Crop Development and Components of Seed Yield Thomas G Chastain CSS 460/560 Seed Production
White clover seed field Seed Yield Seed yield results from the interaction of the following factors: 1. Genetic yield potential. 2. Environment. 3. Management practices. 4. Pests.
Plant Stand Seed crops are biological solar energy collectors. How big is this collector? For every acre of perennial ryegrass 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. Normal stand (far left), loss of stand due to anoxia in low portions of field (near left).
Tiller Rhizome Roots Leaf Mainstem Tillers and Seed Yield 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.
Tillers and Seed Yield Fall vegetative tiller number and seed yield relationships in tall fescue Stand age Correlation Coefficient 1 st -year a 0.95** 2 nd -year b 0.87** 3 rd -year b 0.45 4 th -year b 0.05 a Chastain and Grabe, 1989 b Chastain et al., 1996 Tall fescue seed crop at peak anthesis
Leaf Development A new leaf is produced on each tiller in a perennial ryegrass seed field every 118 growing degree days (base temperature = 0 C). 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. The rate of leaf appearance varies with temperature and with species (ranges from Chewings fescue at 97 GDD to tall fescue at 135 GDD).
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.
Tillers (number/m 2 ) Tillers 20000 18000 16000 14000 12000 10000 Total C tillers D tillers F tillers 8000 6000 4000 2000 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
Seed Yield (lbs/acre) Fertile tillers C and F 2 tillers Tall fescue panicle (left), perennial ryegrass spike (right). 1200 1000 800 600 400 200 0 0 100 200 300 400 500 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).
Flowering and its control Flowering is the most important event in the production of a seed crop, after establishment of the stand. The seed crop s biological requirements for flowering must be completely satisfied for the full expression of flowering. Photoperiodic induction - promotion of flowering by exposure to a critical photoperiod. Photoperiodic time measurement is set by a circadian rhythm. Thermal induction - promotion or acceleration of flowering by exposure to a critical temperature. White lupin in flower (top), cabbage (right)
Vernalization Vernalization is the induction of flowering by exposure to low temperature. Exposure to long days is required for further development of the flower for many species. 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. No flowering without vernalization Vernalization effects on flowering in vernalization-requiring clone of perennial ryegrass: plant will not flower without vernalization Flowering after vernalized at 6 C for 12 weeks in 8 hour days
Vernalization Some plants have dual induction requirements, including many of the temperate perennial grasses such as perennial ryegrass. Perennial ryegrass needs vernalization, followed by long days, for flowering. MacMillan, C. P., et al. Plant Physiol. 2005;138:1794-1806 Flowering response to vernalization and long days (LD) and short days (SD) in perennial ryegrass. Ryegrass floret (right).
Vernalization VRN1 is the vernalization gene found in several grasses including wheat and perennial ryegrass. VRN2 is also present in some species. VIN3 is the vernalizationinsensitive gene although deletions in VRN1 will make plants vernalizationinsensitive. No vernalization Flowering after vernalized at 6 C for 12 weeks in 8 hour days Vernalization effects on flowering in vernalization-insensitive clone of perennial ryegrass: plant will flower without vernalization
Vernalization Vernalization requirements for flowering in economically important ryegrass species (Aamlid et al., 2000) Species Crop L. perenne Perennial ryegrass L. perenne x L. multiflorum Perennial and annual ryegrass hybrids Vernalization requirement Obligate, high Facultative, intermediate Much variability in flowering responses exist within some crop species. Some species have obligate requirements while other have facultative responses. L. multiflorum Italian ryegrass biennial types L. multiflorum Italian ryegrass annual types L. rigidum Wimmera ryegrass L. multiflorum Westerwolds ryegrass Facultative, intermediate Faculative, low Faculative, low None
Vernalization and Seed Yield Autumn tiller number, fertile tiller number, and seed yield in orchardgrass and tall fescue Species Autumn (no/m 2 ) Fertile (no/m 2 ) Seed yield (kg/ha) Orchardgrass a 486 227 1066 1565 367 1833 Tall Fescue b 863 216 775 a Chastain and Grabe, 1989a b Chastain and Grabe, 1989b 2417 593 1705 Reduced autumn tiller production shifted tiller production into the spring after vernalizing conditions were no longer present. Consequently, fewer fertile tillers were formed and seed yield was low. Increased autumn tiller production caused greater numbers of fertile tillers to be formed and resulted in higher seed yield. Poor stand conditions entering the winter season cause poor flowering and seed yield.
