Scion Size Research Articles

Managing Cashew Rootstock Grafting Size Through Organic Fertilizers

Seed born cashew (Anacardium occidentale L) seedlings are planted directly when they are produced from polyclonal orchards. In a common scenario, cashew seedlings are grafted before transplanting. For this purpose, adjusting the size between scions and rootstock is highly important for the success of grafts and it can be achieved through a visual selection of scions. However, when working with large numbers of seedlings physical and visual selection becomes laborious and time consuming for the workers. Therefore, creating uniformity in seedlings size before grafting is crucial. We present experimental results showing the linear regression between the fertilization level and seedling stem size. Two experiments were conducted in Mozambique: One at Nassuruma cashew Research Station, Nampula province, following a Completely Randonmized Block Design (CRBD), seven treatments, ten bags per treatment and five replicates. The treatments consisted of a fertilizer organically composted from cashew nut shells and applied at rates of 0, 4, 8, 16, 32, 40 and 48% of the total amount of soil in each bag. The second experiment was carried out at Chizavane nursery, in Gaza Province, also based on CRBD, in factorial arrangement of 4 and 3 levels of Kelp and Stimu biofertilizers respectively. Two stem size variables, diameter and height, were considered and data collected at 120 days after seedlings emergence in Nampula and 45 days after emergence in Gaza Province. Polynomial or simple regression analysis model for stem diameter and plant height was performed. The stem diameter was linearly described as an increasing equation. The height was also linearly related to fertilizer but following a decreased equation. We concluded that applying appropriate dosage of fertilizer in the soil or on the leaves could adjust the stem size of the rootstock required for grafting and therefore adjust the stem to the size of scions available. The treatments with high level of Kelp, Stimu and cashew compost fertilization resulted in increase of 8,5%, 6% and 16,6% of diameter respectively. However, the treatments caused a reduction of height at rate of 14,3%, 3,2% and 25,08% respectively. The stem and scion size adjustment are highly important for increasing the grafting success rate in a cashew nursery.

Systemic signalling through translationally controlled tumour protein controls lateral root formation in Arabidopsis.

The plant body plan and primary organs are established during embryogenesis. However, in contrast to animals, plants have the ability to generate new organs throughout their whole life. These give them an extraordinary developmental plasticity to modulate their size and architecture according to environmental constraints and opportunities. How this plasticity is regulated at the whole-organism level is elusive. Here we provide evidence for a role for translationally controlled tumour protein (TCTP) in regulating the iterative formation of lateral roots in Arabidopsis. AtTCTP1 modulates root system architecture through a dual function: as a general constitutive growth promoter enhancing root elongation and as a systemic signalling agent via mobility in the vasculature. AtTCTP1 encodes mRNAs with long-distance mobility between the shoot and roots. Mobile shoot-derived TCTP1 gene products act specifically to enhance the frequency of lateral root initiation and emergence sites along the primary root pericycle, while root elongation is controlled by local constitutive TCTP1 expression and scion size. These findings uncover a novel type for an integrative signal in the control of lateral root initiation and the compromise for roots between branching more profusely or elongating further. They also provide the first evidence in plants of an extracellular function of the vital, highly expressed ubiquitous TCTP1.

In vitro micrografting using three diverse indigenous rootstocks for the production of Citrus tristeza virus-free plants of Khasi mandarin

The present work reports the prospective applicability of three indigenous rootstocks belonging to different species viz. Nemutenga, Tayum and Tasi cultivars of north eastern Himalayan region for producing Citrus tristeza virus (CTV; a viral species of the Closterovirus genus) free quality planting materials of Khasi mandarin (Citrus reticulata Blanco) through micrografting or shoot-tip grafting (STG). The development of disease-free plants through STG is essential as CTV is in vivo transmissible through infected bud sticks. The technique of STG along with the diverse culture parameters like effect of sucrose, plant growth regulators, pre-treatment of scion and stock, effect of scion size after thermotherapy and grafting method was analysed. Among the three indigenous tested rootstocks, Nemutenga was found superior showing maximum STG success of 58.5%. STGs using scion size ranging from 0.3 to 0.5 mm, survival was up to 42.0% and completely virus-free. Pre-treatment of scion and stock with kinetin (1.0 mg L−1) was found more suitable than N6-benzylaminopurine (BAP) and further increased the rate of micrografts. For further growth of micrografts, Murashige and Skoog medium fortified with 0.5 mg L−1 BAP and 0.1 mg L−1 indole-3-acetic acid (IAA) along with 5% sucrose resulted in maximum (56.8%) response. Considering the two techniques applied for STG, cleft grafting was found more suitable than inverted T grafting. Viral assessment with enzyme-linked immunosorbent assay (ELISA) and reverse transcriptase polymerase chain reaction (RT-PCR) revealed negative results for all plants from 0.3 to 0.5 mm scion while 0.7-mm scion-raised micrografts showed 60% negative with RT-PCR for CTV.

