EFFECTS OF FLOWERING ON SUCROSE CONTENT AND SUCROSE YIELD IN FIVE SUGARCANE VARIETIES

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1 EECTS O LOWERING ON SUCROSE CONTENT AND SUCROSE YIELD IN IVE SUGARCANE VARIETIES By K. J. NUSS Suth African Sugar Assciatin Experiment Statin, Munt Edgecmbe 43 Abstract The yield and quality traits f flwered and vegetative stalks were determined frm May t Octber in five sugarcane varieties, and frm September t December in ne ther variety. rm July till Octber mass f sucrse was greater in flwered stalks than in vegetative stalks. The increase in stalk mass and sucrse cntent ccurred mainly in the tp part f the stalk. lwered stalks f variety NIl appeared t deterirate after Octber, prbably because f the absence f side shts. Intrductin lwering has frequently been reprted t reduce yields f sugar in sugarcane. In Barbads in a variety which flwered at the age f eight mnths the flwered stalks weighed less than nn-flwered stalks at the time f harvest (Ra 7 ). Similarly, in Hawaii, flwering was reprted t affect the yield fsucrse ifthe cane flwered in the first year fa tw year crp (Clements, as quted by Mre and Nuss'), Hwever, in variety NC376, flwered stalks were fund t cntain mre sugar than nn-flwered stalks (Gsnell and Lng'). In a detailed investigatin in Mauritius Julien and c-wrkers (Julien et ai V,4) fund flwered stalks t cntain mre sucrse than vegetative stalks fr tip t fur mnths after anthesis, as lng as the flwered stalks had prduced side shts. The increase was due t a greater fresh mass and mre sucrse in -tps f flwered stalks. The effect f flwering n sucrse yield has been little studied in Suth Africa. This paper presents results t shw the effect fflwering n cane yield and quality traits f five varieties sampled frm May t Octber, and fne variety sampled frm September t December. Materials and Methds Trial] ive varieties were included in three replicatins: NC376, the majr cmmercial variety which flwers prfusely n rare ccasins nly; NC3 and N55/5, varieties which flwer freely with little apparent effect n sucrse yield; and N5219 and Nil which flwer prfusely and seemingly lse yield as a result. The plts cnsisted f rws m lng and 1,5 m apart. lwering was prevented in half f each plt by night light breaks ftw hurs, frm 15 ebruary t 3 March in 191. the lights, w incandescent glbes at I m intervals, were suspended between tw cane rws I t 1,2 m abve the canpy. The height abve the canpy was adjusted as the cane grew taller. The cane was sampled n 1 May (ne mnth befre flwer emergence), July, 11 August, 15 September and 11 Octber. On each date twenty stalks were then taken at randm frm a sub plt, 4 rws X 1,5 min size, in the lighted plts (artificial vegetative - AV), and 2 stalks with flwers () and 2 withut flwers (natural vegetative - NV), frm a subplt f the same size in nn-lighted plts. The stalks were divided int the base (, m) and the tp (rest fthe stalk). These samples were then subjected t quality analysis. Trial 2 Variety N II was planted in 192in the field that had been used fr trial 1, with the same design and lighting. Because f a drught the cane was cut back in September 193. In 194, flwering was prevented in the designated plts by switching n the lights at 4h3 till sunrise frm 15 ebruary t 3 March. On 23 September, 22 Octber, 19 Nvember and December samples f 2 flwered () stalks frm nn-lighted plts and f 2 nn-flwered (AV) stalks frm lighted plts were taken fr sucrse analysis. Anther set f 2 stalks frm each treatment was divided int the base (, m) and tp (rest f the stalk). Results and discussin Trial] There was n flwering in the lighted plts. In the nnlighted plts flwering, which ccurred in June, was nt prfuse, with nly 9% fnc376, 31%fNC31O, 23%fN55/ 5,43% fn52/219 and 42% fnil stalks flwering. Table 1 Mean dry matter % cane, fibre % cane and brix values f flwered (), natural vegetative (NV), and artificially induced vegetative (AV) stalks f.five varieties Type f stalk Sampling date 1 May July II Aug 15 Sept Oct Dry matter - 27,2 2,4 29, 29,6 % cane NV 24, 26,4 27, 2,7 29, AV 24,4 27, 27,9 2,4 29, ibre % - 11,3 11,5,3,3 cane NV, 11, 11,6,1,4 AV 9, 11,2 11,5,1,6 Brix % - 16, 16,9 16, 17,3 cane NV,1 15,6 16,3 16,6 16,7 AV,5 15,7 16,4 16,3 16,3 Sme quality traits are given in Table 1. There were n majr differences in respect f % dry matter, fibre cntent and brix between, NV and AV stalks in any fthe varieties. Dry matter, fibre and brix cntents increased t abut the same extent in flwered and nn-flwered stalks between May and Octber. Increases in pl % cane were mre rapid in the tp part f the stalk than in the stalk as a whle (igure I). With varieties NC376 and NC3 the final (Octber) pl % cane values were smewhat lwer in AV than in and NV stalks; with the ther three varieties differences were negligible. By July bth the fresh mass (nt shwn) and the mass f pl per stalk f stalks were greater than thse f AV and NV stalks (igure 2). Althugh there is a tendency fr heavier stalks t flwer and lighter stalks nt (Julien et a1 4 ) the flwered stalks in this trial and thse tested in Mauritius als, increased faster in fresh mass and sucrse cntent than artificially vegetative stalks after. the initiatin f inflrescences. 11

