Tolerant Rootstocks Research Articles

Chlorophyll Fluorescence, Photosynthesis and Growth of Tomato Plants as Affected by Long-Term Oxygen Root Zone Deprivation and Grafting

A greenhouse experiment was conducted to study the effects of the O2 root zone level and grafting on chlorophyll fluorescence, photosynthesis and growth of cherry tomato grown in a hydroponic system. Two O2 concentrations in the root zone, namely Ox (saturation level) and Ox- (2–3 mg L−1), were applied for 30 days on self-grafted cherry tomato Dreamer or grafted onto the hybrids Arnold, Beaufort, Maxifort and Top Pittam. Root hypoxia increased minimum fluorescence (by 10%) while it decreased variable fluorescence and the maximum quantum yield of PSII (up to 16 and 8%, respectively). Moreover, it reduced leaf photosynthesis, transpiration and stomatal conductance (by 12, 17 and 13%, respectively), whereas it increased leaf electrolyte leakage (by 2.1%). The graft combinations showed a different ability in buffering the effects of root hypoxia on plant growth and related components, and these differences were related to their root biomass. The minimum fluorescence was negatively correlated to plant growth, so it may be a useful indicator to select tolerant rootstocks to root hypoxia. Our results suggest the occurrence of both diffusive and metabolic constraints to tomato photosynthesis under root hypoxia, a condition that can be mitigated by selecting rootstocks with a more developed root system.

Impact of Salt-tolerant Rootstock on the Enhancement of Sensitive Tomato Plant Responses to Salinity

In the present study, salt-tolerant (Tom 174) and sensitive (Tom 121) tomato genotypes were grafted onto their own roots (174/174 and 121/121), and a susceptible genotype was also grafted onto tolerant genotype 121/174. The grafted plants were grown under 50 mm NaCl and control conditions in a greenhouse. Plant physiological parameters, fruit yield, and physical measurements of fruit (e.g., weight, height, diameter, volume), and chemical analysis of fruit (e.g., vitamin C, pH, and total dry matter content) were investigated. When the sensitive genotype was grafted onto tolerant genotype 121/174, the tolerant genotype Tom 174 reduced the yield loss of susceptible genotype from 44% to 3%. Also, fruit size, total dry matter content, and vitamin C increased, while pH decreased under saline conditions. The rootstock Tom 174 seemed to be able to control sensitive scions’ stomatal openness and closure for transpiration and CO2 transition on photosynthesis because dry matter content was increased. It was found that the tolerant genotype played a role in ameliorating leaf osmotic adjustment of the sensitive genotype in grafting under salt stress. The combination 121/174 had the lowest Na+ concentration in young leaves. Thus, the tolerant rootstock Tom 174 decreased the transport of accumulation of Na+ ions to young leaves in this grafting combination.

Potential impacts of the ring nematode, Mesocriconema xenoplax, on grapevines in British Columbia: a microplot study.

The Okanagan Valley of British Columbia hosts a wine grape industry that has grown substantially in the past three decades in terms of both acreage and economic benefit to the region. The ring nematode, Mesocriconema xenoplax, has recently been found to be widespread in vineyard soils in the region. This study used field microplots to assess the potential impacts of a local population of M. xenoplax on the first four years growth of either self-rooted ‘Merlot’ or ‘Merlot’ vines grafted onto three commonly used rootstocks: 3309C, 44-53M, and Riparia Gloire. The population of M. xenoplax multiplied to comparable levels on self-rooted vines and all rootstocks, indicating that none of the vine genotypes were resistant to M. xenoplax. Inoculation with M. xenoplax reduced cumulative pruning weights of self-rooted vines by 58%. Inoculation with M. xenoplax reduced trunk cross-sectional areas of 3309C by 45% and that of self-rooted vines by 38%, whereas it did not affect trunk cross-sectional areas of 44-53 or Riparia Gloire, indicating differing levels of rootstock tolerance to M. xenoplax. Our data suggest that M. xenoplax is likely impacting vineyard health and productivity in the region, and the selection of rootstocks and management practices to minimize impacts of this nematode should be considered in future vineyard replant management programs.

