Ustilago maydis (DC) Corda is the phytopathogenic fungus that produces “huitlacoche” on the ears of corn. Its production is of high commercial interest, but yield and quality can be affected by the presence of antagonistic yeasts associated with the gall. Depending on the degree of infection, the galls may have a higher content of yeasts than of U. maydis, which may be a cause of low infestation in the field. The goals of this study were to determine the presence of yeast isolates in a collection of U. maydis and from fresh huitlacoche gall and to explain the association in this structure. To differentiate the two types of microorganisms, the urease test was used and identity was confirmed by molecular techniques and ITS sequencing of the yeast. The results indicated that the yeasts belong to the species Candida railenensis, C. quercitrusa and Pichia guilliermondii and were able to inhibit the growth of U. maydis under laboratory conditions.

Jalapeño pepper can provide important antioxidants for the human diet. In Mexico, there is a tendency to improve its yield and quality. Recently, the use of bioregulators and oxidation promoters in tomato, broccoli and cabbage has been shown to improve harvest yield and quality. The objective of this study was to evaluate the effect of prohexadione calcium (P-Ca), benzoic acid (BA) and salicylic acid (SA) on yield and the levels of capsaicin and vitamin C in jalapeño pepper var. M. The study was conducted under greenhouse and laboratory conditions at the Universidad Autonoma Agraria Antonio Narro in 2007. The treatments were, P-Ca, BA, SA, and water (control) applied in the seed, seedling and plant stages. The variables were concentrations of capsaicin and vitamin C in ripe fruits and total yield per plant. The content of capsaicin and yield were statistically higher in the three stages with applications of P-Ca (100, 150 and 200 mg·liter-1) individually or in combination with BA and SA (1x10-6 M). The level of vitamin C increased when P-Ca at 100 mg·liter-1 was applied to the seed.

Sprouts are a low-cost fresh vegetable that can be grown indoors in any season and can contribute many nutrients to the diet. The purpose of this study was to evaluate the effect of sprouting on nutrimental composition and total saponin content of huauzontle (Chenopodium nuttalliae Saff.), zucchini (Cucurbita pepo L.), canola (Brassica napus L.) and amaranth (Amaranthus leucocarpus S. Watson syn. hypochondriacus L.) sprouts. A proximal analysis and quantification of saponins were performed in seeds and sprouts from the four species. The protein content in canola sprouts was higher than in the corresponding seeds but did not vary in huauzontle, zucchini and amaranth. Lipid content in canola, huauzontle and amaranth seeds decreased in the sprouts, but in zucchini it increased. Saponin content in sprouts was: 2,873.23 in huauzontle, 155.40 in squash, 429.81 in canola, and 491.45 mg 100·g-1 dry weight in amaranth. Saponin content in seeds was: 5,280.57, 0.00, 35.77 and 42.84 mg 100·g-1 dry weight, respectively. Valor nutricio y contenido... The levels of saponin content found in seeds and sprouts of the four species studied are not toxic for human beings. The nutrient value was better in canola sprouts than in huauzontle, amaranth and zucchini. Taste was better in huauzontle and amaranth than in canola and zucchini.

The objective of this study was to evaluate compost tea as a source of N and other nutrients in the production of greenhouse tomato. Four fertilization treatments were evaluated in three cultivars. Fertilization types were nutrient solution in sand, compost tea in sand, diluted compost tea in sand + compost and split application of compost. Tomato cultivars were Bosky, Romina and PX01636262. The evaluation was carried out up to the eighth fruit cluster. The fertilization type and cultivar effects were significant for tomato yield, while their interaction was not significant. Plants treated with nutrient solution showed the highest yield with 21.8 kg·m-2, whereas compost-tea-treated plants yielded 17 % less; this reduction was related to a higher electrical conductivity (EC) in the substrate solution. Compost tea also reduced fruit weight by 21 % and increased soluble solids by 19 %. Bosky and PX01636262 cultivars yielded about 20 kg·m-2, whereas Romina yielded significantly less, because of lower fruit weight. Leaf N concentration at the beginning of flowering and beginning of harvest was similar in plants with nutrient solution and compost tea; since no deficiency Té de composta... symptoms were observed, compost tea supplied the N and other nutrients required, producing more than 18 kg·m-2 of extra large fruits, with more than 4 oBrix and lower fertilization cost.

