Horticultural Performance Research Articles

Horticultural performance of ‘Hass’ avocado grafted onto seedling and clonal rootstocks under tropical wet-dry climate conditions

In Brazil, avocado nursery trees are traditionally grafted onto seedling rootstocks obtained from chance seedling trees of unknown origin, which results in great tree variability within the commercial orchards. This study aimed at comparing the horticultural performance of ‘Hass' avocado trees grafted onto seedling rootstocks and onto ‘Dusa’ clonal rootstocks, a well-known root-rot tolerant cultivar. Both rootstocks were studied in an ‘Hass’ avocado orchard between year 4 to 8 after planting, by assessing individual fruit yield (number of fruit and kg plant−1), tree size, yield efficiency, Phytophthora cinnamomi presence in the soil under the canopy and fruit quality variables, such as weight, length (L), diameter (D) and L:D ratio. Postharvest fruit quality was evaluated under cold storage at 5°C and ± 85% relative humidity (RH) during a 28-day period. Along a 5-year period,‘Hass’ avocado trees grafted onto ‘Dusa’ clonal rootstock yielded a larger number of bigger and more elongated fruits per tree, which were classified within the most valued fruit size classes in the market, as compared to ‘Hass’ trees grafted onto seedling rootstocks. No significant differences were found between rootstocks regarding postharvest fruit quality or the abundance of P. cinnamomi in the soil under tree canopy.

Parent selection for hybridization in chili (Capsicum annuum L.) using multivariate analysis and K-means clustering

The study was conducted to elucidate the extent of genetic diversity of 28 chilli (Capsicum annuum L.) genotypes. Chilli plants of the selected genotypes were grown in the Field Laboratory of the Department of Genetics and Plant Breeding of Bangbandhu Sheikh Mujibur Rahman Agricultural University, Bangladesh with recommended agronomic practices. The experiment was laid out in a randomized complete block design with tree replications. The analysis of variance revealed considerable variability among the genotypes for the character studied. Genetic diversity in chilli genotypes were estimated based on 16 growth and yield contributing characters using Mahalanobis’s D2 statistics and K-means clustering. The genotypes were grouped into four different clusters by non-hierarchical clustering. Cluster III had the maximum number (13) of genotypes followed by cluster I, IV and II with 7, 5 and 3 genotypes, respectively. The highest inter-cluster genetic divergence (9.87) was recorded between clusters II and IV, whereas the highest intra-cluster distance was recorded in cluster II (4.37). Cluster II was observed to be the most important with maximum cluster means for most of the valuable traits including number of fruits per plant and number of fruit yield per plant. The characters fruit yield/plant, days to 100% fruiting, days to first flowering and individual fruit weight contributed maximum towards divergence. Considering diversity pattern and other horticultural performance the Gen7 and Gen20 from cluster I, Gen8 and Gen10 from cluster IV and Gen24 from cluster III may be taken into consideration as better parents for an efficient hybridization programme of chilli.

Horticultural performance of ‘Fuji Suprema’ and ‘Maxi Gala’ apple trees trained at Tall Spindle and Bi-Axis systems grafted on different rootstocks in Southern Brazil

ABSTRACT: The use of new rootstocks combined with different training systems have been studied to increase productivity, fruit quality, and reduce costs. Another important factor is the validation of studies under replanting conditions, due to the growing limitation of new areas for planting commercial apple orchards in Brazil. The present study aimed to evaluate the behavior of ‘Fuji Suprema’ and ‘Maxi Gala’ apple trees in two training systems grafted on two rootstocks. The study occurred during the seasons 2016/17, 2017/18 and 2018/19, in an orchard located in southern Brazil in an area previously cultivated with apple trees. A randomized block design consisting of a 2x2 factorial was used, with Tall Spindle and Bi-Axis as the training system and ‘M.9’ and ‘G.213’ as rootstocks of Fuji Suprema and Maxi Gala cultivars. Variables were evaluated to determine tree vigor, as well as yield and fruit quality characteristics. It was observed that ‘G.213’ promoted higher vigor for both cultivars as well as the Bi-Axis training system in the Maxi Gala cultivar. The highest yield was observed in Tall Spindle as well as the rootstock ‘G.213’ in both cultivars. The most significant changes on fruit quality occurred in the Bi-Axis training system, presenting higher intensity of red color as well as ‘Maxi Gala’ grafted on ‘G.213’ rootstock.