A Susceptible Scion Reduces Rootstock Tolerance to Ralstonia solanacearum in Grafted Eggplant

The bacterial wilt pathogen (Ralstonia solanacearum) is a highly pathogenic soil-borne bacterium that invades the vascular system of a host plant leading to plant wilting and death. In agricultural systems, tolerant rootstocks are usually used to enhance disease resistance and tolerance in crop plants to soil-borne pathogens. Here, two distinct eggplant cultivars with different tolerances to R. solanacearum infection, the disease-tolerant cultivar ‘S21′ and the disease-susceptible cultivar ‘Rf’, were used to investigate if scion tolerance level can affect tolerance of rootstock upon an infection of the same pathogen. Three scion/rootstock grafted combinations were considered: Rf/S21, S21/S21, and Rf/Rf. Plants that resulted from the combination Rf/S21, composed of the susceptible scion grafts, showed weak tolerance to R. solanacearum infection, and exhibited the poorest growth compared to the tolerant scion grafts (S21/S21). As expected, the combination Rf/Rf showed the lowest level of disease tolerance. Furthermore, a high level of exopolysaccharides (EPSs) and cell wall degrading enzymes (CWDEs) were detected in susceptible scion grafts. These factors are involved in plant growth inhibition due to blocking transport between scion and rootstock and damage of vascular tissues in the plant. A high level of reactive oxygen species (ROS) and active oxygen scavenging enzymes were also detected in susceptible scion grafts. Excess accumulation of these substances harms the dynamic balance in plant vascular systems. These results indicated that the use of a susceptible scion in scion/rootstock eggplant grafts contributed to a reduction in rootstock tolerance to Ralstonia solanacearum.

Assessment of changes in physiological and biochemical traits in four pistachio rootstocks under drought, salinity and drought + salinity stresses.

In this study, 7-month-old UCB-1, Badami, Ghazvini and Kale-Ghouchi pistachio rootstocks were exposed to control, drought, salinity and drought + salinity environments for 60 d. Total chlorophyll and total carotenoid contents decreased in all cultivars under drought, salinity and drought + salinity stresses. Under drought and salinity stresses, alone or in combination, Na+ and Cl- ions increased in all four pistachio rootstocks, while K+ ion decreased only in Ghazvini and Kaleh-Ghouchi cultivars. The enzyme activities of ascorbate peroxidase, polyphenol oxidase, catalase and guaiacol peroxidase increased in all cultivars when subjected to all three stresses with the exception of the ascorbate peroxidase activity in Kale-Ghouchi cultivar during drought stress. Oxidative stress parameters including electrolyte leakage, malondialdehyde, other aldehydes and hydrogen peroxide increased under all three stress conditions in all genotypes. The content of proline, total free amino acids and total soluble carbohydrates were enhanced under drought, salinity and drought + salinity stresses, whereas the protein content decreased in all pistachio rootstocks. In all evaluated traits, except for the K+ ion content and APX activity, the highest impacts was seen for drought + salinity > salinity > drought stresses, respectively. For the first time, we have proven that K+ ion content has a positive correlation with the ascorbate peroxidase, polyphenol oxidase, catalase and guaiacol peroxidase enzymes activities under drought + salinity stress. Finally, based on the bi-plot and cluster analyses, we have selected the UCB-1 > Badami > Ghazvini > Kale-Ghouchi cultivars as the most tolerant pistachio rootstocks under drought + salinity stress, respectively.

