This study was conducted to characterize and analyze genetic variation in a squash (Curcurbita pepo L.) population with a broad genetic base cultivated under a system of maize-squash intercropping. Simultaneously, a process of combined selection was carried out with progeny from the same mother plant. A random block design and a completely random design were used with 100 and 120 treatments, or squash families (first and second selection cycle, respectively), with 17 replications for the random block design and five replications for the completely random design. One row of maize was alternated with one row of squash (family), and one row of ‘Grey Zucchini Tala' hybrid squash was planted every 12 families to estimate environmental variance and determine the components of genetic variance of the population. In general, a broad genetic diversity was found for all of the traits evaluated, but it decreased with selection. Also, total genetic variance was determined principally by additive effects of the genes. Variances of dominance were negative and highly significant. The magnitude of heritability varied from trait to trait from 29.2 to 95.4 % and 28.96 to 88.8 % for important advances: in the first year undesirable pulp colors and tastes predominated (light yellow and insipid) with 50 and 30 %, respectively, but by the second year very sweet and sweet tastes and orange colors predominated in the fruit pulp with 62.9 and 61 %, respectively.

This study was conducted during the spring-summer cycle 1996 in Chapingo, Mexico. The following factors were studied: soil application of CO2 dissolved in water at concentrations of 0 (control), 300 and 1200 mg×liter-1; use of plastic mulches, which included transparent plastic, white-on-black plastic, and a control without plastic mulch; and a training system with and without (control) trellis. The results indicated that soil application of CO2 dissolved in water, especially the treatment with 1200 mg×liter-1, significantly increased the leaf area, weight of leaf and stem dry matter, and yield in the last harvest. However, initial and total yield, fruit weight, number and volume, branch length, total leaf acidity, percentage of CO2 in the soil and CO2 assimilation rate were not significantly affected, possibly because CO2 was not absorbed by the roots and neither was there additional formation of organic acids. Also, soil pH decreased slightly with 1200 mg×liter-1 of CO2. The use of plastic mulches, principally the transparent mulch, significantly modified the morphology of the plants: increase in stem diameter, number of leaves and flowers, plant height, branch length, leaf area, dry matter, fruit weight, initial and total (73.8 t×ha-1) weight, and soil temperatures. The highest total yield was obtained with white-on-black mulch (78.7 t×ha-1) and the lowest with the control (44.9 t×ha-1). Management on trellises produced a higher total yield (67.73 t×ha-1) than traditional management on the ground (63.87 t×ha-1), which modified the initial pattern of translocation of assimilates in the plant, increasing the dry matter in stems and leaves at the expense of initial fruit yield. The highest total yield was obtained with trellis training with white-on-black mulch and 1200 mg×liter-1 of CO2 (83.3 t×ha-1); this treatment had a benefit/cost ratio (B/C) of 0.52. The highest B/C ratio resulted from the treatment without trellises with white-on-black mulch and without CO2, producing 75.6 t×ha-1. The control treatment (without CO2, without mulch, and without trellis) yielded 42.8 t×ha-1 with a 0.55 B/C ratio.

During the winter of 1993-1994, a field evaluation of the effect of bean straw mulch, in terms of frost damage in potato (Solanum tuberosum L.) cv. Atlantic, was conducted to determine the advantages of mulching with plant residues to reduce the effects of frosts by reducing loss of energy from the soil. Treatments comprised a control without mulch (T1), mulching at emergence (T2), and mulching 30-day-old plants (T3). It was found that mulching had a favorable effect on plant growth when mulching was done at emergence. This was related to a better conservation of soil moisture, but also frosts had a greater effect since there was a larger leaf area exposed to freezing temperatures. It was found that yield was higher when mulching was done when the plant was 30 days old (251.82 g·plant-1), relative to the control (233.53 g·plant-1) and mulching at emergence (158.04 g·plant-1). This was associated with a higher water content in these plants than in the control plants, but also because a smaller leaf area was exposed to the cold than when mulching was done at emergence; thus, there was less frost damage.

