Beans/seeds
Seeds are elliptical or egg shaped, plano convex processing longitudinal furrow on the plane surface. Seed coat is represented by the ‘silver skin’ which is also made up of scleroides. The size, thickness and number of pits in the wall of scleroides are considered as important taxonomic characters in evaluating differences between species. Bulk of the seeds is formed by endosperm which is hard, consisting of polyhedral (many sided) cells.
Seeds do not exhibit any dormancy. Viability is also short in coffee. Germination takes place in about 45 days.
Bean defects
Pea berry’ formation in a normal coffee plant is due to abortion of one of the two ovules in a flower at the time of fertilization. The fertilized ovule in the other locule grows into a round seed called ‘pea berry’. At times, three locules having single ovule in each locule are formed in the ovary which gives rise to triangular seeds. Endosperm sometimes shows partial development with or without any embryo. These occur commonly in floats (jollu). Formation of more than one ovule per locule is seen occasionally in Arabica, but quite frequently in S.288 and S.795. Seeds resulting from these ovules are called ‘elephant beans’. There are two types of elephant beans:
- Beans inside the parchment cover inter locked(hollow and bit)
- Seeds occurring side by side (bits). When one of the ovule gets aborted, the other functional ovule usually assumes irregular shapes (defective).
Black or spotted bean is a physiological abnormality where the endosperm is completely or partially blackened.
Arabica (coffea Arabica L)
Popularly known as ‘Arabica coffee’, it is a tetraploid species i.e., 4n=44 chromosomes. Under natural conditions Arabica grows like a small tree, but under regulated conditions looks like a bush. The plants produce profuse branches and the matured leaves are dark green in colour while the young leafs (leaf tips) are either green or bronze. The flower buds are produced in clusters in the axils of leaves at each node. Under South Indian conditions, initiation and subsequent growth of flower buds takes place from September to March. Water is essential for flowering and so the blossoms occur 8 to 10 days after showers. Arabica is self-fertile. The fertilized ovary grows into a fruit (drupe) in about 8 to 9 months and finally ripens into dark a red berry which ranges in number from 10 to 20 per node. Arabica coffee is susceptible to major pest and disease of coffee viz., coffee leaf rust and white stem borer. Arabica is considered as superior in quality to Robusta with rich flavor and aroma.
Robusta (coffea canephora pierre ex froehner)
Robusta, as the name implies, grows vigorously (compared to Arabica). It is a diploid species (2n=22) and has broad, large leaves that are pale green in colour. Flowers are fragrant and borne in compact clusters at each node. The numbers of flowers per node are higher than in Arabica. Under the climatic conditions of South India, the buds initiate during November and are ready for blossom in February and M arch, the flowers open on 7th or 8th day after rains. Unlike Arabica, Robusta is self-incompatible, I,e., the ovule of the same flowers cannot be fertilized with its own pollen. Hence, cross pollination is essential in Robusta. The fruits mature in 10 to 11 months later than Arabica. Canephara is shallow rooted and susceptible to drought. It is tolerant to major diseases and pets of coffee like coffee root rust and white stem borer. The quality of Robusta coffee is inferior to that of Arabica in bean size as well as in organoleptic characteristics like aroma, flavor and taste.
Tree coffee (Coffea liberica bull ex hiern)
Liberica is known as tree coffee because of its growth habit and is cultivated along the fence and boundary line of estates. It is also a diploid species with 2n=22 chromosomes. The leaves are dark green, leathery and are 2 to 3 times larger than Arabica. The flowers are large and fleshy. Flower to fruit maturity is slow; taking about a year. The fruits are larger in size than Arabica and are yellow to reddish-brown on colour. Cup quality is generally considered inferior to Robusta.