Designing and managing biodiverse streetscapes: key lessons from the City of Melbourne

Underutilised public spaces such as streetscapes offer substantial opportunities to integrate habitats that increase biodiversity into existing urban landscapes and create more ecologically connected cities. Cooperation and collaboration from diverse stakeholders are paramount to achieving this because growing conditions for plants in streetscapes are often much harsher than remnant habitats or urban parks and little is known about the horticultural performance of many native understorey species in these novel urban environments. This paper describes how the City of Melbourne collaborated with researchers from the University of Melbourne to develop and test a suite of understorey plant species to increase streetscape biodiversity. To do so, we selected species using criteria from a horticultural planting guide which guided the design and creation of four streetscape plantings within the municipality. Here, we document the process and discuss lessons learnt from this project to assist other cities to design, construct and maintain streetscapes with successful, cost-effective plantings that improve urban biodiversity and aesthetic value. Key to the long-term success of these biodiverse plantings was thorough soil preparation and weed management before planting, and the implementation of a clear, ecologically sensitive management plan. To support this plan, suitably qualified and experienced landscape maintenance staff were essential, particularly those with horticultural knowledge and experience with indigenous and native plant species. Our project highlights the often conflicting needs of local authorities and ecological researchers and the necessary trade-offs needed to meet realistic goals and achieve successful project outcomes for creating more biodiverse urban landscapes.

Development of biotic stress resistant F1 interspecific hybrid rootstock derived from Solanum lycopersicum and Solanum habrochaites

Tomato is major horticultural plant consumed worldwide. Biotic stress (nematodes, fungus and bacteria) has negative effect on tomato production due to causing reduced yield or plant death. Rootstocks confer resistance to soil-borne pathogen are considered the most effective and environment friendly approach for such a stress management. Thus, development of genetic resources having multiple resistance genes is essential for sustainable tomato breeding. Solanum habrochaites is one of the most studied wild tomato species due to its high genetic potential for biotic and abiotic stresses. In the present study, rootstock potential of an interspecific F1 hybrid derived from S. habrochaites was evaluated as using resistance genes (Frl, I-2, I-3, Mi-3, Pto Ty-1, Ty-3 and Sw-5) specific molecular markers for 6 major tomato diseases and 31 fruit quality traits. The study reported that F1 hybrid had resistance alleles for 5 genes (Frl, I-2, I-3, Pto and Sw-5) confer resistance to fusarium crown rot disease, crown – root rot disease, race 2 and 3 of Fusarium oxysporum f. sp. radicis lycopersici, bacterial speck and tomato spotted wilt virus (TSWV), respectively. Despite high performance of F1 hybrid for biotic stress, the study pointed S. habrochaites specific graft incompatibility due to poor rate of grafting efficiency, small fruit formation and low yield. This is the first comprehensive study evaluated the horticultural performance of an interspecific hybrid in tomato.

Review of Options for Horticultural Research and Development: A Case of Zambia

This review focused on horticultural development as a key economic subsector sector. Although practiced by more than 60 % of the population, agriculture and horticulture largely remain small scale in Zambia. Partly due to the relatively high income generation potential of commodities, the horticultural sector holds immense potential to make significant contribution to the poverty reduction. It has been estimated that since 1960, worldwide demand for fresh produce has more than doubled compared to a 20 % increase in demand for cereals. However, in Africa per capita supply of fresh produce has been declining since 1970. The key challenge therefore remains how to expand horticultural production in a manner that is sustainable and beneficial to all players throughout the food system. A vision of ‘An efficient and dynamic horticulture sector responsive to changing needs of society’ is advanced. This article reviews the emergence of horticulture sub sector contributing significantly to the agricultural GDP and poverty reduction, outlines its limitations and explores options for improving the sector. While the traditional biotic and abiotic approaches are the primary focus (improved research and development to drive production, and reduce postharvest losses), emerging challenges such as globalization, and climate change are considered. The findings suggest poor production technologies, limited crop varietal choices, high postharvest loses and inadequate marketing infrastructure and low smallholder participation horticultural markets contributing to overall poor sector performance. To achieve sustained and environmentally safe horticultural performance there is need to establish effective linkages, networks and partnerships among different players throughout the horticulture value and supply chains, both from private and public sectors.

