Flowering is essential in any breeding programme, particularly in genetic introgression programmes in which flowering synchronism is required. In this work, 16 sugarcane genotypes were evaluated using three different flowering-inductive photoperiod treatments (30 s, 45 s, and 1 min of a daily photoperiod decrease from 12 h 55 of light). Each genotype was planted in 43 L pots (equal proportion of soil, sand, and substrate) with three tillers per pot. Plants with 4 to 6 internodes were placed in a photoperiod facility with three controlled chambers, each chamber containing all 16 genotypes (one treatment per chamber). The temperature range (21 °C to 32 °C) and humidity were the same for all of the treatments. The flower induction started in September 2010 and ended in April 2011. The plant elongation and flag leaf and inflorescence emergence were recorded and the pollen viability was evaluated by using the iodine staining method. The photoperiod facility provided suitable conditions for flowering, as the plants in the three treatments successfully flowered. The genotypes in the three treatments behaved differently in relation to the date of panicle emergence, with the treatment of 45 s showing better results. The results here presented contribute to synchronise flowering for desired sugarcane crosses, particularly those from introgression programmes between commercial cultivars and species from the Saccharum complex.
In Brazil, sugarcane crosses have been performed under natural conditions in the Northeast coastal region, which has ideal climate conditions for floral induction. However, sugarcane breeders have found difficulties in synchronising flowering in specific crosses, such as those between commercial cultivars and Saccharum spontaneum to broaden the genetic base of sugarcane and to increase the fibre content and biomass.
The process of inflorescence formation is difficult to define because it depends on the genotype, weather and changes that occur during the growing season. The flowering stimulus occurs during 18 - 25 days ([
Among the external factors that influence flowering induction, photoperiod is of high importance. Although sugarcane behaves as a short-day plant, successive long nights are also required to induce flowering ([
Another important factor that affects sugarcane flowering is the soil moisture, which can interfere with tassel formation, as a water deficit during the inductive period can delay flowering. Indeed, a lack of water inhibits the translocation of photoassimilates to the apex, and therefore elongation of the inflorescence peduncle and anthers exposure ( [
Photoperiod management in areas of unfavourable natural conditions of flowering can be conducted by using photoperiod facilities. Controlled temperatures have been adopted by some sugarcane breeding programmes in Australia, South Africa and the USA to synchronise panicle emergence among desirable cultivars. In Brazil, the first fully automated photoperiod facility capable of simulating the ideal conditions of temperature and photoperiod to induce sugarcane flowering was built at the Campinas Agronomic Institute (IAC)―Sugarcane Center, which is an unfavourable site for natural sugarcane flowering ( [
Due to the instability of sugarcane flowering and pollen viability in São Paulo State, techniques that artificially synchronise flowering and maintain pollen viability have a great impact on sugarcane breeding programmes. Moreover, the inductive photoperiod of the Brazilian sugarcane genotypes is still unknown mainly due to a lack of studies related to flowering induction at photoperiod facilities. Therefore, the present study aimed to study the behaviour of 16 sugarcane genotypes using different inductive flowering photoperiod treatments. The results will contribute to synchronise flowering to planning crosses and also help breeders in genetic introgression programmes between commercial sugarcane cultivars and wild sugarcane species, especially those from Saccharum spontaneum.
The experiment was conducted at the IAC―Sugarcane Center at Ribeirão Preto, São Paulo State in the period of September 2010 to April 2011. Sixteen sugarcane genotypes (
The 16 sugarcane genotypes were planted in pots of 43 L with equal amounts of clay soil, sand and substrate (Plantmax®), with the recommended fertilisation, maintaining three tillers of each genotype per pot. The pots were placed randomly on three mobile wagons in separate chambers with controlled photoperiods (
Genotypes | |||
---|---|---|---|
IACSP94-2101 | IACSP00-8206 | CTC12 | SP89-1115 |
IACSP93-2060 | IACSP97-2055 | CTC8 | SP90-1638 |
IACSP96-7569 | IACSP95-5094 | CTC6 | SP80-1842 |
IACSP00-8095 | CO213 | CTC15 | RB867515 |
The treatments were 30 s (Treatment I), 45 s (Treatment II) and 1 min (Treatment III) of a decrease in the daily photoperiod, starting from 12 h 55 min ( [
The opening and closing of the photoperiod chamber gates and the movement of the wagons was controlled automatically according to the programmed period of light and external temperature. The temperature was controlled in the range of 21˚C - 32˚C, with an internal optimum control at 27˚C for the three treatments. To achieve this, reversible air conditioners (hot/cold) were installed in each photoperiod chamber, and devices that detect temperature were placed both inside and outside of the photoperiod chamber. The automation of the photoperiod chamber allowed the identification of the optimal conditions for induction and flowering.
The induction began in September 2010, and daily evaluations were performed until the end of April 2011. During the induction period, all of the morphological changes that indicate flowering, such as elongation and the date of flag leaf emergence were recorded as also the date of panicle emergence. In the period of inflorescence emergence, the relative humidity was maintained above 80 % (to simulate an intense period of rain).
The inflorescences were harvest to test the pollen viability under the artificial flower induction. Mature anthers were mixed with iodine 0.1 N solution to visualise the percentage of blue pollen grains in relation to the total stained pollen grains in a microscope slide ( [
The first sign of flower induction which is characteristic of the Saccharum species, i.e., plant elongation, was observed at 60 days after the beginning of the flower induction treatment, indicating that the genotypes responded to the treatments. Among the tillers of the same genotype, in Treatments I (30 s) and II (45 s), some were etiolated leading to a visual lack of uniformity compared to treatment III (1 min).
Overall, the period of flag leaf emission was 110 to 179 days from the beginning of induction, and the emergence of inflorescences occurred at 137 to 207 days after the beginning of induction (
Percentage of blue pollens (%) | Score |
---|---|
0 | 9 |
1 to 9 | 8 |
10 to 19 | 7 |
20 to 40 | 6 |
41 to 60 | 4 |
61 to 80 | 3 |
81 to 99 | 2 |
100 | 1 |