hyperlipidaemic rats were given 10 mg/kg body weight of either aqueous or methanolic extract of P. americana leaf daily for 8 weeks. There were no significant differences (p>0.05) in the overall body weight gain of the hyperlipidaemic rats compared to normal control. However, the administration of the aqueous and methanolic extracts provoked 14 and 25% reduction, respectively, in the body weight gain of the treated rats compared to the hyperlipidaemic control. Mean liver weights were markedly increased (p<0.05) in rats fed hyperlipidaemic diet (groups B, C and D: 70, 69 and 57%, respectively) compared to normal control rats. The methanolic extract provoked a minimal (8%) decrease in mean liver weight compared to the hyperlipidaemic control rats. It can be hypothesized that P. americana leaf extracts increase catabolism of lipids accumulated in adipose tissue causing a decrease in body weight but does not influence liver lipid levels in rats. Key words: Persea Americana, body weight gain, hyperlipidaemia, leaf extracts, albino rats.

(145) Water Relations of Avocado in Response to Changes in Relative Humidity

Vapor pressure deficit (VPD) is the driving force for plant water loss. However, air relative humidity (RH) can be used as a surrogate for VPD. While plants can adapt to environments with varying RH, little is known about how they respond to sudden shifts in RH. Areas of Southern California can experience drastic shifts in RH, from 60% or greater to less than 20% in just a few hours. The effect of these shifts on avocado (Persea americana Mill.) tree productivity is a major concern to growers. We studied the effect of shifts in RH on `Hass' avocado leaf stomatal conductance (gs) and branch sap flow in trees grafted on Duke 7 clonal rootstock. Under many conditions, the avocado assimilation rate is governed by gs. When gs is high in morning (&gt;150 mmol·m-2·s-1), the water loss generally leads to some stomatal closure in the afternoon (50% or more). Conversely, low morning gs results in a higher gs rate in the afternoon (10% to 20% stomatal closure). This relationship between morning and afternoon gs is intensified by a shift from high to low RH in the afternoon. Therefore, in a drier atmosphere in the afternoon, the afternoon depression in gs is greater, leading to an impaired assimilation capacity. We hypothesize that the afternoon decrease in gs is due to low root/shoot hydraulic conductivity since soil water is readily available. While it is possible that low hydraulic conductivity on gs is exacerbated at the graft union, sap flow of grafted trees in greenhouse studies was nearly equal to trees on their own roots (ungrafted); in fact, often the depression in the afternoon was less on grafted trees. This suggests that while avocado is not suited to areas with low RH, water flow through the roots could be an additional criterion in selecting improved rootstocks.

Anticonvulsant effect of Persea americana Mill (Lauraceae) (Avocado) leaf aqueous extract in mice

Various morphological parts of Persea americana Mill (Lauraceae) (avocado) are widely used in African traditional medicines for the treatment, management and/or control of a variety of human ailments, including childhood convulsions and epilepsy. This study examined the anticonvulsant effect of the plant's leaf aqueous extract (PAE, 50-800 mg/kg i.p.) against pentylenetetrazole (PTZ)-, picrotoxin (PCT)- and bicuculline (BCL)-induced seizures in mice. Phenobarbitone and diazepam were used as reference anticonvulsant drugs for comparison. Like the reference anticonvulsant agents used, Persea americana leaf aqueous extract (PAE, 100-800 mg/kg i.p.) significantly (p < 0.05-0.001) delayed the onset of, and antagonized, pentylenetetrazole (PTZ)-induced seizures. The plant's leaf extract (PAE, 100-800 mg/kg i.p.) also profoundly antagonized picrotoxin (PCT)-induced seizures, but only weakly antagonized bicuculline (BCL)-induced seizures. Although the data obtained in the present study do not provide conclusive evidence, it would appear that 'avocado' leaf aqueous extract (PAE) produces its anticonvulsant effect by enhancing GABAergic neurotransmission and/or action in the brain. The findings of this study indicate that Persea americana leaf aqueous extract possesses an anticonvulsant property, and thus lends pharmacological credence to the suggested ethnomedical uses of the plant in the management of childhood convulsions and epilepsy.

