Leaf emergence and beginning of starch accumulation in roots of a cassava variety as a function of planting date

摘要

The accumulated number of leaves (NF) on the main stem is related to the appearance of several developmental stages in cassava. The beginning of starch accumulation (IAA) in the fibrous roots of cassava switches the source/sink ratio because of the translocation of photoassimilates to the major storage organ in this species. This study was aimed at estimating the phyllochron and identifing a morphological indicator based on NF for IAA in cassava grown in several planting dates. A field experiment was carried out in Santa Maria, RS, Brazil, with four planting dates (28/09, 11/10, 16/11 and 27/12/2005). The variety RS 13 was used and planted in 12 l pots, buried in the soil in a 2.0 x 0.8m spacing. The experimental desing was a completely randomized with 11 replications. Daily degree-days (STd, °C day) were calculated starting at emergency and accumulated by STa = SSTd. IAA was determined on the plants when one root reached a diameter of 0.01m. NF on the date of IAA and the main sterm final leaf number (NFF) up to the first sympodial branches were determined. The plyllochron varied from 20.3 to 29.5°C day leaf -1, with larger values in the two latest planting dates. The NFF varied among planting dates, increasing as planting was delayed. The NF at IAA was similar for the four planting dates and occurred when NF was on average 20.9 (± 1.0) leaves.