Growth and Seed Yield in Kentucky Bluegrass. Thomas G Chastain George Hyslop Professor of Crop and Soil Science

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1 Growth and Seed Yield in Kentucky Bluegrass Thomas G Chastain George Hyslop Professor of Crop and Soil Science

2 Central Oregon Grass Seed Urban Grass Seed Winter Wheat Spring Wheat Barley Corn Beans Peas Madras Potatoes Sugar Beets for Seed Alfalfa/Clover Vegetables/Fruit Grapes Christmas Trees Grass (non-agricultural) Wetlands Shrubland Woodland Water

3 Seed Yield (lbs/acre) Kentucky Bluegrass Seed Yield Trends in Oregon Central Oregon Grande Ronde Valley Columbia Basin

4 Seed Yield Seed yield in Kentucky bluegrass results from the interaction of the following factors: 1. Genetic yield potential. 2. Environment. Kentucky bluegrass seed field 3. Management practices. 4. Pests.

5 Photosynthesis CO 2 Kentucky bluegrass seed crops capture solar energy and CO 2 from the atmosphere and convert this energy into a stable chemical form. Instead of solar panels to capture solar energy, the crop employs a canopy of leaves and stems to collect the sun s energy. Conversion of solar energy to chemical energy is known as photosynthesis. Carbon from atmospheric CO 2 is reduced in several steps to a reduced and stable form, a carbohydrate. CO 2 + H 2 O Oxidized Carbon Reductant CH 2 O Reduced Carbon

6 Plant Stand Kentucky bluegrass seed crops are biological solar energy collectors. How big is this collector? For every acre of Kentucky bluegrass field, there are 3 acres of leaves. The number of plants in the stand as well as number of tillers and leaves must be managed so as to optimize the size and efficiency of this biological solar energy collector. The shoot apical meristem in grasses, is hidden within the stem and is the source of new leaves and tillers.

7 Tiller Rhizome Roots Leaf Mainstem Stems and Branches The tiller is a branch on a grass plant. Rhizomes are specialized stems which grow horizontally below the soil surface and eventually turn upward. At the point where the rhizome emerges from the soil, a new plant, genetically identical to the parent plant is formed. Structure of a Kentucky bluegrass plant in the vegetative state.

8 + FR - FR Annual ryegrass grown with and without supplemental far-red light (Casal et al., 2004) Proximity Perception and Light How do plants sense the density of plant population? Neighboring plants reflect an increased level of far-red light (FR) which is sensed by phytochrome in the plant. Grass plants grown in close proximity to neighbors (high population density) grow upright with extended internodes and have few tillers (high FR). Plants grown in low density are prostrate and spreading with many tillers (low FR).

9 Light is Required for Tiller Production Tiller Number (no. m -2 ) Photon flux = 12% Photon flux = 35% Photon flux = 100% 0 April 4 April 17 May 10 May 31 June 14 Date Light effects (photon flux) on tiller populations (Chastain and Grabe, 1988)

10 Flowering and its control Seed cannot be produced in Kentucky bluegrass unless tillers become fertile (flower). In Kentucky bluegrass, tillers must be exposed (6-12 weeks) to low temperatures (37 F to 53 F) accompanied by short days for flowering to be induced. Vernalization is the induction of flowering by exposure to low temperature. Exposure to long days is required for further development of the flower. No flowering without vernalization Flowering after vernalized at 6 C for 12 weeks in 8 hour days

11 Tillers D tillers emerge from axillary buds on the previous season s stubble as a non-leafy bud-forms either rhizomes or leafy tillers. F 1 tillers Green leafy tillers that grow from axillary buds on D tillers. Form in spring or late fall. Adapted from Holman and Thill (2005) F 2 tillers Green leafy tillers that grow from axillary buds on D tillers. Form in early fall, flowers and contributes 30% of seed yield. C tillers Green leafy tillers that regrow from shoot apical meristems from the previous season. C tillers did not flower last season and account for 70% of seed yield.

12 Tillers (number/m 2 ) Tillers Total C tillers D tillers F tillers Kentucky bluegrass tiller numbers in seed production fields in Idaho (left adapted from Sylvester and Reynolds, 1999), Kentucky bluegrass tillers (top) 0 Sept Oct Nov Dec Mar Apr

13 Seed Yield (lbs/acre) Fertile tillers C and F 2 tillers Fertile tillers (No. ft 2 ) Fertile tiller number and seed yield in two cultivars of Kentucky bluegrass, redrawn from Chastain et al., 1997 (top), and fertile tillers (right).

