THE SORGHUM PLANT, GROWTH STAGES AND ASSOCITED MANAGEMENT PRACTICES By IDK Atokple
Trait Bicolor Guinea Caudatum Kafir Durra Panicles Medium sized open panicles with long, slightly stiff rachis branches Long, loose, glabrous, and pendulous Medium to large, oblong, dense to slightly open, hairy with stout peduncle with rigid primary branches Erect, elongated, mostly semi compact and cylindrical panicles Stiff, dense, compact, ovate to oblong, covered with dense pubescence; branches short, semi-erect, hairy; rachis elongated or hidden; peduncles often recurved, but occasionally erect Glumes Long, clasping, thick and coriaceous with obscure nerves, lower glumes are depressed and hairy Involute, opening widely, hairy; awns conspicuous Coriaceous, shorter than the large grain, pubescent Glossy at maturity, moderately coriaceous, and much shorter than grains Coriaceous on the lower half and slightly to strongly depressed with a central transverse wrinkle, tends to be lightly pigmented Spikelets Pedicellate- persistent Pedicellate- both persistent and deciduous; Sessile- open when mature, thus exposing the grain Pedicellate- deciduous; Sessile- ovate to elliptical Sessile- hairy Pedicellate- large, persistent; Sessile- Obvovate elliptic or rhomboidal Grains Elliptic to subglobose, enclosed by the glumes, persistently attached to the panicle, pigmented Small to medium, biconvex and nearly ovate, some flattened, slightly pigmented Flat on one side and round or bulging on the other (turtle backed), chalky white or pigmented Broadly elliptic, sometimes compressed, flattened or biconvex Medium sized to large, biconvex with broad tip, wedge-shaped base.
Sorghum Plant Stem Nodes and internodes Length – 0.5 to 4.0m Diameter: 0.5 to 5.0 cm Leaf Alternate arrangement in two rows Sheath+blade/lamina Width: 1.5 to 13cm Length: 30 to 135cm Number: 7 to 30 Panicle Compound raceme Width: 2 to 20cm Length: 4 to 25cm Central rachis; 1o,2o,3o branches Peduncle: erect or recurved Spikelets in pairs – i) sessile & bisexual; ii) pedicillate & male/sterile; Terminal sessile has two pedicillate spikelets
Outer glume Inner glume Outer lemma Inner lemma Outer palea Inner palea Lodicules Anther Filament Stigma Style Ovary
Anthesis Sorghum - often-cross pollinated crop Flowering pattern: basipetal Lodicules swell, create pressure on glumes – flower opens Stigma, anthers emerge simultaneously, varietal differences exist Flowering starts in 1-4 days of complete panicle exertion Flowers in a horizontal plane open at the same time. Flowering is completed in 7 to 8 days – depends on size of panicle, temperature and humidity at flowering, genotype. Pedicellate spikelets flower 2 to 4 days after the sessile spikelet on the same branches. The blooming occurs at early in the morning at about midnight 2 am and continues until 8am in south India
Pollination Primarily wind pollination Filaments elongate rapidly, anthers become pendant Pollen viability – 3 to 6 hours in anther sac, 20 min. after release, depends on weather Stigmas receptive for a day or two after blooming, but up to a week reported, depends on weather 2000 to 4000 sessile spikelets in a single inflorescence 5000 pollen grains in each anther on an average Pollen under refrigeration is capable of fertilization for 3 to 4 days
Seed Development After fertilization, ovule develops, changes color - light green, cream-colored; dark green to genotype specific color at maturity Grain development stages - milky, soft dough, hard dough, physiological maturity, maturity Physiological maturity – max. dry wt., black layer at the hilar region Seed moisture level - 10 to 15% at 20 to 25 days after physiological maturity Seed harvested at any time from physiological maturity to seed dryness; seed with more than 12% moisture to be dried before storage. Seeds harvested and dried at physiological maturity – good quality
Growth stages Stage 0 (Emergence) Seedlings seen above the soil surface. Takes about 4 days. Emergence depends on depth of planting, seed vigor and soil moisture, temperate and physico-chemical characteristics. Management guide: Adequate moisture in the top 015 cm soil profile to be maintained. Use of pre-emergence herbicide, atrazine (@ 1.0 kg ha-1) immediately after planting will prevent weed growth. In case of crust, light sprinkler irrigation allow rapid emergence.
Stage 1 (3-leaf stage) Seedlings have three fully expanded leaves Occur at 6 days after emergence (DAE) Seedlings grow to a height of 20 cm. Management guide: Weed control is crucial for increasing crop yields. Seedlings are infested by shoot fly at this stage.