Evaluation of the salinity tolerance of Iranian citrus rootstocks using morph-physiological and molecular methods

Salt tolerant citrus rootstocks are extremely important in the area with brackish water and soil. To identify salt tolerant accessions, two well-recognized tolerant and susceptible cultivars, Cleopatra mandarin and Troyer citrange, and 42 genetically diverse citrus accessions from Iran, were evaluated under three levels of sodium chloride (NaCl) including 0, 40 and 90 mM. Five genotypes named G25, G8, G34 (Cleopatra), G42 (Bergamot) and G44 (Sour orange) were the most salinity tolerant based on stress tolerance score. Salinity tolerance was highly correlated with chlorophyll fluorescence (r = 0.55**), Na+ concentration (r=-0.51**), ascorbate peroxidase (r = 0.56**) and leaf necrosis and loss (r=-0.64**). Iranian rootstocks, G8 and G44, were more tolerant than Cleopatra. These results showed that Iran is an appropriate gene pool for salinity tolerance in citrus. The findings of relative gene expression indicated that G44 had salinity tolerance alleles for SLAH, ABCT2 and ABCT3. Considering genotypic and phenotypic results, G44 was recognized as the most salinity tolerant rootstock.

Responses of Apple Plants to Drought Stress

In order to screen apple rootstocks for drought tolerance, two different drought levels moderate and severe stress, and a control were applied to apple cultivar Red Chief grafted onto M9 and MM106 rootstocks. Apple plants were subjected to drought stress by withholding water for 15 and 19 days in the greenhouse conditions, while the control treatment was continued watering. Data were recorded 15 (moderate drought stress) and 19 days (severe drought stress) after application of drought stress. At the end of the experiment, both rootstocks were significantly affected under drought conditions. Severe drought stress caused decrease in SPAD value in Red Chief grafted onto M9 and MM106 by 15.7 % and 11.1 %, respectively. Severe drought stress declined anthocyanin content in M9 and MM106 by 7.8 % and 28.4 %, respectively. Stomatal conductance was remarkably affected by drought stress. Effects of drought stress on plants depended on rootstocks, severity and duration of drought stress. As a result, the more invigorating rootstock MM106 was found more drought-tolerant when compared to M9 that is needed to be evaluated with more parameters.

The physiological response of ‘Hass’ avocado to salinity as influenced by rootstock

With increasing demands on both potable and agricultural water supplies, drought, and extreme temperatures worldwide, agricultural production is challenged with reduced water availability and lower water quality. Salinity, which is associated with low water quality is a critical issue for California avocado growers and, coupled with avocado root rot, threatens the long-term sustainability of the industry since avocados (Persea americana Mill.) are known to be extremely salt sensitive. Salt tolerance of the ‘Hass’ variety, the most commonly grown scion in California, is influenced by rootstock. We investigated ‘Hass’ scions grafted onto three different avocado rootstocks under control (irrigation using water with EC = 0.65 dS/m) and salinity (irrigation using water with EC = 1.5 dS/m) conditions. Results indicated that, compared to control conditions, the irrigation of avocado trees using water with EC = 1.5 dS/m increased canopy damage by 44%, reduced survival by half of the trees tested, and caused yield losses of more than 63%. Avocado leaves visibly damaged by the salinity treatment (named as partially burned or PB leaves) experienced photoinhibition, and reduction of photosynthetic rate and water-use efficiency, suggesting that the poor performance in carbon assimilation contributed to reductions in yield and increases in mortality. The salinity treatment did not cause water stress and the poor performance of treated trees was attributable to chloride accumulation previously reported. Leaf carbon isotopic composition was affected in trees under salinity treatment by increasing the values of δ13C however, this affect was nor correlated with water-use efficiency. Overall, ‘R0.05’, ‘PP40’ and ‘Dusa’ performed similarly and, considering the conditions of the experiment and the intrinsic susceptibility of avocado trees to salinity, were superior to all other rootstocks tested. Future screenings for salinity tolerant rootstocks are required to improve yield when poor quality soil or water is used. Overall, our results showed a coordination between the physiological performance, health and productivity of the ‘Hass’ scion and how these parameters were negatively affected by salinity.