Horticultural Performance of Greenhouse Cherry Tomatoes Irrigated Automatically Based on Soil Moisture Sensor Readings

Precision irrigation is essential to improve water use efficiency (WUE), defined as the amount of biomass produced per unit of water used by plants. Our objective is to evaluate the effect of different soil volumetric water content (VWC) in plant growth, fruit yield, quality, and WUE of cherry tomatoes grown in a greenhouse. We tested four VWC thresholds (0.23, 0.30, 0.37, and 0.44 m3 m−3) to trigger a drip irrigation system in two tomato cultivars (‘Sweet Heaven’ and ‘Mascot F1’). The experiment was arranged in a split-plot design with four replications. We used capacitance sensors connected to an open-source, low-cost platform to monitor and control the irrigation in real-time based on demand. Plants were watered every time the soil VWC dropped below the set thresholds. The treatment with VWC 0.44 m3 m−3 resulted in the highest fruit yield, with 102.10% higher WUE when compared to the VWC 0.23 m3 m−3 in both cultivars. Fruit quality traits such as longitudinal and equatorial diameter increased asymptotically with soil water content. In contrast, treatments with deficit irrigation increased the fruit soluble solids by 15.73% in both cultivars. These results strongly suggest that accurate control of the soil VWC is essential to modulate the fruit yield and quality attributes in tomatoes produced in the greenhouse.

Initial performance of ‘Gem’ avocado trees in the Central-Western region of São Paulo State

The introduction of new avocado cultivars into producing countries of the Southern Hemisphere may extend the offer period of fresh fruit for export. The ‘Gem’ (‘3-29-5’) avocado is known for extending the marketing period of ‘Hass’-like avocados. This study aimed to evaluate the horticultural performance of ‘Gem’ avocado trees between the 4th and 6th years after planting (2016-2018), in a commercial orchard in the Central-Western region of the State of São Paulo, Brazil. ‘Gem’ avocado trees grafted onto seedling rootstocks were evaluated regarding tree size, shoot growth, flowering, and fruit yield, quality and maturation. In the evaluated biennium, the trees showed a strong upright growth habit and compact tree size. Flowering occurred mainly in indeterminate inflorescences. Fruit yield varied between 106.89 to 116.89 kg tree-1, and 75-91% of the fruit classified within size counts 12 (306 to 365 g/fruit) to 18 (211 to 235 g/fruit), and reached physiological maturity in late June, but could be picked until October, i.e, four to eight months later than ‘Hass’. ‘Gem’ is a new alternative for extending fruit offer of late-maturity avocado cultivars and allowing higher profit to the farmers.

Fungos micorrízicos arbusculares influenciam o desempenho hortícola de cultivares de morangueiro

The inoculation of strawberry cultivars with arbuscular mycorrhizal fungi (AMF) is a profitable and viable biotechnological tool, with potential to improve the horticultural performance of plants. However, this biotechnology is lacking and unknown to producers. The aim of the research was to investigate whether strawberry cultivars in the absence and presence of inoculation with AMF differ in their horticultural performance. The treatments, delineated in a bifactorial scheme, were four strawberry cultivars in the absence and presence of two AMF-based inoculants. The experiment was designed in randomized blocks, with three replications. The root system of ‘Albion’ cultivar showed the highest mycorrhizal colonization. Claroideoglomus etunicatum showed greater capacity to infect plant roots. ‘Portola’ was the most productive cultivar and ‘Albion’ and ‘Aromas’ produced strawberries with the highest levels of total anthocyanins. It is concluded that the use of mycorrhizal biotechnology enhances the levels of total flavonoids in fruits of the ‘Albion’ cultivar inoculated with the fungal species C. etunicatum. The root system of ‘Albion’ cultivar has greater mycorrhizal colonization. The fungal species C. etunicatum is more effective in colonizing the roots of the plant host. It is suggested to use the ‘Portola’ cultivar to obtain higher fruit yields and the ‘Albion’ and ‘Aromas’ cultivars for producers who aim to obtain strawberries with higher levels of total anthocyanins. ‘Aromas’ is recommended for those seeking a dual purpose (production and quality).

