Vigorous Rootstocks Research Articles

The Role of Rootstock Selection in Pistachio Cultivation

Rootstocks are critical in selecting pistachio (Pistacia vera L.) cultivation and its impact on scion performance. Pistachio rootstocks exhibited distinct absorption capabilities, impacting leaf nutrient concentrations and tree health. The review discusses current knowledge on the influence of various rootstocks on growth habit, nutrient uptake, yield, nut quality, alternate bearing, and responses to abiotic stresses such as salinity, drought, and cold. Contrary to the traditional belief linking higher yield solely to vigor and size, the review emphasized the need for an in-depth understanding of the interplay between rootstock, scion, and their interaction to optimize yield. Additionally, we discussed the influence of rootstock selection on pistachio nut quality, including early splitting, hull cracking, and fatty acid composition. It addressed the complex phenomenon of alternate bearing, highlighting how vigorous rootstocks could affect cyclic variations in crop yield through increased carbohydrate resources. Rootstocks mitigate salinity stress, enhancing drought tolerance and preserving nut quality under water stress. The study emphasized the significance of rootstock choice in cold climates, advocating for identifying and using cold-tolerant rootstocks to enhance orchard resilience against cold stress. The findings provide valuable insights for growers and researchers, facilitating informed decision-making regarding rootstock selection in pistachio cultivation worldwide.

Genetic variability in macadamia rootstocks and their effects on early vigor traits of ‘HAES 741′

Early vigor in tree crops is crucial as it accelerates orchard establishment and enhances resilience to environmental stresses. Rootstocks play an essential role in determining vigor of tree crops. Macadamia is propagated through grafting, however research into rootstocks is rare. This study evaluated a range of macadamia rootstocks including cultivars, standard rootstocks, breeding selections and wild germplasm, focusing on their effects on early vigor (age 4). Phenotypic variability in the scion ‘HAES 741′ was assessed using 24 accessions of seedling and cutting rootstocks over 4 years (2018–2021), analyzing 7 early vigor traits and growth rates. Principal coordinate analysis and cluster analysis revealed high genetic diversity among accessions, clustering into 4 groups. Significant rootstock effects on early vigor were observed. Broad-sense heritability estimates of rootstock effects were moderate for scion height (H2=0.48) and total height (H2=0.44), holding promise for improvement through selection. Positive correlations among scion growth traits, particularly trunk circumference, (rg= 0.50 to 0.99) suggested their potential as indicators of early vigor. The strong genetic correlations for canopy area (rg = 0.84) and canopy volume (rg = 0.63) between scions of grafted trees and the ungrafted trees of the same rootstock accessions reflect the possibility of trait transmission from rootstock to scion. Among the studied rootstocks, ‘BHI1’, ‘BHY2’ and ‘BHI3’ imparted the highest early vigor. Compared with the current industry standard rootstocks ‘H2’ and ‘Beaumont’, the least vigorous rootstocks ‘Mjan1’ and ‘BDW3’ showed reductions of 18 % and 47% in tree height, 54 % and 74% in trunk circumference and 97 % and 210 % in canopy volume respectively. These findings suggest promising rootstock candidates for high performing orchard systems, although ongoing evaluation until maturity is crucial.

Genetic diversity of Passiflora cincinnata in the Chapada do Araripe, Northeast Brazil

Passiflora cincinnata Mast. belongs to the Passifloraceae family and is a plant native to the Brazilian semi-arid region, popularly known as maracujá-do-mato. This species has food, pharmaceutical and ornamental potential. It is used as a source of genes of interest in yellow passion fruit breeding programs or as vigorous rootstocks in commercial plantations. Thus, morphologically characterizing native species and measuring genetic diversity between accessions are essential steps for the success of plant breeding in the world. This study aimed to characterize and estimate the genetic diversity between accessions of a natural population of Passiflora cincinnata in the Chapada Nacional do Araripe, Northeast Brazil, in order to provide subsidies for the creation of a passion fruit breeding program. Twenty-six passion fruit accessions were evaluated for 10 morphological characters: plant neck diameter, height of the first fork, leaf length, leaf width, diameter at breast height, flower diameter, petal length, stamen length, pistil length and fillet length. The accessions were georeferenced and characterized with the aid of a graduated tape measure and a digital caliper. Four replicates were measured for each characteristic in the P. cincinnata accessions evaluated. The results were submitted to analysis of variance using the F test (p<0.05), estimation of genetic parameters, optimization grouping (Tocher) and the relative contribution of the characters to divergence. The results show that there is variability among the accessions of this natural population and that there is potential for them to be used as germplasm for passion fruit breeding programs.

