Ž . Field Crops Research 56 1998 257–264 Grain yield components in maize II. Postsilking growth and kernel weight G.A. Maddonni a , M.E. Otegui a, ) , R. Bonhomme b a Departamento de Produccion Vegetal, Facultad de Agronomıa, UniÕersidad de Buenos Aires, AÕda. San Martın 4453, ´ ´ ´ 1417 Buenos Aires, Argentina b Unite de Recherche en Bioclimatologie, Institut National de la Recherche Agronomique, 78850 ThiÕerÕal-Grignon, France ´ Received 23 September 1996; accepted 29 July 1997 Abstract Ž . Ž . Maize kernel weight KW results from kernel growth during two stages of grain filling, the lag phase formative period and the effective grain-filling phase. Environmental conditions may affect kernel biomass accumulation in each phase. This Ž. Ž . Ž. work analyzed: 1 changes in duration and rate of kernel growth on a thermal time 8C day basis; and 2 KW response to y1 Ž . postsilking biomass production kernel source:sink ratio . Sowing date, plant population, and nitrogen fertilization experiments were conducted in France and Argentina to induce changes in assimilate availability per kernel. Hybrids of different KW were tested. Hybrids differed in the duration of the lag phase, which determined kernel growth rate during the Ž . effective grain-filling period for hybrids with similar grain-filling duration ca. 7458C day . Environments with low air Ž . temperature -198C and less incident solar radiation led to a smaller final KW due to reductions in photoassimilate production and its partition to the grains. A value of 240 to 270 mg kernel y1 during grain filling was determined as a Ž . Ž threshold to have mobilization or storage of reserves. Small-kernel hybrids KW-300 mg , with large kernel number 3500 y2 . Ž . to 5500 kernels m , depended more on reserve mobilization than large-kernel hybrids KW)300 mg with reduced Ž y2 . kernel number 2800 to 4000 kernels m . For the former, grain yield increments should not be based on increased kernel number but on increased biomass production. q 1998 Elsevier Science B.V. Keywords: Maize; Kernel weight; Hybrids; Postsilking growth; Zea mays 1. Introduction Final KW of maize is the result of kernel growth during two stages of the grain-filling period, and these stages may experience different resource avail- Ž ability Frey, 1981; Ouattar et al., 1987; Cirilo and . Andrade, 1996 . The first stage, usually known as lag phase, starts after ovary fertilization and precedes ) Corresponding author. Tel.: q54-1-5248039; fax: q54-1- 5228395; e-mail: meotegui@mail.retina.ar. the linear grain-filling period stage. The lag phase Ž corresponds to a formative period Reddy and Day- . nard, 1983 , when kernel sink capacity is set, and it always overlaps to some extent with the postsilking Ž period for ear growth and kernel set Cirilo and Andrade, 1994b, 1996; Otegui and Bonhomme, . 1998 . Effective grain filling takes place during the second phase, and is highly dependent upon tempera- Ž ture and assimilate availability Cirilo and Andrade, . 1996 . Both grain-filling phases differ in duration Ž and kernel growth rate among genotypes Jones et 0378-4290r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved. Ž . PII S0378-4290 97 00094-4