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Highlights:
Pinus patula grafting performance ranged from 70 to 82.5 %
The scion genotype and rootstock family interaction influenced graft survival.
Grafting with genotype G115 and family F105 were the most successful.
Scions and rootstocks of the same genotype or family were not favorable for graft compatibility.
Introduction
Pinus patula Schiede ex Schltdl. & Cham. is a widely distributed subtropical pine, due to high productivity, wood quality and easy management (Vargas-Hernández & Vargas-Abonce, 2016). There is growing interest in its genetic improvement, which contemplates the establishment of asexual seed orchards (ASO) from outstanding trees (Aparicio-Rentería, Viveros-Viveros, & Rebolledo-Camacho, 2013). Currently, the Fondo Sectorial CONAFOR-CONACYT project 2017-2-291322 aims to establish four ASO of P. patula in the states of Hidalgo, Oaxaca, Puebla and Veracruz.
Through cloning, outstanding genotypes are multiplied to produce seed of high genetic quality (Hartmann, Kester, Davies Jr., & Geneve, 2014). In conifers, trees express their superiority at maturity, but the ability to develop adventitious roots is reduced making it difficult to use layering and rooting cuttings (Wendling, Trueman, & Xavier, 2014). At present practice, clones used for ASO establishment in pines are obtained by grafting (Pérez-Luna et al., 2020), as with P. elliottii Engelm. var. elliottii and P. taeda L. in the Unites States (White, Duryea, & Powell, 2018) and P. patula and P. pseudostrobus var. oaxacana (Mirov) Harrison in México (Barrera-Ramírez et al., 2020; Vargas-Hernández & Vargas-Abonce, 2016).
Grafting is the physical union of two genetic entities of different origin (Darikova, Savva, Vaganov, Grachev, & Kuznetsova, 2011). It has recently been shown that both the scion and the recipient plant maintain their original genomes and do not share DNA, but epigenetic information does communicate within the plant by RNA flow between contiguous cells of the scion and rootstock and acts in activating or deactivating genes in the recipient plan (Lewsey et al., 2016). This propagation technique in conifers is characterized by low grafting percentages and survival associated with the genetic and epigenetic basis, as well as its internal anatomy, health, taxonomic affinity between scion and rootstock, bud phenology, rootstock age, grafting technique, soil and climate conditions, and management during grafting (González-Jiménez, Jiménez-Casas, López-Upton, López-López, & Rodríguez-Laguna, 2022).
Scion and rootstock genotype are an important factor in compatibility and a source of variation in grafting, survival, development and morphology (Warschefsky et al., 2016). Scion-rootstock compatibility studies in conifers have focused at the species level with satisfactory results in intraspecific grafting (Darikova et al., 2011). In the case of Pinus rzedowskii Madrigal & M. Caball., scions show higher affinity when grafted on the same species (Solorio-Barragán, Delgado-Valerio, Molina-Sánchez, Rebolledo-Camacho, & Tafolla-Martínez, 2021), suggesting that the graft affinity could increase when scion and rootstock come from the same genotype or family.
Other authors report morphological and physiological variation among genotypes or interspecific, therefore, the response will be different when being part of a plant grafted as scion or rootstock (Tandonnet, Cookson, Vivin, & Ollat, 2010); therefore, it is necessary to identify favorable scion-rootstock combinations at the genotype level. In this regard, Pina, Cookson, Calatayud, Trinchera, and Herrea (2017) suggest evaluating graft compatibility before considering the use of a rootstock for a specific scion genotype. In P. elliottii, scion genotype had an effect on survival and stromule formation one year after grafting, mainly due to differences in the specific ability to flower and respond to tissue attachment (Medina Perez, White, Huber, & Martin, 2007). On the other hand, in Larix gmelinii var. japonica, grafting survival depended more on the clonal characteristics of the scion than on the rootstock (Kita, Kon, Ishizuka, Agathokleous, & Kuromaru, 2018). For the case of P. patula, there are no references about the performance of scion or rootstock genotype on grafts.