The selection of appropriate rootstock and training system towards sustainable production of stone fruits

In stone fruit species, such as peach, cherry, apricot and plum labour requirement is important ranging from 45% to 71% of the total cost of production. In this sense, combining size controlling rootstocks as Rootpac® series, Isthara® and others in peach and plum, or Gisela® and Corette® series in cherry, with intensive bidimensional training systems based on central axis or bi axis resulted in earlier and higher yields, compared with the traditional open vase associated with vigorous rootstocks. The association of these intensive orchards with bidimensional canopies and good accessibility to canopy by labour and machines, is essential to reduce the cost of production. These canopies allow an efficient use of labour and mechanization. Regarding peach, under Ebro Valley (Spain) conditions, the reduction on total cost of production ranged from 15% to 20% and the harvest rate increased by 41%, enhancing also fruit quality due to better light distribution within the tree canopy. In cherry the increase of harvest rate increased by 72% when UFO was compared with the traditional open center. Regarding what in Washington State (US). With European and Japanese varieties, intensification by using Rootpac®20 rootstock and super high density plantings (SHD), allowed to get more than 40 t ha-1 in the third year in Ebro Valley (Spain). With ‘Agen’ European plum, using the same rootstock, under Chilean conditions training trees in a small hedge (SHD) allowed the full mechanization of the harvest by using over-the-row harvester or pedestrian harvest for the needs of fresh market. In this case, manual harvest efficiency increased by 49% compared with the traditional open vase. In all species, the use of size controlling rootstocks offers different options to growers when selecting the training systems concerning skilled labour requirements to train the trees in the first years. Thus, an increase was recorded when the number of axes increased from central axis to bi-, tri- and multi-axes. Furthermore, all these planar canopies were better adapted to the application of precision technologies based on artificial vision (AV) for monitoring pest and diseases, neural network and AV for fruit counting, yield forecasting and robotic harvesting.

Modulating ‘Xinomavro’ (Vitis vinifera L.) Vine Growth and Berry Composition: A Comparative Analysis of Rootstock Effects

Rootstocks serve as a strategic tool for grapevine adaptation to specific biotic and abiotic conditions and for managing vine growth, grape yield, and berry composition in commercial vineyards. This study investigates the influences of four different rootstock varieties (101-14 MGt, 3309 C, 110 R, and 140 Ru) on the viticultural performance of ‘Xinomavro’ vines, a prominent Greek red winegrape varietal. By conducting a two-year field experiment using various rootstocks, we assessed parameters related to water status, vegetative growth, yield, and berry composition. Our results revealed that rootstock selection has a significant impact on vine development, especially in terms of berry size and the concentrations of secondary metabolites. Principal component analysis confirmed the complex interaction between rootstock vigor and vine productivity. This study underscores the importance of rootstock variety in manipulating grapevine characteristics, particularly for the ‘Xinomavro’ variety, in response to regional climatic conditions.

The Efficiency of CBD Production Using Grafted Cannabis sativa L. Plants Is Highly Dependent on the Type of Rootstock: A Study.

The global cannabis market is continuously expanding and as a result, the cannabis industry demands new and improved agronomic cultivation practices to increase production efficiency of cannabidiol (CBD), which is valued for its therapeutic benefits. This study investigates the influence of three rootstock types on the survival rate, morphological parameters, and biochemical composition of cannabis: potentially dwarfing rootstocks (PDR), potentially vigorous rootstocks (PVR), and seedlings-as-rootstocks (SAR). Rootstocks were used for grafting two scion genotypes: 'ScionII' = chemotype II of industrial hemp, and 'ScionIII' = chemotype III of high CBD accumulating variety. Contrary to expectations, PVR and SAR did not outperform PDR on most of the measured variables. SAR showed the highest survival rate of the grafted cannabis plants (40-70%). The rootstock type had a statistically significant influence only on the bud compactness index in 'ScionII', with PDR being particularly noticeable. A comparative analysis of the 'rootstock/scion' combinations with their controls (non-grafted scions) revealed grafting's substantial improvement in most traits. Specifically, PDR increased CBD content by 27% in 'ScionIII', inflorescence yield and CBD yield per plant increased by 71% and 84%, respectively, when SAR was used in 'ScionII'. SAR showed to be the most effective rootstock type for CBD production. Our findings suggest grafting as a promising technique for optimizing cannabis's agronomic and medicinal potential, highlighting the necessity for further research on its underlying mechanisms to refine production efficiency and quality.

