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THE SORGHUM PLANT, GROWTH STAGES AND ASSOCITED MANAGEMENT PRACTICES By IDK Atokple. 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
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THE SORGHUM PLANT, GROWTH STAGES AND ASSOCITED MANAGEMENT PRACTICES By IDK Atokple
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 palea Inner palea Outer lemma Inner lemma Outer glume Inner glume Stigma Anther Style Ovary Filament Lodicules
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.