Studies of vegetative propagation of the lychee (Litchi chinensis ...

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W. S. Abutiate & N. Y. Nakasone (1972) Ghana Jnl agric. Sci. 5,201-211 Introduction Incompatibility between stock and scion has Litchi chinensis (Sonn.), a subtropical fruit tree, also been put forward by Mergen (1954) as another belongs to the family Sapindaceae, the Soapberry possible explanation for graft failures. Other family. The tree is evergreen, low-branching and workers (Buck, 1953; Kostoff, 1928; Saas, 1933) round-topped with pinnately-compound leaves have dwelt on the origin of the unifying callus borne on generally brittle branches. Growth tissue, the absence of which results in graft failure. occurs in flushes, there being several flushes in a Venning (1949), in his study of the anatomy and year. The small flowers are apetalous and are borne secondary growth in the axis of the lychee, stated on leafless terminal inflorescences. All evidence that successful grafting depends upon the activpoints to the probability that lychee is native in ities of the vascular cambium. Southern China where its cultivation is well Rapid multiplication of new cultivars in many established. Its culture has spread to part of South plants is accomplished universally by cuttings, Mrica, Hawaii and Florida (Chadler, 1958). budding or grafting methods. The need for The plant is propagated commercially by air- accurate diagnosis of the causes of graft failures, layering. There has been very little success with especially in hard-to-root or hard-to-graft subjects, grafting and rooting of cuttings, even with the aid seems worthwhile. of rooting hormones. Many reasons have been put This investigation was an attempt to elucidate forward by workers to explain the low success of the causes of side-graft failures in the lychee and vegetative propagation in various plants. Fahmy the ways and means of overcoming them to achieve (1952) states that successful graftage involves the commercially feasible propagation. interplay between the external and internal environment of the plant or part of the plant used. Carbohydrate, the main energy source fOl plant activity is thought to be one of the limiting factors in the successful vegetative propagation of plants (Carlson, 1929; Kraus & Kraybill, 1918; Schrader, 1924; Starring, 1923). Working with macadamia, Jones & Beaumont (1937) recorded an increase from 10% to 75-80 % graft takes with girdled scions. They also found that starch accumulation rarely exceeded 0·4 to 0·5 % of the branch dry weight in non-flowering branches of lychee but when branches were girdled for 3-4 weeks, starch reserves rose to 11·4 %. Even though photoperiodism has not been shown to improve graft take, its beneficial effects have been shown in the rooting of cuttings, seed germination and abscission (Nitsch, 1957). Photoperiodic effect on cambial activity has also been shown experimentally by Mollart (1954). However, Snyder (1955) working with Taxus cuspidata failed to find any significant photoperiodic effect on cuttings of this subject. Since the accumulation of photosynthates in plant parts depends in part on the amount and quality of light received, one might expect daylength, through its effect on carbohydrate synthesis to influence vegetative propagation, especially grafting and rooting of cuttings when plant parts high in carbohydrates are employed. Materials and methods The study was divided into two parts. The first part deals with the effect of root-inducing hormones on root development in the girdled and non-girdled stem cuttings, whilst the second part involves the effect of girdled and non-girdled scionwood and daylength on graft take. The experimental plants consisted of three popular cultivars of lychee, Kwai Mi, Hak Ip and Brewster, grown at Kona and the Poamoho Branch Stations. Rooting experiments Suitable branches of the three cultivars were girdled both at Poamoho and Kona in March and April 1965. Thirteen to 15-em cuttings with two to three leaves were taken from both girdled and non-girdled branches at Kona on 4 June, treated with the appropriate concentration of NAA-Na and IBA and set in vermiculite with mist and without mist in a polyethylene enclosure. Similar cuttings were taken from Poamoho on 22 June and set under the above regime on 23 June. The experiment was set up in a randomized block design with four replications of 10 treatments. Each treatment consisted of 15 cuttings for the Kona material but six to 10 for the Poamoho material. Treatments were as follows: Control,
