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Alternative Approaches to Estimate the Dynamics of Silk Exsertion in Maize

Alternative Approaches to Estimate the Dynamics of Silk Exsertion in Maize. E. Sebastian Schneider and Mark E. Westgate Agronomy Department, Iowa State University Mohammad Ghaffarzadeh Pioneer Hi-Bred Intl., Inc. Background. Goals in Hybrid Seed Production - Kernel yield per area

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Alternative Approaches to Estimate the Dynamics of Silk Exsertion in Maize

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  1. Alternative Approaches to Estimate the Dynamics of Silk Exsertion in Maize E. Sebastian Schneider and Mark E. Westgate Agronomy Department, Iowa State University Mohammad Ghaffarzadeh Pioneer Hi-Bred Intl., Inc.

  2. Background • Goals in Hybrid Seed Production • - Kernel yield per area • - Genetic purity 100 80 • Important to maintain synchrony between male and female • Usually measured as 50% of population shedding pollen or silking (ASI) • Shorter ASI increases number of successful pollinations 60 % Shedding 40 20 0 195 200 205 210 215 220 Day of year 100 80 60 %Silking 40 • Kernel set decreases dramatically when silk emergence starts after peak of pollen shed • Late emerging silks are at risk to be pollinated by adventitious pollen 20 0 195 200 205 210 215 220 Day of year

  3. 1000 1000 800 800 600 600 Number of silks Number of silks Silk exsertion on the ear is a progressive process 400 400 200 200 0 0 0 2 4 6 8 10 12 0 2 4 6 8 10 12 Days after silking Days after silking 140 140 120 120 Pollen shed progresses in intensity over the course of several days 100 Pollen sehd (grains cm-2) 100 Pollen sehd (grains cm-2) 80 80 60 60 40 40 20 20 0 0 200 205 210 215 220 200 205 210 215 220 Day of the Year Day of the Year Simply documenting the percentage of plants reaching silking or shedding does not provide an accurate measure of the pollination process The patterns can vary dramatically between genotypes

  4. kernels (#/ha) Pollen shed rate (grains/cm Total number of silks or 2 d) Fortunately, the daily progress of pollen shed and silk emergence are fairly predictableCombining flowering dynamics with pollination efficiency curves (Bassetti and Westgate, 1994), it is possible to predict kernel set under field conditions. 3.0E+07 500 450 Cumulative silk emergence 2.5E+07 400 350 2.0E+07 Cumulative 300 Pollen shed kernels set 1.5E+07 250 200 1.0E+07 150 100 5.0E+06 50 0 10-Jul 14-Jul 18-Jul 22-Jul 26-Jul 30-Jul 3-Aug Date

  5. Rapid Method Available √ √ √ √ X Inputs needed to predict Kernel Set • Male: • Phenology: % of plants starting to shed (first anther visible) • Pollen Shed Duration: days of shed duration per tassel • Pollen Production per tassel: grains per tassel • Female: • Phenology: % of plants reaching silking (first silk visible). • Pattern of Silk Exsertion: silks exposed each day Typically Manual Counting: -- 15 to 25 minutes per ear for silks collected at several dates after silks first appear

  6. Perimeter Time Rationale for developing a simple, reliable, and rapid method for estimating the number of silks exposed for pollination Monitor the perimeter of the ‘silk bouquet’ as silks are exposed from the surrounding husks

  7. A B C A digital caliber was modified for the task Loop placed around silks

  8. Initial Goals • Evaluate bouquet perimeter technique for accuracy and precision of silk counts • Determine the minimum number of measurements needed to quantify silking dynamics reliably

  9. Materials and Methods • Source of genetic variation • Six female inbreds • Grown under standard production practice in seed production fields and research plots • Measurements • Perimeter values collected 1, 3, 5,and 8 days after silks first appeared • Technique Evaluation • Estimated vs measured values • Accuracy of predicted values for 1 to 4 days of data

