In order to know the avocado genetic resources distribution in México, and their genetic diversity, collecting missions have been achieved in 24 States. The collecting sites and areas are described, and the gathered material - vegetative, fruits and seeds –is characterized according the UPOV Guide. We have a preliminary taxonomic dassification inside the genus Persea, and the major areas of genetic diversity are presented. Additionally, relationships between taxons and their environments have been established. Up to date, we have treated with about 600 accessions form Persea americana Mili. induding the three horticultural races, and Persea schiedeana Nees.

At the present time the society has a better concern for the conservation of the genetic diversity, beca use the gene tic diversity of each country is the most essential tool for the breeding program, of this manner must put special attention to establishment the plots or germplasm banks. At the Fundación Salvador Sánchez Colin, since 1989, with the support of the different national and intemational institutions we have carried out activities of exploring, collection, preservation and evaluation of different materials of Persea genus. Today the natural patrimony of the preserved genetic diversity is of 185 collections among the Persea and Beilschmiedia genus. Of the Persea genus in addition to the three races and of the local selections grouped as hybrids are counted on the following species: Persea steyermarkii, Persea schiedeana, Persea nubigena, Persea lingue, Persea indica, Persea fIoccosa, Persea cinnerascens, Persea gigantea and the other dassified like Persea spp. Conceming related species has to Bei/schmiedia with the following species: Bei/schmiedia anay, Bei/schmiedia miersii.

Avocado gene pool plots, established in Mexico(CICTAMEX)and Israel (VolcaniCenler) during Ihe lasl 10 years, inelude a few hundred germplasm ilems. They were evalualed in Israel as 'rootslocks for avocado under soil slress condilions. Several ilem showed lolerance lo eilher one or more faclors, such as salinity,lime,poor aeralion, rool-rol and drought.

Genetic resource collections are important to the future security of fruit industries. Without research to locate, preserve, characterize and develop these resources they will be lost to future generations of avocado (Persea americana Mili.) growers and consumers. Dwarfing rootstock programmes rely on continued access to wild germplasm and to more formal collections in field gene banks. Such research provides an economic incentive to maintain and expand these collections. Strategies and progress on characterizing traits potentially useful for identifying dwarfing genotypes in the avocado germplasm are discussed in this paper.

Clonal avocado rootstocks were developed In Israel on a small scale between the years 1962 to 1977 and on a large scale In the years following. During the entlre period about 220 dlfferent rootstocks have been developed In an attempt to solve 5011 problems caused by stress factors such as salinity, lime, poor aeratlon and root-rot, and various comblnations of these factors, whlle slmultaneously Improvlng productlvity. Unlformlty among trees and dwarfness were also taken into account as part of the search for better rootstocks. The development process included fleld evaluatlon on a very large scale, In which 350 experiments and 65000 trees took part.

A potential problem in regard to avocado (Persea americana MilI.) crop in Mexico, is the use only of one cultivar, 'Hass' that represents the 95% of cultivated area. There is a need to look for another cultivar with characteristics of quality and productivity equal or superior to 'Hass', with stable characteristics in our different production areas. For this reason, the "Fundación Salvador Sánchez Colin-CICTAMEX, S. C: has a breeding avocado programo In the present work we made a short history of the advantages until to the new selections, results obtained of the establishment and evaluation of seedlings like: 'Fundación 11',the dwarf tree; 'Encinos' whith high fruit quality and little seed; 'Aguilar' the production out of season. Selections with possibility the cultivation a commercial scale.