Therefore, the objective of the study was to evaluate the compatibility between scion and rootstock of P. patula in response to genotypic variation. Greater compatibility is expected in scions grafted on the same progeny.
Materials and Methods
Selection of biological material
From the Fondo Sectorial CONAFOR-CONACYT 2017-2-291322 project, four genotypes were selected from the ejido Peñuelas in Pueblo Nuevo, municipality of Chignahuapan, Puebla (G105, G106, G114 and G115). The trees selected showed superiority in height, diameter at breast height and stem straightness within each of their sources (Table 1). The source of G105 and G106 was a progeny trial (19° 57´ 43.14” LN and 98° 06´ 15.25” LW, 2 574 m elevation) at a distance of 50 m between trees; while that of G114 and G115 was a sexual seed orchard (19° 57´ 36.09” LN and 98° 06´ 18.92” LW, 2 592 m elevation), at a distance of 36 m between trees. The distance between both sources was 250 m.
Table 1 Characteristics of the four superior Pinus patula genotypes selected as scion stock plants and their progeny for rootstock, obtained from a progeny trial (G105 and G106) and a seed orchard (G114 and G115) located in Chignahuapan, Puebla.
| Genotype | Age (years) | Height (m) | Diameter (cm) |
|---|---|---|---|
| G105 | 11 | 9.40 | 19.8 |
| G106 | 11 | 9.80 | 21.6 |
| G114 | 15 | 17.1 | 25.2 |
| G115 | 15 | 16.3 | 24.8 |
Age at bud collection (2020). Height and diameter at the time of genotype selection (2018).
Sexual propagation
In October 2018, 10 cones were collected from the upper third of the open-pollinated crown of the four genotypes selected for rootstock production. A total of 300 seeds were extracted from each genotype, separating the cores by flotation, and 160 full seeds were selected from each tree. Seeds were sown and germinated in individual 320 mL plastic containers under greenhouse conditions at the Colegio de Postgraduados, Campus Montecillo, Texcoco, Mexico. The substrate was pine bark, perlite and tepezil in a 60-20-20 ratio, respectively. In the mixture, 8 g∙L-1 of eight-month controlled release fertilizer Multicote® 18-6-12 + 2MgO + microelements were included. In September 2019, rootstock plants were transplanted into 1 L rigid plastic container maintaining control of the genotype that originated each sapling. A mixture of peat moss, perlite and vermiculite (60-20-20 %, respectively) was used as substrate, including the nutrient formula and amount of controlled-release fertilizer used in the gemination stage. Three months later, the rootstocks were removed from the greenhouse and placed under direct sun.
Each rootstock was irrigated with 400 mL of water three times per week with a hand watering can, adjusting the pH to 5.7 with 85 % phosphoric acid. Peters Professional® 20-20-20 soluble fertilizer was added at the rate of 1 g∙L-1, once a week. A total of 80 vigorous plants from each family were selected for use as rootstock on March 25, 2020. Plants averaged 60 cm in height and 8.1 mm stem base diameter.
Asexual propagation
Scions were collected on 01 April 2020 from the same four genotypes used as seed donors for the rootstock plant (G105, G106, G114 and G115) (Figure 1a). The buds (scions) presented a phenological stage of active growth before emitting strong needles without apparent pests or diseases; average length and diameter were 13 cm and 4.9 mm, respectively.
A trained person climbed to the top of each tree with the use of a tree vertical bike and safety equipment. Buds were collected from the upper half of the canopy with extension scissors, cutting them at the base of the new growth. The cut buds were gathered at the base of the tree and moistened, wrapped in newspaper and stored in plastic bags. Packages of 120 scions per genotype (considering 50 % more than required) were transported inside the cooler with ice to the Colegio de Postgraduados facilities. The packages were kept refrigerated at 4 °C until the following day to be grafted. Scions were adjusted to a length of 7 cm before grafting. On April 02, 2020, grafting was performed in a reciprocal manner, grafting the scion of each of the four genotypes evaluated on the progeny of the same genotype and on the progeny of the other three genotypes; in total 20 grafting procedures were performed for each of the 16 combinations.
