Uniform Rootstock Research Articles

Genetic and epigenetic uniformity of polyembryony derived multiple seedlings of Hevea brasiliensis.

Hevea brasiliensis Muell. Arg (Para rubber tree) is a tropical tree species of Amazonian origin widely cultivated in several parts of the world for natural rubber, a highly priced commodity inevitable for the world rubber industry. Large, tree to tree variation in growth and latex yield among individual plants of high yielding Hevea clones is a common phenomenon observed in mature rubber plantations. The genetic heterogeneity of the seedlings which are used as rootstocks for propagation through budgrafting is considered as a major factor responsible for this variation. In order to minimize this variation, attempts were made to develop highly uniform rootstock material via an in vitro technique by inducing zygotic polyembryony in Hevea. Immature open pollinated fruits of a high yielding clone RRII 105 were cultured by half ovulo embryo culture technique. Multiple embryos were induced from the 8-10-week-old zygote with a novel combination of gibberellic acid (GA3), kinetin, and zeatin. Plantlets were successfully generated from the multiple embryos and raised in the field post hardening. Screening using genetic and epigenetic molecular markers revealed that the multiple seedlings developed are highly uniform and are of single zygotic origin. Development of plants having genetic and epigenetic uniformity suggests that this technique is ideal for raising uniform rootstock material in Hevea which may significantly reduce intraclonal variations. Moreover, these plants could serve as ideal material for physiological and molecular investigations towards the understanding of stock-scion interaction process in rubber.

The development of techniques for tissue culture of mango (Mangifera indica L.) var. Carabao and successful transfer of ex vitro-grafted plants to soil and the field

The mango, a virtually neglected fruit before the advent of nitrate-induced flowering, is now the third leading export fruit in the Philippines, with the ‘Carabao’ mango being the only variety exported. Delay or control of ripening, as well as the ability to program market availability, would further increase the value of mango. Prolonging its shelf life and improving other characteristics can be achieved through biotechnology, requiring a reliable tissue culture regeneration protocol, and a successful transfer-to-soil system. Between 2004 and 2008, immature fruits were collected and cultured in vitro. Primary somatic embryo (SE) induction ranged from 16–100% depending on the strain, collection time, and tree source. A single SE was required to initiate SE proliferation. When subcultured, the SEs proliferated, germinated, and produced plantlets. Initial shoot formation was 8–64%, while succeeding true leaf formation was reduced to 0–36%. In some cultures, abscission and browning were observed, but gas chromatography assays ruled out ethylene as the cause. Regenerated plants survived transfer to soil, but at low percentages. While it took 1 y to develop the tissue culture protocol, it took 3 y to develop the technique for successful transfer of plantlets to soil, and to the field. This is the first report, of a polyembryonic mango, variety Carabao, for which successful tissue culture and field transplantation systems were developed. The technology is equally important as a way to rapidly propagate uniform rootstocks of superior ‘Carabao’ strains or other varieties, for generation of variability, genetic transformation, and for germplasm conservation and exchange.

Indução de brotação apical em mudas provenientes de sementes e do enraizamento de estacas de mangostãozeiro

With the objective to induce apical bud sprouting in young mangosteen seedlings an experiment was carried out with the application of the plant growth regulators kinetin (0, 100 and 400 mg L-1) and gibberellin GA4+7 (50 mg L-1). To obtain rooted cuttings two other experiments were performed: a) application of indolbutyric acid at the concentrations of 0, 100, 500 and 1000 mg L-1 and b) application of α naphtaleneacetic acid, at 6000 mg L-1. In these trials cutting from orthotropic branches were utilized. The results indicated the possibility of using plant growth regulators to obtain more uniform root stocks in a shorter nursery stage and, despite the low percentage of rooting the planting material obtained from cuttings has a great practical potential, since the size of the rooting cuttings is equivalent to that of one year old seedlings.

Indução de brotação apical em mudas provenientes de sementes e do enraizamento de estacas de mangostãozeiro

With the objective to induce apical bud sprouting in young mangosteen seedlings an experiment was carried out with the application of the plant growth regulators kinetin (0, 100 and 400 mg L-1) and gibberellin GA4+7 (50 mg L-1). To obtain rooted cuttings two other experiments were performed: a) application of indolbutyric acid at the concentrations of 0, 100, 500 and 1000 mg L-1 and b) application of α naphtaleneacetic acid, at 6000 mg L-1. In these trials cutting from orthotropic branches were utilized. The results indicated the possibility of using plant growth regulators to obtain more uniform root stocks in a shorter nursery stage and, despite the low percentage of rooting the planting material obtained from cuttings has a great practical potential, since the size of the rooting cuttings is equivalent to that of one year old seedlings.

