RICE CROP DURATION AND LEAF APPEARANCE RATE IN A VARIABLE THERMAL ENVIRONMENT - III - HERITABILITY OF PHOTOTHERMAL TRAITS

In arid, irrigated, rice environments, crop duration is highly variabl e, resulting in uncertain crop calendars for double cropping. The main causes of this variability are varying temperature and daylength. Bre eding for stable crop duration in such environments might make a major contribution to rice production. A previous study established genetic differences in phenological responses to temperature and photoperiod, based on a field study with sequential planting dates in Senegal. The present study applied this experimental approach to a five-parent com plete dialled scheme. The five parents and 20 Fl progeny populations w ere sown on 14 dates at 2-week intervals at Ndiaye, Senegal (16 degree s 14' N) during the cold-dry, hot-dry and wet seasons in 1996. The mod el LAP (Leaf Appearance) described previously was used to disaggregate photoperiodic and thermal traits, which gave reproducible results for the thermal component, but not for the photoperiodic responses. Respo nses to photoperiod were therefore measured using a subset of environm ents in the wet season (stable temperatures and 12.6-13.1 h daylength) . Cross involving IR29725-40-3-2-3 (IR29725; short duration) and IR463 0-22-2 (IR4630; medium duration), in combination with any of the other lines in the diallel, gave consistent patterns of heritability for ea rliness of flowering in the different seasons, the sensitivity of pani cle induction to low temperatures, and photoperiod-sensitivity in the range of 12.6-13.1 h daylength. The results permitted three conclusion s: (1) short duration in the wet season was a dominant trait, and in t he cold-dry season, a super-dominant trait. IR29725 is a promising don or for this trait. (2) Despite its moderate to high phenological sensi tivity to low temperatures, IR29725 acted as donor for low sensitivity of panicle initiation to temperature. This trait was dominant. (3) At least under the thermally stable conditions of the wet season, IR4630 acted as donor of a dominant trait for photoperiod-sensitivity, where as IR29725 acted as donor for photoperiod-insensitivity. In summary, I R29725 is a promising donor of traits, such as short duration, low pho toperiod-sensitivity and low sensitivity of phenological processes to temperature. (C) 1998 Elsevier Science B.V. All rights reserved.