In this experiment, the lateral grafting technique was used at 10 cm from the base of the main stem of the rootstock (without cutting it), making a cut of 2 cm in length and 80° of inclination with a cutter. The scion was cut twice with a scalpel and a number 12 blade to give it a wedge shape in the basal part, exposing two planes of the cambium. In this experiment, the lateral grafting technique was used at 10 cm from the base of the main stem of the rootstock (without cutting it), making a cut of 2 cm in length and 80° of inclination with a cutter. The scion was cut twice with a scalpel and a number 12 blade to give it a wedge shape in the basal part, exposing two planes of the cambium. Subsequently, the cambium of both parts was made to coincide by inserting the graft. Then, to seal the grafted area, a strip of plastic (thin, 1 cm wide and 50 µm thick) was placed with several turns around the area. Finally, a transparent polyethylene bag (15 x 25 cm) was placed over the graft to prevent dehydration (González-Jiménez et al., 2022).
Post-grafting management activities included the gradual opening of the bag at 35 to 60 days; removal of the plastic at the point of union at two and a half months (when complete healing was observed); and pruning of the rootstock in three stages (40, 60 and 100 days), removing approximately one third of the aboveground part at each date, until only the grafted bud was left as rootstock leader. Irrigation, fertilization and fungicide application continued with the same management as in the rootstock production.
Between the 30th and 60th day after grafting, once a week, visual inspections of the union point of each graft were carried out through the plastic bag to identify phytosanitary problems. Phytopathogenic fungi were detected at the union point in less than 5 % of the total grafts. To correct the problem, the bag was removed, the affected area was left exposed and cleaned with a swab moistened with Pursue® 5 mL∙L-1; quaternary ammonium salts; finally, the area was exposed, and the plastic bag was replaced.
Experimental design
A randomized block experimental design with factorial arrangement was applied: 1) scion genotype with four levels (G105, G106, G114 and G115) and 2) rootstock family with four levels (F105, F106, F114 and F115). Four blocks with 16 treatments were established; each treatment was represented with five grafts per block, so a total of 320 grafts were inserted.
Data were analyzed using the statistical model Y ijk = µ + β k + G i + F j * GF ij + ε ijk ; where, Y ijk = value of the response variable corresponding to repetition k of level i of G and level j of F; µ = overall mean; β k = effect of block; G i = effect of scion; F j = ffect of rootstock family; GF ij = interaction scion genotype* rootstock family; Є ijk = experimental error; i = G105, G106, G114 and G115; j = F105, F106, F114 and F115; k = 1, 2, 3 and 4 replicates.
The variables studied were grafting (%) and number of grafts that developed needles (%) at two months, graft survival (%) monthly until 12 months, and length (cm) and diameter (mm) of the grafted scion at five months.
Statistical analysis
Data were subjected to Tukey's analysis of variance and multiple comparison of means in the statistical program SAS 9.4 (Statistical Analysis System [SAS], 2013). The data of the variables evaluated in percentage, as they did not meet the assumption of normality using the Shapiro-Wilk test, were transformed with the function [T = arcsine (√Y)] before performing the ANOVA and subsequently retransformed to the original units with the function [Y = 100 sine2 (T)] (Barrera-Ramírez et al., 2020).
Results and Discussion
Based on the information in Table 2, the effect of scion genotype was different (P < 0.05) in all variables and the effect of rootstock family was different for survival, diameter growth and needle development. The interaction between the evaluated factors only had an effect on survival. In general, an average of 74.7 % of the grafts were attached, 50.0 % survived, with 20.8 cm of growth in length and 1.6 mm in diameter; 65 % of the grafts attached developed needles (Table 3).