Examination of ion accumulation and some physiological characteristics of grafted eggplants grown under salinity conditions

Salinity is one of the most severe environmental stresses, and it affects over 20% of the world’s irrigated land. Eggplant (Solanum melongena L.), the third most important vegetable crop worldwide after potato and tomato, is relatively salt sensitive. Grafting over tolerant rootstocks is an effective tool to avoid or reduce yield losses caused by salinity stress. In this study, different rootstock/scion eggplant combinations were grown under two salinity treatments, 1.8-2 dS m‑1 (control) and 6-7 dS m‑1 (stress) in pots under greenhouse conditions. Four eggplant genotypes were used as rootstock (‘Koksal’ F1, ‘AGR703’, ‘Vista’, and the Turkish genotype ‘Burdur’), while two genotypes were used as scion (‘Naomi’ F1 and ‘Artvin’). Concerning leaf area, chlorophyll content, and leaf ions content (Na+, Cl-, K+ and Ca2+) parameters tested, there were significant differences between combinations. ‘Koksal’ and ‘Vista’ rootstocks showed the best performance under salinity conditions and were more tolerant to salinity, and were efficient in preventing Na+ ions to be transferred to the plants’ upper parts. ‘Burdur’ genotype showed good performance as rootstock in comparison to the commercial genotype, and it also showed that it is a potential genetic source to be used in breeding programs for new eggplant rootstocks tolerant to salinity.

Grape Rootstock Response to Salinity, Water and Combined Salinity and Water Stresses

Diminishing availability of non-saline water in arid and semiarid regions is of concern to all irrigated agricultural producers, including wine and grape producers. Grapes are not a salt tolerant crop and producers often face the choice of either limiting fresh water application, using alternative saline waters or a combination of both. We examined the salt tolerance and effect of restricted water application on three purported salt tolerant rootstocks grafted to Cabernet Sauvignon scion in a 4-year replicated field experiment. ANOVA indicated significant effects of salinity water stress and rootstock on fruit yields. The 140 Ruggeri scion was the top producer across all treatments including control, followed by Salt Creek, with St. George significantly less productive than 140 Ruggeri across all treatments. In terms of salt tolerance, Salt Creek and 140 Ruggeri were not statistically different but St. George was significantly less tolerant than Salt Creek. In terms of drought tolerance (relative yield), there were no statistical differences among rootstocks. Soil salinity profiles and soil moisture sensors indicated reduced water consumption under high salinity, thus no matric stress under 60% of optimal water application when high salt stress was present. The multiplicative stress model where salt and water stress are individually evaluated did not satisfactorily predict yield under combined salinity and reduced water application, likely due to decreased water consumption under saline conditions. Short term (one year) experiments underestimate salt damage to grape vines as salt tolerance decreased over the 4-year experiment.

Validation of micrografting to identify incompatible interactions of rootstocks with virus‐infected scions of Cabernet Franc

Background and Aims Grafted grapevines are a key component of modern viticulture. Grafting provides not only resistance to soil-borne pests, but can also improve adaptability to the environment and can improve fruit yield and quality. Graft incompatibility induced by grapevine viruses causes damage to vineyards worldwide. The aim of the present study was to create a rapid and reliable means of evaluating graft incompatibility resulting from grafting virus-infected scions onto healthy grape rootstocks. Methods and Results Scions of Control (healthy Cabernet Franc), LR131 (Cabernet Franc infected with GLRaV-1) and LR132 (Cabernet Franc infected with GLRaV-1 and GVA) were grafted onto different rootstocks by micrografting, green grafting and bench grafting methods. All the micrografts infected with LR132 failed, while LR131 and Control micrografts had similar survival rates. The impact of LR132 was less severe on green grafted plants, followed by bench grafts. Analysis of variance showed an interaction of grafting method × virus variety × rootstock, affecting grafting survival. When grafted onto Freedom and 101-14, LR131 inhibited the growth of both scion and rootstock, but no significant impact was seen when LR131 was grafted onto St. George and AXR1. Well-established callus was visible between the surfaces of LR131 and the rootstocks. The virus GLRaV-1 was detected moving from the LR131 scion source to rootstocks 7 days after micrografting. Callus formation was delayed by LR132 between scion and rootstock surfaces, and a scion-rootstock vascular connection did not establish, resulting in the death of all micrografts. Conclusions Micrografting is a reliable and sensitive method to screen for virus tolerant graft combinations compared with green and bench grafting. Significance of the Study The results of the present study validate micrografting as a means of producing credible information for selection of virus tolerant rootstocks, and ultimately vineyards with higher rates of compatible grafts.