Evaluation of factors influencing augmentative releases of Chrysoperla carnea for control of Scirtothrips perseae in California avocado orchards

Weekly releases of Chrysoperla carnea for control of Scirtothrips perseae were evaluated in replicated field plots in two commercial avocado orchards in southern California, USA. Two release techniques and rates commonly employed by commercial pest control advisors who routinely use this generalist predator for S. perseae control were assessed. Release technique one utilized C. carnea eggs glued to paper squares that were stapled to leaves of experimental trees at a rate of 41,000 eggs per ha. Release technique two used a motorized backpack sprayer to apply a dry mixture of lacewing eggs and larvae to trees at a rate of 514,501 per ha. Pest populations were monitored by making bi-weekly population counts of S. perseae larvae and adults on leaves, and adult densities were simultaneously monitored in each experimental plot with yellow sticky cards. In the laboratory, degree-day accumulation until death of immature C. carnea was determined at temperatures representative of field conditions when predators were provisioned with varying amounts of food or different food types. Preference for S. perseae instars by first, second, and third instar C. carnea was assessed in the laboratory, and intraguild predation towards larvae and adult females of a co-occurring generalist predatory thrips, Franklinothrips orizabensis , was investigated along with intraspecific predation rates. Both release strategies failed to significantly reduce S. perseae populations in comparison to non-treated control plots. Approximately 35–96% of C. carnea eggs and larvae applied with the motorized sprayer landed on the ground. C. carnea larvae lived for approximately 1–2 days when provisioned with either no food, an avocado leaf or avocado pollen. Longevity was extended to 14–15 days when prey was provided. C. carnea larvae showed no preference for first or second instar S. perseae , all predator instars attacked first instar F. orizabensis , but only second and third instar C. carnea managed attacks on second instar F. orizabensis larvae. No adult female F. orizabensis were attacked and no attacks by F. orizabensis on C. carnea were recorded. Second instar C. carnea engaged in the highest levels of intraspecific predation.

Solid-phase microextraction and gas chromatography–mass spectrometry of volatile compounds from avocado puree after microwave processing

Microwave processing offers an alternative to blanch fruits and vegetables, since the application of high temperature and short time often results in minimum damage. An experimental design was used to investigate the effect of microwave time, pH, and avocado leaves (independent variables) on avocado flavor (response) using solid-phase microextraction (SPME)–GC–MS. Among the fully characterized flavor volatiles, 19 compounds were derived from lipid oxidation and only 4 from the avocado leaves. The main components derived from lipids were aldehydes, ketones and alcohols. Terpenoids, estragole, and 2-hexenal [ E] were volatiles derived from avocado leaves. When leaves were added to fresh and microwaved avocado terpenoids and 2-hexenal [ E]/hexanal ratio increased, this behavior was considered to have a positive effect on the sensorial quality of the product. From the statistical analysis of the experimental design, it was possible to determinate that the most important factors influencing the abundance of flavor compounds derived from lipids were microwave time and pH. Maximum values of these compounds were detected at high levels of microwave time and low values of pH. On the other hand, response surface of terpenoids and estragole showed an increment when microwave time and avocado leaf was increased. The region of optimum response was 30 s microwave time, pH 5.5, and 1% of avocado leaf.

Predation behaviors of Franklinothrips orizabensis (Thysanoptera: Aeolothripidae) towards Scirtothrips perseae and Heliothrips haemorrhoidalis (Thysanoptera: Thripidae)