The aim of this work was to study the influence of plant density (45, 25, 16 and 8 plants·m-2) on hydroponic greenhouse production of Gigant variety potato minitubers larger than 10 mm in diameter and on physiological growth indicators. With high population density (45 plants·m-2) the leaf area index was 13.4 at 75 days after emergence and plant height was 45 % higher than plants grown at 8 plants·m-2. At this density, the total plant biomass (67.5 g), tuber number (16.5) and tuber biomass (52.5 g) were significantly higher than at 45 plants·m-2, with 44.5 g, 10.2 and 36.8 g, respectively. The absolute growth rate (AGR) of whole plant varied from 0.4 to 0.7 g·d-1depending on plant density and the growth stage, and the absolute tuber growth rate (TGR) in the lower density treatment was 45 to 59 % higher than the TGR of plants growing at 45 plants·m-2, Photosynthetic efficiency and carbohydrates diverted to the tuber, estimated as net assimilation rate (NAR) and economic assimilation rate (EAR), with 8 plants·m-2 were 118 to 160 % higher than the NAR and EAR with 45 plants·m-2. However, the crop growth rate (CGR) with 8 plants·m-2 was only 12 % of the value obtained with 45 plants·m-2 (64.4 g·m-2·d-1) at 75 DAE. This was also manifested in a larger number of tubers over 10 mm in diameter and tuber biomass (470 units and 1,658 g·m2, respectively).

The infrared thermometer used to measure crop water stress index (CWSI) is a reliable tool for irrigation scheduling, which, combined with efficient irrigation systems can maximize crop productivity. A study was conducted to determine the crop water stress index in husk tomato, or tomatillo, (Physalis ixocarpa Brot.) under a drip irrigation system, its relationship with irrigation depth and plastic mulch in scheduling irrigation and predicting fruit yield. The experiment design was completely randomized with three replicates Treatments consisted of five irrigation depths (replacement of 40, 60, 80, 100 and 120 % of the reference evapotranspiration estimated by the Penman-Monteith method). CWSI was estimated using infrared radiation gun measurements of canopy temperature, air temperature, and relative humidity, and water vapor pressure deficit was calculated. The equation which defines the lower limit expresses the relationship between vapor pressure deficit (VPD) and temperature difference (crop and air (Tc-Ta)). When the crop transpires, the relationship is: Tc -Ta = 1.21 - 131 DPV (r2 = 0.68, P <0.01, n = 42), and the upper limit (stressed) was 2.8 °C, when transpiration stops. Fruit yield showed a positive linear correlation with average CWSI values: Y = 52.53-69.7CWSI, (r2 = 0.65, P<0.01 and n=30). Prediction models of CWSI and means of the effect of irrigation water and plastic mulch were fit with r2 = 0.87 to 0.96, P<0.01 and n=30. The CWSI increases linearly when the soil water potential decreases.

In the milpa cropping system (intercropping corn and squash), production of high quality mature squash can be an alternative for increasing the farmer’s income per unit of area. Considering this, from 1997 to 2001, during each spring-summer cycle, combined selection of maternal half-sib families was carried out in a synthetic squash population. The objective was to improve mature fruit quality evaluated on the basis of fruit flesh color and flavor traits. Frequency of high quality fruits was increased by combined selection; in the fifth selection cycle it reached 73 % in contrast with 18 % found in the original population. Despite five selection cycles, participatory plant breeding approach has maintained the genetic diversity observed in the original population, although the frequency of fruits with intense yellow, light yellow and white flesh was low in the fifth cycle. The greatest genetic gain was for intense orange flesh color (207 %) contrasting with that of fruits with intense yellow flesh (5.5 %). Combined selection improved the very sweet flesh flavor: a larger percentage (25 %) of fruits were grouped in this category while that of fruits with insipid flavor decreased. Genetic gain was 211 and -15 % for very sweet and insipid fruits, respectively.