Assessment of genetic divergence through cluster analysis of chilli varieties

Our study on genetic diversity was conducted with six chilli genotypes with inter- and intra-specific cross varieties of the three most popular chilli species (Capsicum annuum L., Capsicum chinense Jacq., and Capsicum frutescens L.). Twelve quantitative characters, viz. plant height (cm), primary branches, secondary branches, number of flowers, number of fruits/plant; dry fruit weight (g), fruit length (cm), fruit diameter (cm), pedicel length (cm), pericarp thickness (mm), seeds/fruit, and seed weight (g), were taken into consideration. The analysis of variance revealed considerable variability among the genotypes for the character studied. Cluster analysis was used for grouping of parental and hybrid chilli genotypes under the study grouped into five clusters. Cluster I had the maximum (12) and clusters IVand V had the minimum number (1) of genotypes. The inter-cluster D2 values ranged between 40.404 and 127.530. The minimum inter-cluster distance was between clusters III and IV (40.404). The maximum inter-cluster distance was observed between clusters II and V (127.53). Diversity pattern and other horticultural performance among the genotypes of new varieties were generated due to the cross between Local Line Mahadev Pramanick and Sukhia bullet and also the cross between Local Line Mahadev Pramanick and Habanero orange (cluster II) as well as single parental variety i.e. Habanero orange. These genotypes were identified as promising varieties with respect to various characters may be taken into consideration as better parents for an efficient hybridization programme of chilli.

Field Performance of ‘Hamlin’ Orange Trees Grown on Various Rootstocks in Huanglongbing-endemic Conditions

Most of the commercially important citrus scion cultivars are susceptible to Huanglongbing (HLB), which is the most devastating disease the citrus industry has ever faced. Because the rootstock can influence the performance of the scion in various ways, including disease and pest tolerance, use of superior rootstocks can assist citrus growers with minimizing the negative effects of HLB. The objective of this study was to assess rootstock effects on the horticultural performance and early production potential of ‘Hamlin’ sweet orange (Citrus sinensis) trees in commercial field settings under HLB-endemic conditions. Two field trials were conducted in different locations in Central and Southeast Florida. The trials were established in 2015 and included 32 diverse diploid and tetraploid rootstock cultivars and advanced selections. One trial was performed in Highlands County, FL, on a poorly drained flatwoods-type site. Another trial was performed in Polk County, FL, on a well-drained sandy Central Florida Ridge site. Horticultural traits including tree height, canopy volume, trunk diameter, canopy health, leaf nutrient content, yield, and fruit quality were assessed during the 2018–19 and 2019–20 production years. Significant differences were found among trees on different rootstocks for most of the measured traits, particularly tree vigor and productivity, but rootstock effects also varied by location. Rootstocks that induced large tree sizes, such as the diploid mandarin × trifoliate orange hybrids ‘X-639’, ‘C-54’, ‘C-57’, and ‘C-146’, also induced higher yield, but with lower yield efficiency. Most of the tetraploid rootstocks significantly reduced tree size, among which ‘Changsha+Benton’, ‘Green-3’, ‘Amb+Czo’, ‘UFR-3’, and ‘UFR-5’ induced high yield efficiency. Therefore, these rootstocks have the potential to be used in high-density plantings. However, trees on some of these small size-inducing rootstocks had a higher mortality rate and were more vulnerable to tropical force winds. This study provides important information for the selection of rootstocks with the greatest production potential in an HLB-endemic environment, especially during the early years of production.

