The isolation and characterization of genes encodi ng useful traits, and the development of techniques to modi these genes in viti-o and to transfer the constructs into target plants have altogether revolutionized plant biology. The transfer of genes has generated numerous transgenic plants with new or improved traits such as the ability for delayed fruit ripening, for the synthesis of pharmaceutically interesting components, for resistance to virus, bacteria, fungi, nematodes and various abiotic stress factors. Though horticultural aspects were oniy of marginal interest in plant genetic engineering, we nevertheless start out with portraying the achievements on this particular fleld, so that the reader can compare them with the advancements in other areas of plant genetic engeneering.

During the present century, the avocado (Persea americana Mill.) has been developed into a commercial fruit crop in some countries including Israel. The practice is to graft cultivars on rootstocks. The trees have been found to be very sensitive to some soil stresses but different rootstocks vary in their sensitivity. Very little information has been available regarding the effect of rootstock on the development, resistance and productivity of the grafted tree. A large-scale field study appeared te be essential te collect the required information and to further successful development of the crop.

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This paper embraces an analysis of prices and demand for plum for fresh consumption in the South of Brazil, with three objectives: to prove if regularities are observed in the seasonal and cyclic variation of the prices; to know which are the variables that influence the quantity demanded of this fruit; and to examine the advantages and limitations of alternative methods of analysis.

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Production of specific monoclonal antibodies for plant hormones can be carried out today. Endogenous plant hormones concentrations have always been a great challenge for scientists who are interested in explaining physiological processes. In recent years, it has been established immunoassays for the detection and quantification of plant hormones. Monoclonal antibodies are used for the immunoassay because The immunoassays can detect even lower concentrations of plant hormones than physicochemical methods. They are very specific and do not react with other compounds similar to the hormones. The advantages for the use of immunoassays in plant samples are: that the samples do not need to be as pure as those needed for physicochemical methods, and several samples can be analyzed at the same time. In the present report we updated basic information on this topic.

The possibility of doing seedling preselection to obtain dwarfing avocado rootstocks at an early stage was determined in this study. Fifty seedlings, one year oId (1981), of Cv. Colin V-33 were used to evaluate: height; diameter of the stem; principal, secondary and tertiary branches. The trees were grafted in 1984 with different cultivars and selections of normal, intermediate and dwarf size. In 1990 the reduction of height and canopy diameter and the rootstock circumference were evaluated. The correlation analyzes indicate that there is no relationship between the characteristics of the seedlings and the dwarfing effect of the rootstock when analized by cultivar or selection and by the total. When they were analized by tree size, some significant correlations (P = 0.05) were found in the dwarf type between height-height reduction (r 0.64); diameter height reduction (r = 0.76); total branches height reduction (r = 0.65); principal branches/height-height reduction (r = 0.66); and in the group of tall size between total branches-rootstock circunference (r = 0.51). Due to the fact that in the total, tau and in termediate size and in cultivars and selection there was no relationships between one year oid seedlings characteristics and the darfing effect over the scion, we think that is not possible to do preselection at a early stage of the seedling.

In ten agroecosystems of ‘Manila’ mango in the State of Veracruz an association between vesicular-arbuscular endomycorrhizae and roots was found. The root colonization was significantly different throughout the different environments studied and varied from 38 to 55%. In the soil of the agroecosystems there were significant differences (P≤ 0.05) in the number of mycorrhizae spores of the genus Glomus and Sclerocystis mainly. Two other different non-identified mycorrhizae were also observed.

The effect of different pregerminative treatments on the percentage of pecan seed germination during 30,60 and 90 days were evaluated: T1) pecan seeds soaked in water for 48 hours. T2) soaked in water for 48 hours + stratification at 5°C for 45 days; T3) soaked in water for 48 hours + soaked in a 0.5% thiourea solution for 15 hours; T4) soaked in water for 48 hours + soaked in gibberellic acid at 500 ppm for 6 hours, and T5) control. Statistically the best treatment was T2. It increased the velociry and percentage of seed germination, reaching 52.0% 30 days after sowing followed by T1 (44.4%) and T3 (43.4%). No statistical difference was found between T4 and control (34.4 and 29.9%, respectively'). Sixty days after sowing, all the treatments showed a germination percentage, being statistically the same (66.4, 60.8 and 59.3%, respectively) but higher that T4 and control (49.9 and 40.7%, respectively). Ninety days after the sowing, all the treatments showed the highest germination percentage in relation to first and second evaluation dates. They also continued with the same patterns of behavior as in first and second dates (88.8, 90.4, 87.1, 75.5 y 70.4%). Three months later, the seedling growth and stems diameter were measured. Statistically there were not differences between treatments on these dependent variables

We handled three different humidity lewIs (100, 60 y 20% on A. hypochondriacus 32c1133-6 INIFAP.All the experimental units were sustained in thom fleld capacity during 40 days. From that day on, we took a total of 5 measurements starting every 10th day and in which morphologic and physiologic variables were evaluated and rogistered. The results showed that the photosyntetic actMty and the leaf area are diectly proportional in 60 an 100% profitable humidity. In the regard to the dry weight acumulated. Water potential measurement did not give and significant differences between tho control treatments and 60% of profitable humidity during the eveluation tests that were made. With respect to the stem/root relationship significant differences were not found between the treatments during the experimental phase. The analysis of principal compononts showed that biomass variables explain in major proportion the responso of the observations in the treatments evaluated. The specter of physiological veriation determined that the phase near to reprocluction is more sensitiva to drought. We conclude that drought affects the plants that seemed turgent at 60% of humidity. The results of the stem/root relationship, oven in 20% of moisture could mean that tho rootpresents high efficiency in water absortion oven the water stress condition that can be specifled as a means of awiding drought.

The leaf area per shoot can be estimated using the shoot total lenght and the shoot total numer of nodes. Valid regressions were obtained for Cardenal, Carignane, Emperador, Italia and Morroco selfrooted cultivars.For Tokay cultivar no valid regression was found. The results were obtained sampling shoots of field grown plants.

Heteregeneity of plants in each cultivar was investigated in three rows located at equal distance in the following cultivars: Carignane, Emperador, Italia, Morroco and Tokay. The number of observations varied with the cultivar. The variability was measured using the number of infrutescences of commercial value. The cultivars varied much in number as in percent of sample size needed for the selected characters and varied with the character measured. The formation of specialised nurseries is suggested in order to secure the chanl reproduction of high yielding clonal plants for each cultivar.The production of certified material should secure homogeneously yielding plants, higher yields and plantations of extended productive age.