Physiological and Agronomical Responses of ‘Vairo’ Almond and ‘Big Top’ Nectarine Cultivars Grafted onto Different Prunus Rootstocks and Grown under Semiarid Mediterranean Conditions

Two trials were conducted under Mediterranean conditions to monitor several physiological indicators before harvest (leaf chlorophyll concentration, quantum yield of photosystem II electron transport, stem water potential, and stomatal conductance) and some agronomic performance parameters before and at harvest (vigor, fruit growth, fruit size, fruit weight, and yield), of ‘Vairo’ almond and ‘Big Top’ nectarine cultivars grafted onto eight Prunus rootstocks, six of which are common in both cultivars. For both ‘Vairo’ almond and ‘Big Top’ nectarine cultivars, factors including rootstock, date, and the interaction between rootstock and date, from fruit set to harvest were evaluated. Significantly affected were certain physiological and agronomical traits which were evaluated before harvest, with stem water potential being the parameter affected by interaction in both cultivars. In fact, the stem water potential presented low levels in Rootpac-20 and high levels in Rootpac-40 for both cultivars. With regard to the other physiological traits evaluated during the growing period, changes in stomatal conductance were observed in ‘Vairo’, but not in ‘Big Top’. Comparing rootstocks throughout the season, Rootpac-40 and IRTA-1 exhibited the highest stomatal conductance values, whereas the lowest was observed in Rootpac-R; Rootpac-20 and Ishtara also presented low values. Regarding agronomical traits at harvest, GF-677 and IRTA-1 produced high yields for ‘Vairo’ almond cultivar, whereas Rootpac-40 and Ishtara performed better with ‘Big Top’ nectarine cultivar.info:eu-repo/semantics/publishedVersio

Remote Sensing Energy Balance Model for the Assessment of Crop Evapotranspiration and Water Status in an Almond Rootstock Collection

One of the objectives of many studies conducted by breeding programs is to characterize and select rootstocks well-adapted to drought conditions. In recent years, field high-throughput phenotyping methods have been developed to characterize plant traits and to identify the most water use efficient varieties and rootstocks. However, none of these studies have been able to quantify the behavior of crop evapotranspiration in almond rootstocks under different water regimes. In this study, remote sensing phenotyping methods were used to assess the evapotranspiration of almond cv. “Marinada” grafted onto a rootstock collection. In particular, the two-source energy balance and Shuttleworth and Wallace models were used to, respectively, estimate the actual and potential evapotranspiration of almonds grafted onto 10 rootstock under three different irrigation treatments. For this purpose, three flights were conducted during the 2018 and 2019 growing seasons with an aircraft equipped with a thermal and multispectral camera. Stem water potential (Ψstem) was also measured concomitant to image acquisition. Biophysical traits of the vegetation were firstly assessed through photogrammetry techniques, spectral vegetation indices and the radiative transfer model PROSAIL. The estimates of canopy height, leaf area index and daily fraction of intercepted radiation had root mean square errors of 0.57 m, 0.24 m m–1 and 0.07%, respectively. Findings of this study showed significant differences between rootstocks in all of the evaluated parameters. Cadaman® and Garnem® had the highest canopy vigor traits, evapotranspiration, Ψstem and kernel yield. In contrast, Rootpac® 20 and Rootpac® R had the lowest values of the same parameters, suggesting that this was due to an incompatibility between plum-almond species or to a lower water absorption capability of the rooting system. Among the rootstocks with medium canopy vigor, Adesoto and IRTA 1 had a lower evapotranspiration than Rootpac® 40 and Ishtara®. Water productivity (WP) (kg kernel/mm water evapotranspired) tended to decrease with Ψstem, mainly in 2018. Cadaman® and Garnem® had the highest WP, followed by INRA GF-677, IRTA 1, IRTA 2, and Rootpac® 40. Despite the low Ψstem of Rootpac® R, the WP of this rootstock was also high.info:eu-repo/semantics/publishedVersio

Almond Fruit Drop Patterns under Mediterranean Conditions

Almond is an important tree nut crop worldwide, and planted areas have been increasing year after year. While self-fertility is one of the key factors when it comes to improved almond productivity of new cultivars, yield is also affected by the number of flowers produced, pollination, fruit set, fruit drop, and fruit weight. Almond fruit drop patterns of 20 Mediterranean almond cultivars were studied over three years. In addition, fruit drop patterns of two scion cultivars ‘Marinada’ and ‘Vairo’ budded onto eight to 10 different rootstocks managed with three different pruning strategies were studied for two years. Cumulative flower and fruit drop ranged from 50% to 90% among cultivars and treatments, and there were up to four fruit drop events during the growing season, the main one occurring from 20–60 days from full bloom (DFFB). Subsequent drops were at 100 DFFB, 120–140 DFFB, and the last one at 160–180 DFFB. The later drops were less apparent. In general, about half of the cumulative drop was comprised of buds and flowers, and the remaining percentage was fruit that dropped 20 or more days after full bloom. Furthermore, different fruit drop patterns were observed depending on the cultivar. For late- and extra-late flowering cultivars, cumulative fruit drop began to decrease earlier, with most of the drops occurred already at full bloom, whereas the opposite was observed for the early flowering cultivars. Rootstocks also had an important effect on the fruit drop pattern, with different effects depending on the scion cultivar. Tree management, such as type of pruning, also had an important effect on the rate of fruit drop and cumulative drop. Therefore, each combination of cultivar × rootstock × pruning type will require different strategies in order to reduce the fruit drop and optimize crop loads.info:eu-repo/semantics/publishedVersio