Mid-season sweet oranges for fresh and processing markets in Brazil

AbstractPera sweet orange (Citrus sinensisL. Osbeck) is the most important mid-season sweet orange cultivar in Brazil, not only because of its desirable fruit quality for both juice processing and the fresh fruit market, but also because there is a lack of adequate mid-season alternative sweet orange cultivars. This study aimed to evaluate the horticultural performance of other sweet oranges in an attempt to identify similar or superior selections to the standard cultivar, Pera IAC sweet orange. Seventeen sweet oranges selections, including the standard Pera IAC, were budded on Sunki mandarin [C. sunki(Hayata) hort. ex Tanaka]. The experiment was planted in 2007, using 12-month-old nursery trees, with 6.5 × 2.5 m spacing in the Southern region of São Paulo state, Brazil. The experimental orchard was maintained with standard commercial management practices, and without supplementary irrigation. Data collection started three years after planting and was carried out until seven years after the experiment had been installed. Vegetative growth, plant yield, fruit drop, fruit quality, and fruit maturation regressions were assessed. Averages of the alternative selections were compared with those of the standard cultivar by Dunnett test. Performance indexes were calculated in order to identify potential superior selections for the fresh fruit market and for juice processing. Results indicated significant differences among the selections evaluated when compared with the standard cultivar, suggesting better alternatives to be exploited. Five selections (Biondo, Finike, Pera Alexandre Maróstica, Seleta Rio, and Vaccaro Blood) offered superior performance in terms of attributes required for the fresh fruit market, while one selection (Pera Alexandre Maróstica) was superior for juice processing traits. These alternatives to Pera IAC represent an opportunity for more efficient and productive scions with higher fruit quality, and with a slight shift within the mid-season harvest time of sweet oranges in Brazil.

Horticultural potential of nine strawberry cultivars by greenhouse production in Brazil: A view through multivariate analysis

Yield is commonly the main focus of strawberry producers. However, we must encourage the choice of cultivars to meet consumer demands for foods rich in bioactive compounds. Thus, the aim of this study was to investigate whether strawberry cultivars produced in a greenhouse differ in their horticultural performance. An experiment with nine cultivars (‘Albion’, ‘Aromas’, ‘Camarosa’, ‘Camino Real’, ‘Fronteras’, ‘Merced’, ‘Monterey’, ‘Portola’ and ‘San Andreas’) was carried out in a randomized complete block design with six replications. Plant yield and fruit quality were evaluated. The application of multivariate analysis indicated the formation of heterogeneous groups among the nine cultivars studied, bringing together the cultivars mainly because of the similarity of fruit size and total polyphenol content. ‘Merced’ stood out as the most productive cultivar and generated the largest fruits, whereas ‘Camarosa’ produced the greatest number of strawberries. ‘Aromas’ and ‘Camarosa’ produced fruits with higher phytochemical properties than other cultivars. We conclude that strawberry cultivars differ in their horticultural performance. Among the nine analyzed cultivars, we suggest to producers the use of ‘Aromas’ and ‘Camarosa’ to obtain better phytochemical properties of strawberries, and ‘Camarosa’ and ‘Merced’ to obtain higher yield and number of fruits. ‘Camarosa’ is recommended for those producers who seek a dual purpose.

Performance and Resistance to Phytophthora Crown and Root Rot in Squash Lines

Phytophthora crown and root rot, caused by the oomycete pathogen Phytophthora capsici, is a devastating disease of squash and pumpkin (Cucurbita pepo). No currently available cultivars provide complete resistance to this disease. Three newly developed squash lines and four hybrids were evaluated in greenhouse and field experiments for their resistance to phytophthora crown and root rot as well as for their horticultural performance. The three newly developed lines ranked among the most resistant entries included in 2 years of field trials. In addition, in a separate greenhouse experiment, one of the lines was shown to display the least severe disease symptoms among a group of accessions previously reported to possess partial resistance to phytophthora crown and root. Furthermore, the resistance was observed to be robust to several isolates of P. capsici. However, the phytophthora-resistant lines had reduced yield relative to standard squash cultivars. These lines are useful for continued breeding efforts toward a phytophthora crown and root rot-resistant cultivar.

