Pearl millet (Pennisetum glaucum) is considered to be a

short-day species that flowers, or flowers earlier, when

day lengths are short. A few studies with two to six

planting dates and few selected entries have been

conducted in USA (Burton 1965), Senegal (Ramond

1968), and India (Patil et al. 1978, Das 1991). However,

there is no known research on the flowering response of

pearl millet to photoperiod changes over the entire year.

Likewise, knowledge about the photoperiod-sensitivity

in West and Central African pearl millets is insufficient

Boureima, S S

Clerget, B

Haussmann, B I G

Weltzien, E

ICRISAT Open Access Repository

Surprising flowering response to photoperiod: Preliminary characterization of West and Central African pearl millet germplasm

An Open Access Journal published by ICRISATSAT eJournal ⏐ ejournal.icrisat.org - 1 - December 2007 ⏐ Volume 5 ⏐ Issue 1Surprising flowering response to photoperiod: Preliminarycharacterization of West and Central African pearl millet germplasmB Clerget1*, BIG Haussmann², SS Boureima3 and E Weltzien11. ICRISAT/CIRAD-UPR Biodiversité en savanes, BP 320, Bamako, Mali2. ICRISAT, BP 12404, Niamey, Niger3. Université Abdou Moumouni, BP 10662, Niamey, Niger*Corresponding author: b.clerget@cirad.frIntroductionPearl millet (Pennisetum glaucum) is considered to be ashort-day species that flowers, or flowers earlier, whenday lengths are short. A few studies with two to sixplanting dates and few selected entries have beenconducted in USA (Burton 1965), Senegal (Ramond1968), and India (Patil et al. 1978, Das 1991). However,there is no known research on the flowering response ofpearl millet to photoperiod changes over the entire year.Likewise, knowledge about the photoperiod-sensitivityin West and Central African pearl millets is insufficient.Materials and methodsMonthly sowings of 12 pearl millet varieties atSamanko, Mali. A set of 12 West African pearl milletvarieties from Senegal, Mali, Burkina Faso and Niger,covering a large range of photoperiod-sensitivity, wassown every month at Samanko, Mali (12°32’ N, 8°04’W) during 2 years from June 2004 to May 2006.Plantings were on or about the 10th of each month, exceptfor the first two sowings on 26 June and 27 July 2004.Plots of four rows, 0.75 m apart and 5 m long were sownwith 10 seeds per hill at 20 cm within rows and thinned toone plant per hill two weeks after emergence. Plots wereirrigated twice a week during the dry season. Two plantsper plot were sampled weekly and dissected to count thenumber of leaves initiated at the apex and record the dateof panicle initiation. Air temperature at 2 m above groundwas recorded and thermal time was calculated on anhourly basis, using 11, 34 and 54°C as base, optimal andmaximum temperatures, respectively.Two sowings of 360 landraces at Sadoré, Niger.Three-hundred sixty pearl millet landraces from all overWest and Central Africa were sown in Sadoré, Niger(13°06’ N, 2°21’ E) on 14 July and 15 August 2006. TheJuly sowing was done using two-row plots, with 0.75 minterrow and 0.8 m intra-row distance and 7 hills per row.The entries were randomized using a-design with 8 plotsper incomplete block and 3 replications. The Augustplanting was an unreplicated observation nursery using 1-row plots of 7 hills, with the same spacing as above. TheAugust planting was irrigated once a week with 30 mmfrom 3 October until 15 November. Plots were thinned totwo plants per hill in both sowings. ANOVA of thereplicated flowering data from the July sowing was usedto estimate the standard error for flowering dates(assumed to be equal also in the August planting) as:with t = student,          = error variance and n = number ofreplications.Results and discussionMonthly sowings in Samanko, Mali. The 12 varietiesshowed large variation for the duration of their vegetativephase (sensu stricto, from sowing to panicle initiation) inresponse to the different sowing dates (Fig. 1). This largevariation was observed both when measured