The foraging behaviors of predatory female Franklinothrips orizabensis Johansen towards Scirtothrips perseae Nakahara and Heliothrips haemorrhoidalis (Bouch e in avocado leaf arenas were videotaped and analyzed. F. orizabensis encountered and attacked more second instar S. perseae with 80% ðn ¼ 113Þ attacks on this life stage being observed compared to 20% on first instars ðn ¼ 28Þ when equal numbers of these prey were presented simultaneously. However, there was no significance difference by life stage for the probability of being attacked after being encountered. Successful attacks by F. orizabensis only occurred against propupal H. haemorrhoidalis ðn ¼ 6Þ that lacked protective fecal droplets, 65% of prey encounters were with this life stage, and 6% of encounters with propupae resulted in attacks. Second instar H. haemorrhoidalis larvae bearing protective droplets were encountered less frequently and were not attacked when contacted even though equal numbers of both stages were presented simultaneously. Consequently, the mean proportion of the time spent grooming by F. orizanbensis females attacking immature H. haemorrhoidalis was four times greater than that for females attacking S. perseae larvae even though there was no significant difference in mean time (s) spent in each grooming bout. Significant differences in mean consumption times by F. orizabensis existed across life stages and prey species. Consumption times were shortest for first instar S. perseae larvae, intermediate for second instars, and longest for H. haemorrhoidalis propupae. Mean consumption times for sequentially attacked second instar S. perseae declined significantly indicating satiation of predators. Predators would spend on average approximately 7–13 s probing leaves with mouthparts and feeding on fluids; a behavior that on average occupied 2–5% of their time. This result may explain observed mortality of F. orizabensis in the laboratory and field when this predator forages on avocado leaves that have been treated with insecticides that exhibit translaminar activity. 2003 Elsevier Science (USA). All rights reserved.

Phenology of Arthropod Pests and Associated Natural Predators on Avocado Leaves, Fruit, and in Leaf Litter in Southern California

Abstract Abundance of Scirtothrips perseae Nakahara (Thysanoptera: Thripidae), Oligonychus perseae Tuttle, Baker & Abbatiello (Acari: Tetranychidae), predators, and associations among their population trends on avocado leaves and fruit were determined in three untreated avocado orchards in Ventura and Santa Barbara Counties, CA, from 1998 to 2000. Objectives were to understand pest-predator dynamics and to assess which predators have potential as biological control agents. Numbers of S. perseae and predators from leaf litter/soil were also determined in one orchard from 1998 to 2000. On leaves, O. perseae was the most abundant pest, followed by S. perseae, and Oligonychus puniciae (Hirst) (Acari: Tetranychidae). Phytoseiid mites and spiders were the most abundant predators. The predatory thrips Franklinothrips orizabensis Johansen and Aeolothrips kuwanaii Moulton (Thysanoptera: Aeolothripidae) were also relatively abundant compared with at least 13 other species of predators on leaves. On immature avocado...

A preliminary study on the hypotensive activity of Persea americana leaf extracts in anaesthetized normotensive rats

The effect of the constituents of the leaves of Persea americana on arterial blood pressure was investigated in anaesthetized normotensive rats. The intravenous administration induced a marked fall in mean arterial blood pressure which lasted 2–3 min. The short duration of action may be due to rapid metabolism.

Isolation and identification of a compound from avocado (Persea americana) leaves which causes necrosis of the acinar epithelium of the lactating mammary gland and the myocardium.

It is well known that when lactating livestock eat avocado (Persea americana) leaves they may develop non-infectious mastitis and agalactia. This is associated with extensive coagulation necrosis of the secretory acinar epithelium and interstitial oedema, congestion, and haemorrhage. Similar lesions have been produced in mammary glands of lactating mice fed a diet containing a small percentage of freeze-dried avocado leaf. Tests using these animals have been used to isolate the active principle, termed "persin," from avocado leaves. The purified persin was examined using IR, NMR, and UV spectroscopy and mass spectrometry, and identified as (Z,Z)-1-(acetyloxy)-2-hydroxy-12,15-heneicosadien-4-one. Persin has previously been isolated from avocado leaves and shown to have antifungal properties and to be toxic to silkworms. Our tests have shown that persin at the dose rate of 60-100 mg/kg has the same effect on mammary glands in lactating mice as leaves from avocado. Enantioselective syntheses of the R and the S isomers of persin and related derivatives were carried out. These compounds were tested for activity required to induce widespread lactating mammary gland necrosis in mice, and only the R isomer was found active. At doses of persin above 100 mg/kg necrosis of myocardial fibres may occur and hydrothorax may be present in severely affected animals. The mechanism of action of persin on both the mammary gland and the myocardium remain to be resolved.

