Sorghum is a member of the grass family and originally a wild plant in Africa. 

The evolution of sorghum under the pressures of drought and high temperatures imparted the ability to tolerate drought, soil toxicities, and extremes of temperature more effectively to cultivated sorghum plants than other cereals.

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Varieties of sorghums are classified into 4 groups:

• grain sorghums
• grass sorghums or forage Sorghum
• sweet sorghums and
• broomcorn.

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Grain sorghums are grown for the grain - round, starchy seeds used as human food or cattle feed.

 

Grass sorghums are grown for green feed (forage) and making silage or hay (dried

fodder)

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Sweet sorghums have sweet juicy stems and are grown for making sorghum syrup. Sweet sorghums can also be used for animal feed or for making silage.

Broomcorn is grown for the branches of the seed cluster, which are used to make brooms

 

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Germination: At optimum temperature (25 to 300 C) and moisture, the sorghum seed germinates in 3 to 5 days. When sorghum seed is sown in moist soil, the seed swells due to moisture absorption. The seed coat breaks a small shoot (coleoptiles) and a primary root (radicle) emerge.

Initially the young seedlings take nutrients from the endosperm of the seed.

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Seedling Development: The shoot (coleoptiles) emerge from the ground and first leaf breaks through the tip. The mesocotyle grows during this period and a node is formed at the base of the coleoptiles just below ground level.

Secondary roots begin to grow from this node, 3 to 7 days after the plant emerges from the soil. Seedlings get the nutrients through these roots. 

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Root system: The sorghum root system consists of 3 types of roots: Primary roots Secondary or Adventitious roots Brace or Buttress roots

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Primary roots: These roots develop from the radicle and die subsequently.

 

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Brace or buttress roots These roots develop from the first node from the mesocotyle. These rots occupy 5 to 15 cm area in the soil around the base of the stem.

 

Adventitious roots are small, uniform, and form a small portion of the root system. Another type of permanent adventitious roots develop from the second internodes and above. These roots are branched laterally (about 1 sq.m) interlacing the soil vertically. These roots mainly supply nutrients to the plant.

 

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Secondary or Adventitious roots: These roots develop from the root primordia of the basal nodes above the ground level. They are stunted, thick, and above ground level. These roots provide anchorage to the plant.

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Shoot system: Sorghum shoot system consists of stem, leaves, nodes, and internodes during the vegetative stage. Leaves nodes develop @ of one in 3 to 6 days. The plant remains in vegetative stage for 30 to 40 days during which all leaves (12 to 18) are formed.

 

The stem of sorghum consists of many alternating nodes and internodes. It ranges from slender to very strong, 0.5 to 5 cm in diameter near the base.

The length of stem varies between 0.5 to 4 m depending on the variety. A bud is formed at each node. At time, these buds develop tillers. About 6 to 10 days before flowering, the boot forms a bulge in the sheath of the flag leaf (uppermost leaf). This stage is called boot leaf stage. Sorghum usually flowers 55 to 70 days.

The flowering structure (inflorescence) in sorghum is called as panicle or head. In cultivated sorghums, the panicle starts developing from 30 to 40 days after germination.

 

The tiny panicle can be observed by carefully cutting the stem of a 30 t0 40 days plant.

Two days after the emergence of the inflorescence from the boot, the flowers begin to open. The flowering can be observed from the yellow pollen from the anthers on the panicle (sorghum head).

The maximum flowering takes place on 3rd or 4th day. It takes 6 days for the whole inflorescence to complete flowering.

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Seed Development: The sorghum seed is called grain. The grain matures in 30 to 35 days after fertilization. Sorghum seeds are spherical in shape but some what flat on one side.

 

The seeds vary in color - red, brown, white, yellow, or cream and are with a dull or pearly luster.

 

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Physiological maturity: Maximum total dry weight of the plant reaches at the physiological maturity. Uptake of nutrients also mostly cease at this stage. So, if there are problems like bird damage etc. it is advantageous to harvest the crop at this stage. As the seed moisture at this stage will be around 25 to 35%, proper drying of the seeds is important. Physiological maturity can be determined by the dark spot on the seed.

 

The seed on the left is physiologically mature; the one on the right is not. The cultivated sorghums mature in 100 to 140 days depending on the variety.

The right time to harvest sorghum is at the physiological stage of the plants or when the seed moisture content is below 25%.The subsequent Modules in this course deal with the important insect pests that attack sorghum crop.