VARITIES AND PROPAGATION OF ANNONA

Varieties

           Custard-apple seedlings are found growing wild in India. Since custard-apple is a cross-pollinated crop, wide variation in forms and sizes of fruit as well as colour of the pulp are available. This natural variability available within the species is often exploited to identify superior gentoypes which are usually named after the place of collection or selection and fruit colour. Depending on external fruit colour, custard-apple is distinguished into green, red and yellow. But green ones are by far more common and popular than the other types. Balanagar, Barbados Seedling, British Guinea, Kakarlapahad, Local Sitaphal, Mahaboobnagar, Saharanpur Local and Washington are some of the varieties with green skin. Most of these varieties are not easily identifiable. Some of the traits that distinguish them are fruit shape and size, form of areoles and number of seeds/fruit. But in fruits of a given tree, these attributes vary considerably as they are largely influenced by pollination and the environment. Thus, the varietal or genetic differences get masked confusing the varietal identification. Moreover, variety-specific pulp qualities are not clearly explained. However, some varieties can be recognized by the plant habit and foliage attributes. Two natural hybrids (mostly between custard-apple and cherimoya), Israeli Selection and Israeli Hybrid, have been introduced. Fruits of both are less seeded. A hybrid Arka Sahan has slow ripening (6–7 days), better shelf-life (2–3 days), less number of seeds (10/100g fruit weight) and high brix (31°). On an average its fruits weigh 210g each. A 6-year-old plant yields 17kg fruits. Other annonas are usually propagated by seeds. There are no well-recognized varieties used for cultivation.

Propagation and rootstock

     Most of the annonas are traditionally propagated by seeds. The seed viability lasts for 3–4 years. However, fresh seeds germinate better. Hard seed-coat can be softened either by soaking the seeds in water for 2–3 days or keeping them under running water for 50–70hr. Treating seeds with GA₃ at 500ppm assists germination. Seeds are sown 2cm deep either in nursery beds or in pots under partial shade. Regular watering is necessary to maintain good soil moisture. Seeds are slow to germinate and take 3 weeks. Nevertheless it may extend to as long as 8–10 weeks. When seedlings are 10–12cm tall, they are transferred to pots or plastic bags containing sand and peat or equal parts of garden soil, sand and decomposed farmyard manure. The 30cm tall seedlings become ready for transplanting.

Seed originated plants are not true-to-type, lack precocity and vigour, whereas grafting or budding helps largely to overcome these drawbacks. A. squamosa, A. reticulata, A. cherimola and A. atemoya are grafted or budded on their own species and each other. A. muricata can be grafted on A. reticulata and A. glabra. However, A. reticulata which promotes vigour and shows good graft congeniality is commonly employed as a rootstock for most of the annonas.

         Generally, 18-month-old or 30cm tall plants having pencil thickness are selected for grafting. Scion of well-matured wood from which the leaves have dropped at the end of the dormant phase is used to graft either by veneer or cleft technique. Shield or T-budding carried out in spring is also equally effective. Patch and chip budding are other methods. Large buds, about 4cm in length, collected from 1-year-old wood after the leaf drop give good success. The graft should be uncovered once it has taken in order to avoid rots. Since propagation by cuttings and air-layers gives poor results, they are not widely practised. Commercial production of plants through tissue culture is not yet successful. However, multiple shoot production from leaf explants of seedlings and root initiation from shoots are successful.