Interaction of Brassicaceae Seed Meal Soil Amendment and Apple Rootstock Genotype on Microbiome Structure and Replant Disease Suppression.

Preplant soil application of a Brassica juncea-Sinapis alba seed meal formulation (SM) at a rate of 6.6 t ha-1 alters composition of the orchard soil microbiome in a manner that yields sustainable long-term suppression of soilborne pathogens in apple production systems. However, the cost of SM amendment has hindered the adoption of this tactic to manage apple replant disease in commercial orchards. Greenhouse trials were conducted to assess the effect of reduced SM application rates in concert with apple rootstock genotype on structure of the rhizosphere microbiome and associated disease control outcomes. At all application rates assessed, SM treatment increased tree growth and reduced disease development relative to the control. In general, total tree biomass and leader shoot length were similar in soils treated with SM at 4.4 or 6.6 t ha-1 regardless of rootstock genotype. Equivalent increase in tree biomass when cultivated in soil treated at the lowest and highest SM amendment rate was attained when used in conjunction with G.41 or G.210 apple rootstocks. Suppression of Pythium spp. or Pratylenchus penetrans root densities was similar at all SM application rates. When cultivated in nontreated replant orchard soil, Geneva rootstocks (G.41 and G.210) exhibited lower levels of Pythium spp. and P. penetrans root colonization relative to Malling rootstocks (M.9 and MM.106). For a given rootstock, structure of the rhizosphere microbiome was similar in soils treated with SM at 4.4 and 6.6 t ha-1. G.41 and G.210 rootstocks but not M.9 or MM.106 cultivated in soil treated with SM at 2.2 t ha-1 possessed a rhizosphere bacterial community structure that differed significantly from the control. Findings indicate that effective control of apple replant disease may be attained at lower SM amendment rates than employed previously, with lower effective rates possible when integrated with tolerant rootstock genotypes such as G.41 or G.210.

Rosellinia necatrix infection induces differential gene expression between tolerant and susceptible avocado rootstocks.

Rosellinia necatrix is the causal agent of avocado white root rot (WRR). Control of this soil-borne disease is difficult, and the use of tolerant rootstocks may present an effective method to lessen its impact. To date, no studies on the molecular mechanisms regulating the avocado plant response towards this pathogen have been undertaken. To shed light on the mechanisms underpinning disease susceptibility and tolerance, molecular analysis of the gene’s response in two avocado rootstocks with a contrasting disease reaction was assessed. Gene expression profiles against R. necatrix were carried out in the susceptible ‘Dusa’ and the tolerant selection BG83 avocado genotypes by micro-array analysis. In ‘Dusa’, the early response was mainly related to redox processes and cell-wall degradation activities, all becoming enhanced after disease progression affected photosynthetic capacity, whereas tolerance to R. necatrix in BG83 relied on the induction of protease inhibitors and their negative regulators, as well as genes related to tolerance to salt and osmotic stress such as aspartic peptidase domain-containing proteins and gdsl esterase lipase proteins. In addition, three protease inhibitors were identified, glu protease, trypsin and endopeptidase inhibitors, which were highly overexpressed in the tolerant genotype when compared to susceptible ‘Dusa’, after infection with R. necatrix, reaching fold change values of 52, 19 and 38, respectively. The contrasting results between ‘Dusa’ and BG83 provide new insights into the different mechanisms involved in avocado tolerance to Phytophthora cinnamomi and R. necatrix, which are consistent with their biotrophic and necrotrophic lifestyles, respectively. The differential induction of genes involved in salt and osmotic stress in BG83 could indicate that R. necatrix penetration into the roots is associated with osmotic effects, suggesting that BG83’s tolerance to R. necatrix is related to the ability to withstand osmotic imbalance. In addition, the high expression of protease inhibitors in tolerant BG83 compared to susceptible ‘Dusa’ after infection with the pathogen suggests the important role that these proteins may play in the defence of avocado rootstocks against R. necatrix.