Young, tender spinach leaves 8 to 10 cm and leaves cut the traditional length of more than 15 cm were exposed to different atmospheric conditions: air (control), 0.5 % O2 + 10 % CO2, 5 % O2 + 10 % CO2, and 5 % O2 + 20 % CO2, and stored for 15 days at 7.5 °C. In general, it was found that visual quality of mature leaves was lower from harvest (with values of 7) and during storage than that of young leaves (with values of 9). The treatment of 5 % O2 + 10 % CO2 maintained initial appearance up to 12 days at 7.5 °C. The young leaves retained a more tender and succulent appearance from its harvest and maintained these characteristics up to day 6 under the treatment of 0.5 % O2 + 10 % CO2, with values of 8 in visual quality. In both states of maturity, it is evident that the treatment of 5 % O2 + 20% CO2 deteriorated visual quality even more than storage in air. An increase in pH and a decrease in titratable acidity were found due to the elevated concentrations of CO2. Chlorophyll maintained the highest levels in both types of spinach under the treatment of 5 % O2 + 20 % CO2. Carotenoids were present in a lower proportion with the treatment 5 % O2 + 10 % CO2. The content of ammonia was higher in treatments with controlled atmospheres than with air, varying from 0.52 to 3.52 mg·g-1 in tender leaves after storage and from 0.53 to 3.32 mg·g-1 in mature leaves. In the two states of maturity of the leaves, an effect of the levels of CO2 and O2 in reducing lightness was observed.

Plants grown in vitro have anatomical modifications compared to those grown in the field. These modifications can limit their survival. In this study, anatomical observations were made with light microscopy to compare modifications in the anatomy of the leaves of grapevine shoots (Vitis vinifera L.) ‘Malaga Roja’ grown in “woody plant medium” ( WPM) culture medium with the anatomy of leaves from field plants. Samples of leaves were fixed in FAA and processed with the paraffin microtechnique and dyed with fixed safranine green and red 7B oil. Anatomical differences were found: thinner leaves and leaf cuticle in in vitro plants; in the organization of the mesophyll there was an absence of palisade parenchyma in the in vitro leaves, the vascular tissue was less developed, and there was a higher stomatic density in plants grown in vitro.

A study of inflorescence and flower development of the ‘Hass’ avocado (Persea americana Mill.) was undertaken in California, USA. Eleven macroscopic stages of external bud and subsequent inflorescence development were correlated with microscopic organogenesis for subsequent use in predicting specific stages of inflorescence development to schedule cultural practices in a commercial orchard. Transition from vegetative to reproductive growth on summer shoots occurred in July-August and was followed by inflorescence initiation from August to October. Anthesis occurred seven months later. A period of dormancy was not required for transition to flowering. At the time of transition, apical buds of mature vegetative shoots consisted of a convex primary axis meristem with two lateral, secondary axis inflorescence meristems lacking apical bracts. Under floral-promoting conditions (low temperature), apical buds fully committed to flowering were not distinguishable anatomically from those that were not committed to flowering. Avocado inflorescence development was correlated with night temperature £ 15 ºC. Crop load influenced the proportion of determinate and indeterminate floral shoots and vegetative shoots produced during spring bloom.

The effects of GA3 (25 or 100 mg×liter-1) canopy sprays applied to Hass avocado (Persea americana Mill.) trees in a commercial orchard in the months preceding an “off” or “on” bloom year on inflorescence and vegetative shoot number and yield were quantified. GA3 (100 mg×liter-1) applied in September (early stage of inflorescence initiation) reduced inflorescences number both years, but not yield. GA3 (25 or 100 mg×liter-1) applied in November (early stage of inflorescence development) before the “on” bloom reduced inflorescence number with a concomitant increase in vegetative shoot number and a 47 % yield reduction. GA3 in January (initial development of the perianth of apical flowers) or March (cauliflower stage of inflorescence development) caused precocious development of the vegetative shoot apex of indeterminate inflorescences, but had no effect on inflorescence or shoot number either year. GA3 (25 mg×liter-1) applied in March of an “off” bloom year increased production (2-fold) of commercially valuable fruit (213-269 g per fruit) and delayed skin blackening. This paper provides basic information that can be used to develop strategies for manipulating yield and evening out alternate bearing in avocado.

A variant of the cucumber mosaic virus (CMV) was isolated. This variant causes yellow mosaic or yellow stripes and deformation and abortion of flowers in gladiola (Gladiolus grandiflorus Hort.) plants cultivated in the states of Puebla and Morelos, Mexico. This particular isolate caused intense yellow mosaic, ring spots, and severe deformation in plants of several species of Solanaceae that were inoculated by mechanical transmission. These symptoms were not caused by other common variants of CMV with which it was compared. The isolates of CMV obtained from gladiola probably belong to a yellow variant of CMV not previously reported in Mexico and which we preliminarily call CMV-Ys (“Yellow strain”). The characterization of this variant of CMV was verified by tests of mechanical transmission to differential and indicator host plants, by electronic microscopy, serology (ELISA and double diffusion in agar), by transmission by insect vectors, and by electrophoretic analysis of double-stranded RNA.