Grafted Tomatoes Removed More Soil Phosphorus than Nongrafted Tomatoes under High-phosphorus Conditions

Nonpoint-source phosphorus (P) from agricultural fields is a contaminant of surface waters, and high soil P fertility exacerbates this problem. Many vegetable growers and gardeners have a history of applying more P than is necessary for optimum plant growth. Avoiding unnecessary P applications is an important part of the long-term solution to reducing P loading in water. When soil P levels are very high, management practices that result in more intense P removal are recommended to reduce these levels and the potential for aquatic ecosystem contamination with P. Growers may apply soluble starter fertilizer containing P to encourage rapid transplant establishment; however, the effectiveness of this practice is unknown for soil P levels considered high or very high. Grafting tomatoes (Solanum lycopersicum L.) onto vigorous rootstocks may help the plant remove more P from the soil than nongrafted plants. This study investigated the effects of organic starter P fertilizers applied to three hybrids of nongrafted tomato and the same hybrids grafted onto ‘Estamino’ rootstock in field-grown conditions during three site-years with high preplant P fertility. The yield, fruit P concentration, and amount of P removed from the field were measured to elucidate starter P and grafting impacts on P removal. Starter P was not impactful on all responses. Grafting increased the total yield by 11.6%, fruit P concentration in a genotype-dependent manner (average of 12.6%), and net P removal from the field by 28.4% (6.0 kg P/ha). Net P removal was positively correlated with the total yield (r = 0.821) and fruit P concentration (r = 0.502), suggesting that practices to increase the yield or P concentration independently increase net P removal.

Transcriptome and metabolome profiling reveal the effects of hormones on current-year shoot growth in Chinese ‘Cuiguan’ pear grafted onto vigorous rootstock ‘Duli’ and dwarf rootstock ‘Quince A’

BackgroundDwarf rootstocks have important practical significance for high-density planting in pear orchards. The shoots of ‘Cuiguan’ grafted onto the dwarf rootstock were shorter than those grafted onto the vigorous rootstock. However, the mechanism of shorter shoot formation is not clear.ResultsIn this study, the current-year shoot transcriptomes and phytohormone contents of ‘CG‒QA’ (‘Cuiguan’ was grafted onto ‘Quince A’, and ‘Hardy’ was used as interstock) and ‘CG‒DL’ (‘Cuiguan’ was grafted onto ‘Duli’, and ‘Hardy’ was used as interstock) were compared. The transcriptome results showed that a total of 452 differentially expressed genes (DEGs) were identified, including 248 downregulated genes and 204 upregulated genes; the plant hormone signal transduction and zeatin biosynthesis pathways were significantly enriched in the top 20 KEGG enrichment terms. Abscisic acid (ABA) was the most abundant hormone in ‘CG‒QA’ and ‘CG‒DL’; auxin and cytokinin (CTK) were the most diverse hormones; additionally, the contents of ABA, auxin, and CTK in ‘CG‒DL’ were higher than those in ‘CG‒QA’, while the fresh shoot of ‘CG‒QA’ accumulated more gibberellin (GA) and salicylic acid (SA). Metabolome and transcriptome co-analysis identified three key hormone-related DEGs, of which two (Aldehyde dehydrogenase gene ALDH3F1 and YUCCA2) were upregulated and one (Cytokinin oxidase/dehydrogenase gene CKX3) was downregulated.ConclusionsBased on the results of transcriptomic and metabolomic analysis, we found that auxin and CTK mainly regulated the shoot differences of ‘CG–QA’ and ‘CG–DL’, and other hormones such as ABA, GA, and SA synergistically regulated this process. Three hormone-related genes ALDH3F1, YUCCA2, and CKX3 were the key genes contributing to the difference in shoot growth between ‘CG–QA’ and ‘CG–DL’ pear. This research provides new insight into the molecular mechanism underlying shoot shortening after grafted onto dwarf rootstocks.