Pepper Rootstock and Scion Physiological Responses Under Drought Stress.

In vegetables, tolerance to drought can be improved by grafting commercial varieties onto drought tolerant rootstocks. Grafting has emerged as a tool that copes with drought stress. In previous results, the A25 pepper rootstock accession showed good tolerance to drought in fruit production terms compared with non-grafted plants and other rootstocks. The aim of this work was to study if short-term exposure to drought in grafted plants using A25 as a rootstock would show tolerance to drought now. To fulfill this objective, some physiological processes involved in roots (rootstock) and leaves (scion) of grafted pepper plants were analyzed. Pepper plants not grafted (A), self-grafted (A/A), and grafted onto a tolerant pepper rootstock A25 (A/A25) were grown under severe water stress induced by PEG addition (-0.55 MPa) or under control conditions for 7 days in hydroponic pure solution. According to our results, water stress severity was alleviated by using the A25 rootstock in grafted plants (A/A25), which indicated that mechanisms stimulated by roots are essential to withstand stress. A/A25 had a bigger root biomass compared with plants A and A/A that resulted in better water absorption, water retention capacity and a sustained CO2 assimilation rate. Consequently, plants A/A25 had a better carbon balance, supported by greater nitrate reductase activity located mainly in leaves. In the non-grafted and self-grafted plants, the photosynthesis rate lowered due to stomatal closure, which limited transpiration. Consequently, part of NO3- uptake was reduced in roots. This condition limited water uptake and CO2 fixation in plants A and A/A under drought stress, and accelerated oxidative damage by producing reactive oxygen species (ROS) and H2O2, which were highest in their leaves, indicating great sensitivity to drought stress and induced membrane lipid peroxidation. However, drought deleterious effects were slightly marked in plants A compared to A/A. To conclude, the A25 rootstock protects the scion against oxidative stress, which is provoked by drought, and shows better C and N balances that enabled the biomass to be maintained under water stress for short-term exposure, with higher yields in the field.

Evaluation of breeding potential of wild grape originating from Armenia

Crop wild relatives provide a useful source of genetic variation and represent a large pool of genetic diversity for new allelic variation required in breeding programs. Armenia is an important center of origin both for cultivatedVitis viniferassp. sativaand wildVitis viniferassp.sylvestris.Owing to recent prospection in Armenian woods and river floodplains many forms of wild grapevine were discovered and inventoried, which is an important prerequisite to unlock their breeding potential in the future. The fact that some genotypes ofV. sylvestriscan withstand the diseases is likely to be due to a more efficient basal immunity. The overall goal of the proposed research was to characterize the diversity ofV. sylvestrisfrom Armenia with respect to its capacity for stilbene biosynthesis, which might be exploited as genetic resource for resistance breeding. The realized research stimulates the recovery, characterization and preservation of wild grape germplasm, presently at risk of extinction. The recovery and characterization of wild genotypes will be the base of selection of genetic traits important in breeding programs for the generation of biotic and changing climate tolerant grapevine varieties and rootstocks, both necessary for the future of viticulture in Armenia and in Europe.

Polyphenolic profiling of roots (Vitis spp.) under grape phylloxera (D. vitifoliae Fitch) attack

Many plants respond to herbivore attacks by the formation of secondary metabolites, such as polyphenols. Grape phylloxera (Daktulosphaira vitifoliaeFitch) induces organoid root galls on fibrous root tips of tolerant Vitis spp. rootstocks. We aim to understand if and how secondary metabolites are involved in the compatible interaction of D. vitifoliae and tolerant Vitis ssp. rootstocks belowground. We hypothise that D. vitifoliae infestation triggers the accumulation of phenolic key compounds in root gall tissue without preventing the compatible host-parasite interaction on two tolerant rootstocks with different genetic background: Teleki 5C (V. berlandieri x V. riparia) and Fercal (B.C. n°1B x 31 Richter). Plants and insects are grown in isolated climate chambers to sample root tips of non-infested plants (control) as well as root tips and galls of D. vitifoliae infested plants (5–14 dai). HPLC-MS-based analyses of phenolic key compounds are compared with gene expression levels of the biosynthetic phenylpropanoid pathway analysing temporal sequences of D. vitifoliae infested root tissue. The results show that the induction of the phenylpropanoid pathway by D. vitifoliae infestation plays an important role in the plant response. Concentrations of phenolic key compounds vary significantly among the rootstocks tested. Both rootstocks display an accumulation of flavan-3-ols and stilbenes in infested root gall tissue. Comparing the host responses of the two rootstocks Fercal shows a stronger accumulation of stilbenes locally in infested root galls, whereas Teleki 5C indicates elevated amounts of stilbenes in non-infested root tip tissue.