The geographic area in which the avocado originated, stretching from Mexico through Guatemala and probably to Pacific coastal Costa Rica, presents a diverse set of environments. The three races that gave rise te modern avocado cultivars-Antillean (West Indian), Guatemalan and Mexican-accordingly are adapted te quite distinct environmental conditions. The apparent Mexican-Guatemalan hybrids that originated around Atlixco in Puebla State, Mexico, exemplified by 'Fuerte', showed remarkable adaptation when moved to the Mediterranean-type subtropical microcIimates cornmon in southern California, permitting a commercial industry to develop and later be transferred to other parts of the world with similar climates, such as South Africa, Israel and Chile. Selection from the material originally brought from Mexico and Central America permitted California to develop commercial cultivars exemplified by 'Hass', 'Fuerte' and 'Reed', among others, that lead the world in the area planted. Guatemalan cultivars are adapted te elevated situations in Central America, yielding well under cool conditions and forming an important dietary staple. The Antillean race, 'which probably originated aIong the Pacific coast in Central America, yields well in lowland tropical situations and warm subtropical areas such as southern Florida. Planting Guatemalan and Antillean avocados side-by-side in Florida ea¡'ly in this century produced a new group of hybrid cultivars with quality superior to that of most Antillean cultivars, adaptation te sea level locations, and an extended range of season of maturity that permitted Florida te market fruit into the autumn and winter, well past the season of pure Antillean cultivars. The best of these hybrids, 'Booth 7', 'Booth 8', 'Lula', 'Choquette' and a few others have been exported te warm locations about the tropical world for commercial planting. Thus, selection of avocado germplasm imported from Mexico and Central America into California and Florida produced a group of cultivars that are of significant commercial importance in the world.

En el presente trabajo se estudiaron dos tipos de genotipos que sobresalen por su precocidad a la floración, su porte bajo y producción de buena calidad (calibre 12 a 14). Estos genotipos son la selección Jiménez 1 y la selección Jiménez 2; además de un testigo. Las variables estudiadas fueron: (v1) largo del fruto, (v2) ancho del fruto, (v3) largo del pedúnculo y (v4) ancho del pedúnculo; asi como conocer la fenologia de los árboles, aparición de plagas que dal'lan al fruto, calibres y rendimientos. Los resultados obtenidos fueron: para la (v1) el mejor genotipo resultó la selección Jiménez 1, superando a la selección Jiménez 2 con un 19.88% y al testigo con un 43.89%. Para la (v2) el mejor material resulto ser también la selección Jiménez 1 superando a la selección Jiménez 2 con un 20.5% y al testigo con un 41.15%. Para las variables 3 y 4 no hubo significancia estadistica, ya que son medidas pequel'las y muy homogéneas. En cuanto a la fonologia de los árboles la selección Jiménez 1 empezó a florecer a mediados del mes de septiembre, la selección 2 a principios de octubre y el testigo a mediados del mes de octubre. En cuanto a la aparición de plagas que dal'lan al fruto, estas aparecieron cuando los frutos presentaban cierta tolerancia al dal'lo (Jiménez 1 y 2), en cuanto al testigo coincidlan los mayores picos de la plaga con la máxima floración. Para los calibres, las selecciones Jiménez 1 y 2 se obtuvieron calibers 12 a 14 y para el testigo 14 a 16. Por último para el rendimiento, se siguen haciendo los muestreos ya que la cosecha inicia el 15 de agosto y termina el 15 de septiembre. En conclusión ambas selecciones presentan precocidad en la floración y por lo tanto cosechas tempranas, además de presentar un porte bajo 5.33 m A los 10 al'los y fruta de buena calidad calibre 12 a 14.

The southern Sonora valleys in Mexico are grown to 377,125 ha under irrigated conditions, high percent of the surface is devoted to small grain crops. The NAFTA (North American Free Trade Agreement) signing offers a series of advantages and challenges to Mexican agriculture in order to share vegetable and fruit intemational markets. In this scenery Mexican avocado has played an important roll during the past couple of years because of the United States commercial opening. This research was conducted in Southem Sonora, Mexico (26. 41' and 290 NL, and 1090 12' and 109041: WL), from 1989 to 1997. Four cultivars ('Fuerte', 'Hass', 'San Miguel' and 'Ensenada') were planted on a sandy loam soil during march, 1989 in a array 10 x 10 m with five trees each cultivar. A completely random design was used with five replications a DMS P$0.05 test to separate treatrnents under study was used. Measured parameters were round-year stem diameter growth and height, number of fruits per tree, average weight of fruits and yield (t. ha"'). Analysis showed that stem diameter growth and height was !¡Iow during the first year in the field, but after that time, values increase gradually, with a maximum of 15 cm, and 150 cm in stem diameter and height respectively. The before-mentioned was as the result of an absence of strong sink and source relationship. A strong phenomenon of altemate bearing was observed in better performers such as 'Fuerte' and 'San Miguel', even when in a accumulative yield analysis, were high yielders. 'Hass' always yielded in an uprising manner throw the period of study average weight of fruits ranked between 107 to 242 9 being distributed from bigger to smaller size as follows: 'Hass', 'San Miguel', 'Fuerte' and 'Ensenada'.