Soil Nitrogen Fertilization Increases Yeast Assimilable Nitrogen Concentrations in ‘Golden Russet’ and ‘Medaille d’Or’ Apples Used for Cider Production

The recent growth in the U.S. hard-cider industry has increased the demand for cider apples (Malus ×domestica Borkh.), but little is known about how to manage orchard soil fertility best to optimize horticultural performance and juice characteristics for these cultivars. To assess whether nitrogen fertilizer applied to the soil can improve apple juice and cider quality, calcium nitrate (CaNO3) fertilizer was applied at different rates to the soil beneath ‘Golden Russet’ and ‘Medaille d’Or’ trees over the course of three growing seasons. The experiment started when the trees were in their second leaf. The trees were cropped in their third and fourth leaf. At the end of the first growing season of the experiment, the greatest fertilizer rate increased tree trunk cross-sectional area (TCSA) by 82% relative to the control, but this difference did not persist through to the end of the study. Yield and crop load were unaffected by the nitrogen fertilization treatments. Increasing the nitrogen fertilizer rate correlated positively with more advanced harvest maturity in ‘Golden Russet’ fruit, which resulted in greater soluble solid concentration (SSC). Fruit from the greatest fertilizer rate treatment had an average starch pattern index (SPI) that was 1 U greater than in the control, and an SSC that was 3% greater than the control. The fertilizer treatments did not affect juice pH, titratable acidity (TA), or total polyphenol concentrations. Yeast assimilable nitrogen (YAN) concentrations were increased by nitrogen fertilization for both cultivars in both harvest years. The greatest fertilizer treatment increased juice primary amino nitrogen by 103% relative to the control. Greater nitrogen fertilization rates correlated positively with less hydrogen sulfide production during the fermentation of ‘Golden Russet’ juice from the first, but not the second, harvest. During the first year, cumulative hydrogen sulfide production for the ‘Golden Russet’ control treatment was 29.6 μg·L–1 compared with the ‘Golden Russet’ high treatment, which cumulatively produced 0.1 μg·L–1. Greater maximum fermentation rates and shorter fermentation durations correlated positively with increased fertilization rate for both cultivars after the second harvest. High treatment fermentations had maximum fermentation rates 110% greater, and fermentation durations 30% shorter than the control. Other horticultural and juice-quality parameters were not affected negatively by the CaNO3 treatments. In orchards producing apples specifically for the hard-cider industry, nitrogen fertilizer could increase juice YAN, thus reducing the need for exogenous additions during cider production.

Field Performance and Susceptibility to Fungal Pathogens of Eleven Blackberry Cultivars

ABSTRACT Horticultural performance of eleven blackberry cultivars, including two primocane-fruiting cultivars, was evaluated over three years after fruiting began at the Musser Fruit Research Center in South Carolina, United States. Results showed differences in yield between cultivars for each year of the study. ‘Natchez’ had the highest cumulative yield after three years, followed by ‘Navaho’, ‘Von’, and ‘Osage’, whereas ‘Prime-Ark® Traveler’ produced significantly less than these four cultivars. Yield steadily declined for all cultivars over the three years, except for ‘Osage’, which remained consistent. ‘Prime-Ark® Freedom’ always had the largest fruit, although it had the greatest yield reduction after the second year. Multiple factors may explain yield decline for the majority of the cultivars studied, including freeze damage and tip dieback. Tip dieback was observed in 2016 in multiple cultivars, but dieback incidence was highest on ‘Prime-Ark® Traveler’. The dieback was associated with an outbreak of broad mites and thrips in the experimental block and with secondary pathogens isolated from the decaying tissues primarily Fusarium spp. and Alternaria spp. Cultivar differences in susceptibility to Alternaria spp. were confirmed in laboratory studies.

Photo-selective nets and potassium concentrations on Costus lasius crop

ABSTRACT The practice of using different photo-selective nets, associated with the technique of fertigation, represents a new agrotechnological concept that aims to promote specific physiological responses for growth and production, which are regulated by light. The aims of the study were to evaluate the effect of photo-selective nets and potassium concentrations in the fertigation solution on the horticultural performance of Costus lasius. The study was conducted at the Universidade de São Paulo, ESALQ, Piracicaba, SP, Brazil. Three experiments were carried out separately to evaluate five potassium concentrations in the fertigation solution (40, 80, 120, 160 and 200 mg L-1) under three colours of photo-selective nets (red, blue and black) in a randomized block design, with five repetitions. The variables plant height and numbers of leaves, stems and flower buds were evaluated. The data were submitted to the joint analysis of experiments. The association between the K+ concentration of 200 mg L-1 and the black photo-selective net results in higher stem and inflorescence production.