Evaluation of Bacterial Epiphytes Isolated from Avocado Leaf and Fruit Surfaces for Biocontrol of Avocado Postharvest Diseases

Bacteria isolated from Fuerte avocado leaf and fruit surfaces were evaluated for in vitro antagonism toward Dothiorella aromatica. Thirty-three bacteria exhibiting pronounced growth inhibition were further tested for antibiosis against Colletotrichum gloeosporioides, Thyronectria pseudotrichia, Phomopsis perseae. Pestalotiopsis versicolor, and Fusarium solani. Optimum disease-reducing concentrations of Bacillus subtilis (isolate B246) exhibiting the highest degree of antibiosis were determined according to a checkerboard-type titration assay, by artificial inoculations on Fuerte and Edranol avocado fruit in the laboratory. Various concentrations (10 5 , 10 6 , 10 7 , and 10 8 cells ml -1 ) of B. subtilis were also incorporated into commercial Tag-wax and applied to Hass avocado fruit in the packinghouse for control of anthracnose, Dothiorella/Colletotrichum fruit rot complex (DCC), and stem-end rot (SE). In the artificial inoculation study, increasing concentrations of B. subtilis were effective against increasing concentrations of C. gloeosporioides, F. solani, and T. pseudotrichia. Control of D. aromatica was significant at the lower (10 3 and 10 4 cells ml -1 ) pathogen concentrations, whereas inhibition of P. perseae and P versicolor was more readily achieved at the lower (10 5 and 10 6 cells ml -1 ) antagonist concentrations. In the packinghouse, a B. subtilis concentration of 10 7 cells ml -1 significantly reduced anthracnose and SE externally and internally, while the lower B. subtilis concentrations (10 5 and 10 6 cells ml -1 ) were effective against internal DCC. Based on treatment means of all external and internal postharvest disease data, all B. subtilis concentrations performed equally well in controlling postharvest diseases.

Isolation and selection of bacteria and yeasts antagonistic to preharvest infection of avocado by Colletotrichum gloeosporioides

Bacteria and yeasts were isolated from leaves, flowers and fruit of avocado trees that had not been sprayed with pesticides for several years. Of the 1050 microorganisms isolated, 37% inhibited mycelial growth of Colletotrichum gloeosporioides on potato dextrose agar. Many of these organisms also significantly reduced spore germination of the fungus on cellophane overlaying weak sugars agar and a greater proportion of yeasts than bacteria were more effective. Some bacteria and yeasts also reduced spore germination of the pathogen on avocado leaf disks. The predominant group of suppressive bacteria was Bacillus spp., and the antagonistic yeasts included Aureobasidium spp. and a variety of pink and white colony types. Antibiotic resistant isolates of Bacillus, carbendazim resistant isolates of two yeasts and an Aureobasidium sp. were sprayed on avocado leaves and survived for at least 2 months on the phylloplane. On the basis of performance in these tests, isolates with biocontrol and colonization potential were selected and tested for their capacity to provide disease control on fruit. In repeated tests, several bacteria and yeasts consistently reduced lesion development and lesion size on detached avocado fruit when applied prior to inoculating fruit with the pathogen.

Phagostimulants enhancing the efficacy ofBacillus Thuringiensis formulations against the Giant Looper,Boarmia (Ascotis) Selenaria, in avocado

In both laboratory and field trials, as well as in semicommercial scale applications, the minimum concentration ofBacillus thuringiensis (B.t.) required to secure satisfactory larval mortality ofBoarmia selenaria could be halved, from 0.5% to 0.25%, by addition of 1% of the commercial phagostimulant Coax. Another phagostimulant product, Gustol, was inactive. Coax did not attract caterpillars from a distance. However, individual, Coax-treated spots on the avocado leaf surface were consumed by the larvae to a significantly greater extent than control. The same difference in palatability was recorded when the spots were treated with a mixture of Coax and aB.t. formulation. This explains, at least partially, the aforementioned advantageous effect of Coax in practical control of the looper byB.t.

Effect of Fruit Removal on Net Gas Exchange of Avocado Leaves

Abstract In the article “ Effect of Fruit Removal on Net Gas Exchange of Avocado Leaves”, by Bruce Schaffer, L. Ramos, and S.P. Lara (HortScience 22:925-927, October 1987), ref. 2 was incorrect. The correct citation is: Annu. Rev. Plant Physiol. 33:317-345.