  10. 2 2 y = 11.14x + 0.22x y = 16.75x + 0.09x 600 r 2 = 0.99 r 2 = 0.99 400 200 Female A Female D 0 y = 11.44x + 0.24x2 y = 8.18x + 0.42x2 600 Silk Number Ear -1 r 2 = 0.99 r 2 = 0.99 400 200 Female B Female E 0 y = 14.33x + 0.33x2 y = 18.01x + 0.12x2 600 r 2 = 0.98 r 2 = 0.99 400 200 Female C Female F 0 0 10 20 30 0 10 20 30 Silk Bouquet Perimeter (mm) Perimeter of the silk bouquet was closely related to exserted silk number (r2 = 0.98 – 0.99) Differences among regressions were detected in only one case. Female E

  11. Bouquet perimeter explained 99% of the variation in silk number for data pooled across six female inbreds. Regression using pooled data 2 y = 14.33x + 0.19x 2 r = 0.99 600 400 Silk Number Ear -1 200 0 0 10 20 30 Silk Bouquet Perimeter (mm) Depending on the accuracy required, a single regression model might be sufficient to compare silking dynamics across inbreds.

  12. ▲ Measured Estimated 2 2 r =0.96 r =0.90 600 600 400 400 200 200 Female A Female D 0 0 0 2 4 6 8 10 0 2 4 6 8 10 2 2 r =0.97 r =0.96 600 600 400 400 Number of Silks 200 200 Female E Female B 0 0 0 2 4 6 8 10 0 2 4 6 8 10 r 2=0.94 2 r =0.96 2 r =0.95 600 600 600 400 400 400 200 200 200 Female C Female F Female F 0 0 0 0 2 4 6 8 10 0 2 4 6 8 10 0 2 4 6 8 10 Day after first silks appear Estimating the dynamics of silk exsertion using the bouquet perimeter Using the unique regression developed for each genotype, average error of estimated vs measured silk number was 2.6% Silk number …average error using the pooled regression was 10.1%

  13. 20 15 Average Error (%) 10 5 • Error decreases as the number of days included in the estimate increase • Two measurement dates limited to 5.7%, on average. 0 0 1 2 3 4 5 Number of dates How many sampling dates are required to generate a satisfactory silk exsertion dynamic from bouquet perimeter measurements? • Silk numbers estimated at 1, 3, 5, and 8 days after first silks appeared. • Percent error averaged across genotypes and sampling dates.

  14. What is the best 2-day combination for sampling?? Females Days Average After A B C D E F Error Silking Days % % 4.6 1 and 3 3.7 4.4 5.1 7.3 2.9 3.9 3.7 1 and 5 4.2 1.0 4.5 7.3 1.8 3.6 8.5 1 and 8 3.0 7.6 6.9 7.5 18.3 7.7 4.8 3 and 5 3.1 3.3 7.6 7.3 4.4 3.0 6.2 3 and 8 3.2 2.0 8.4 7.3 7.9 8.1 6.7 5 and 8 8.2 2.1 5.0 7.5 8.0 9.2 • Sampling on days 1 and 5 was the best 2-day combination, when averaged across genotypes. • Sampling on days 1 and 8 resulting in significantly (P < 0.05) greater error than other combinations

  15. CONCLUSIONS • Dynamics of silk exertion can be estimated accurately using the silk bouquet perimeter technique. • Average error was 2.6% using regressions for individual genotypes. Error averaged about 10% using pooled regression. • Sampling on 1st and 5th days of silk exsertion provided sufficient information to estimate the dynamic of silk exsertion within 4% of measured values. • This technique provides a simple and reliable approach • for comparing flowering characteristics of a large number of female inbreds • for generating flowering coefficients for crop modeling

  16. with thanks to… Pioneer Hi-Bred Intl., Inc Scholarship for International Agricultural Development to E.S. Schneider

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