Vegetative SAM in left photo (A = apical meristem and L = leaf primordium). Right photo depicts reproductive SAM (DR = Double ridge). The upper ridge is the spikelet ridge and the lower is the leaf ridge. Floral Initiation Initiation of the inflorescence is indicated by a visible change in the shoot apical meristem (SAM) from the vegetative to the reproductive condition. The double ridge stage marks the beginning of visible floral development in grasses. Before this stage the stem apex produces only leaves, but afterwards flower parts are produced which are modified leaves.
Stem Elongation and Flowering Leaves Leaf Sheath SAM Internode Internode Internode Node Axillary Bud As each tiller proceeds from vegetative to reproductive development, the tillers elongate. 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).
5000 Grass Roots and Seed Yield 15-cm rows 30-cm rows 45-cm rows 60-cm rows Fertile Tiller Population (no. m -2 ) 4000 3000 1000 500 Creeping red fescue Chewings fescue Tall fescue Perennial ryegrass Fertile tiller number increases with autumn root biomass. Seed yield increases up to a maximum with root biomass. 0 tumn 1 Spring 1 Autumn 2 Spring 2 Autumn 3 2500 0 500 1000 1500 2000 2500 3000 15-cm rows 30-cm rows 45-cm rows 60-cm rows Seed Yield (kg ha -1 ) 2000 1500 1000 500 Perennial ryegrass Chewings fescue umn 1 Spring 1 Autumn 2 Spring 2 Autumn 3 Stand Age and Season 0 0 2000 4000 6000 8000 10000 Autumn Root Biomass (g m -3 ) Garbacik and Chastain, 2003
Seed Yield and Yield Components Seed yield is the biological and mathematical product of the components of yield. For example, yield of a grass 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
Sterile Floret Yield Components: Perennial Ryegrass Rachilla 12,022,560 Spikes Acre 21 Spikelets Spike Floret 9.4 Florets Spikelet 0.213 Seed Floret 4.19 x 10-6 lbs. Seed = 2215 lbs./acre Expanded spikelet (left), seed (inset)
Yield Components: White Clover Seed Yield = Plants Area Inflorescences Plant Flowers Inflorescence Seeds Flower Weight Seed White clover seed field (left), inflorescence (right)
Seed Yield and Yield Components Changes in one or more of the yield components can be compensated for by changes in other components. For example, lowered production of one yield component can be offset by an increase in production of another component without a loss in yield. This process is known as yield component compensation. This is a form of phenotypic plasticity. Relationship of tall fescue yield components with seed yield (Chastain and Grabe, 1988). Yield Component Correlation with Seed Yield Panicles/m 2 0.99** Vegetative tillers/m 2 0.37 Spikelets/panicle -0.31 Florets/spikelet -0.93** Tall fescue seed
Seed Yield and Yield Components Several yield components may be related to yield. Seed number and pod number both have an impact on seed yield. Even though the individual seed weight is not correlated with seed yield, the weight of seed on an inflorescence basis is related to yield. Relationship of alfalfa yield components with seed yield (Bolanos-Aguilar et al. 2002). Yield Component Correlation with Seed Yield Weight per seed 0.10 Seeds per pod 0.39 ** Seed weight per inflorescence Pods per inflorescence 0.40 ** 0.20 * Alfalfa seed
Ergot sclerotia Seed Yield and Yield Components Relationship of seed number to seed yield in tall fescue (Huettig et al, 2011). Stem rust Ergot seed yield can be reduced by seed replacement with sclerotia (top), rust can cause loss in seed weight and in seed number (bottom)
Seed Yield and Yield Components Fertile tillers can die after they are formed, reducing seed yield. For instance, a combination of fungal disease and insects may contribute to the death of fertile tillers in Kentucky bluegrass. This is known as silvertop. Silvertop in Kentucky bluegrass