Effect of Fruit Removal on Net Gas Exchange of Avocado Leaves

Abstract All but 10 current-year leaves were removed from girdled branches of avocado (Persea americana Mill.) trees having one remaining fruit or all fruit removed. Removing all fruit resulted in increased leaf dry weight per area (Wa), a 250% increase in the number of starch grains in leaves, and a reduction in leaf conductance (gl) and net CO2 assimilation (A). Internal CO2 concentration (Ci) was lower for leaves of branches with fruit than for leaves of branches without fruit. The results suggest that the accumulation of starch in defruited, girdled branches results in an inhibition of A. The data suggest that the increased gl associated with the presence of avocado fruit is possibly a result of increased A and reduced Ci levels.

Evaluation ofTrichoderma as a biocontrol agent forRosellinia necatrix

Different isolates ofTrichoderma harzianum andTrichoderma hamatum were isolated from naturally infected roots ofRosellinia necatrix. T. harzianum andT. hamatum isolates overgrew cultures ofR. necatrix placed simultaneously in petri dishes. Relative levels ofR. necatrix population were assessed by the avocado leaf colonization method.T. harzianum isolate T-8, significantly reducedR. necatrix colonization of avocado leaves in comparison to other isolates in artificially and naturally infested soils.R. necatrix inoculum decreased steadily over 4 and 6 week periods in artificially inoculated soil and naturally infested soil respectively when isolate T-8 was applied, to a point where noR. necatrix could be recovered. Disease incidence of almond seedlings was significantly reduced when isolate T-8 was added to naturally infested En-Zurim soil.

Endogenous Content of a Leaf Substance(s) Associated with Rooting Ability of Avocado Cuttings

Abstract Root promotion activity in avocado leaf extracts was determined by the mung bean bioassay. Ten different clones representing a wide range of rooting abilities were compared. Following chromatography of methanol extracts in 8 isoprapanol : 2 water (v/v), a positive correlation was found between rooting ability of avocado cuttings and a mung bean rooting promoter at Rf 0.9–1.0 of the chromatograms. The same zone inhibited the straight growth of wheat coleoptile.

Ultrastructural Changes in Avocado Leaf Tissue Infected with Avocado Sunblotch

Ultrastructural Changes in Avocado Leaf Tissue Infected with Avocado Sunblotch

Natural phenolic Substrates for Peroxidase and Polyphenol Oxidase from Avocado Leaves

SummaryTwo methods were used to extract and hydrolyse phenolic acids from avocado leaves. The conventional method, used in earlier work, converted caffeic acid to aesculetin. A new modified method has now been developed and is described. Both caffeic acid and aesculetin acted as substrates for peroxidase (PO) and polyphenol oxidase (PPO) enzymes. The former enzyme showed a preference for caffeic acid whereas the latter showed a higher activity for aesculetin. The possibility that catechin may be the principal substrate for PPO is discussed.

Procyanidins (Condensed Tannins) in Green Cell Suspension Cultures of Douglas Fir Compared with Those in Strawberry and Avocado Leaves by Means of C18-Reversed-phase Chromatography

The procyanidins (the most common type of proanthocyanidin or condensed tannin) from cell suspension cultures derived from cotyledons of Douglas Fir have been compared with those isolated from leaves of strawberry and avocado. Seventy per cent methanol (v/v) extracts from 100 milligrams fresh weight samples were analyzed by a combination of C(18)-reversed-phase columns with high-performance liquid chromatography, and normal phase paper chromatography. (-)-Epicatechin and its oligomers were generally retarded longer on C(18) columns than the corresponding units made of (+)-catechin when eluted with solvents made up of 5% acetic acid alone or mixed with methanol up to 15% (v/v). Douglas fir preparations contained the most complex set of procyanidins and consisted of oligomers of catechin and epicatechin, whereas strawberry and avocado contained mainly (+)-catechin and (-)-epicatechin derivatives, respectively.

A Phytophthora-induced Inhibitor of Peroxidase Activity in Avocado Leaves

A Phytophthora-induced Inhibitor of Peroxidase Activity in Avocado Leaves