Table 2 P values of the analysis of variance for the scion compatibility variables of four superior Pinus patula genotypes grafted on rootstocks of the same four families.
| Source of variation | Grafting (%) | Survival (%) | Length (cm) | Diameter (mm) | Needles (%) |
|---|---|---|---|---|---|
| Block | 0.5046 | 0.3378 | 0.6548 | 0.8307 | 0.1262 |
| Scion genotype (SG) | <0.0001 | <0.0001 | <0.0001 | <0.0001 | 0.0002 |
| Rootstock family (RF) | 0.5046 | <0.0001 | 0.3274 | 0.0201 | 0.0159 |
| SG*RF | 0.4684 | 0.0050 | 0.1701 | 0.8348 | 0.1173 |
Effect of scion genotype
Grafting
Table 3 indicates that the percentages of P. patula grafting success ranged from 70 to 82 %. Genotype G115 had 12.5 % higher grafting (P < 0.0001) compared to G106. Differences between scion genotypes suggest that each has a different ability to bind to the host plant tissue.
In conifers, variable results have been reported, but in most cases with grafting success rates of less than 50 % (Flores García, Morales González, Muñoz Flores, Prieto Ruiz, & Pineda Ojeda, 2013). In lateral grafting of P. patula, more favorable results have been recorded when grafting scions from juvenile trees (73 %) than from mature trees (35 %) (Aparicio-Rentería et al., 2013; González-Jiménez et al., 2022). Although it was not a factor considered in the present study, the age difference (four years) between scion donor trees was not favorable for grafting with the younger age genotypes (G105 and G106; Table 1); on the contrary, G115 had the highest grafting values (82.5 %).
The high percentages of grafting in this study show that the scion genotypes had the capacity to join their tissues in a functional way. The phenological stage of the buds (active growth) was suitable for grafting, because they come from trees with superior characteristics, healthy and young age, which is recommended to achieve grafting success (Pérez-Luna et al., 2019). In addition, environmental conditions during grafting allowed the cellular processes, which start when grafting, to be carried out correctly (Hartmann et al., 2014), regardless of scion genotype.
Although the genotype*family interaction effect was not significant (P = 0.4684), the grafting percentage was higher with an unrelated genotype and rootstock family: G105 + F106 (85 ± 9.6), G106 + F105 (85 ± 9.6), G114 + F115 (85 ± 5.0) y G115 + F114 (90 ± 10.0). Pina et al. (2017) suggested testing and selecting, for each genotype of interest, the rootstock plant that improves grafting and reduces initial incompatibility.
Survival
Besides grafting, graft survival is a factor of great relevance since the graft must be kept alive to fulfill its purpose. A difference (P < 0.0001) was detected in the survival of G115 and G114 compared to G105 and G106. The highest survival at 12 months was obtained with G115 buds (73.8 %) with a difference of 41.3, 46.3 and 7.5 % compared to G105, G106 and G114 (Table 3). In grafts of P. elliottii, Medina Pérez et al. (2007) found differences in survival and stolon formation between scion genotypes, one year after grafting.
In the case of pine trees, it has been identified that graft survival decreases considerably over time. For P. patula, survival was reduced 71 % seven months after grafting (Aparicio-Rentería et al., 2013); in P. engelmannii Carr. it decreased to 12.5 % six months after grafting (Pérez-Luna et al., 2020) and to 27 % in P. pseudostrobus 90 days after grafting (Barrera-Ramírez et al., 2020).
In the two scion genotypes with high survival (G115 and G114), the highest number of dead grafts was in the grafting stage (first two months) and only 8.7 % (G115) and 7.5 % (G114) in the month 2-12 interval (Figure 2a). Barrera-Ramírez et al. (2020) agreed that the highest percentage of grafting mortality was recorded during the first 40 days, because more than 50 % had grafting problems. On the contrary, the highest mortality rate in G105 (40 %) and G106 (42.5 %) was recorded after grafting (Figure 2a). Aparicio-Rentería et al. (2013) attributed the mortality of P. patula grafts in the first year to extreme environmental conditions due to high temperatures, excessive rain, hail and frost under nursery conditions before being taken to the open field. In the present study, the main cause of mortality in the 2-12-month period was root necrosis resulting in total plant death (scion and rootstock) in almost 100 % of the cases. Ford, Jones, and Chirwa (2014) reported that P. patula is susceptible to attack by phytopathogenic fungi in the early years.