Compatibility and horticultural performance of Pera sweet orange clones grafted to Swingle citrumelo rootstock

ABSTRACT Despite its interesting agricultural traits, Swingle citrumelo (Citrus paradisi Macfad. ‘Duncan’ × Poncirus trifoliata L. Raf.) rootstock exhibits severe incompatibility when grafted with Pera sweet orange [Citrus sinensis (L.) Osb.] scions, and this fact limits its use for propagation purposes. Nonetheless, the existence of certain Pera sweet orange clones that are compatible with Swingle citrumelo represents a substantial gain for the entire citrus industry. This study investigated the compatibility between seven Pera sweet orange clones and Swingle citrumelo rootstock, regarding the presence of a necrotic line at the graft union junction, the difference in diameter between rootstock and scion, the influence of clonal cleaning by micrografting, and the horticultural performance of the selected combinations. No trees died because of grafting incompatibility, even after twenty years (trial I), except for clone CV1, or after six years and nine months (trial II) from planting. The rootstock/scion trunk diameter ratio was not related to the presence of a necrotic line in the graft-union region. Additionally, these variables did not influence fruit yield and quality, and they were not affected by clonal cleaning or pre-immunisation of the old Pera sweet orange clones.

II. Horticultural performance of ‘Honeycrisp’ grown on a genetically diverse set of rootstocks under Western New York climatic conditions

A field experiment with 31 rootstocks representing a genetically diverse group of rootstocks featuring ‘Honeycrisp’ as the scion was planted in 2010 at Geneva, NY USA. Rootstocks included three from the Malling series (UK), nine from the Budagovsky series (Russia), 16 from the Cornell Geneva series (USA) and three from the Pillnitz series (Germany). Over the first 8 years (2010–2017) we measured final tree size (trunk cross-sectional area: TCA) and cumulative yield. In the last 4 years we measured fruit soluble solids, bitter pit incidence, biennial bearing, and leaf zonal chlorosis. Tree size varied dramatically with the largest trees on B.70-20-20 and smallest trees on B.71-7-22. Setting the most vigorous rootstock at 100% we categorized rootstocks into 5 size categories: sub-dwarfing class (10–25%), dwarfing class (25–35%), semi-dwarfing class (35–50%), semi-vigorous category (50–70%) and vigorous class (70–100%). Cumulative yield varied 8 fold between the highest yielding rootstock (CG.3001) and the lowest yielding rootstock (B.71-7-22). We calculated theoretical yield per ha by multiplying cumulative yield per tree by a theoretical optimal tree density (trees/ha) based on tree size (TCA). The dwarfing rootstocks G.814, G.41TC, G.11 and B.10 had the highest yields per hectare while the most vigorous rootstocks B.70.20.20 and B.71-7-22 were the least productive. Theoretical cumulative yields varied from a high of 400 t/ha to a low of 50 t/ha, an 8-fold difference. Rootstock also influenced the incidence of bitter pit with the lowest levels of bitter pit with the rootstocks B.10, CG.2034, B.71-7-22, G.41N, CG.4003, G.202N, G.214, and Supporter 3. Considering bitter pit, yield, and optimum tree density, the theoretical yield of bitter pit free fruit varied from a high of 340 t/ha to a low of 35 t/ha, almost a 10-fold difference. The dwarfing rootstocks B.10, G.11, G.41TC, G.214 and G.814 had the highest yields per hectare of bitter pit free fruit. Rootstocks B.9 and M.26 had significantly lower cumulative bitter pit free yield/ha. These data indicate that rootstock not only has a large influence on mature tree cumulative yield but also bitter pit incidence which combine to create a large economic impact of rootstock choice on the long-term economic result of an orchard. This leads to the need for “designer rootstocks” which combine the rootstock characteristics needed to maximize the economic potential of each scion cultivar.

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.