Mutagenesis and Biotechnology Techniques as Tools for Selecting New Stable Diploid and Tetraploid Olive Genotypes and Their Dwarfing Agronomical Characterization

In Olea europaea L. subsp. europaea, tetraploid genotypes do not exist in nature. Herein, we report the first example of selection of tetraploid olive plants, obtained by combining physical mutagenesis and biotechnology techniques. Stable tetraploid (4n) and diploid (2n) genotypes were isolated in vitro through shoot-tip fragmentation of two mixoploid mutants derived from the gamma irradiation of self-incompatible Leccino and self-compatible Frantoio cultivars. In this study, the stable mutants FRM5-4n, FRM5-2n, LM3-4n, and LM3-2n were characterized in the field for vegetative and reproductive behavior with the aim to use them as varieties or dwarfing rootstocks. The stable 4n genotype of Leccino acquired self-fertility whereas the 4n Frantoio maintained it. A high and constant yield was showed by LM3-2n during 9 years of observation, maintaining the same oil quality as the Leccino wild type (wt). Moreover, the LM3-2n acquired the capacity to be intercompatible with the diploid mutant Leccino dwarf (LD) and with the Leccino wt. This acquired property would allow for a reduction of heterozygosity in the offspring, if crossed with each other for some generations and with the Leccino wt, because it is a sort of self-fertilization. When used as rootstocks, both 4n and 2n Leccino mutants proved to be very effective for reducing the scion size of the high-vigor Canino cultivar, which is well known for its excellent extravirgin oil. Finally, it was demonstrated that the self-grafting of vigorous cultivar caused a reduction in plant size, thus suggesting that it is possible to produce semidwarf plants from vigorous genotypes to consider them in high-density olive orchards.

Fine root dry matter relative to mango (Mangifera indica) tree scion size grafted on size-controlling rootstocks, is negatively related to scion growth rate

The effects of mango rootstock cultivars on scion vigour may be predicted by scion growth rate being negatively related to fine root dry matter/scion trunk cross sectional area. Knowledge of root dry matter (DM) allocation, in relation to differing vigour conferred by rootstock cultivars, is required to understand the structural relationships between rootstock and scion. We investigated the mass of roots (four size classes up to 23 mm diameter) by coring proximal to five polyembryonic mango rootstock cultivars known to differ in their effects on the vigour and productivity of scion cultivar ‘Kensington Pride’, in a field trial of 13-year-old trees. Significant differences in fine (<0.64 and 0.64–1.88 mm diameter) and small (1.88–7.50 mm) root DM contents were observed between rootstock cultivars. There was a complex relationship between the amount of feeder (fine and small size classes) roots and scion size (trunk cross sectional area, TCSA), with intermediate size trees on rootstock MYP having the most feeder roots, while the smallest trees, on the rootstock Vellaikulamban had the least of these roots. Across rootstock cultivars, tree vigour (TCSA growth rate) was negatively and significantly related to the ratio of fine root DM/scion TCSA, suggesting this may be a useful indicator of the vigour that different rootstocks confer on the scion. In contrast non-ratio root DM and scion TCSA results had no significant relationships. The significant rootstock effects on orchard root growth and tree size could not be predicted from earlier differences in nursery seedling vigour, nor did seedling vigour predict root DM allocation.

Disease-free khasi mandarin (Citrus reticulata Blanco) production using in vitro microshoot tip grafting and its assessment using DAS-ELISA and RT-PCR