Moreover, physiological and anatomical incompatibility between scion and rootstock also affect survival, as either party can weaken or kill the grafted tree; few studies had focused on the impact of scion on rootstock (Han, Guo, Korpelainen, Niinemets, & Li, 2019). Tandonnet et al. (2010) determined that root vigor is conferred by the grafted scion, as the scion genotype induced necrosis in rootstock roots. In the present study, G115 and G114, after grafting, could have efficiently assimilated the resources provided by the rootstock and vice versa, because the interaction capacity determines grafting success (Goldschmidt, 2014).
Graft growth and needle development
The genotypes used as scions had a significant effect (P < 0.0001) on the initial growth response for length and diameter (Table 2). The greatest growth in graft length was observed with scions of genotype G105 (26 cm) with a difference of 9.9, 5.3 and 5.5 cm compared to G106, G114 and G115, while G115 (2.0 mm) and G105 (1.8 mm) favored the greatest growth in diameter (Table 3).
The scions of the genotypes evaluated expressed their initial growth potential because they were collected and grafted in early spring, when the main shoot elongation occurs in actively growing pines (Guadaño et al., 2016) (Figure 1a). Each genotype may have different ability to be propagated by grafting. Genotype influences variations in both reproductive phenology and morphological characteristics among clones due to genetic diversity among individuals of the same species (Sivacioglu, Ayan, & Celik, 2009). Han et al. (2019) found that scion genotype caused strong effect on proline concentration in graft roots in Populus. Meanwhile, Sivacioglu et al. (2009) found genotype effect on the growth of several Pinus sylvestris L. clones from an asexual seed orchard.
The grafted scions that developed needles more rapidly, at two months, were the scions of G115 (80.9 %), G114 (69.7 %) and G105 (69.2 %) with significant differences (P = 0.0002) with G106 (40.6 %). These three genotypes also had the highest values in length and diameter growth (Table 3). This can be attributed to the fact that plants grafted with these scion genotypes, by developing faster, reactivated growth favoring photosynthesis and carbohydrate production (Barrera-Ramírez et al., 2020). This speed of response is important in lateral grafting, since the aboveground part of the rootstock is pruned gradually and at the end only the needles that the grafted scion has managed to develop remain (Muñoz et al., 2013).
Table 3 Mean values and standard error (±) of the compatibility analysis of scions of four superior Pinus patula genotypes grafted on rootstocks of the same four families.
| Factor | Grafting (%) | Survival (%) | Length (cm) | Diameter (mm) | Needless (%) |
|---|---|---|---|---|---|
| Scion genotype | |||||
| G105 | 72.5 ± 6.3 ab | 32.5 ± 6.8 b | 26.0 ± 1.2 a | 1.8 ± 0.1 a | 69.2 ± 7.0 a |
| G106 | 70.0 ± 5.5 b | 27.5 ± 6.3 b | 16.1 ± 1.0 c | 1.1 ± 0.2 b | 40.6 ± 8.0 b |
| G114 | 73.8 ± 4.7 ab | 66.3 ± 4.7 a | 20.7 ± 0.8 b | 1.3 ± 0.1 b | 69.7 ± 6.8 a |
| G115 | 82.5 ± 4.8 a | 73.8 ± 5.7 a | 20.5 ± 0.9 b | 2.0 ± 0.1 a | 80.9 ± 5.2 a |
| Rootstock family | |||||
| F105 | 80.0 ± 5.2 a | 65.0 ± 4.7 a | 21.3 ± 1.0 a | 1.9 ± 0.1 a | 64.3 ± 2.5 ab |
| F106 | 70.0 ± 6.1 a | 56.3 ± 7.1 ab | 21.9 ± 1.5 a | 1.6 ± 0.2 ab | 81.9 ± 6.0 a |
| F114 | 71.3 ± 5.8 a | 46.3 ± 7.9 bc | 20.6 ± 1.3 a | 1.3 ± 0.2 b | 56.2 ± 8.4 b |
| F115 | 77.5 ± 4.4 a | 32.5 ± 8.7 c | 19.4 ± 1.5 a | 1.5 ± 0.2 ab | 58.0 ± 9.2 b |
| Average | 74.7 | 50.0 | 20.8 | 1.6 | 65.1 |
For each factor, means with different letters in the same column are statistically different according to Tukey's test (P ≤ 0.05).