En la actualidad, 'Hass' es la principal variedad de aguacate cultivada en los principales centros de producción y también en Chile…

La República Mexicana tiene una riqueza invaluable en tipos criollos y silvestres de aguacate (persea Americana Mill.), CICTAMEX (1991), que es importante preserver y rescatar del peligro de la inminente extinción (Olvera, 1998), debido a que se están sustituyendo en la mayoría de los huertos de este frutal en el Estado de Michoacán, que es considerado como posible centro de origen y dispersión de la raza Mexicana Sánchez (1994), en la región de Tacámbaro y en otras áreas con el mismo clima y suelo los genotipos naturales y "criollas" de aguacate por cultivares de mayor rendimiento como 'Hass' principalmente (Sánchez, 1991), por su alta demanda en el mercado de consumo tanto nacional como internacional. Por otro lado no obstante que el aguacate es originario del sur de Norteamérica y Centroamérica, las mayors colectas de esta especie se encuentran en Estados Unidos de América e Israel (CICTAMEX, 1991). El objetivo del proyecto es definir"un catálogo y un método de conservación de semillas y plantas de ecotipos de tipos "criollos" y silvestres con la finalidad de usarlos en un Banco de Germoplasma (Barrientos, 1997), y posteriormente para el enriquecimiento y generación de nuevos cultivares (Pérez, 1986), para estudios filogenéticos y de fitomejoramiento, (Gallegos, 1982). Para contribuir a su rescate, preservación y conservación.

With the purpose to proceed at productivity study ot tour avocado cultivar and influence ot tour rootstocks, Dire~o Regional de Agricultura do Algarve has established avocado trials at Centro de Experimenta~o Horto-Fruticola do Patacao, on May 1983. From several parameters, which have been registered, some results were already published. Only data relating to cultivar production were not yet matter ot any writed reterence. For their productivity were selected 'Hass', 'Reed', 'Bacon' and 'Fuerte' as scion cultivars, as well as Topa-Topa, Lula, Antilhano ot Canárias and Duke 7 as rootstocks. Along tourteen years ot observations (1985 - 1998), it was confirmeda significanteffect ot variety x rootstock interaction on the production, being in the limelight the 'Bacon'I'Lula" symbiont.

In spite of seleetion for thousands of years, the avocado is still a poorly domesticated tree in the early stages of adaptation to an orehard environment. Cultivars based on Guatemalan and Mexican germplasm, for the subtropics and Mediterranean elimates, have only been available since the 1920's, and even in the best growing conditions the yield barrier of 30 t.ha-1 is hard to breaeh. Tropical "West Indian" (Iowland) avocado eultivars and produetion teehnology is less well developed. Orehard performance is therefore still largely influenced by evolutionary hangovers and constraints. For "subtropical" types, we have to deal with the residual survival strategies of a late-successional, K-seleeted, small-gap colonizing mountain eloud forest tree. These inelude potentially vigorous vegetative growth in flushes, counter-produetive to flowering and fruiting; delayed and typically irregular (mast) fruiting; unnecessarily profuse flowering in late'winter synchronized by winter cold and drought; short-lived shade-adapted leaves bome in creasingly further from the trunk on the tree periphery; energy-expensive fruits for large dispersal agents, hence the exhaustive nature of eropping on reserves, espeeially in large trees; and the tree's strategy to effieiently hoard, store and recyele carbohydrate and mineral reserves (hence "mineral-eheap" fruiting). Physiological attributes inelude potentially rapid C assimilation, but reduced photosynthesis under shade, water of Phytophthora stress; reasonable drought tolerance which however is at the expense of C assimilation and leaf effieiency; and the poorly researehed dependence on perseitol rather than sucrose as the main translocation sugar. Manipulation implications center around canopy/tree size/light management and the alleviation of stress at criticar times, to optimize C gain and allocation to fruiting on a sustainable basis. The prime need remains breeding for more manageable seion and rootstock combinations.