Citrus plantation using nucellar seedlings suffers from various limitations. Biotechnological tools of microshoot-tip-grafting (STG) for disease elimination and finding compatible rootstock for budding Khasi mandarin need to be implemented so as to rejuvenate the declining citrus industry of North-East India. Considering this fact, study of micrografting using three rough lemon varieties (Champra Maunthabi, Kachai Lemon and Meitei Champra) and different parameters of culture like concentration of sucrose and benzyl aminopurine (BAP), scion size and photoperiod was analysed. Depending on the genotypes used, the success rate of STG ranged from 30.15 to 42.69%. A sucrose concentration of 6% gave the optimum performance with 51.54% success on micrografting, with observable decrease in success rate on either increase (35.43% success at 9%) or decrease (33.44% success at 3%) in Murashige and Tucker (MT) liquid media supplemented with BAP 0.5mg/l. Photoperiod also has significant influence, as 51.08% success could be achieved in dark incubation for 2 weeks after micrografting, compared to no observable response at continuous light exposure (16h photoperiod). Size of scion also has significant influence on STG as smaller scion <0.5mm size gave a low performance of 7.24% success, compared to a higher success rate of 45.09% at optimal scion size of 0.5–0.65mm. Different concentrations of BAP in liquid media (MT with 6% sucrose) gave variable responses – 1mg/l of BAP gave scion vitrification and poor response while a stable growth of scion and higher micrograft success was obtained at 0.5mg/l BAP. Disease elimination from the micrografted plants using this technique of STG was confirmed using DAS-ELISA and RT-PCR techniques. Samples tested negative for citrus tristeza virus (ctv) with DAS-ELISA were further analysed with RT-PCR using ctv-specific primer pairs CTV P25F/CTV P25R and PM50/PM 51 for confirmation of the absence of viral pathogen. Providing a high humidity and ambient temperatures during acclimatization, 72.35% survival of the micrografted plants was achieved.

Effect of the scion size and ages for rooting rate and first-year growth rate at two willow species

Effect of the scion size and ages for rooting rate and first-year growth rate at two willow species

In vitro micrografting for production of Indian citrus ringspot virus (ICRSV)-free plants of kinnow mandarin (Citrus nobilis Lour × C. deliciosa Tenora)

Production of Indian citrus ringspot virus (ICRSV)-free plants from an infected plant of kinnow mandarin (Citrus nobilis Lour × C. deliciosa Tenora) is reported. The shoot apices of different sizes (0.2–1.0 mm) excised from the ICRSV-infected plant were micrografted onto decapitated rootstock seedlings of rough lemon (C. jambhiri). Micrograft survival depended on the size of shoot apex and the sucrose concentration of the culture medium. Increase in scion size from 0.2 to 0.7 mm resulted in an increase in micrografting success rate from 30.55 to 51.88%. Further, micrograft survival obtained with 0.2 mm was improved from 30.55 to 38.88% by increasing sucrose concentration in the culture media from 5 to 7.5%. The micrografted plants were tested for ICRSV using ELISA and RT-PCR. All plants raised from 0.2-mm scion were found negative with both ELISA and RT-PCR whereas only 20% of the ELISA negative plants raised from 0.3-mm scion were found negative for ICRSV with RT-PCR. The outcome of this research is the successful establishment, acclimatization and virus testing of micrografted plants.

SPECIAL MICROGRAFTING TECHNIQUE FOR CHERRY (PRUNUS AVIUM L.)

The success of different in vitro micrografting techniques and scion size for cherry (Prunus avium 'Seeyahe Mashad') was studied. Grafting success (union of grafts) was significantly dependent on the method of grafting. The highest percentage (65%) of successful grafts was obtained with the homoplastic apex graft (shoot-tip), with apical bud scion length greater than 6 mm. However, the success of heteroplastic side bud apices (wedge) grafts was only 16%. The homoplastic micrografting method in vitro can be a useful technique in the improvement, rejuvenation and freeing from viruses for fruit crops. There was good efficiency and maintenance of good contact between scion and rootstock until fusion took place by using this technique. In vitro germinated sour cherry seedlings (Prunus cerasus 'Albaloo') which emerged one month after inoculation, were decapitated and used as rootstocks. One-month-old in vitro-cultured meristematic apices with length of 5-15 mm were used as microscions. The highest amount of successful grafts was obtained with the homoplastic apex graft (shoot-tip), when compared with wedge grafts and heteroplastic grafts. The graft union, as measured by graft compatibility, was satisfactory, although, it formed very slowly during the first month. Contamination and necroses occurred more often under in vitro conditions. Nutrient disorders and mineral deficiency symptoms were observed. This technique has a good potential for mass propagation of disease-free sweet cherry.

