Page 42 - Introduction to Agriculture by: Aqleem Abbas

Introduction to Agriculture Notes prepared by: Aqleem Abbas

Based on propagation
More plants are produced from single desirable plants to preserve its characteristic. A successful method
is one that transferred all the desirable characters.

Sexually propagated.
These crops are propagated by seeds. Most common for example wheat, maize etc.

Asexually propagated plants

Propagated by using special parts or using certain techniques like cutting, grafting, budding and layering
e.g. sugarcane, potato

Modes of photosynthesis or plant efficiency

This classification is based on the effective utilization of resources and mode of carbon dioxide fixation

1. C3 plants or inefficient plants
2. C4 plants or efficient plants
3. Crassulation acid metabolism plants

C3 plants or inefficient plants

During photosynthesis, some plants fix carbon dioxide and form a three carbon molecule called 3-
phosphoglyceric acid. This pathway was first worked out by calvin and his co-workers(basham and calvin
1957). Plant with this pathway of carbon-assimilation is called C3 pathway plants. Such plants cannot
utilize carbon dioxide, light, temperature and water efficiently. Therefore they are called inefficient plants

e.g. wheat, oat, rice, soybean, rye , banana, cotton

C4 plants or efficient plants (hatch and slack)

Another pathway of carbon dioxide fixation was found in some plants by Hatch and Slack (1966). In
these plants the first product of photosynthesis is a four –carbon molecule. Plants which fix carbon
dioxide in this way have no photorespiration and make efficient use of carbon dioxide, light, temp and
water. Therefore these plants are called efficient plants. E.g. sugarcane, maize, sorghum.

Crassulation acid metabolism

Cam plant fix carbon dioxide into 4-carbon acids as do the c4 plants but fixation of carbon dioxide occurs
at night when the stomata are open. Typical cam plants grow in deserts and have succulent fleshy leaves
and stems with low transpiration and water requirement e.g. pineapple, prickly pear and cactus.