in days andin thermal time, with quite close agreement between thetwo measures. The duration of the vegetative phase ofGB 8735 did not respond to sowing dates in the first sixmonths of the year and the minimum vegetative phase,lasting 23 days or 277°C.d, occurred when sown in July,while the maximum (40 days or 527°C.d) occurred withthe October sowing. The varieties Sanko and Kapelga, incontrast, were highly responsive, and Bandiagara wasσσ22*eent +σ2eCitation : Clerget B, Haussmann BIG, Boureima SS and Weltzien E, (2007) Surprising flowering response tophotoperiod: Preliminary characterization of West and Central African pearl millet germplasm. Journal of SATAgricultural Research 5(1).An Open Access Journal published by ICRISATSAT eJournal ⏐ ejournal.icrisat.org - 2 - December 2007 ⏐ Volume 5 ⏐ Issue 105010015020001 Jan 01 Apr 01 Jul 01 Oct 01 JanSowing datesDays to panicle initiationSanko Kapelga Bandiagara GB8735 Hombori, Haini Kirei, ICMVIS 90311, LCICDMR15, 3/4 Ex-Borno, SOSAT C88, Souna 3, Zongo0500100015002000250030003500400001 Jan 01 Apr 01 Jul 01 Oct 01 JanSowing datesThermal time to panicle initiation (°C.d)Figure 1. Average duration of the vegetative phase, from sowing to panicle initiation, in days and thermal time, of 12 pearl milletvarieties sown monthly at Samako, Mali during the period of June 2004 to May 2006. Bars indicate the confidence interval (P = 0.05)of each monthly average.July01020304040 50 60 70 80 90 100 110Days to flowerNumberAugust01020304040 50 60 70 80 90 100 110Days to flowerNumberintermediate. The vegetative phase of Sanko was 151days or 2462°C.d at its maximum when sown in March,and only 36 days or 424°C.d when sown in September.The remaining 8 varieties had similar and fairly stableduration of their vegetative phase for the first six sowingsof the year, which averaged 41 days, suggestingphotoperiod-insensitivity. However, they exhibited anunexpected minimal duration of 35 days for the sowingsin early July. Durations were a bit more variable forsowings during the last five months of the year. Theaverage durations of the vegetative period for the 8 earlyvarieties (Hombori, Haini Kirei, ICMVIS 90311, LCIC-DMR15, ¾ Ex-Borno, SOSAT C88, Souna 3 and Zongo)plus GB 8735, expressed in thermal time, showed twoannual minima, 460°C.d in July and 424°C.d in December,and two annual maxima, 650°C.d in May and 659°C.d inSeptember. These observations indicate that these early-maturing varieties achieved panicle initiation fastest forsowings done both when the day lengths were the longest(late June to early July) and the shortest (December).These observations are surprising and actually raisequestions about the classification of pearl millet as ashort-day plant.Two sowing dates of 360 accessions in Sadoré, Niger.The flowering of 360 West and Central African milletaccessions occurred between 43 and 109 days aftersowing when sown on July 14, with an average of 70.1days. The range of flowering for the 15 August sowingFigure 2. Frequency distributions of the durations from sowingto 50% flowering recorded on 360 West and Central Africanpearl millet accessions at Sadoré, Niger for sowings done on 14July and 15 August 2006.An Open Access Journal published by ICRISATSAT eJournal ⏐ ejournal.icrisat.org - 3 - December 2007 ⏐ Volume 5 ⏐ Issue 1051015202530-30 -20 -10 0 10 20 30Difference of vegetative phase durations for sowings done in July and August (d)Number051015202530-600 -400 -200 0 200 400Difference of vegetative phase durations for sowings done in July and August (°C.d)Numbera) b)date was between 45 and 94 days, with an average of 63.2days (Fig. 2). Thus the vegetative phase (sensu lato, fromsowing to flowering) was 6.9 days shorter in the Augustsowing. The varietal differences for duration of theirvegetative phase between the July and August sowingdates ranged from −27 (strong shortening of the time toflower in the August planting) to +23 days (prolongedtime to flower in the August planting) (Fig. 3a). Theconfidence