Effect of rootstock family
Grafting
The statistical difference was not significant (P = 0.4684) among the four rootstock families (Table 2), even though there is a 10 % difference between the highest and lowest grafting success (Table 3), which may be associated with the sample size and may need to be increased in subsequent tests. In addition, it should be considered that there is genetic variability in the species and each family is composed of half-siblings, where each plant is a different genotype. The high percentage of grafting among the rootstock families (between 70 and 80 %) could also be related to the quality of the rootstock plant, since the seed of each family comes from superior trees: F105 and F106 (progeny trial) and F114 and F115 (purified sexual seed orchard). In this sense, the genotypes were crossed with other superior trees in the trial or orchard and as a product of genetic recombination may have generated higher quality seed (Muñoz-Gutiérrez et al., 2017); furthermore, the phytosanitary and nutritional status of the genotypes was adequate at the time of grafting.
Survival
F105 showed the highest average value (65 %) with significant differences (P < 0.0001) of 8.7, 18.7 and 32.5 % with F106, F114 and F115, respectively (Table 3). During the first two months after grafting, only the grafted scion died and the rootstock remained alive, indicating that tissue union was not achieved during grafting. The highest mortality occurred in the period from month 2-12 and varied for each family, decreasing 15, 13.7, 25 and 45 % in F105, F106, F114 and F115, respectively (Figure 2b). In this period, mortality occurred in the whole plant and could have been caused by phytosanitary problems related to some fungus or group of phytopathogenic fungi or by physiological, genetic or mechanical incompatibility of the tissues between the scion and the rootstock.
In this period, plant mortality occurred in the whole plant and could have been caused by phytosanitary problems related to fungi or groups of phytopathogenic fungi or by physiological, genetic or mechanical incompatibility of the tissues between scion and rootstock. Perhaps the better performance of F105 could be more related to a greater tolerance to the problems that caused mortality in the other three families evaluated. Martínez-Ballesta, Alcaraz-López, Muries, Mota-Cadenas, and Carvajal (2010) suggested that improper formation of scion-pattern healing callus can also affect the flow of nutrients and water from the root to the aboveground part, and photosynthates in the opposite direction, eventually leading to death of the entire plant. In South Africa, Ford et al. (2014) reported root damage of P. patula by seed and cutting propagation, and detected that it is susceptible to Fusarium circinatum, which reduced nursery survival by up to 32 %.
Grafting has been widely used in other areas to increase productivity and improve resistance to diseases and abiotic stresses, therefore, scion grafting should be considered on rootstocks with high resistance to phytosanitary problems in roots (Han et al., 2019). In this regard, the F105 rootstock family could be used for rootstock production in future grafting studies; however, it is necessary to continue with trials to identify the best P. patula families for this purpose. Furthermore, variation within rootstock families should be considered because they originate from seed; this heterogeneity may affect the rootstock performance at the family level (Izhaki et al., 2018).
Differences found in rootstock families suggest that rootstocks may vary in functionality; for example, in their ability to capture soil resources and transport them to the scion or in root system architecture, behavior and interaction with the rhizosphere (Gautier et al., 2019).
Graft growth and needle development
The ANOVA showed no difference in the effect of rootstock family on length growth (P = 0.3274), but only in diameter (P = 0.0201; Table 2). This homogeneity in graft height could favor their management in the seed orchards. F105 (1.9 mm) showed a difference in diameter growth compared to F114 (1.3 mm; Table 3), so the use of rootstocks from half-sib families, originated from seed, may produce growth variability. Clonal rootstocks decrease variability, but P. patula has no efficient protocol to produce them (Izhaki et al., 2018).
