4. Summary and conclusions
Using a non-linear regression technique for modeling the relationship of sunflower seed dry matter accumulation and seed moisture to estimate PM, we have shown that PM for two modern oilseed hybrids occurred at approximately 40% moisture, while that for a confectionary hybrid was 50%. We have also shown that this relationship was relatively constant across environments and across the capitulum for seeds in the outer and middle concentric zones. However, the inner seed (i.e., at the center) of the capitulum, which only makes up about 11% of the total seed, responded differently than the outer and middle seed. The number of accumulated GDD from R6 to PM for the oil hybrids ranged from 599 to 622 °C d for outer and 633 to 666 °C d for middle seed. The period from R6 to PM was even shorter for the confectionary hybrid, which ranged from 486 to 572 °C d for outer and 515 to 612 °C d for middle seed. Overall, the data indicate that modern sunflower hybrids could be desiccated earlier at seed moisture content greater than that currently recommended (i.e., 35%) without yield loss, especially confectionary (i.e., non-oil cultivars) sunflower, whose seed have a large proportion of pericarp. However, because PM in middle seed lagged about 3 d behind outer seed, desiccant application should be based on when the middle concentric third of seed around the capitulum reach PM. Our results further suggest that if moisture content is used as criterion for when to apply desiccant to sunflower that a wider range of confectionary sunflower genotypes be tested. Our study clearly showed substantial differences in seed moisture content at PM can exist between confectionary and oilseed genotypes, which could necessitate different desiccation management strategies for the two sunflower types.
4. สรุปและบทสรุปUsing a non-linear regression technique for modeling the relationship of sunflower seed dry matter accumulation and seed moisture to estimate PM, we have shown that PM for two modern oilseed hybrids occurred at approximately 40% moisture, while that for a confectionary hybrid was 50%. We have also shown that this relationship was relatively constant across environments and across the capitulum for seeds in the outer and middle concentric zones. However, the inner seed (i.e., at the center) of the capitulum, which only makes up about 11% of the total seed, responded differently than the outer and middle seed. The number of accumulated GDD from R6 to PM for the oil hybrids ranged from 599 to 622 °C d for outer and 633 to 666 °C d for middle seed. The period from R6 to PM was even shorter for the confectionary hybrid, which ranged from 486 to 572 °C d for outer and 515 to 612 °C d for middle seed. Overall, the data indicate that modern sunflower hybrids could be desiccated earlier at seed moisture content greater than that currently recommended (i.e., 35%) without yield loss, especially confectionary (i.e., non-oil cultivars) sunflower, whose seed have a large proportion of pericarp. However, because PM in middle seed lagged about 3 d behind outer seed, desiccant application should be based on when the middle concentric third of seed around the capitulum reach PM. Our results further suggest that if moisture content is used as criterion for when to apply desiccant to sunflower that a wider range of confectionary sunflower genotypes be tested. Our study clearly showed substantial differences in seed moisture content at PM can exist between confectionary and oilseed genotypes, which could necessitate different desiccation management strategies for the two sunflower types.
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