MdARF3 switches the lateral root elongation to regulate dwarfing in apple plants.

Apple rootstock dwarfing and dense planting are common practices in apple farming. However, the dwarfing mechanisms are not understood. In our study, the expression of MdARF3 in the root system of dwarfing rootstock 'M9' was lower than in the vigorous rootstock from Malus micromalus due to the deletion of the WUSATAg element in the promoter of the 'M9' genotype. Notably, this deletion variation was significantly associated with dwarfing rootstocks. Subsequently, transgenic tobacco (Nicotiana tabacum) cv. Xanthi was generated with the ARF3 promoter from 'M9' and M. micromalus genotypes. The transgenic apple with 35S::MdARF3 was also obtained. The transgenic tobacco and apple with the highly expressed ARF3 had a longer root system and a higher plant height phenotype. Furthermore, the yeast one-hybrid, luciferase, electrophoretic mobility shift assays, and Chip-qPCR identified MdWOX4-1 in apples that interacted with the pMm-ARF3 promoter but not the pM9-ARF3 promoter. Notably, MdWOX4-1 significantly increased the transcriptional activity of MdARF3 and MdLBD16-2. However, MdARF3 significantly decreased the transcriptional activity of MdLBD16-2. Further analysis revealed that MdARF3 and MdLBD16-2 were temporally expressed during different stages of lateral root development. pMdLBD16-2 was mainly expressed during the early stage of lateral root development, which promoted lateral root production. On the contrary, pMmARF3 was expressed during the late stage of lateral root development to promote elongation. The findings in our study will shed light on the genetic causes of apple plant dwarfism and provide strategies for molecular breeding of dwarfing apple rootstocks.

Rootstock vigor dictates the canopy light environment that regulates metabolite profile and internal fruit quality development in peach

Five rootstock cultivars of differing vigor: vigorous (‘Atlas™’ and ‘Bright's Hybrid® 5’), standard (‘Krymsk® 86’ and ‘Lovell’) and dwarfing (‘Krymsk® 1’) grafted with ‘Redhaven’ as the scion were studied for their impact on productivity, mid-canopy photosynthetic active radiation transmission (i.e., light availability) and internal fruit quality. Αverage yield (kg per tree) and fruit count increased significantly with increasing vigor (trunk cross sectional area, TCSA). Α detailed peach fruit quality analysis on fruit of equal maturity (based on the index of absorbance difference, IAD) coming from trees with equal crop load (no. of fruit cm−2 of TCSA) characterized the direct impact of rootstock vigor on peach internal quality [dry matter content (DMC) and soluble solids concentration (SSC)]. DMC and SSC increased significantly with decreasing vigor and increasing light availability, potentially due to reduced intra-tree shading and better light distribution within the canopy. Physiologically characterized peach fruit mesocarp was further analyzed by non-targeted metabolite profiling using gas chromatography mass spectrometry (GC-MS). Metabolite distribution was associated with rootstock vigor class, mid-canopy light availability and fruit quality characteristics. Fructose, glucose, sorbose, neochlorogenic and quinic acids, catechin and sorbitol were associated with high light environments and enhanced quality traits, while sucrose, butanoic and malic acids related to low light conditions and inferior fruit quality. These outcomes show that while rootstock genotype and vigor are influencing peach tree productivity and yield, their effect on manipulating the light environment within the canopy also plays a significant role in fruit quality development.

Uptake and distribution of perfluoroalkyl substances by grafted tomato plants cultivated in a contaminated site in northern Italy

Poly- and perfluoroalkyl substances (PFAS) are highly persistent and mobile pollutants raising alarming concerns due to their capability to accumulate in living organisms and exert toxic effects on human health. We studied the accumulation of different PFAS in the leaves and fruits of tomato plants grown on a PFAS-polluted soil in North-East Italy. Tomato plants were grafted with different rootstocks characterized by different vigor, and irrigated with PFAS-polluted groundwater. Leaves and fruits of the first and sixth truss were analyzed at full plant maturity. All tomato varieties accumulated PFAS in leaves and fruits, with the highest concentrations detected in the most vigorous rootstock and reflecting the PFAS concentration profile of the irrigation water. PFAS with a chain length from 4 to 8 C atoms and with carboxylic and sulfonic functional groups were detected in plant leaves, whereas only carboxylic C4, C5, and C6 PFAS were detected in tomato fruits. A general trend of decreasing PFAS concentrations in fruits upon increasing height of the plant trusses was observed. Calculation of the target hazard quotient (THQ) showed increasing values depending on the plant vigor. The hazard index (HI) values showed values slightly higher than 1 for the most vigorous plants, indicating potential risks to human health associated with the consumption of contaminated tomato fruits.

