Reproduction of horticultural crops

Plant species extend themselves in two ways, sexually or asexually. Reproduction through seed is sexual, except some parthenogenetic species which do not involve sex. Seeds of some species, including mango, give rise to more than one seedling per seed.

Reproduction of horticultural crops through seed

Reproducing horticultural plants from seed has various drawbacks. Ordinarily, when cross-pollinated plants produce seeds, the seedlings do not bear the characteristics of their parents. It takes so long for fruit trees to come into bearings and have the potential to grow tall, which may increase maintenance and harvesting costs. 

However, reproduction through seed also has some goodness. Seedlings are generally hardy, bear heavy crops, and are long-lived. Moreover, it is vital in the breeding of hybrids and new varieties. It can also raise seedlings that we can use as rootstock in vegetative propagation. 

Preparation for sowing

We should consider several factors before actually sowing the seed. 

Collection of seed: 

Collecting seeds from authentic sources can reduce the chances of seedling variation. We should select those fruits for seed extraction which possess good fruit and high-quality characteristics. In most cases, they should be healthy and fully mature and have a high degree of disease resistance. 

Storage of seed:

Seeds of most of the evergreen fruit species lose viability soon after extraction. Growers should sow them before any prolonged storage period. If it is necessary to store seeds, carefully wash them, surface dry, mix with an equal part of charcoal, and pack in suitable containers and store them in a dry and cool place. 

Pre-germination seed treatment:

In some deciduous fruit species, like apple, pear, peach, plum, and cherry, the seeds need a certain period of rest after extraction before they will germinate. To store such seeds, place them with alternate layers of moist sand, at a controlled cold temperature and suitable moisture conditions before sowing. This process is called stratification. It allows the embryos in the seeds to complete their development. 

Plants with hard shells like ber and guava need to have the seed coat cracked or softened by soaking in water for several hours or days. 

Sowing:

The seed is either crop up in pots, trays, or plastic bags; or in beds in nursery rows. When we need a small number of seedlings, we sow seeds in earthen pots, wooden trays, plastic bags. The container consists of a potting mixture of equal parts of topsoil, sand, and well-rotted leaf mold or FYM. 

Methods of asexual propagation

Asexual or vegetative reproduction uses a part of the plant for multiplication. Growers use stems, leaves, buds, roots, bulbs, corms, rhizomes, suckers, and tubers as plant parts. Plants resulting from asexual reproduction are identical to parent plants in all aspects. These traits result in saving in cultural operations and make harvesting of the crop and its marketing easier. 

In budding and grafting, use only the most compatible scion and rootstock combinations. Incompatible combinations result in poor bud take, weak graft or bud union, overgrowth of stock as compared to scion or vice versa, low disease resistance, excessive leaf drop, earl decline, low yields of poor quality fruit, and short life span.

Budding

Budding is relatively easy to do. Experts use it in the vegetative propagation of vast numbers of species of fruit and flowering trees, particularly evergreens. Generally, there are four different methods of budding.

Shield budding or T-budding

This type of budding is the most common method of vegetative propagation of citrus, jujube, apple, loquat, roses, and many other ornamental trees and shrubs.

Pre-condition the rootstock seedling and bud wood and prepare when the sap is moving freely. For convenience in handling, before removing the buds, the leaf blades are cut off, leaving the petioles intact. Remove a narrow shield of bark 3-4cm in length, with a single bud. The shield will have a thin layer of wood. On the rootstock, make a vertical cut 3-4cm in length just through the bark. At the top end of this cut, make a horizontal cut about 1.25-1.5cm long, so that the cut resembles the letter T. Use the plastic or bone spur of the knife, insert the bud in the bark after loosening it from the wood. To hold the bud firmly in position and to exclude air and moisture, wrap the bud union carefully using stable plastic strips and keep the bud exposed. 

Ring budding

In this method, loosen a ring of bark 1.5-2cm in length, containing a well-developed bud on the scion shoot and gently pull out from the thinner end of the shoot. Use handkerchief in pulling off the ring, to avoid injury to the bud. Remove the top of the stock seedling and peel off the bark downward where the ring of the bark bearing the bud fits tightly. No tying is necessary in ring budding. 

Chip budding

Place a single bud with a large piece of wood on a corresponding cut on the stock and tie it firmly. Growers use this method rarely. 

Flapped-patch budding

Loosen a rectangular or square flap of bark on the stock on three sides. Insert the corresponding bud shield underneath the loosened flap of bark. Then place the flap over the bud shield and wrap it. It takes about two months for the bud to sprout. Remove the wrapping material after this. 

Grafting methods

Inarching or approach grafting

Unlike other grafting operations, in inarching, attach the scion to the stock while it is still attached to the parent plant. In Pakistan, this method extensively produces mango. The method involves potting healthy one-year-old seedlings in earthen pots, which are usually 12 inches deep and 8 inches wide at the top. Kepp the earth ball intact along with the root system and place it in the pot. Fill the unfilled space in the pot with a mixture of well-rotted manure and canal silt. Press the soil firmly around the earth ball and water the transplanted seedlings. 

Bring the potted seedlings near the parent plant for inarching. The size of the rootstock and scion shoot should be the same. Make a slanting cut of about 5 cm long and 2cm  deep on the stock seedling at the height of 15-20cm. Make a similar cut on scion shoot and bring together the corresponding cuts and tie them with plastic film.