Evidence for age- and size-mediated controls of tree growth from grafting studies

Vegetative propagation techniques such as grafting can be used, in conjunction with field studies, to decouple the relative effects of age and size on tree metabolism and growth. Despite interest in this approach, little attention has been paid to the best metrics for assessing the growth performance of grafted plants over time. Based on an analysis of the grafting literature and our own data, we show that the choice of metrics to assess tree growth can entirely change the conclusions reached about the relative importance of age versus size. We recommend that absolute as well as relative rates of growth are calculated and that scion size be standardized as much as possible at the start of the experiment. Once proper metrics are chosen, all of the available published evidence is largely concordant with two concepts: (1) age-mediated controls of tree growth are likely to be important during the first few years of a tree's life (before phase change); and (2) after the first few years of a tree's life, size-mediated factors largely prevail over age-mediated factors in determining tree growth rates. We found no support for theories invoking age-mediated sink limitations in old trees.

Factors influencing in vivo and in vitro micrografting of sandalwood (Santalum album L.): an endangered tree species

In vivo micrografting of Santalum album was achieved (50%) by grafting 4- to 5-cm-long scions, collected from a candidate plus tree (CPT) of 50–60 years of age, onto 90-day-old nursery-grown rootstock. Scion size, rootstock age, and scion collection season were found to influence graft success. Grafted plants were incubated under greenhouse conditions for 6–8 weeks during the graft union process. In vitro micrografts were achieved by placing 1- to 2-cm-long scions derived from nodal shoot segments (collected from CPT) onto the hypocotyl of 45-day-old in vitro rootstocks. Use of in vitro grown shoots as a source of scion gave better graft success (60%) than scions collected directly from field-grown trees. In vitro grafting was also influenced by scion size and rootstock age. Under favorable conditions, scions and hypocotyls unite to form complete plants that produced two to four leaves after 6–8 weeks. This is the first report on in vivo and in vitro micrografting of S. album having potential for production of disease-free clonal plants for conservation and improvement targets.

An efficient grafting system for transgenic plant recovery in cotton (Gossypium hirsutum L.)

A successful transformation program relies on the number of survival plants in soil that can be obtained. Low recovery of transgenic plants is still a key restrictive factor for transgenic cotton production. In order to utilize genetic transformation in cotton breeding program effectively, an efficient grafting system for recovering plants derived from somatic embryogenesis following Agrobacterium infection and kanamycin selection was developed. Various aspects of in vitro grafting were examined in efforts to improve the efficiency of transformant recovery. Using strong seedling rootstocks was the first important step to obtain high rate of successful grafts. Scion size >0.6 cm and seedling rootstock at age of 6–12 days were appropriate for grafting. The successful grafting ratio was higher when using hypocotyls without radicle. Shoot-tip and shoot stem with axillary bud were also suitable for in vitro grafting, which meant we could significantly improve the survival ratio of transgenic plantlets, because one plantlet has a shoot-tip but several axillary buds. Based on our data, the period from in vitro seedling rootstock germination to transplant of grafts to field usually takes one month. Over 90% successful grafting ratio could be obtained under optimal conditions, which represented a significant improvement over currently available methods for recovery of cotton plantlet from somatic embryogenesis after transformation. Ex vitro grafting could also be used for plant recovery, which gave an average of successful grafting ratio of 71.9%. However, this method was strongly affected by environmental factors.

Micrografting of ASBVd-infected Avocado (Persea americana) plants

Shoot tips (meristem plus 2–3 leaf primordia) from in vitro-germinated avocado seedlings of 2 ASBVd-infected cultivars were micrografted in vitro onto decapitated seedlings from 2 ASBVd-free cultivars, and plants were recovered. Shoot tips consisted of two different sizes, i.e., 0.5 mm but 0.5 mm than from those that were <0.5 mm (10.3%). RT-PCR demonstrated that ASBVd replicated in all micrografts from infected sources irrespective of the scion size, while no ASBVd was detected in micrografts from plants that tested negative. ASBVd therefore cannot be eliminated by in vitro micrografting.

In vitro shoot-tip grafting improves recovery of cotton plants from culture

A rapid in vitro shoot-tip grafting (STG) technique was adapted to increase recovery of intact cotton plants from shoots developed in culture. Induction of root organogenesis in cotton shoots is genotype dependent and unreliable. The resulting loss of regeneration potential due to failure to form roots can vary from 30 to 80% according to genotype and represents a significant bottleneck in the overall recovery of plants from culture. If the non-rooting shoots are transgenic, the loss in regenerated plant material can be substantial. In vitro grafting of cotton shoots to seedling rootstock proved to be a simple and reliable method allowing 90–100% recovery of non-rooting shoots from culture. Success of any given graft was directly related to scion size (0.8–1.0 cm) and age (14–35 days) of the seedling rootstock. The method appeared to be genotype independent, and varietal differences between rootstock and scion did not effect the rate of plant recovery from culture.