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Abstract :

Grain abortion is one of the primary causes of yield loss in water-deficient maize. It is most often attributed to a lack of carbon supply to the ovaries. We tested the link between abortion and i) the development of ovary cohorts, ii) the kinetics of silk emergence, and iii) the availability of carbon to the ovaries, characterised by the quantities and concentrations of carbonaceous metabolites, as well as by the activities and abundances of key enzyme transcripts at 3 developmental stages around flowering. The carbon status of the plant and ovaries were favourable in water deficit, making carbon metabolism-related abortion unlikely. Abortion occurred in the youngest ovaries, located at the apical position of the spike. The abortion was a consequence of the disruption of silk growth, which altered the kinetics of silk emergence, thus reducing the number of silks that emerged. The final number of grains was clearly related to the number of emerged silks in three experiments involving different water deficit intensities and 4 genotypes. A carbon-independent mechanism therefore triggers abortion as soon as the silks emerge, during fertilisation of the first ovaries. It occurs before the abortion linked to the lack of carbon classically described in the literature, and could explain the majority of yield losses during drought periods in the field. This work opens up new perspectives for the selection and modelling of maize in water shortage situations.

Key words: Abortion, water deficit, development, ovary, silks, grain, soluble sugars, invertases, maize, growth, reproduction