This work, which was a part of the M.Se. studies in the Faculty of Agriculture in the Hebrew University of Jerusalem, was carried out under the supervision of Prof. E.E. Goldschmidt. Two basie processes which take place concurrently in the avocado tree dwing the yearly cyde of growth and reproduction are discussed In thls essay: Dry matter production and its utllization.

The various stages of abscission of buds, fIowers and fruiUetswere recorded in the early spring in 12 'Fuerte' traes. Summer fruiUetabscission was recorded in 60 traes of each cultivar: 'Ettinger', 'Fue,rte' and 'Hass' and winter fruit drop in 60 'Hass' traes only. Total number of organs abscised was 0.230-1.277 milllon and the abscission process was independent of flowering intentsity. Total abscission balance for a 'Fuerte' trae showed that fruitset percentage was 1.5% but 99% of the fruiUets dropped and only 1% were picked. Thus only 0.015% of the flowers developed jnto mature fruits. No relationship was found between buds and flower abscission and yield. Increased productionmay be achieved by reducingsummer drop in 'Ettinger'and 'Hass' or earlierdrop In 'Fuerte'. Total dry weight of abscised organs was only 15%of the aop. Therefore, the massive abscission is not the only factor determiningavocado productivity.

The total nutritionalloss in an avocado trae due te abscission of buds, flowers, fruiUets and fruits is relatively small. Only 25.8 kg.ha.1 N, 3.7 kg.ha.1 P and 31.0 kg.ha.1 K are found in the abscissed organs. Among the microelements Fe is lost 7 to 50 times more than the other microelements (1.40 kg.ha.I). No relationship was found between the nutrients and the previous or future yield except for phosphorous. Decrease in P level in the flowers was followed by an increase in yield the following winter. The small nutritionalloss seems to be of minor importance as a factor in avocado productivity.

To study the effect on some physiological aspects of 'Colín V-33' as interstock the following treatments used: 'Colín V-33'/ Mexican Race, 'Hass'/ 'Colín V-33'/ Mexican Race, and 'Hass'/ Mexican Race, in two phenologycal phases: 1) the end of flowering, fruitset and beginning of vegetative growth, and 2) when plants had growing fruits (2.5 months before harvest).The photosintetically active radiation was larger than 1000 J.lmol.m'2's'1; the temperature near to the leaf varied from 22.8 to 32.1 .C in phase 1 and from 22.8 to 27.5 .C in fase 2. The effect of 'Colín V-33' was not different for assimilation rate of CO2 from the control (4.14 and 4.28 J.lmol'm,2's.1, respectively). These two, however, produced effects which were statstically different relative to those from 'Colin V-33'/ Mexican Race for these two variables (6.94 J.lmol'm.2's,1 and 103.2 mmol:m,2.s' respectivelly). The water potential from the treatment with interstock 'Colín V-33' was -14.85 bars while without interstock was -12 bars. The difference was not statiscally significant (P~ 0.05). Within treatments, means for the relationship ABA:AIA (mg.g.1 fresh weight) were always statistically significant (P s 0.05). In 'Colín V-33'/ Mexican Race it was found 28.7 mg in the cultivar an 22.7 mg in the rootstock; in the same order it was fuond 13.9 and 24.2 mg for 'Hass'/ Mexican Race and 32.2, 30, and 23.9 mg in.

The evolution of moisture, oil content and the oil composition in avocado (Persea americana Mill.), cvs. Hass and Fuerte, were measured every 15 days, during three seasons 1996,1997 and 1998, at the end period of fruit development. The oil content was estimated using the moisture content and the oil composition measured by gas chromatography, using a Perkin Elmer model 3920 chromatograph, with FID detector (250"C) and 1.8 m x 3.1 mm column, filled with 5% of DEGS chromosorb W, acid washed and salinized, 100 mesh, heated at 190°C with 40 ml'min-1nitrogen flow. The fatty acids: oleic, linoleic, palmitic, palmitcleic, linolenic and estearic were measured. In both, it was found, that the oil and moisture level. were different at the same date, in each season,probably because of the weather conditions, specifically the rainfall. The oleic acid rose up to 50% and was the highest fatty acid component in the avocado oil. palmitic and linoleic acids were found in 10% and 8% respectively and palmitoleic in 3-5%. Estearic and linoleic acids were found in very low amounts (Oto 1%), during the fruit development. The oleic acid decreases in each season, fter the minimum oil content (10%) to peak was reached. It was not found a correlation, between the development of the different fatty acids measured

