Evaluation of Phenological and Agronomical Traits of Different Almond Grafting Combinations under Testing in Central Italy

In the new introducing almond areas, it is necessary to test the more promising almond cultivar and rootstock combinations able to guarantee the best agronomic performances according to the specific pedoclimatic conditions. With this aim, two almond trials have been established in an experimental farm located in the Latium region (Italy). The first trial (A) focused on the phenological, and agronomical influences induced by the clonal rootstock ‘GF677’ on the grafted cultivars ‘Tuono’, ‘Supernova’ and ‘Genco’, in comparison to those induced by peach seedling rootstocks, in order to identify the best grafting combination for developing “high density” plantings in this new growing area. The second trial (B) tested the phenological and agronomical influences induced by three different clonal rootstocks (‘GF677’, ‘Rootpac® 20’ and ‘Rootpac® R’), on the Spanish cultivar ‘Guara’ to identify suitable dwarfing rootstocks for “super high density” plantings in the same environment. Flowering and ripening calendars of the trial A highlighted as the medium-late flowering cultivars ‘Genco’, ‘Supernova’ and ‘Tuono’ could be subject to moderate risk of cold damages. The clonal rootstock ‘GF677’ seems to anticipate flowering and vegetative bud break by a few days in ‘Tuono’ when compared to the same cultivar grafted on peach seedling rootstocks. Furthermore, the yield per plant was always higher in plants grafted on ‘GF677’. The observations carried out in trial B highlighted as the flowering of cultivar ‘Guara’ were affected by the rootstock, with ‘Rootpac® 20’, which postponed its full bloom of about one week when compared to other rootstocks, whereas ‘GF677’ imposed more vigor to the cultivar than ‘Rootpac® 20’ and ‘Rootpac® R’.

Resistance to Aspergillus flavus and A. parasiticus in almond advanced selections and cultivars and its interaction with the aflatoxins biocontrol strategy

Aflatoxin contamination of almond kernels, caused by Aspergillus flavus and A. parasiticus, is a severe concern for growers due to its high toxicity. In California, the global leader of almond production, aflatoxin can be managed by applying the biological control strain AF36 of A. flavus and selecting resistant cultivars. Here, we classified the almond genotypes by K-Means cluster analysis into three groups [Susceptible (S), Moderately Susceptible (MS), or Resistant (R)] based on aflatoxin content of inoculated kernels. The protective effects of the shell and seedcoat in preventing aflatoxin contamination were also examined. The presence of intact shells reduced aflatoxin contamination over 100-fold. The seedcoat provided a layer of protection, but not complete. In kernel inoculation assays, none of the studied almond genotypes showed a total resistance to the pathogen. However, nine traditional cultivars and four advanced selections were classified as R. Because these advanced selections contained germplasm derived from peach, we compared the kernel resistance of three peach cultivars to that shown by kernels of a R (‘Sonora’) and a S (‘Carmel’) almond cultivar and five pistachio cultivars. Overall, peach kernels were significantly more resistant to the pathogen than almond kernels, which were more resistant than pistachio kernels. Finally, we studied the combined effect of the cultivar resistance and the biocontrol strain AF36 in limiting aflatoxin contamination. For this, we co-inoculated almond kernels of R ‘Sonora’ and S ‘Carmel’ with AF36 72 h before or 48 h after inoculating with an aflatoxin-producing strain of A. flavus. The percentage of aflatoxin reduction by AF36 strain was greater in kernels of ‘Carmel’ kernels (98%) than in those of ‘Sonora’ (83%). Cultivar resistance also affected the kernel colonization by the biological control strain. AF36 strain limited aflatoxin contamination in almond kernels even when applied 48 h after the aflatoxin-producing strain. Our results show that biocontrol combined with the use of cultivars with resistance to aflatoxin contamination can result in a more robust protection strategy than the use of either practices in isolation.

Temporal Response to Drought Stress in Several Prunus Rootstocks and Wild Species

Prunus species are important crops in temperate regions. In these regions, drought periods are predicted to occur more frequently due to climate change. In this sense, to reduce the impact of climate warming, obtaining new tolerant/resistant cultivars and rootstocks is a mandatory goal in Prunus breeding. Therefore, the current study assembled three Prunus species including almond, (P. dulcis Mill D.A. Webb), apricot (P. armeniaca L.) and peach (P. persica L.) to model the temporal effects of drought. A hybrid peach × almond and a wild almond-relative species Prunus webbii were also included in the study. Physiological traits associated with photosynthetic activity, leaf water status, and chlorophyll content were assessed under three watering treatments. Results showed that effects of time, genotype, and treatment interact significantly in all traits. In addition, results confirmed that P. webbii have a greater tolerance to drought than commercial rootstocks. However, “Real Fino” apricot showed the fastest recovery after re-irrigation while being one of the most affected cultivars. In addition, from the better response to these watering treatments by the almond genotypes, two different trends were observed after re-irrigation treatment that clearly differentiate the response of the almond cultivar “Garrigue” from the rest of Prunus genotypes. A better characterization of the short-term drought response in Prunus, an accurate and more efficient evaluation of the genotype effect was obtained from the use of mixed models considering appropriate variance–covariance structures. Although the advantages of these approaches are rarely used in Prunus breeding, these methodologies should be undertaken in the future by breeders to increase efficiency in developing new breeding materials.

Comparison of SHD and Open-Center Training Systems in Almond Tree Orchards cv. ‘Soleta’

The increase in the demand for almonds, the development of novel self-fertile and late-flowering varieties, and the establishment of plantations in new irrigated areas have led to significant progress in the productive techniques of almond tree cultivation. One of the most important has been the increase in planting density, due to the development of dwarfing rootstocks. This paper presents a comparison between two training systems with ‘Soleta’ almond cultivar: a super high density (SHD) system using Rootpac-20 dwarfing rootstock versus an open-center training system using GF-677 rootstock. To this end, several parameters related to chlorophyll content (fluorescence and SPAD) and light interception (from photosynthetically active radiation (PAR) measurements) were monitored throughout two vegetative cycles, and other productive conditions (flowering, fruit set and production) were tracked at specific times of the cycle. The open-center system resulted in higher PAR interception than the SHD system, but also in the presence of poorly illuminated fractions of the canopy. Differences were observed between both systems in terms of average fruit weight and yield per canopy volume. Lower yields were obtained in SHD system than in open-center, which may be significantly increased by adapting the inter-row spacing. However, the degree of efficiency in the use of resources or productive inputs, such as irrigation, was favorable to the new SHD training system, so its potential to become a reference system in modern plantations (using over-the-row harvesters similar to those used for vine and olive trees) seems promising.