To identify and quantify strains of Botrytis cinerea that are resistant to benomyl and thiabendazol, one susceptible isolate was collected in Santa Catarina, Texcoco, and 12 in Villa Guerrero, State of Mexico. Bioassays were conducted and the data were processed with PROBIT-SAS to obtain EC50 and EC95. With benomyl, the results indicate that the susceptible isolate had a EC50 of 0.055 mg·ml-1 and a EC95 of 0.49 mg·ml-1. The EC50 of the isolates from Villa Guerrero fluctuated between 250.59 and 831.68 mg·ml-1, and the factor of resistance (FR), relative to the susceptible control, was between 4,555.18 and 15,120.45. In contrast, EC95 was found to be between 12,241.09 and 18,279.08 mg·ml-1, and FR fluctuated between 24,980.63 and 37.303.24. With thiabendazole, the EC50 and EC95 of the susceptible isolate reached 0.028 and 0.327 mg·ml-1, respectively. The EC50 of the isolates of Villa Guerrero was 88.51 to 129.96 mg·ml-1, and FR was 3,160.00 to 4,440.42, while EC95 was between 2,830.00 and 10,839.00 mg·ml-1. These results confirm that the fungus is resistant to benomyl and thiabendazole in the study region.

The leaf tissue of chrysanthemum (Dendrathema grandiflorum) cv. Tikara with the reporter gene b-glucoronidase (GUS) was transformed using 0.7 mm tungsten microprojectiles accelerated to high velocity with helium gas. Different pre-culture and bombardment conditions were evaluated. It was found that the appropriate pre-culture period was 3 days, the period in which the tissue acquires sufficient resistance to withstand physical damage inflicted by the microprojectiles. Using histochemical staining, transient expression of the GUS gene was detected in explants bombarded at a distance of 10 cm in a non-commercial biolistic system. The statistical tests indicated that some morphogenetic responses, as well as obtaining transformants with transient expression, depend on the distance and diameter of the microprojectile used during bombardment.

Flowers of succulent plants are seldom being used as cut flowers, although they were appreciated in the past. This report summarizes the results of a five years study conducted upon wild grown plants as weed. B. pinnatum (syn. Kalanchoe pinnata: common name: los botoncitos) flowering from December till March in the climatic conditions of the state of Puebla, México, forming beautiful groups in the rural landscape. From such stands samples were taken to evaluate the aesthetic value of the inflorescence under ordinary room conditions. Shoots with first flowers opened were used whenever possible. The following data were collected: total length of flowering stalk, length of lateral inflorescences, total initial and final fresh weight, number of lateral inflorescences, number of flowers opened and buds present at weakly intervals, dry weight of the inflorescence components at the end of the experiment (only 1999-2000). Plants giving inflorescences in the shadow or at greenhouse conditions produced greenish buds with fading red-brownish colors on both parts of the inflorescence. Inflorescences from sunny sites placed at room conditions, in few days started fading its red color. Inflorescences kept in water or in dry-vase produced constantly new opened flowers in both the southern and northern windows exposition. The collapse of stalk tissue was more pronounced when kept in dry vase. No collapse of peduncle tissue was noticed. The gradient of fresh mass at the and of experiment was: stalk > flowers > peduncles > opened flowers > closed flowers > calyx. Generaly, the vase life and the aesthetic appreciation were better when the inflorescences were kept in southern exposition.

This paper presents results of evaluation of keeping flowering stems of Bryophyllum pinnatum Kurz. in dry and wet vase, under ordinary room conditions, with S and N window exposition (2x2 factorial treatment design; 5 replicates; 1 stem was the experimental unit). The experiment was conducted in February for 3 weeks, using stems cut in their natural habitat. The results indicate that the stems kept in the wet and dry vase continued flowering. Better hydration was secured with stems kept in wet vase and in southern window exposition. Long appreciation of aesthetic values of both, the open flowers and the buds, was secured with flowering continuing up to three weeks. The results indicate, that flower development from mature buds is independent from the water status of the stem and, seems to depend, upon the state of flower hydration itself. The calyx may play a crucial role in protecting the internal water status of developing flowers.