Tuber necrosis is one of the symptoms associated with potato purple top (PT) disease. In 2005 in Texas, USA, this symptom was named “zebra chip” or striped potato and was associated with the presence of Xyllela fastidiosa. The aim of this research was to detect the bacterium in plants exhibiting symptoms of PT. The three major regions of potato production in the State of Mexico were selected (Toluca, Atlacomulco and Valle de Bravo). Directed sampling was carried out in the spring-summer season of 2006. Polymerase Chain Reaction (PCR) with the specific primers RST31/RST33 was used to detect Xyllela fastidiosa; 25 % of the plants tested positive for the pathogen. Sequences of amplified fragments compared with sequences registered in the GENEBANK were 97 and 99 % homologous. The results suggest that necrosis and the symptoms of PT expressed in the potato plants in the State of Mexico are associated with X. fastidiosa.

Using records of environmental temperature and floral development obtained from 1998 to 2006 in a semiwarm subhumid climate of the state of Nayarit, five floral development prediction models for winter and summer shoots of eHassf avocado were developed. The study was conducted to test prediction models generated in Nayarit for their capacity to predict the floral development on winter, spring and summer shoots of eHassf avocado originally cultivated in the climates of the avocado producer region of the state of Michoacan. The prediction model summerDFA.19 developed in Nayarit showed a strong capacity to predict floral development on summer shoots (R2 = 0.94), in a data set from four climates of Michoacan which accounted for 85 % of the avocado producer region: warm subhumid Aw1(w), semiwarm subhumid (A)C(w0)(w), semiwarm subhumid (A)C(w1)(w) + (A)C(w2)(w), and temperate subhumid C(w2)(w). Other prediction models tested did not predict floral development on winter, spring or summer flush shoots in any of the studied climates.

This study was conducted during the 2004-2005 winter to analyze the effect of whitewashing (with calcium hydroxide) entire apple trees (Malus domestica Borkh) at the beginning of the winter season, on the branches and trunks internal temperature (under the bark), the accumulation of chill units (CU), its effect on fruit yield and quality and its relation to the use of thidiazuron (TDZ) to induce budbreak. The results of this study indicated that at the hours of highest incidence of solar radiation, total tree whitewashing decreased the internal temperature of the branches up to 4 oC and of the trunks up to 9 oC. The accumulated CU during the time of the study, calculated with the internal temperature of the whitewashed branches, were 27.9 % higher than those recorded on the branches with no whitewashing, while the CU lost at the hours of highest solar radiation were up to 37.2 % lower. Efecto del encalado... Total whitewashing increased the yield per tree up to 20 % more than application of TDZ. No statistical difference in fruit quality parameters was observed between total whitewashing and the application of TDZ to induce budbreak.

This study is an inventory of the genetic resources of fruit-bearing tree species present in Michoacán and the state of their conservation and use. Studies on fruit-bearing species were reviewed exhaustively. The information collected was ordered by botanical family, genus, species, and collection. The 134 species found in Michoacán belong to 24 taxonomic families. In the management of genetic resources of this group of plants, ex situ conservation plays an important role: 38 species are conserved ex situ; of these, eight species are conserved in botanical gardens, three species are conserved in vitro, 23 are in field collections, and, only three species are in bank collections. A total of 271 accessions are conserved ex situ. Four species are subject to genetic breeding. Five species are conserved in situ in home gardens. Forty species are found in herbariums and there is a notable increase in the register of people consulting the information existing in the research institutions of the state.

The purpose of this paper is to provide an overview of the published research about chitosan, which is the deacetylated form of chitin, a natural biodegradable compound derived from crustaceous shells whose major attributes corresponds to its polycationic nature. This review points out its chemical and structural characteristics, obtainment methods, antimicrobial activity and its action mode. The potential of chitosan to induce a series of defence reactions correlated with certain enzymatic activities carried out by PAL, â-1,3-glucanase, chitinase and chitosanase is also reviewed.