Grafting is one of the most widely used methods for vegetative propagation, particularly for multiplying trees considered important, but there has been little research done on the effect of hybridization on grafts from the genus Pinus. Sometimes hybrids show the ability to reproduce and adapt efficiently to the environment. However, they reduce the genetic gain of seed orchards. The objective in this research was to evaluate the effect of scion grafts from pure species donor Pinus engelmannii Carr. and from putative hybrid trees P. engelmannii × P. arizonica Engelm., grafted on rootstocks of pure species P. engelmannii, along with the effect of the position of the scion in the donor tree crown (upper third and middle third). The scions were collected from three trees of the pure species and three hybrids. In each tree, 20 scions were collected from each third of the crown evaluated. 120 side-veneer grafts were made at the beginning of spring (March) 2018. Variance analyses were performed to evaluate the treatments and adjustments of the Logit and Weibull models to obtain the probability of graft survival. Significant differences were found between the origins of scions (p < 0.0083, after Bonferroni correction), showing grafts with hybrid tree scions taking hold better. In addition, the probability of survival at 5 months after grafting with hybrid tree scions was greater (p < 0.0001) than in grafts with scions from trees of the pure species (Logit model), which coincides with the results of the Weibull model, which indicated that the probability of graft death with pure species donor tree scions is greater than for grafts with hybrid scions. There were no significant differences regarding the position of the scion in the donor tree crown.

The establishment of clonal seed orchards is a viable option for the continuous production of improved seed of desired genotypes. Grafting is the main technique used to establish clonal seed orchards. The objective of this study was to examine how the geographic location and the age class of the donor trees of buds, the phenological status of the buds, and the anatomical characteristics of the scions and the rootstocks affect the survival and growth of Pinus engelmannii Carr. grafts. Scions were collected from two trees in each of three age classes (young, middle-aged, and old). Grafting was performed with buds in two physiological states (end of dormancy and beginning of sprouting). Cross-sections of the grafted organs were obtained for anatomical analysis. A Cox proportional hazards model was used to determine the effects of the variables that were considered. The age class of the scion donor trees, the total area of the cut surface of the scion, and the density of resin channels in the scions significantly affected (p < 0.05) survival of the grafts. By contrast, the physiological state of the buds and the other anatomical characteristics of the grafted organs did not significantly affect graft survival. In P. engelmannii, grafting was most effective when scions from middle-aged trees were used. Graft survival was enhanced by a small total area of the cut surface of the scion and low density of resin channels in the scions. The area of the cambium of the scions directly influenced growth of the grafts.

Rooting substrate and fertilization are key components in the production of containerized seedlings, as they can influence the morphological and physiological characteristics of the plants, which in turn can impact outplanting performance. The objective of the study was to evaluate the effect of four substrates based on mixtures of peat moss (PM), composted bark (CB) and raw pine sawdust (PS), combined with two doses of controlled release fertilizer (CRF) and one non-fertilized control, on the growth of Pinus cembroides Zucc. in the nursery. The treatments were: M1: 50+25+25, M2: 25+25+50, M3: 25+50+25 and M4: 50+50+0 of PM+ CB+ PS (% by volume), respectively. Fertilizer treatments used a controlled release fertilizer (Multicote^®): F1: 3 kg m⁻³ and F2: 6 kg m⁻³ and a control (WF: with no added fertilizer). The treatments were distributed in a randomized complete block design, with a factorial arrangement of 4 × 3 and six replications. The variables evaluated were: height, seedling diameter, dry biomass, Dickson Quality Index, N, P and K content. Regardless of the substrate, the high fertilizer dose (6 kg m⁻³) improved most morphological variables. In addition, the high fertilizer dose resulted in foliar N, P and K concentrations within recommended ranges for all substrates. The substrate containing only peat moss and composted bark (M4 + F1 and M4 + F2) had the best growth response. However, the substrate composed of 25% peat moss, 50% composted bark and 25% raw pine sawdust with the high fertilizer dose (M3 + F2) resulted in acceptable seedling growth, and may be preferred if the cost of the substrate is a concern to nursery manager.

Spatial genetic structure (SGS) characterizes the geographical distribution of genetic variation. Pinus arizonica and P. cooperi are two of the most important timber tree species in Mexico. Certified seed stands of these species are needed to increase productivity and recover degraded areas. In the present study, we analyzed neutral and putatively adaptive AFLPs to examine the SGS in 12 natural seed stands of P. arizonica and P. cooperi at local (within the seed stands) and large scales (among the seed stands). Since these pine species are wind pollinated, widespread, and often occur at high population densities, we did not expect to find any SGS at the fine scale or significant differences in the SGS of the two species. At the fine scale, we observed highly significant spatial genetic autocorrelation for both species in only two of the 12 seed stands. At the large scale, we observed significant spatial structure, which may be the result of isolation by distance. We recommend establishing a fine-meshed network of seed stands, with maximal distances of 9–18 km between them to prevent greater loss of local genetic structure.