Tree Fruit Rootstock Development in Arkansas

The Arkansas tree fruit research program has a history of involvement in rootstock development. The elements of rootstock development are rootstock cultivar testing and rootstock breeding and evaluation. Research is focused on apple and peach rootstocks. Rootstock testing is done in conjunction with the NC-140 cooperative uniform rootstock research project. Currently, there are 10 NC-140 trials in progress for apples, peaches, pears, and cherry rootstocks in Arkansas. The Arkansas rootstock breeding projects were established in the early 1970s as components of the fruit breeding program. The objectives are to develop apple and peach rootstocks which are adaptable to the Arkansas edaphic and adaphic conditions, have size control, have some degree of pest resistance, and are efficient in production. To date, 92 apple rootstock selections have been made and 41 are still in early evaluation for propagation and growth characteristics, while 56 peach rootstocks have been selected and are in early evaluation. Arkansas apple rootstocks selections are sequentially numbered with numbers preceded by AAR (ex: AAR-92). Peach rootstocks selections are numbered with numbers preceded by APR. Data from 2 NC-140 apple rootstock trials were presented and discussed.

Apple Shoot and Trunk Growth as Affected by Rootstock

Annual shoot and trunk xylem growth increment of `Starkspur Supreme' in the 1984 NC-140 uniform rootstock trial was studied of 10 selected rootstocks representing a range of tree sizes. Shoot growth was measured weekly from budbreak through harvest in each of four seasons. After 11 seasons of growth, whole trees were cut, placed in water containing diffuse fuschin dye for 30 to 60 min during mid-day. After that, a section of trunk (10 to 15 cm long) was excised at 25 cm above the graft union. Trunk xylem thickness and percent of water transport active xylem were measured. Shoot length during the study was related to both the duration and rate of growth; however, growth duration contributed more to variation among stocks. In all stocks, it appears that almost all xylem translocated water and that there was very little “plugged” or active xylem. There were no differences among stocks for the relative percentage of active xylem. Annual xylem increment width varied with stock. The vegetative growth of these trees will be discussed relative to the production efficiency of scions on these stocks.

Apple Shoot and Trunk Growth as Affected by Rootstock

Annual shoot and trunk xylem growth increment of `Starkspur Supreme' in the 1984 NC-140 uniform rootstock trial was studied of 10 selected rootstocks representing a range of tree sizes. Shoot growth was measured weekly from budbreak through harvest in each of four seasons. After 11 seasons of growth, whole trees were cut, placed in water containing diffuse fuschin dye for 30 to 60 min during mid-day. After that, a section of trunk (10 to 15 cm long) was excised at 25 cm above the graft union. Trunk xylem thickness and percent of water transport active xylem were measured. Shoot length during the study was related to both the duration and rate of growth; however, growth duration contributed more to variation among stocks. In all stocks, it appears that almost all xylem translocated water and that there was very little “plugged” or active xylem. There were no differences among stocks for the relative percentage of active xylem. Annual xylem increment width varied with stock. The vegetative growth of these trees will be discussed relative to the production efficiency of scions on these stocks.

FORMATION AND ROOTING OF ADVENTITIOUS SHOOTS IN HEVEA BRASILIENSIS

YOUNG PLANTS often differ both morphologically and physiologically from older plants of the same species. For example, immature trees of various species often have more thorns, greater vigor, and a more erect habit than mature plants (Furr et al., 1947) and different leaf shapes (Stoutemeyer, 1937). Numerous photoperiod-sensitive species do not respond to photoperiodic treatment when very young, and others which display marked sensitivity to day length when young, lose it with age (Naylor, 1953). Sometimes adventitious or juvenile shoots on older plants can be used for propagation, whereas cuttings from branches of mature trees root poorly if at all (Stoutemeyer, 1937; Dermen, 1948). The problem of juvenility is of particular interest in the Para rubber tree (Hevea brasiliensis (Wild. ex. Adr. Juss.) Muell. Arg.), in which cuttings from young trees regenerate roots readily, but cuttings from old trees do not root at all (Baptist, 1939; Muzik, 1953). The rubber tree generally is propagated by budding, but the effect of stock on yield is still unsettled (Dijkman, 1951). Stahel (1947) reported the rooting of cuttings from Hevea trees of seedling origin under a water spray. This paper describes methods to induce the development of adventitious shoots on seedlings and mature trees of Hevea brasiliensis and compares the rooting ability of these shoots to axillary shoots. Such studies are of fundamental interest in relation to the general phenomenon of juvenility in plants as well as of potential practical interest in developing uniform rootstocks for experimental purposes. The long first internode (epicotyl) in seedlings of Hevea brasiliensis has been described by Calvert (1887) and Petch (1911). The length of this internode is fairly constant within a population but mav vary from 12 to 23 cm. in mixed plantings. The buds at the first node are opposite but they are alternate on the rest of the stem, thus making it easy to distinguish this node. The first internode was very useful in the present study because any buds which sprouted in this region must necessarily be of adventitious origin. On ordinary stems it is often difficult to determine the exact origin of new sprouts. MATERIALS AND METHODS.-The stems of rubber seedlings from 3 weeks to 18 months of age were excised at various heights to stimulate bud sprouting. A similar study of grafted plants was also made. Mature clonal trees were laid horizontally