Salt Tolerance and Growth of 13 Avocado Rootstocks Related Best to Chloride Uptake

Avocado (Persea americana Mill.) is one of the most salt-sensitive crops and one of the highest value crops per acre. In the United States, avocados are grown primarily in California, in regions experiencing both scarcity of freshwater and salinization of available water supplies. Thus, our objectives were to evaluate avocado rootstocks for salt tolerance and evaluate the relationship between leaf ion concentrations, trunk diameter, leaf burn, and fruit yield. Our field experiment evaluated the salt tolerance of the Hass scion grafted onto 13 different avocado rootstocks using the Brokaw clonal rootstock technique. The experiment consisted of 156 trees arranged in a randomized complete block design with six replications of each saline [electrical conductivity (EC) = 1.5 dS·m–1, Cl– = 4.94 mmol·L–1] and nonsaline (EC= 0.65 dS·m–1, Cl– = 0.73 mmol·L–1) irrigation water treatment. We collected soil samples and leaves, then analyzed them for major ions. The rootstocks R0.06, R0.07, PP14, and R0.17, which had high concentrations of Cl and Na in the leaves, were the least salt tolerant, with 100% mortality in the rows irrigated with saline water for 23 months. The rootstocks R0.05, PP40, R0.18, and Dusa, which had low concentrations of Cl ions in the fully expanded leaves, were least affected by salinity, and these rootstocks exhibited the greatest yields, largest trunk diameters, and greatest survival percentages in the saline treatment. Yield and growth parameters correlated well with leaf Cl concentration, but not Na, indicating that salt damage in avocado is primarily a result of Cl ion toxicity. Under arid inland environments, no variety performed satisfactorily when irrigated with an EC = 1.5 dS·m–1 water (Cl– = 4.94 mmol·L–1). However, the more tolerant varieties survived at soil salinity levels that would apparently be fatal to varieties reported earlier in the literature.

Peach rootstock tolerance to excess zinc in sandy acidic soil

In some areas dedicated to the cultivation of peach plants, soils are characterized by high levels of zinc (Zn) as a consequence of successive applications of Zn-containing fungicides and/or use of animal manure as fertilizer. In these cases, choosing an appropriate Zn-tolerant rootstock is essential to optimize orchard production. The current study evaluated the behavior of three peach rootstocks grown in a soil containing variable levels of Zn availability. Samples of a Typic Hapludalf soil were collected from a natural grassland in southern Brazil. The soil was dried and sieved. Subsamples of the soil were amended with increasing rates of Zn added as ZnSO4, incubated for 60 days, transferred to rhizoboxes, and planted with three types of peach rootstocks (Tsukuba-1, Rigitano and Flordaguard). The treatments were arranged in a completely randomized experimental design with three replications per rootstock X Zn dosage treatment. The rootstocks were grown for 65 days, at which time dry matter production of leaves, shoots and stem, as well as increase in height and stem diameter at ground level, were measured. Total concentrations of Zn, Fe, N, P, Ca and Mg were analyzed in each organ. The photosynthetic pigments and catalase (CAT) activity were analyzed in the leaves. Concentrations of Zn increased linearly in all the organs of all the rootstocks; however, the Tsukuba-1 rootstock presented greater sensitivity to high levels of Zn availability in soil, with a reduction in leaf dry matter production, chlorophyll a and carotenoid concentrations, and CAT activity. The Flordaguard rootstock showed an increase in height with increasing Zn concentration applied to the soil. Development of the Rigitano rootstock plants was unaffected by Zn amendment.