Stage 2 (5-leaf stage) Seedlings have five fully expanded leaves Occur at 16 days after emergence (DAE) Seedlings grow to a height of 50 cm. Seedlings enter in to ‘grand period of growth’ Management guide: Shoot fly, weed competition, nutrient, and water stress reduce the crop stand. Prolonged cold, wet, and cloudy weather causes purple coloring on the leaf sheath and blades, besides iron chlorosis. Crop should be thinned to one seedling per hill Soil application of carbofuan 3G (20 kg ha-1) or phorate10G (15 kg ha-1) for shoot fly; and need-based application of carbofuran 3G or phorate 10G inside the plant whorls (@ 8 and 12 kg ha-1) at 30 and 45 DAE protects the plant from stem borer damage.
Stage 3 (Panicle initiation stage ) Identified at 32 DAE Meristem transforms from vegetative (leaf producing) to reproductive phase (panicle producing) Seedlings grow to a height of 95100 cm, develop 9-10 leaves, depending upon maturity group, and the basal 23 leaves become senescenced Panicle initiation can be observed Culm growth increases rapidly following this stage. Management guide: Top-dressing of nitrogen fertilizer to hasten the panicle growth Inter-cultivation and weeding promotes root growth and conserve the soil moisture Stem borer can be managed with the application of carbofuran granules inside the plant whorls
Stage 4 (Flag leaf (final leaf) visible) Identified at 50 DAE Appearance of tip of flag leaf in the whorl Exhibit rapid leaf and culm elongation Seedlings grow to a height of 115-120 cm, All the leaves except the top 34 are expanded, and the basal 35 leaves may be dropped due to senescence Management guide: Severe water, nutrient and insect pests damage reduces the potential seed number Inter-cultivation should be avoided to prevent pruning of expanding root system, loss of soil water, and nutrient uptake. Continuous stem tunneling by the spotted stem borer may delay the emergence of flag leaf.
Stage 5 (Boot stage) Identified at 60 DAE Swollen flag leaf sheath enclosing the panicle, gives the appearance of boot shape Maximum leaf area attained and panicle development completed Seedlings grow to a height of 125-130 cm Plant experiences high water demand Management guide: Severe drought stress during this stage may shorten the peduncle length and prevent complete exertion of the panicle Protective irrigation under moisture stress over a period of >10 days help realize maximum yields. Due to stem tunneling by stem borer, panicle exertion may be either affected or delayed.
Stage 6 (50% flowering) Identified at 6870 DAE when 50% of the plants in the field are in anthesis Plant grow to a height of 150160 cm. Flowering typically start 57 days after panicle exertion and progress from the tip to bottom of the panicle. Flowering duration (from starting to end) usually takes 49 days. Management guide: Moisture stress results in poor seed filling. Midges will get attracted due to flowering panicles, and lay eggs inside the florets resulting in poor/no seed setting. Head bug is another insect pest that affects grain development. These pests can be managed by spraying of endosulfan 35EC or carbaryl 50 SP (@ 1 L in 500 Lt water ha-1).
Stage 7 (Soft dough stage ) Identified at 80 DAE Presence of little or no milk when kernel is squeezed between fingers This stage signals the end of culm elongation, plants grow to about 170 cm tall About 8 to 10 functional leaves are observed and may vary with the cultivar. Management guide: High humid conditions and prolonged rainfall following flowering result in grain mold, and cause loss in grain weight and quality. Head bug population buildup may increase rapidly, if unchecked, which may result grain shriveling and predispose the seed to grain mold infections. Spraying malathion 10D (@ 20 kg ha-1 helps manage headbugs.
Stage 8 (Hard dough stage ) Identified at 96 DAE Seed cannot be compressed between fingers Plants become susceptible to lodging and charcoal rot if the crop suffers from severe moisture stress, severe pest and disease attack, heavy rain or hail driven by wind Management guide: Adequate application of farm yard manure helps retain soil moisture for longer period. Management of stem borer enhance crop yield. The use of appropriate maturity duration cultivars and those with genetic tolerance to grain mold are best ways to minimize damage due to grain mold.
Stage 9 (Physiological maturity stage ) Identified at 106 DAE Dark spot (black layer) appears at the basal portion of seed Seed moisture content at this stage varies between 25% and 35% and seeds gain maximum dry weight. The crop could be harvested at 20% seed moisture content. The seeds but must be dried to 14% moisture content for safe storage. Management guide: Crop should be harvested immediately after physiological maturity to avoid the grain mold incidence and crop lodging. Grain mold incidence to some extent can be controlled by spraying captan (0.3%) plus dithane M-45 (0.3%) thrice at 10 day intervals during grain filling stage. Harvested grains are predisposed to storage pests when kept for long term storage. The seed may be treated with malathion 10% dust (@ 2 g kg-1 seed to protect from storage pests.
How a sorghum plant grow & develop
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