Jatropha curcas is a plant with great agricultural and industrial potential. In this study, two fungal species were isolated from ungerminated seeds. The fungal isolates were morphologically and molecularly identified as Fusarium equiseti and Curvularia lunata. Effects of chitosan on mycelial growth, sporulation and spore germination of F. equiseti and C. lunata were evaluated. In addition, its effect on seed germination of J. curcas was studied. The results showed that all tested chitosan concentrations (0.5, 1.0, 2.0 and 4.0 mg·mL-1) inhibited the mycelial growth of the fungi. Sporulation and spore germination responses differed depending on the fungal species. Chitosan completely inhibited sporulation of C. lunata and spore germination of F. equiseti. Inoculation with F. equiseti and C. lunata reduced seed germination of J. curcas by 20 and 26.6 %, respectively. However, application of chitosan before inoculation inhibited pathogenic activity. Therefore, chitosan did not affect seed germination and caused inhibitory effects on F. equiseti and C. lunata. This is the first report on the effect of chitosan on J. curcas.

Contamination by potentially toxic elements (PTE) is not periodically evaluated, given that the chemical analyses have a high cost. The ashes and combustion fumes give the ground a dark color, which could serve as a proxy indicator. In this study, a methodology was designed to prove the use of the color of urban dust as an indicator of contamination by PTE, and the most contaminated color was identified. 86 dust samples from Ensenada, Baja California were analyzed. The color of the samples was measured and the color indices (CI) were calculated using the RGB system. Nickel (Ni), Copper (Cu), Zinc (Zn), Lead (Pb), Rubidium (Rb), Vanadium (V), Strontium (Sr), and Yttrium (Y) were analyzed through x-ray fluorescence methods. The samples were grouped by color using the Munsell tables; the groups were validated with a discriminant analysis using the color indices. The multiple regressions indicated that there exists a relation between the CI and the PTE. The averages of the analyzed elements in the samples grouped by color were different (Kruskal-Wallis, P < 0.05). Gray dust contains higher concentrations of Pb, Cu, Zn and Ni. The color indices of urban dust can be considered a proxy methodology given their low cost, speed and reliability.

Quercus germana is an endemic species from the cloud forest of Mexico. The selection pressure resulting from fragmentation and environmental changes suggests the presence of phenotypic differentiation. We evaluated the relationship between the environment and the leaf morphology of Q. germana at six sites in the area of Xalapa, Veracruz. Ten leafs of 30 specimens per site were collected. Ten leafs morphometric and seven environmental characteristics were measured and variance analyses were performed with a discriminant analysis. Additionally, UPGMA phylogenetic trees were constructed and the Mahalanobis distances were compared using a Mantel test to estimate the relationship between morphometry and the environment. The morphological variables that best separated the sites were mucrones, ribs and petiole size. Environmentally, the most discriminant variables were light, temperature and loss of humidity. The Mantel test did not show any relationship between the morphometric and the environmental differences (r = 0.090, P = 0.3060), so there is not any association between the two. Because morphological differences were found in sub-populations despite of the short distance between them, these may be affected by fragmentation even without environmental influences.

The ecological role of fires in ecosystems can be studied through the fire regime. The objective of the study was to evaluate the structure and species composition in an area with a potential regime of frequent and low severity fires under two frequency scenarios in Iturbide, Nuevo León. Two 1-hectare parcels were established with different fuel loads (P1 = smaller load, P2 = larger load); the diameter, size, and coverage of the smaller and larger species were recorded. The forest mensuration variables were analyzed in order to obtain knowledge of the species composition of the forest. In the larger woodland, the Pinus group dominates in both parcels; this species has higher density and coverage values in P1, unlike the Quercus group and Others group (broadleaved). In the smaller woodland, all groups showed higher coverage values in P1, indicating active regeneration in the area with a shorter fire absence period. The diameter distributions were adjusted to the Weibull distribution and reflected the fire regime. It is therefore advised to implement a program for the integral management of fires that encompasses the beneficial effects of the fires. 

The seedling variation in four families of Pinus leiophylla with different origins was evaluated regarding the reaction to drought, considering water potential variables (Ψ_a), osmotic potential variables (Ψ₀), components and biomass allocation. The families of P. leiophylla are located in a seed orchard of the Colegio de Postgraduados in the State of Mexico. The study was done with the purpose of identifying the genotypes resistant to water stress. After 26 days without water, 50 % of the seedlings presented permanent decay in the apex of the stem, with Ψ_a = -3.35 MPa and Ψ₀ = -3.23 MPa, which represented a decrease of 596 and 112 %, respectively, due to drought. The accumulation of biomass was also significantly affected (P = 0.05) in the families assessed, with the exception of the family from San Rafael. On average, the biomass of the root of the seedlings in drought was 38 % smaller than that of the seedlings under normal circumstances. The P. leiophylla families from San Juan Tetla and Santa María Atepetzingo (both from the state of Puebla) presented a weaker response to the stress imposed, whereas the family from Tlalmanalco (State of Mexico) was the most affected.

Seed dispersal is one of the processes of plant-frugivore interactions that involves characteristics specific to the plant effecting the attraction of frugivores. In this paper, the individual variance in the attributes of Clusia salvinii in relation to the attraction of frugivores and its effect on the dispersal of fruits and seeds in the Reserva de Nanchititla, State of Mexico was studied. The morphometric characteristics of 25 trees of the C. salvinii species were evaluated (height, coverage, number of fruit, number of seeds per fruit, and fruit below the canopy). The removal of fruits and seeds (dispersal) was also estimated, as well as some of its attributes as estimators of the quantity of biomass assigned to the reproduction or as compensation for the dispersers (average weight per tree, average weight of the arils per tree). According to the results, tree height and harvest size or fruit production have an effect on the removal of seeds. On the other hand, the mass of the fruit, aril and seed had no relation to the removal of the fruit. Tree height and the quantity of fruit play an important role in the attraction of dispersers.