2000, 5000 and 10 000 ppm each of NAA-Na and IBA separately and 2000, 5000 and 10000 ppm mixture of equal parts ofNAA-Na and IBA. Treatments were prepared as powder to which 10% Dithane M-45 fungicide was added. Both vermiculite and air temperatures were recorded at 9 am, 12 noon and 3 pm (local time) at 2-day intervals for 8 weeks and thereafter at 1O-day intervals. Relative humidity within the polyethylene enclosure was recorded by a hygrothermograph. At termination of the experiments on 9 & 17 November for the Kona and Poamoho subjects respectively, the cuttings were dug up, and the number rooted, the number of roots per cutting, the average length of roots, the number callused and the number dead were recorded. Grafting experiments Rootstocks for these experiments were obtained from the Poamoho Experimental Station. Four hundred and thirty suitable branches were selected on each of the three cultivars and air-layered. When enough roots developed, the air-layers were harvested and potted in 3-gallon cans and set in shade until a new flush of growth appeared, after which they were acclimatized. In September 1965, 70 air-layers each of Kwai Mi, Hak Ip and Brewster were transferred into nursery rows on the Manoa Campus Experimental Farm. The remaining air-layers were left in the cans for the photoperiod experiments. Scionwood for the grafting experiments also was obtained from the three cultivars at Poamoho. For scionwood, branches 0·6-1·0 em in diameter were selected from mother trees and girdled on 9 Oct 65. Girdled and non-girdled scionwood were harvested on 9 December, and 8-10-em scions were sidegrafted to 60 each of the three stock cultivars under normal daylength. For the 8- and the 16-hour day photoperiods only Hak Ip rootstock was used with girdled scions from the three cultivars. All rootstocks were side-grafted on 10 December and then transferred to their respective photoperiod regimes. The 16-hour day plants received 9·5 h sunlight daily and 6·5 h supplementary light from two 100-watt incandescent bulbs suspended 0·9 m above the tops of the plants. The experiments were terminated on 10 Mar 66 and percentage takes were recorded for each treatment. Successful grafts were then harvested, fixed in Craf III solution for 5 days and then transferred to 70 % ethyl alcohol until sectioned. Sections were cut on the sliding microtome at 25fL without embedding, stained in Safranin and Fast Green and mounted in Canada Balsam. Histological studies For histological studies inarching technique was employed. However, a few Kwai Mi and Brewster side-wedge grafts were also made. One hundred and forty air-layers of the three cultivars in cans were inarached in different combinations on 5 Nov 65. The first grafts were harvested 2 weeks later and then at 10-day intervals thereafter until January 1966. The last harvest was taken on 10 March, 115 days after inarching. All grafts were fixed, sectioned, stained and mounted as previously described. Sample preparation and carbohydrate determination Girdled and non-girdled sample twigs from Kona and Poamoho were harvested at the same time of taking cuttings for rooting. Twigs were chopped up, oven-dried at 60°C for 12 h and ground in a Wiley Mill with a 4-mm mesh. Similar twigs used as scionwood in the grafting experiments were also taken for analysis. For these latter determinations, girdled twigs were sampled at 3-week intervals until scions were taken for grafting at 9 weeks. Samples taken from nongirdled twigs on each date served as controls. The samples were prepared as already described. Two determinations were made for each sample and the mean recorded. Sugar was extracted from 2 g samples with 90 em 3 of 80 % ethyl alcohol. Total sugar was then estimated in 5 em 3 aliquots according to the Shaffer-Somogyi Micro Method (Horwitz, 1960). For starch determination, the residue from each 2 g sample after sugar extraction was digested with diastase solution for 30 min at 38°C, then refluxed with concentrated hydrochloric acid for 2 h. The resultant solution was filtered and 2 cm 3 aliquots used in the determination of the reducing power of sugar (Horwitz, 1960). The Shaffer- Somogyi Dextrose- Thiosulphate Equivalent Table (Horwitz, 1960) was used for the estimation of total sugar. A factor of 0·90 (glucose to starch) was used to convert percentage sugar to starch.
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