Screening Selected Solanum Plants as Potential Rootstocks for the Management of Root-Knot Nematodes (Meloidogyne incognita)

Root-knot nematodes (RKNs) (Meloidogyne spp.) represent agricultural pest of many economic crops, including tomatoes and potatoes. They advance a complex parasitic relationship with roots of tomato plants leading to modification of host structural and physiological functions in addition to significant yield loss. Resistance in solanaceous plants to RKNs has been identified and associated with the possession of Mi gene. The reaction of four Solanum rootstocks (S. aethiopicum L., S. macrocarpon L., S. lycopersicum L.“Mongal F1,” and S. lycopersicum L. “Samrudhi F1”) was evaluated in pots and in a natural Meloidogyne spp.-infested field in a two-year trial (2015–2016), to identify RKN-resistant rootstock(s), which can be utilized in tomato grafting as a management measure against these nematodes. A rootstock’s reaction to RKNs was assessed using root gall scores (GSs), egg count/g of root, and reproductive factors (Rfs) at the end of 6 and 12 weeks after transplanting (wat) in infested fields, respectively. Solanum macrocarpon, S. aethiopicum, and Mongal F1 showed tolerant responses with reduced root galling and low to high reproductive factors in pot and field experimentation. Although Samrudhi F1 was resistant in both pot and field trials and consistently decreased nematode root galling (<1.00) and reproduction (Rf < 1.00), it failed to significantly increase yield, as compared with the highest yield obtained by the tolerant rootstock, Mongal F1 (870.3 and 1236.6 g/plant, respectively). Evaluation of the four rootstocks against four (0, 500, 1,000, and 5000) RKN inocula levels (Juveniles) showed no significant differences among the growth parameters (fresh and dry shoot and root weights). Root-knot nematode-susceptible tomato varieties, for example, Pectomech F1, a popular tomato variety in Ghana, can be grafted onto the RKN-resistant and RKN-tolerant rootstocks for increased yields.

Zinc pulverization alleviates the adverse effect of water deficit on plant growth, yield and nutrient acquisition in grapevines (Vitis vinifera L.)

Grapevine (Vitis vinifera L.) is an important dryland pulse crop in many parts of the world. However, productivity and quality are often limited by periods of water deficit. In a number of drought regions, drought is accompanied with zinc (Zn) deficiency, one of the most serious problems causing significant decreases in yield and quality in viticulture. In spite of this fact, possible effect of Zn treatment to alleviate the adverse effect of water stress on grapevines has not been studied. A pot culture research was designed under controlled glasshouse condition with the objective to investigate the effects of Zn pulverization on growth, physiology and nutrient acquisition of grapevine cultivars ‘Italia’ and ‘Alphonse Lavallée’ subjected to different irrigation levels. Six years old grapevines of the cultivars grafted on a drought tolerant rootstock Richter 99 (Berlandieri x Rupestris) were cultivated in pots (70 L) and subjected to two different irrigation regimes, FI-100% (replenishing the substrate water storage up to field capacity) and DI (40% of FI). Half of the vines for each irrigation group received leaf Zn pulverization (1%) twice (prior to flowering and berry set). DI caused overall decreases in shoot and leaf developments of cultivars, while Zn pulverization had alleviating effects on such vegetative growth in general. Generally, leaf chlorophyll content of the vines was also improved by Zn under both FI and DI conditions. Spraying of the leaves and green bunches with chelated Zn supported the grapevines of both cultivars ‘Italia’ and ‘Alphonse Lavallée’ in varying degrees by improving acquisition of many plant nutrients, promoting the vegetative and generative developments. Considering the overall response of the vines to Zn pulverization with a particular concern to DI condition, improved shoot and leaf growth, greener leaves, enhanced berry development and vine yield allow us to recommend Zn spraying as an environmentally friendly and sustainable cultural practice under drought stress which has been increasing with global climate change.