14 Leaf Development A new leaf is produced on the plant s mainstem and on each tiller every 100 growing degree days (base temperature = 0 C). Leaf Leaf development in Kentucky bluegrass (Chastain, 1995) Tiller Rhizome Mainstem Roots For a month with average ( F): 54 high, 37 low; 2.2 new leaves are produced 80 high, 55 low; 6.1 new leaves are produced Kentucky bluegrass plant

15 Partitioning of Carbon to Tillers, Leaves, and Roots Translocation is the process of moving carbon needed for growth of leaves and tillers, roots, and rhizomes from mature photosynthetic leaves and from tiller bases for crop regrowth after mowing. Sucrose is the transport form for the translocation of carbon from one part of the plant to another via the phloem. The carbon from sucrose is used to create cellulose, the primary building block of the grass plant. Sucrose Cellulose

16 Labeld Carbon Carbon Partitioning Tiller Roots Young Tillers Crown The crown is the part of the plant where the shoot system (tillers) meets the roots. Age of tiller affects carbon export from the mainstem to tillers. Older tillers are independent of the mainstem while younger tillers are not independent and require carbon from the mainstem for their development Tiller Weight (mg) Old Tillers

17 Hormonal Control of Growth Internode Stem elongation results from activity of the intercalary meristem found above each node. Each internode elongates independently and this growth is promoted by GA (gibberellin). Lodging during flowering restricts pollination and reduces fertilization. Seed filling is reduced due to selfshading of the lodged crop. Seed number is reduced by lodging. Palisade (trinexapac-ethyl) and Apogee (prohexamide-calcium) plant growth regulators (PGRs) are acylcyclohexanedione inhibitors of the 3-β hydroxylation of GA. Inhibition of 3-β hydroxylation of GA by acylcyclohexanedione PGRs.

18 Seed Yield and Yield Components Seed yield is the biological and mathematical product of the components of yield. For example, yield of a Kentucky bluegrass seed crop can be expressed as: Seed yield (lbs/acre) = Plants/acre x Fertile tillers/plant x Florets/fertile tiller x Seed/floret x Weight/seed

19 Awn Lemma Palea Endosperm The Seed The fruit of grasses is known as a caryopsis. The lemma, palea, and awn are parts of the grass flower, known as the floret. The coleoptile is the protective covering for the embryonic shoot, while the radicle is the root. The endosperm is the food storage organ, storing primarily starch (amylose or amylopectin). Amylose Caryopsis Coleoptile Rachilla Radicle Longitudinal section of a grass seed (left), Kentucky bluegrass seed (inset)

20 Concentration in Seed (mg/g) Panicle Partitioning of Carbon to Kentucky Bluegrass Seed Starch synthesis and storage in seed Maximum starch concentration is reached before minimum sucrose concentration Translocation of sucrose through stem Stem Sucrose Starch 50 Flag leaf Photosynthesis in leaf canopy Days after Anthesis

21 Seed Yield (lbs/acre) Spring N (lbs/acre) Why is N needed in Kentucky Bluegrass Seed Crops? Nitrogen is the only fertilizer element that gives consistent, economic increases in seed yield. N is vital because it stimulates growth and development of tillers and leaves. Seed yield is low when N is low because the crop s ability to capture solar energy and carbon is reduced. Fertilizer in Kentucky bluegrass seed field (top). Spring N application effects on seed yield in Kentucky bluegrass (bottom from Chilote and Ching, 1973)

22 Stem rust Ergot sclerotia Why control pests? Ergot is a fungal disease that replaces the seed, and reduces seed yield by reducing seed number and seed weight. Ergot also increases seed cleaning costs and causes lost international marketing opportunities. Stem rust replaces a portion of the plant s leaves with non-photosynthetic pustules, and reduces seed yield by reducing light energy and carbon capture. Sod webworm damages the crown and root system and reduces seed yield by reducing the number of plants in the stand. Sod webworm

23 Why does Burning increase Seed Yield in Kentucky Bluegrass? Stubble condition Rhizomes (g/m 2 ) Fertile tillers/m 2 Seed yield (kg/ha) Burn inch inch Burning removes stubble affecting the type of tillers produced fewer rhizomes and more fertile tillers, and in turn, increases seed yield. Top - table from Hickey and Ensign, 1983, Left - Kentucky bluegrass rhizome

24 Aging in Kentucky Bluegrass Stands Year Etiolated regrowth (g/m 2 ) Fertile tillers/m 2 Seed yield (kg/ha) (From Canode and Law, 1975) Seed yield declines as the stand ages. The declining vigor of the stand is evident in diminished regrowth and fertile tiller production.

25 Conclusions 1. A Kentucky bluegrass seed crop is a biological solar energy collector. 2. Seed yield in Kentucky bluegrass is the product of the individual yield components. 3. Management practices, the incidence and severity of pests, and environment collectively influence the expression of the seed yield components. Irrigation in Kentucky bluegrass seed field near La Grande