Comparative Vegetative, Nutritional and Anatomical Study of Two Almond Varieties Grafted on Bitter Almond and Nemaguard Peach Rootstocks

A comparative study was conducted during the 2017/2018 and 2018/2019 growing seasons for Nonpareil and Ne Plus Ultra almond cvs grafted on Bitter almond and Nemaguard peach rootstocks at the Experimental Research Station of National Research Centre at Nubaria, El Behera governorate, Egypt. The comparison was evaluated through the grafting success percentage, vegetative growth, determination of some leaf mineral composition, as well as, the anatomical examination of scion/rootstock union zone and cross-section of leaves. The obtained results clarified that the grafting success percentage was significantly affected by the different used rootstocks. Using Bitter almond rootstock recorded the highest percentage of grafting success, leaf chlorophyll content, root length, and a number of lateral root /plant in both cultivars. Using Nemaguard peach rootstock recorded significantly the highest values of scion length, stem girth above and below union zone, number of branches and leaves/plant, leaf area as well as seedlings fresh and dry weight. Leaves of both cultivars grafted on Nemaguard peach rootstock recorded the highest concentrations of leaf mineral contents as compared to those grafted on Bitter almond rootstock. Cross-sections of the graft union zone were taken after 28 days and 6 months from grafting for anatomical analysis. The callus cells developed 28 days after grafting, but cambial cells between the rootstock and scion tissues did not occur in all scion/rootstock combinations. After 6 months of grafting, cambial cells were established, vascular differentiation was observed, regular parenchymatic tissue properties and sclerenchyma bundles were seen in the graft union. There was no problem in terms of compatibility of Nonpareil and Ne Plus Ultra on Bitter almond and Nemaguard peach rootstocks. Comparing leaf cross-sections of almond grafted on both rootstocks demonstrated that the density of mesophyll cells was affected as a consequence of the rootstock–scion interaction. Nemaguard peach rootstock can be recommended for grafting Nonpareil and Ne Plus Ultra almond cultivars under Nubaria conditions to produce vigorous trees.

Responses of Root Endophytes to Phosphorus Availability in Peach Rootstocks With Contrasting Phosphorus-Use Efficiencies

Phosphorus (P) is an important macronutrient for all lives, but it is also a finite resource. Therefore, it is important to understand how to increase the P availability and plant uptake. The endophytes can help host plants to improve P uptake and will be apparently affected by plant genotypes. To investigate the mechanism of root endophytes in promoting P uptake of peach rootstocks, we analyzed the variations of the root endophytic fungal and bacterial communities of peach rootstocks with different P efficiencies under high or low level of P addition. Results showed that Proteobacteria was the dominant bacterial phylum in the roots of all rootstocks under the two levels of P addition. At low P level, the abundance of Actinoplanes in phosphorus-inefficiency root system was apparently higher than that at high P level. Actinoplanes produced important secondary metabolites, improving the stress resistance of plants. Under high P condition, the abundance of Ferrovibrio was higher in Qing Zhou Mi Tao than in Du Shi. Fe oxides considerably reduced the availability of applied P, which partially explained why the P utilization in Qing Zhou Mi Tao is inefficient. Further, Ascomycota was the dominant fungal phylum in the roots of all rootstocks under different levels of P addition. The fungi community of roots varied in different rootstocks at each P level, but was similar for the same rootstock at different P levels, which indicated that genotype had a greater effect than P addition on the fungal community of peach rootstocks.

Effect of Propagation Systems and Indole-3-Butyric Acid Potassium Salt (K-IBA) Concentrations on the Propagation of Peach Rootstocks by Stem Cuttings

Traditionally, peach rootstocks are propagated by seeds due to their high availability, low cost, and easy storage and handling. However, stem cuttings allow the propagation of interspecific hybrids and keep the genetic uniformity of heterozygous genotypes. This study compared the effect of four different concentrations of K-IBA (indole-3-butyric acid potassium salt) on softwood cuttings of three peach backcrosses (peach × (peach × almond)) for rootstock propagation in two propagation systems: aeroponics and germination trays. The four concentrations of K-IBA applied were: 0.0% (w/v) as a control, 0.1% (w/v), 0.2% (w/v), and 0.4% (w/v). Data were collected on the survival rate (%), rooting rate (%), and root growth parameters. The relevance of auxin for peach cuttings rooting was evidenced. K-IBA at 0.2% showed the best rooting effect for peach softwood cuttings, evidenced by its high rooting rate and higher survival rate. K-IBA at 0.4% and 0.2% produced the highest number of adventitious roots. The highest root growth parameters were obtained in germination trays, confirming the suitability of this system for root growth. However, aeroponics was demonstrated to be as efficient as the traditional germination trays for the rooting of peach cuttings, allowing for a more controlled environment with a better use of resources.

Simultaneous selection of peach rootstocks by mixed models

The term adaptability refers to the ability of a genotype to respond favorably to environmental spur, while stability is the predictability of genotypic behavior. Therefore, the objective was to select Prunus rootstock cultivars with greater adaptability and genotypic stability for subtropical environmental conditions using the HMPRVG method. The experiment was conducted in Chapecó, Santa Catarina State, Brazil. Twenty-one rootstock genotypes were evaluated under the ‘BRS-Libra’ canopy cultivar and one genotype from self-rooted seedlings. The 22 genotypes were evaluated for canopy volume, yield, fruit diameter and fruit set in the growing seasons 2015/16, 2016/17, 2017/18 and 2018/19. Adaptability and stability were measured by means of the harmonic mean relative performance of genotypic values (HMRPGV). In addition, genetic parameters for heritability and ratio test were measured. According to the results, the self-rooted, ‘De Guia’, ‘I-67-52-4’, ‘Mexico Row 1’ and ‘Rosaflor’ genotypes coincided most frequently in the ranking of the three most adaptable and stable genotypes. On the other hand, the ‘P. mandshurica’, ‘Rigitano’ and ‘Santa Rosa’ genotypes corresponded to the lowest adaptability and stability values, thus constituting low quality genetic materials for cultivation. It can be concluded that under the tested conditions the HMPRVG method is efficient for the Prunus rootstock selection cultivars and the ‘BRS-Libra’ grafted on ‘Mexico Row 1’, ‘Rosaflor’ rootstocks and trees from self-rooted seedlings have greater adaptability and phenotypic stability under the subtropical cultivation conditions.

UTILIZING BIOTECHNOLOGY TOOLS FOR SILECTING SALT TOLERANT ROOTSTOCK OF PEACH HASSAWI

This study was carried out with an aim of evaluation of performance of Hassawi peach rootstocks and testing their variance towards salinity stress thus to find out a quick effective modern technique for their reculture and re-propagation again in the region. Eight different concentrations of sodium chloride (NaCl) that represent progressive gradual levels of salinity were used to investigate tolerability of the explants towards variant levels of salinity stress. Thus to evaluate the performance of these Hassawi peach rootstocks (peach, plum ]ghwj[, and almond). Date and results declared the general superiority of bitter almond to the other rootstocks, as it vitally survived and tolerated salinity to 3500 ppm NaCl, followed by peach that tolerated salinity to 2500 ppm, and eventually ghwj that just survived with maximum tolerance of 2000 ppm of NaCl. The study recommends to count on bitter almond as a salinity tolerant rootstock followed by peach for grafting Hassawi peach rootstocks for its regeneration again in Al-Ahsa oasis, and to exclude plum rootstock because of its low salinity tolerance besides its very low harmonization with peach that negatively affect grafting process.