The Influence of Dwarfing Interstock on Biometric Growth Parameters of Apple

Apple trees grown on seedling rootstock often develop into large and vigorous trees making its management difficult. By using vigorous rootstocks only few trees can be accommodated per hectare making the productivity less profitable. Several dwarfing rootstocks of apple are available which need support system and incur heavy investment during orchard establishment. It would be ideal to obtain a tree with very good root system, to avoid the need for supporting systems and also with a low height, which can be achieved using the interstem. Therefore, in the present investigation M9 clonal interstem comprised of 2,4,6 and 8inches length were grafted between seedling rootstock and scion of two cultivars i.e., Red Delicious and American Apirouge which are most common and predominant cultivars in orchards of Kashmir. The average sapling height was to the tune of 38.85cm and 41.01 cm in Red Delicious and American Apirouge during first year of study. There was a progressive increase in the height of plant with decreasing interstem length. In both the apple cultivars stem diameter increased with decrease in interstem length but was lower than control during both the years of study, The rootstock influences the biometric parameters of the grafted trees. The results showed that increased interstem length significantly decreased sapling height and growth whereas, days taken to sprouting and survival per cent were non significant. Thus, it appeared as if the dwarfing rootstock genotype used as an inter-stem functioned as a kind of physical restriction to water movement and probably reduced the hydraulic conductance of the whole tree.

Impact of aging on the physical-chemical and phenolic stability of tropical red wines from Brazil produced with grapes harvested in the summer season

The São Francisco Valley in the Brazilian Northeast is characterized by the production of tropical wines from grapes obtained from at least two annual harvests. Previous studies showed that wines made with grapes harvested from the second semester (summer season, with high temperatures and solar radiation, as well as low rainfall) presented a shorter shelf-life than those made from grapes harvested in the first semester (winter season). This study aimed to characterize the changes in the chemical composition of three red wines from the summer season, during aging. Wines elaborated with grapes harvested between November and December 2014, with the main red varieties commercially used, were analyzed 12, 24 and 36 months after bottling. Decreases occurred in the concentrations of anthocyanins, flavonols, organic acids, potassium, and condensed tannins, as well as increases in polymerized pigments, hue, turbidity, and calcium. Flavanols and flavonols were associated with Syrah and Touriga Nacional wines, while myricetin was the metabolite considered to be the main indicator of the aging of ‘Alicante Bouschet’ wines. Rootstock vigor was affected by variety. This study showed that the choice of rootstock and variety combination could increase the wine stability after bottling, using grapes harvested from the second semester.

Physiological Behavior of Native Avocado in Nursery

In the State of Guerrero, Mexico, there are several types of native avocados that grow in backyards which die mainly because of adverse environmental conditions and various harmful activities of farmers. This study is one of the pioneers in the area. The aim of this research was to follow the growth in nursery and the physiological behavior of 12 native avocados from the municipality of Ometepec, Guerrero, Mexico, in order to explore their possible use as rootstocks. Thus, 20 fruits per tree of each genotype were harvested, and they were sown on substrate (85% river lama, 5% peat moss and 10% agrolite), at one month of age. A randomized complete block design was used with 12 treatments (each genotype was considered as treatment) and four repetitions. An analysis of variance and Tukey's means tests were performed (P ≤ 0.01 and 0.05) and LSD (P ≤ 0.05). The most vigorous rootstock was OME-7, followed by OME-10. The OME-7 showed higher NO3- and Na+ content; while OME-8, was superior in K+ and Ca++. The length*width of the avocado leaves, multiplied by its conversion factor (0.991), estimated a foliar area very similar to that obtained by the leaf area integrator. It was concluded that the OME-7, OME-3 and OME-10 rootstocks, were the most vigorous and they meet all the characteristics to be used as rootstocks.

Bicarbonate rather than high pH in growth medium induced Fe-deficiency chlorosis in dwarfing rootstock quince A (Cydonia oblonga Mill.) but did not impair Fe nutrition of vigorous rootstock Pyrus betulifolia.

