PROPAGATION

Mango trees grow readily from seed. Germination rate and vigor of seedlings are highest when seeds are taken from fruits that are fully ripe, not still firm. Also, the seed should be fresh, not dried. If the seed cannot be planted within a few days after its removal from the fruit, it can be covered with moist earth, sand, or sawdust in a container until it can be planted, or kept in charcoal dust in a dessicator with 50% relative humidity. Seeds stored in the latter manner have shown 80% viability even after 70 days. High rates of germination are obtained if seeds are stored in polyethylene bags but the seedling behavior may be poor. Inclusion of sphagnum moss in the sack has no benefit and shows inferior rates of germination over 2- to 4-week periods, and none at all at 6 weeks.
The flesh should be completely removed. Then the husk is opened by carefully paring around the convex edge with a sharp knife and taking care not to cut the kernel, which will readily slide out. Husk removal speeds germination and avoids cramping of roots, and also permits discovery and removal of the larva of the seed weevil in areas where this pest is prevalent. Finally, the husked kernels are treated with fungicide and planted without delay. The beds must have solid bottoms to prevent excessive taproot growth, otherwise the taproot will become 18 to 24 in (45-60 cm) long while the top will be only one third to a half as high, and the seedling will be difficult to transplant with any assurance of survival. The seed is placed on its ventral (concave) edge with 1/4 protruding above the sand. Sprouting occurs in 8 to 14 days in a warm, tropical climate; 3 weeks in cooler climates. Seedlings generally take 6 years to fruit and 15 years to attain optimum yield for evaluation.
However, the fruits of seedlings may not resemble those of the parent tree. Most Indian mangos are monoembryonic; that is, the embryo usually produces a single sprout, a natural hybrid from accidental crossing, and the resulting fruit may be inferior, superior, or equal to that of the tree from which the seed came. Mangos of Southeast Asia are mostly polyembryonic. In these, generally, one of the embryos in the seed is a hybrid; the others (up to 4) are vegetative growths which faithfully reproduce the characteristics of the parent. The distinction is not absolute, and occasionally a seed supposedly of one class may behave like the other.
Seeds of polyembryonic mangos are most convenient for local and international distribution of desirable varieties. However, in order to reproduce and share the superior monoembryonic selections, vegetative propagation is necessary. Inarching and approach-grafting are traditional in India. Tongue-, saddle-, and root-grafting (stooling) are also common Indian practices. Shield- and patch-grafting have given up to 70% success but the Forkert system of budding has been found even more practical. After many systems were tried, veneer grafting was adopted in Florida in the mid-1950's. Choice of rootstock is important. Use of seedlings of unknown parentage has resulted in great variability in a single cultivar. Some have believed that polyembryonic rootstocks are better than monoembryonic, but this is not necessarily so. In trials at Tamil Nadu Agricultural University, 10-year-old trees of 'Neelum' grafted on polyembryonic 'Bapakkai' showed vigor and spread of tree and productivity far superior to those grafted on 'Olour' which is also polyembryonic. Those grafted on monoembryonic rootstock also showed better growth and yield than those on 'Olour'. In 1981, experimenters at Lucknow, India, reported the economic advantage of "stone-grafting", which requires less space in the nursery and results in greater uniformity. Scions from the spring flush of selected cultivars are defoliated and, after a 10-day delay, are cleft-grafted on 5-day-old seedlings which must thereafter be kept in the shade and protected from drastic changes in the weather.
Old trees of inferior types are top-worked to better cultivars by either side-grafting or crown-grafting the beheaded trunk or beheaded main branches. Such trees need protection from sunburn until the graft affords shade. In South Africa, the trunks are whitewashed and bunches of dry grass are tied onto cut branch ends. The trees will bear in 2 to 3 years. Attempts to grow 3 or 4 varieties on one rootstock may appear to succeed for a while but the strongest always outgrows the others.
Cuttings, even when treated with growth regulators, are only 40% successful. Best results are obtained with cuttings of mature trees, ringed 40 days before detachment, treated, and rooted under mist. But neither cuttings nor air layers develop good root systems and are not practical for establishing plantations. Clonal propagation through tissue culture is in the experimental stage.
In spite of vegetative propagation, mutations arise in the form of bud sports. The fruit may differ radically from the others on a grafted tree-perhaps larger and superior-and the foliage on the branch may be quite unlike that on other branches.