Evaluation of Fungicides and Application Strategies for the Management of the Red Leaf Blotch Disease of Almond

Red leaf blotch (RLB) of almond, caused by Polystigma amygdalinum, is an important foliar disease of this nut tree in the Mediterranean basin and especially in Spain. In recent years, the control of this disease has become a key factor in the management of Spanish almond orchards. The management of RLB is not easy due to intrinsic factors of the disease (e.g., long infection and latency periods) and the low number of registered fungicides in this country. From 2015 to 2019, different field trials were conducted in the Lleida region, NE Spain, to evaluate the efficacy of several fungicide products and of application strategies to control this disease. Systemic fungicides, which included fluopyram, trifloxystrobin, and mixtures of fluopyram + trifloxystrobin and pyraclostrobin + boscalid, performed better than contact and penetrant products and showed up to 90% control against RLB. However, the efficacy of the tested fungicides varied depending on the year. In terms of application strategies, when fungicide applications were conducted following specific meteorological conditions (after 15 days from >15 mm rainfalls with ≈10–15 ◦C as the minimum average temperature), their efficacy was comparable to that of calendar-based treatments (every 14, 21, or 31 days from petal fall) but with fewer applications (depending on the year, 2–4 applications as compared with 5–9 for calendar treatments)info:eu-repo/semantics/publishedVersio

Susceptibility of Almond (Prunus dulcis) Cultivars to Twig Canker and Shoot Blight Caused by Diaporthe amygdali

Twenty-five almond cultivars were assessed for susceptibility to Diaporthe amygdali, causal agent of twig canker and shoot blight disease. In laboratory experiments, growing twigs were inoculated with four D. amygdali isolates. Moreover, growing shoots of almond cultivars grafted onto INRA ‘GF-677’ rootstock were used in 4-year field inoculations with one D. amygdali isolate. In both types of experiments, inoculum consisted of agar plugs with mycelium, which were inserted underneath the bark, and the lesion lengths caused by the fungus were measured. Necrotic lesions were observed in the inoculated almond cultivars in both laboratory and field tests, confirming the susceptibility of all evaluated cultivars to all inoculated isolates of D. amygdali. Cultivars were grouped as susceptible or very susceptible according to a cluster analysis. The relationship between some agronomic traits and cultivar susceptibility was also investigated. Blooming and ripening times were found to be relevant variables explaining cultivar performance related to D. amygdali susceptibility. Late and very late blooming and early and medium ripening cultivars were highly susceptible to D. amygdali. Our results may provide valuable information that could assist in ongoing breeding programs of this crop and in the selection of cultivars for new almond plantations.info:eu-repo/semantics/acceptedVersio

Horticultural performance of ‘Marinada’ and ‘Vairo’ almond cultivars grown on a genetically diverse set of rootstocks

Evolution of almond planted area and production has been mainly due to the arrival of new cultivars and rootstocks that have contributed to improve agronomic characters such as yield, precocity and efficiency. In recent years, new cultivars that have contributed to provide late blooming time and self-fertility, and with ease to adapt for mechanical harvest and high-density are becoming available. However, there is scarcity of studies where the interaction of these new cultivars with hybrid rootstocks has been tested. The aim of this study was to assess the performance of Cadaman®, Garnem®, INRA GF-677, IRTA-1, IRTA-2, Ishtara®, Adesoto, Rootpac® 20, Rootpac® 40, and Rootpac® R rootstocks with two promising almond cultivars such as ‘Marinada’ and ‘Vairo’. Bloom and nut ripening dates were affected by rootstock genotype. Both ‘Marinada’ and ‘Vairo’ cultivars showed low biennial bearing, with some differences among rootstocks, with IRTA-2 and Adesoto inducing the lowest values. On the other hand, Adesoto had higher number of suckers than the rest of the rootstocks. Garnem® provided the biggest trees, followed by Cadaman®, and then a third group which comprised IRTA-2 and INRA GF-677. Rootpac® 20 was the most dwarfing rootstock, followed by IRTA-1, Adesoto, Ishtara®, Rootpac® R, and Rootpac® 40. In terms of yield efficiency and partitioning index, IRTA-1, INRA GF-677, and Rootpac® R were the ones with higher values. Differences in tree volume and vigor for these rootstocks suggested that INRA GF-677 would be a suitable rootstock for low-medium planting densities with wide spacings; whereas Rootpac® R and IRTA-1 would be suitable rootstocks for medium- and high-density plantings. Findings of this study showed dramatic differences in tree vigor, yield, kernel weight, yield efficiency, and partitioning index, which provide a wide range of options to deem for each cultivar in a particular climate and management.info:eu-repo/semantics/acceptedVersio

