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Quantitative Relationships between Pollen Shed Density and Grain Yield in Maize

^a Department of Agronomy, Iowa State University, Ames, IA 50011
^b Department of Agricultural and Biosystems Engineering, Iowa State University, Ames, IA 50011

View larger version (17K): [in a new window]   Fig. 1. Field arrangement for isolating pollen shed density treatments. MF indicates the percentage of plants in each treatment block that were allowed to shed pollen. The level of male fertility was controlled by detasselling P3978 in 1986 or by a mixture of male sterile and male fertile isolines of P3925 in 1987. Distances are in meters.

View larger version (41K): [in a new window]   Fig. 2. A: Beginning pollen shed. Anthers on the main tassel branch are shedding pollen. B: Maximum shed. Pollen is being shed from the main tassel branch and side branches. C: End shed. Anthers at the base of the side branches and main branch have completed shedding pollen. D: Silk emergence. The first day silks emerge from the surrounding husks. Silks are typically 1 to 2 cm in length.

View larger version (34K): [in a new window]   Fig. 3. Percentage of the plant population in each treatment block that has begun to shed pollen (Beg Shed), is at maximum pollen shed (Max Shed), has completed pollen shed (End Shed), or has silks visible (Silking). MF indicates percentage of plants allowed to shed pollen. The level of male fertility was controlled by detasselling (P3978), or by using a male sterile isoline (P3925). Data are the mean ± SE of 4 reps of 20 to 40 plants each.

View larger version (33K): [in a new window]   Fig. 4. Seasonal pattern of pollen shed for the various male sterility treatments used to decrease pollen shed density. Pollen was collected on passive pollen traps placed at ear height within each treatment block. MF indicates percentage of plants allowed to shed pollen. The level of male fertility was controlled by detasselling (P3978), or by a male sterile isoline (P3925). Each point is the mean ± SE of 3 traps.

View larger version (29K): [in a new window]   Fig. 5. Population Index (Pind) for pollen shed, and the predicted pattern of seasonal pollen shed calculated from three stages of tassel development. The Pind is a daily measure of the percentage of plants shedding pollen. Plant population and average pollen production per plant (Table 1) are used to scale the Pind curve to daily pollen shed on an area basis.

View larger version (30K): [in a new window]   Fig. 6. Predicted seasonal patterns of pollen shed density at four levels of male fertility for P3978 and P3925. Curves were generated from the Population Index (Fig. 4) and the average pollen production per plant in each treatment (Table 1). Symbols are the daily values for pollen shed density from Fig. 2.

View larger version (23K): [in a new window]   Fig. 7. Comparison of measured and predicted rates for seasonal (A) and daily (B) pollen production at four levels of male fertility (MF) for P3978 and P3925. Measured values are field data presented in Table 1 and Fig. 6. Predicted values are taken from the Pind -generated curves in Fig. 6. Predicted seasonal pollen production is the sum of daily Pind -curve values for the entire pollen shed period. Predicted daily pollen production is the Pind -curve value corresponding to the daily measured value for each MF treatment.

View larger version (29K): [in a new window]   Fig. 8. Grain yield and yield components for P3978 and P3925 grown at four levels of male fertility. The level of male fertility was controlled by detasselling (P3978), or by a mixture of male sterile and male fertile isolines (P3925). Fraction of plants shedding pollen is the target value for each treatment. Data from second ears are included in the analysis. Data are the mean ± SE of 4 replicate yield measurements of 40 to 80 plants each within each treatment block.

View larger version (22K): [in a new window]   Fig. 9. Relationships between grain yield, kernel number, and pollen availability per kernel. Pollen grains per kernel were calculated from the seasonal pollen deposition (Table 1) and total kernels per hectare. The curve for grain yield vs. kernel number is Y = 0.4205X - 0035X2, r2 = 0.998.

View larger version (22K): [in a new window]   Fig. 10. Dependence of grain yield and kernels per plant on pollen availability per silk. Differences in total pollen production per ha across treatments were normalized to the total number of emerged silks per hectare. This calculation assumes each plant produces the average number of silks for the hybrid, and second ears (when present) produced an equal number of silks. Average silks per ear for P3978 = 670, and for P3925 = 607. Note that yield and kernel number decrease at pollen densities less than 3000 pollen grains per silk.