The avocado fruit (cv. Hass) is a berry wilh mesocarp and endocarp that contain one seed. In our study, this seed represented 15.0 to 16.0% of the weight in relation to fruit. For microscopy observations, sections were stained wilh tolution blue and was found that parenchima's cells of cotiledons had the major quantity of starch (blue to violet granules), while the embryo axis storage the major portíon of fat which was observed as refringent ambar droplets. The coat seed was observed, perfectly defined in schlerenchima and tannins cells that were brown to red color. Conceming extraction of fat of avocado seed, was found that hexane and CO2 supercritical treatment extracted approximately same quantity of fat, 3.08 and 3.07%, respectively, while ethanol extracted 0.79%. This results are according with microscopy observations where the cells without or poor in fat after CO2 supercritical extraction was observed cell walls destruction.

Avocado (persea americana Mill.), pollinators were colleted in orchards in Coatepec Harinas, (State of Mexico) and Ziracuaretiro (MichoacÁn), Mexico, from January to March of 1998 and 1999. The insects were studied with inddent light microscopy in order to identify and count the avoacado pollen grains attached to each body region. A higher diversity of pollinators were detected in the State of Mexico orchards and a lower in MichoacÁn. There were 45 spedes of Diptera, belonging to 5 families, 20 spedes (6 families) of Hymenoptera, and 5 species of five families of Coleoptera. Apis mellifera L. (Apidae), Eristalis tenax L. (Syrphidae), Phaenicia mexicana Macquart (Calliporidae) and Palpada exicana Macquart (Syrphidae) were the most abundant spedes in both localitieso Geotrigona acapulconis Strand (Apidae), Brachygastra mellifica Say Vespidae), Chrysomya megacephala (Calliphoridae) A. mellifera and had the greater ount of avocado pollen attached to the vertex, ventral thorax and legs, surpassing the spedes efectiveness. Nevertheless, G. acapulconis appeared in very low number, which implies that the honey bee is the main pollinator in the avocado tree complemented by \he other spedes. These results will be integrated into to a greater projet on the avocado pollinators efectiveness, related with their behavior and with the avocado flowering nature.

Insects visiting avocado flowers were collected over the course of five research trips to Mexico, in the states of Michoacan, Mexico, Puebla, Veracruz and Chiapas. Most of the specimens were identified at the species level, and the amount and distribution of pollen on their bodies were determined. 80th the density and behavior of species found to carry a large amount of avocado pollen were observed on the avocado bloom. In commercial orchards sprayed with potent insecticides, only a small number of visitors of a few species were observed, most of them honeybees (Apis mellifera). In contrast, on unsprayed traes (in small plots, backyards, etc) large numbers of visitors of numerous species were usually observed. More than 1,000 individual insects, of about 100 species, were coIlected on avocado bloom, most of them of the orders Hymenoptera, Diptera, CoIeoptera and Heteroptera. Apparently, some of the visitor species did not pollinate the avocado flowers, but most of them did contribute to its pollination. The following species were found to be effective pollinators of avocado: the honeybee, 8 to 10 species of stingless bees (Apidae, Meliponinae) and the. Mexican honey wasp" (Brachygastra mellifica). These species were the main pollinators of the three avocado races: Mexican, Guatemalan and West Indian. Honeybees were active on the avocado bloom at most sites; however, in some cases they abandoned the avocado bloom lo collect nectar and pollen from nearby competing flowers. The stingless bee species and the Mexican honey wasp showed a greater preference for the avocado bloom. We assume that the original pollinators of the avocado, before the introduction of the honeybee to the American continent, were stingless bee and wasp species, which are better adapted for its pollination.