Quince A (Cydonia oblonga Mill.), a typical dwarfing rootstock in pear cultivation, is susceptible to iron (Fe) deficiency in calcareous soils. The aim of this study was to compare the strategies in Fe uptake and utilization in dwarfing rootstock quince A (low Fe efficiency) versus a typical vigorous rootstock Pyrus betulifolia (PB) with high Fe efficiency. Quince A and PB were grown in nutrient solution (pH 6.3) for 4 weeks followed by three pH treatments: pH6.3, pH8.3a (adjusted with hydroxide) and pH8.3b (adjusted with bicarbonate). The Fe uptake and utilization indicators of the rootstocks were assessed at the onset of chlorosis symptoms (after 58 days of treatments). In contrast to PB, quince A exhibited Fe deficiency chlorosis under bicarbonate (pH8.3b). Bicarbonate stimulated the root proton secretion, inhibited root growth and ferric chelate reductase (FCR) activity in both PB and quince A, whereas high pH without bicarbonate (pH8.3a) stimulated only root proton release. Both species accumulated more Fe in roots under high pH treatments than under pH6.3, resulting in Fe sufficiency in leaves. Both high pH treatments increased the activity of leaf FCR in PB and quince A. However, extractable Fe(II) concentration in leaves was increased by high pH treatments in PB only. This study demonstrated that depressed Fe(III) reduction in leaves caused by bicarbonate rather than high pH explained Fe deficiency in quince A grown in bicarbonate-containing medium.

Wood age, rootstocks and cultivars drive the formation of productivity and fruit size in sweet cherry

To maintain the high yields and fruit quality necessary for profitability of sweet cherry production, it is important to consider precision crop load and canopy management techniques during limb renewal. The effects of branch section age, rootstock, and cultivar on spur and flower density and fruit quality have been discussed in previous studies, but most of them focus on a limited range of fruiting wood ages and scion-rootstock combinations. This study aims to analyse the processes of sweet cherry productivity and fruit size formation on a wide range of wood age to determine the limit after which branch preservation is not sustainable, and to evaluate the influence of rootstocks and cultivars on these parameters. The results indicate that wood age is one of the main drivers of productivity formation in cherry. The highest flower density was observed on 3-year-old branch sections – 324 flowers per linear m, due to high spur density, number of reproductive buds per spur and flowers per bud. Productivity on 2-year-old wood was also good (256 flowers per linear m), while a sharp decline in flower density was noted on 4- and 5-year-old wood. The largest fruits were formed on young branch sections, with a significant decline in fruit weight and diameter on 4- and 5-year-old sections. Rootstock vigour had a bigger effect on floral organ induction on 1-year-old shoots, than on spurs. Based on the results, it is advisable to regularly renew lateral branches older than 3 years to maintain high yield efficiency and fruit quality.

Using Paclobutrazol and Leaf-to-fruit-ratio as Tools for Improving Yield and Quality of Non-dwarfing High-density Peach Orchards

Excessive fruit set and foliar shading are the major deterrents to the economic productivity of peach orchards raised on vigorous rootstocks. With the objective of obtaining an appropriate level of crop together with the best quality fruit from the high-density peach orchards, studies were conducted in the sub-Himalayan subtropics of Himachal Pradesh, India. In the Experimental orchard of the Department of Fruit Science, the premium Early Grande cultivar raised on non-dwarfing wild peach seedling rootstock was selected for the studies. The orchard soil was sandy loam soil with normal physico-chemical characteristics. The experiment was laid out in RBD factorial experimental design with paclobutrazol (PBZ) and leaf-to-fruit ratio (LFR) treatment factors; three levels of PBZ viz. P1-1500 ppm, P2-2500 ppm, P3-0 ppm and four levels of LFR i.e. L1-30:1, L2-40:1, L3-50:1 and L4 - normal leaf number were tried. The findings revealed that 2500 ppm PBZ together with 40:1 LFR treatment not only reduced the number of days from full bloom to maturity but also improved fruit thinning. The fruit retention was recorded better with 1500 ppm PBZ and 50:1 LFR; however, the yield was recorded highest with 2500 ppm PBZ and 40:1 LFR treatments. This treatment combination also resulted in better overall fruit quality in terms of fruit surface colour, total soluble solids, firmness, acidity, sugars etc. The control over vegetative growth was also observed better under this treatment combination.