Almond Fruit Drop Patterns under Mediterranean Conditions

Almond is an important tree nut crop worldwide, and planted areas have been increasing year after year. While self-fertility is one of the key factors when it comes to improved almond productivity of new cultivars, yield is also affected by the number of flowers produced, pollination, fruit set, fruit drop, and fruit weight. Almond fruit drop patterns of 20 Mediterranean almond cultivars were studied over three years. In addition, fruit drop patterns of two scion cultivars ‘Marinada’ and ‘Vairo’ budded onto eight to 10 different rootstocks managed with three different pruning strategies were studied for two years. Cumulative flower and fruit drop ranged from 50% to 90% among cultivars and treatments, and there were up to four fruit drop events during the growing season, the main one occurring from 20–60 days from full bloom (DFFB). Subsequent drops were at 100 DFFB, 120–140 DFFB, and the last one at 160–180 DFFB. The later drops were less apparent. In general, about half of the cumulative drop was comprised of buds and flowers, and the remaining percentage was fruit that dropped 20 or more days after full bloom. Furthermore, different fruit drop patterns were observed depending on the cultivar. For late- and extra-late flowering cultivars, cumulative fruit drop began to decrease earlier, with most of the drops occurred already at full bloom, whereas the opposite was observed for the early flowering cultivars. Rootstocks also had an important effect on the fruit drop pattern, with different effects depending on the scion cultivar. Tree management, such as type of pruning, also had an important effect on the rate of fruit drop and cumulative drop. Therefore, each combination of cultivar × rootstock × pruning type will require different strategies in order to reduce the fruit drop and optimize crop loads

Evaluation of Fungicides and Application Strategies for the Management of the Red Leaf Blotch Disease of Almond

Red leaf blotch (RLB) of almond, caused by Polystigma amygdalinum, is an important foliar disease of this nut tree in the Mediterranean basin and especially in Spain. In recent years, the control of this disease has become a key factor in the management of Spanish almond orchards. The management of RLB is not easy due to intrinsic factors of the disease (e.g., long infection and latency periods) and the low number of registered fungicides in this country. From 2015 to 2019, different field trials were conducted in the Lleida region, NE Spain, to evaluate the efficacy of several fungicide products and of application strategies to control this disease. Systemic fungicides, which included fluopyram, trifloxystrobin, and mixtures of fluopyram + trifloxystrobin and pyraclostrobin + boscalid, performed better than contact and penetrant products and showed up to 90% control against RLB. However, the efficacy of the tested fungicides varied depending on the year. In terms of application strategies, when fungicide applications were conducted following specific meteorological conditions (after 15 days from >15 mm rainfalls with ≈10–15 °C as the minimum average temperature), their efficacy was comparable to that of calendar-based treatments (every 14, 21, or 31 days from petal fall) but with fewer applications (depending on the year, 2–4 applications as compared with 5–9 for calendar treatments)

Cultivar Susceptibility and Environmental Parameters Affecting Symptom Expression of Red Leaf Blotch of Almond in Spain

Red leaf blotch (RLB) of almond, caused by Polystigma amygdalinum, is an important foliar disease of this nut tree in the Mediterranean basin and Middle East regions. In recent years, the incidence of this disease has increased in Spain, corresponding to increases in the area of newly planted orchards and the use of susceptible cultivars. In 2009, an experimental orchard including 21 almond cultivars was planted at Les Borges Blanques, Lleida, in northeastern Spain. No fungicide treatments were applied during the 10-year experimental period (2009 to 2018) in order to allow natural disease development. Cultivar susceptibility to RLB was assessed each year, from 2011 to 2018, through visual observations of symptoms in naturally infected trees. The experimental results led us to classify the cultivars into five susceptibility groups. The most susceptible were Tarraco, Guara, Tuono, Marinada, Desmayo Largueta, and Soleta, whereas Mardía was the most tolerant. The annual incidence of disease was positively correlated with accumulated rainfall in spring, and especially in April, while it was negatively correlated with high spring and summer temperatures, especially in May. These findings could be used to improve disease management strategies by identifying the most susceptible cultivars and improving the timing of fungicide application.info:eu-repo/semantics/acceptedVersio