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CROP PHYSIOLOGY & METABOLISM

Pollen Production, Pollination Dynamics, and Kernel Set in Maize

^a Dep. de Producción Vegetal, Fac. de Agronoma, Univ. de Buenos Aires, Av. San Martín 4453, Buenos Aires (C1417DSE), Argentina
^b Dep. of Agronomy, Iowa State Univ., 1563 Agronomy Hall, Ames, IA 50011-1010

* Corresponding author (otegui{at}agro.uba.ar)

Maize (Zea mays L.) pollen production has been found not to limit kernel set, but there is scarce information on pollen production of modern hybrids and the effect that breeding for reduced tassel size has had on this trait. Our objectives were to study genotypic differences in pollen production and flowering dynamics, and to estimate pollen availability per exposed silk. Four F1 hybrids were grown at different plant densities (between 2.5 and 12.5 plants m^-2) in two distinct environments (cool Midwest USA and temperate Argentine Pampa). Pollen availability was also modified by delayed plantings and detasseling treatments. We measured the dates of anthesis and silking of individual plants, the anthesis-silking interval (ASI), the number of exposed silks per apical ear, the number of pollen grains per square meter (PGM), and kernel number per ear. The number of pollen grains produced per tassel (PGT) and per exposed silk were estimated. Increased plant density promoted an increase in ASI, matched by an enhanced interplant variability in this parameter, and a reduction in PGT. The latter was reduced from 10.3 x 10⁶ or 11 x 10⁶ at 2.5 plants m^-2 to about 3 x 10⁶ at 12.5 plants m^-2 (USA), and from 9.7 x 10⁶ or 11.3 x 10⁶ at 3 plants m^-2 to 4 x 10⁶ or 3.6 x 10⁶ at 9 plants m^-2 (Argentina). We estimated two thresholds beyond which kernel set could be affected: (i) 227 pollen grains cm^-2 d^-1 at the end of pollen shedding and (ii) two pollen grains per exposed silk. Some cropping conditions were closer to the second threshold than others.

Abbreviations: A_n, pollen-shedding plants per square meter on Day n after anthesis • ASI, anthesis-silking interval • ASI_ip, ASI of individual plants • ASI_pp, ASI of the plant population • DAA, days after anthesis • E_n, ear number n • PGM_n, pollen grains per square meter on Day n

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