A. F. Barrientos-Priego

Xylem conductivity and vulnerability in cultivars and races of avocado

Abstract Anatomical vessel features of Guatemalan, Mexican and West Indian races and cultivars Colin V-33, Fuerte and Hass of Persea americana Mill. were studied in 10-year-old trees grown in the field under similar environmental and management conditions with the main purpose to get insight on anatomical variation among genotypes. The cultivars differed anatomically from the races, showing an inverse relationship between races and cultivars with respect to vessel frequency and diameter, however, relative conductivity was similar among cultivars suggesting an adjustment between vessel diameter and frequency that maintains a similar relative conductivity among genotypes. The three races had the higher vessel frequency and the narrower vessel diameters as well as the lowest vulnerability index values compared to Hass and Fuerte cultivars. An important finding in this study was that cultivar Colin V-33, a dwarf genotype, had intermediate anatomical characteristics between races and the other cultivars suggesting a better adapted hydraulic system to water deficits.

Variabilidad anatómica de los sistemas de conducción y estomático de genotipos de Prunus spp. de diferentes orígenes

The aim of this research was to study the relationships between environmental humidity availability and the anatomical characteristics of water conduction and stomatal systems, in five Mexican peach genotypes with different origins (Jalatzingo and Misantla, Veracruz; Temascaltepec, Mexico; Tulancingo, Oaxaca; Sombrerete, Zacatecas), one almond and Nemaguard rootstock. Shoots, leaves and stomata of six months old plants were anatomically characterized by means of 25 characters. The almond tree and the rootstock Nemaguard showed differences in relation to the peaches, which had higher similarity, although they maintained a separation according to their origin. Groups were differentiated by the following characters: stomatal density; width of the leaf upper epidermis; number, frequency and perimeter of xylem vessels; and the index of vulnerability of the leaf central vein, pith, xylem and phloem percentage of the shoot. The conditions of humidity availability of their origin showed strong association with the studied anatomical characteristics, because the environment with more deficit of humidity (Tulancingo and Sombrerete) showed plants with bigger size and smaller frequency of vessels of xylem, as well as low xylem and phloem percentage in shoot, which can be interpreted as resistance adaptations to drought. The area where the occurrence of drought (Jalatzingo) is rare showed the opposite characteristics.

Sample size determination of avocado shoot xylem characters by resampling

The objective of this work was to determine the suitable sample size, to detect statistical differences in the analysis of variance of xylem characters, in annual shoots of avocado trees. For this, xylem characters of three trees with contrasting height were registered for frequency, area, perimeter and diameter of xylem vessels. Starting from 50 observations from each tree, a total of 5.000 non parametric bootstraps were done for each of the replicates from 2 to 50 microscopic fields. Starting from a sample size of 15 replicates, the deviations in the five statistical estimates are minimal, so it is proposed as the minimum for sampling the mentioned variables.