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CROP PHYSIOLOGY & METABOLISM

Ovary Growth and Maize Kernel Set

Dep. de Producción Vegetal, Facultad de Agronomía, Universidad de Buenos Aires, Av. San Martín 4453 (C1417DSE). J. Cárcova's present address: Monsanto Argentina, Pergamino, Argentina

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

Synchronous pollination improves maize (Zea mays L.) kernel set, but the physiological reasons behind this response are yet unclear. We registered ovary fresh weight evolution at three floret positions along the ear (base, middle and tip) of plants subjected to natural (NP) or synchronous (SP) pollination during two growing seasons. Synchronous pollination of ears bagged before silking was performed five days after silking (DAS). Ovary weight increased exponentially at all floret positions (P 0.01), but a lag in this trait was detected among those at the base and middle of SP ears. At each sampling date, florets along the ear differed (P < 0.01) in ovary weight, but differences were larger for NP than for SP plants. At pollination of each floret position, however, the range in ovary weight was smaller in NP ears (ca. 4 to 5 mg ovary^–1) than in SP ears (4 to 9 mg ovary^–1). Contrarily, just pollinated ovaries at the tip of the ear of NP plants (i.e. on ca. 4–5 DAS) experienced the high growth rate of those already pollinated at the base (ca. 0.7 mg d^–1 for the former and ca. 3.7 mg d^–1 for the latter). The range in ovary growth rate along the ear was drastically reduced under synchronous pollination on 5 DAS (ca. 0.55 mg d^–1 for the base and ca. 0.47 mg d^–1 for the tip). The larger the tip-to-base ratio in ovary growth rate, the larger the number of kernels set per plant (r²= 0.94; P = 0.03).

Abbreviations: DAS, days after silking • DBS, days before silking • KNP, kernel number per plant • NP, natural pollination • ROGR, relative ovary growth rate • SP, synchronous pollination.