Transcriptome analysis for deep understanding the dwarfing mechanism of Malus dwarf mutant rootstock A1d

A1d is dwarf mutant of Pingyi Tiancha (M. hupehensis var. Pinyiensis, PYTC) with dwarfing effect comparable to that of M26. In order to understanding how it affected scion shoot growth at transcriptional level and identify potential useful dwarf genes from it, the transcriptomic differences between the new spring shoots of apple variety “Fuji6” grafted on vigorous rootstock Pingyi Tiancha (P-F) and A1d (A-F) were investigated by RNA-Seq and followed by qRT-PCR verification in two types of scions as well as rootstocks. 494 differentially expressed genes (DEGs) were identified between two samples by RNA-Seq. Plant signal transduction, phytohormone metabolism and IAA polar transportation pathways were greatly affected by the dwarf A1d rootstock. In particular, gibberellin 2-beta-dioxygenase (GA2OX), which encodes a gibberellic acid (GA) inactivating gene, was down-regulated both in A1d rootstock and A-F, while the contents of active GA forms were higher in A-F shoots. The results of qRT-PCR revealed that genes related with IAA signal, IAA polar transportation and cell wall degradation etc. were significantly down-regulated A1d rootstock and its scions. However, down-regulation of these genes in A-F was not retrieved by GA treatment. Sequence analysis showed that two amino acids in the conserved N-terminal DELLA region of Malus domestica RGA-like 3b (MhRGL3b) were mutated in one chromosome of A1d, and designated as Mhrgl3b. We propose that the transportation of the Mhrgl3b from A1d rootstock play a dominant role in controlling the vigor of scion.

4-methylumbelliferone (4-MU) enhances drought tolerance of apple by regulating rhizosphere microbial diversity and root architecture.

The dwarfing rootstocks-mediated high-density apple orchard is becoming the main practice management. Currently, dwarfing rootstocks are widely used worldwide, but their shallow root system and drought sensitivity necessitate high irrigation requirements. Here, the root transcriptome and metabolome of dwarfing (M9-T337, a drought-sensitive rootstock) and vigorous rootstocks (Malus sieversii, a drought-tolerant species, is commonly used as a rootstock) showed that a coumarin derivative, 4-Methylumbelliferon (4-MU), was found to accumulate significantly in the roots of vigorous rootstock under drought condition. When exogenous 4-MU was applied to the roots of dwarfing rootstock under drought treatment, the plants displayed increased root biomass, higher root-to-shoot ratio, greater photosynthesis, and elevated water use efficiency. In addition, diversity and structure analysis of the rhizosphere soil microbial community demonstrated that 4-MU treatment increased the relative abundance of putatively beneficial bacteria and fungi. Of these, Pseudomonas, Bacillus, Streptomyces, and Chryseolinea bacterial strains and Acremonium, Trichoderma, and Phoma fungal strains known for root growth, or systemic resistance against drought stress, were significantly accumulated in the roots of dwarfing rootstock after 4-MU treatment under drought stress condition. Taken together, we identified a promising compound-4-MU, as a useful tool, to strengthen the drought tolerance of apple dwarfing rootstock.

Long-term performance of grapefruit cultivars on different rootstocks

The present study was conducted to standardize the rootstock(s) for grapefruit cvs. Marsh Seedless andRedblush, suitable to grow commercially in northern India, budded on eight rootstocks. The sour orange andRLC-4 proved to be the vigorous rootstocks for Marsh Seedless (220.32 m3) and Redblush (175.65 m3) cultivars,respectively. The trees of Marsh Seedless were dwarf (51.23 – 52.27m3) on Attani-1 and Attani-2 rootstocks,while statistically similar growth of Redblush (46.52 m3) was observed on Jatti khatti rootstock. Jatti khatti andBillikhichli proved to be the good nutrient accumulators (P, K, and Mg) for Redblush; and Jatti Khati and RLC-4for Marsh Seedless (N, P, and Zn). Billikhichli and sour orange proved to be the sodium excluder rootstocks forboth varieties. RLC-4 and Rough lemon proved to be the most productive rootstocks for Redblush and MarshSeedless, respectively. It was followed by Troyer citrange for both the cultivars. These rootstocks also yieldedthe juiciest fruits in their respective cultivars. Attani-1 and Troyer citrange produced fruits with low acid contentin the tested cultivars of grapefruit.