interval for comparing the duration of thevegetative phase between sowing dates was 5.6 days (at5% level of probability). Using this confidence interval,the 197 accessions (55% of the collection) that hadsignificantly shorter vegetative cycles with the latersowing date were classified as photoperiod-sensitive, andthe 137 (39%) accessions that had vegetative cycledifferences near zero (between −5.6 and +5.6) wereclassified as insensitive. The 22 varieties (6%) that had asignificantly longer vegetative phase for the Augustsowing were particularly surprising. These varietiesflowered between 43 and 77 days in the July sowing;representing the earliest half of the total flowering rangeobserved in the collection. Since September was warmerthan July and August (data not shown), the thermal timeduring 50 days after sowing was also lower for the Julysowing (864°C.d) than for the August sowing (902°C.d).Therefore, the number of varieties with a significantlylonger vegetative phase in August increased to 34 (9% ofthe collection) when the duration was expressed inthermal time (Fig. 3b). These preliminary observationsrequire further validation.Results from the 2006 experiment in Sadoré, Nigerconfirm that many West and Central African pearl milletvarieties are photoperiod-sensitive. Further, they confirmthe results from Samanko, Mali that showed a significantnumber of early varieties of pearl millet which floweredlater when sown in August than in July. This unexpectedresponse is not due to a direct effect of the temperaturebut could be caused by an interaction betweenphotoperiod and temperature. It also could be caused byanother signal which is the daily change of the sunriseand sunset hours, as has been already shown for tropicaltrees (Borchert et al. 2005). The period around 21 June isnot only the moment when day lengths are longest butalso the moment when the daily variation of the sunsettime reaches a minimum. Since long day lengths in Julyare not expected to induce early flowering dates, the dailychange of the sunset time could be the signal that explainsthis behavior.The capacity of early pearl millet varieties to reducetheir vegetative phase by a week when sown late, ie, inJuly, may provide significant adaptive advantages in theSahelian region when later sowing dates correspond withmore limited duration of available moisture. Thiscapacity for growth plasticity in materials traditionallyconsidered to be photoperiod-insensitive certainlywarrants more detailed examinations.Acknowledgments. The Sadoré and Samanko experimentswere supported by funding from the Federal Ministry forEconomic Cooperation and Development (BMZ),Germany. Technical assistance of A Amadou, A Abarchi,D Lankoande and M Sidibe is highly appreciated.ReferencesBorchert R, Renner SS, Callo Z, Navanrrede D, TyoA, Gauthier L, Spichiger R and von Hildebrand P.2005. Photoperiodic induction of synchronous floweringnear the Equator. Nature 433:627–629.Figure 3. Frequency distribution of the difference of the durations from sowing to flowering in (a) days and (b) thermal time, of 357pearl millet accessions when sown on 14 July versus 15 August 2006 at Sadoré, Niger.An Open Access Journal published by ICRISATSAT eJournal ⏐ ejournal.icrisat.org - 4 - December 2007 ⏐ Volume 5 ⏐ Issue 1Burton GW. 1965. Photoperiodism in pearl millet,Pennisetum typhoides. Crop Science 5:333–335.Das LDV. 1991. Quantitative responses of pearl millet todifferent sowing dates. Mysore Journal of Agriculture25:169–174.Patil BD, Reddy BB and Gill AS. 1978. Photoperiodismin relation to forage yield in pearl millet. SABRAOJournal 10:126–129.Ramond C. 1968. Pour une meilleure connaissance de lacroissance et du développement des mils Pennisetum.Agronomie Tropicale 23:844–863.

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Surprising flowering response to photoperiod: Preliminary characterization of West and Central African pearl millet germplasm

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