The genotype*pattern interaction had no significant effect on growth (P > 0.05); however, G105 had the highest growth in diameter when grafted onto the same F105 progeny (2.1 mm). This may be related to the vigor of this particular family and not to genetic affinity, because it was the best in all cases for this variable: G106 + F105 (1.6 mm), G114 + F105 (1.6 mm) and G115 + F105 (2.2 mm).
Needle development was assessed at two months to detect how fast these structures develop. At five months, all grafts had developed needles. The rootstock family F106 favored the formation of needles more rapidly (81.9 %) and had differences with F114 and F115 of 25.7 and 23.9 %, respectively (Table 3). Perhaps the response of F106 is related to a rapid vascular connection between the graft parts allowing the flow of water and nutrients to the scion to restart needle development (Hartmann et al., 2014). The faster the needles appear, the faster photosynthesis and production of carbohydrates required by the grafted plant is expected to start, favoring the reactivation of its growth (Barrera-Ramírez et al., 2020). The formation of needles in P. pseudostrobus was observed after 45 days of age (Barrera-Ramírez et al., 2020). Martínez-Ballesta et al. (2010) mention that the physiological implications of the connection between scion and rootstock on leaf area, morphology, growth, biomass and photosynthesis in grafts are poorly documented.
The interaction of factors on survival
The effect of scion genotype on graft survival in P. patula is influenced by the rootstock family. The best combinations for each of the four scion genotypes were G115 + F114 (85 %), G114 + F105 (80 %), G106 + F105 (60 %) and G105 + F106 (60 %) (Table 4). In this regard, Kita et al. (2018) evaluated grafts of L. gmelinii and concluded that each scion genotype had higher survival being grafted on an unrelated rootstock family and not on its same progeny as expected.
Although each scion genotype has affinity for a particular rootstock family (Table 4), F105 was more stable (first or second highest value) in survival. This family showed characteristics that favored graft viability over time, so it could be considered as a rootstock in future grafting trials. Kita et al. (2018) indicate that with an appropriate rootstock a tree can be obtained showing the best qualities of both genetic entities (scion-rootstock) and Lewsey et al. (2016) suggest considering the epigenetic basis for the interaction that occurs between the parts that integrate the graft. In contrast, F115 was the least favorable, because when grafted with G105 and G106, all grafts died after 12 months (Table 4); therefore, the use of this family as rootstock is not a guarantee for survival.
There is no information in P. patula on important families that can be used as rootstocks, despite their importance for grafting success, survival and vigor (Barrera-Ramírez et al., 2020). In fact, scion donor trees in P. patula have been selected according to their timber characteristics, but not for their physiological response to grafting.
Table 4 Interaction between scion genotype and rootstock family on Pinus patula graft survival at 12 months.
| Scion genotype | Rootstock family | Survival (%) | Scion genotype | Rootstock family | Survival (%) |
|---|---|---|---|---|---|
| G105 | F105 | 45 ± 5.0 | G114 | F105 | 80 ± 8.2 |
| G105 | F106 | 60 ± 14.1 | G114 | F106 | 60 ± 14.1 |
| G105 | F114 | 25 ± 5.0 | G114 | F114 | 55 ± 5.0 |
| G105 | F115 | 00 ± 0.0 | G114 | F115 | 70 ± 5.8 |
| G106 | F105 | 60 ± 8.2 | G115 | F105 | 75 ± 5.0 |
| G106 | F106 | 30 ± 5.8 | G115 | F106 | 75 ± 15.0 |
| G106 | F114 | 20 ± 8.2 | G115 | F114 | 85 ± 15.0 |
| G106 | F115 | 00 ± 0.0 | G115 | F115 | 60 ± 8.2 |
Mean values ± standard error.
Conclusions
P. patula graft compatibility varied according to the combination between genotype and family. Grafting with genotype G115, in combination with any family, was the most successful; similarly, grafting with family F105 in combination with any genotype was the most successful. On the other hand, scions and rootstocks of the same genotype or family were not a guarantee of graft compatibility. These results indicate that the detection and selection of good families such as F105 for rootstock production would ensure greater graft compatibility with any genotype to be cloned. This would increase the production of grafted plants with high genetic gain required in asexual seed orchards of P. patula.