2 Prceedings (If The Suth African Sugar Technlgists' Assciatin - June CI.l c 1' u *' NC376 Whle stalk -==-=- ---_NV AV 16 NC376 Tp f stalk ~ 1' ~ NC3 ~ NC3,~~,:/ '" /'" "v --..,- -AV / -:;.----_. NV N55/5 N55/5 CI.l ~ *' _1 2 N52/21~ N52/219 ~. ~.~ 1' U ~ N N11 ~ 1' ~ -t r-----,--., tg'----y------r-----,-----r-- ~ May June July Aug Sept Oct May June July Aug Sept Oct IGURE 1 Pl % Cane in whle stalks and tps f flwered () natural vegetative (NV) and artificial vegetative (A V) stalks f five varieties sampled frm May t Octber. Mst fthe increase in mass pl per stalk after July tk place in the tps f the stalks. In flwered plts stalks accumulated sucrse (mass pl) mre rapidly than NY stalks. Increases in mass pl were similar in NV and AV stalks f NC376 and N55/5; in NC3 mass pl f AV stalks reached an intermediate level between thse f and NV stalks; in N5219 and Nil mass pl fav stalks increased at a rate such as t equal the mass pl f stalks by Octber. In the case f NIl, at least, the similar final pl masses f AV and stalks can be explained by the cmmnly bserved 12

tendency in this variety, fr leaves n flwering stalks t senesce cmparatively quickly, with cnsequently impaired prductin f phtsynthate t supprt sucrse accumulatin.

3 tendency in this variety, fr leaves n flwering stalks t senesce cmparatively quickly, with cnsequently impaired prductin f phtsynthate t supprt sucrse accumulatin. N side shts had develped by that date. It can be seen (igure 2) that there was little increase after August in the mass pl f stalks f Nil. Estimates fchanges with time in mean pl yields f flwering and nn-flwering plts were derived frm the values shwn in igure '2 and the bserved percentages f stalks flwering in the respective varieties. Differences in yield between lighted and nn-lighted plts within varieties were generally small (igure 3). Hwever, the pltted pints suggest that by Octber, in varieties N52/219 and NIl, the mean pl yield per stalk in flwering plts was beginning t fall behind that in nn-flwering plts. Trial 2 Virtually all the stalks flwered in nn-lighted plts and nne flwered in the lighted plt, s the nly pssible cmparisns were between and AV stalks. The dry matter cntent f stalks f Nil decreased frm September t December, by which time their dry matter cntent was significantly lwer that that f AV stalks (Table 2). ibre cntent fav stalks increased mre with time than did that f stalks. The pl cntent f AV stalks remained mre r less cnstant during the perid that samples were taken but that f stalks decreased frm 15,3%in September t 13,2% in December. Yield f cane did nt differ greatly between and AV plts (differences were never significant) and changed little with time. Differences in yield f sugar between and AV plts were generally nt significant; but while sugar yield remained nearly cnstant in AV plts, in plts it apparently decreased slwly between September and December. Table 3 Pl % cane, mass per stalk and mass f pl per stalk f bases and tps f flwered () and artificial vegetative (AV) stalks f NIl Time f sampling and part f stalk Trait Type f stalk Bases Tps Sept Oct Nv Sept Oct Nv 16,3 15,6,2,1 13,1 11,6 Pl % cane AV 15,7 16,1 15,3,,,9 LSD (,5),9 1,5 1, 3,7 2,4 1,3 resh mass (glstalk) AV LSD (,5) Mass Pl, 66, 62,1 4,6 36,2 32,7 (glstalk) AV 71, 7,1 69, 49,4 57, 49,3 LSD (,5) 17, 15,9 11,6 5, 36,5 23,1 eldana, with,6%f interndes damaged, while 6% f AV stalks and,7% f interndes were damaged. The apprximately cnstant yield f sugar in AV plts up t December (Table 2) suggeststhat this degree finfestatin did nt result in much lss fyield in AV plants. Similarly, the smewhat greater degree f infestatin fstalks may nt have placed much part in the fall with time in sugar yield f plts. Small side shts had develped in stalks by December but were absent in stalks damaged by eldana. The results f Experiment 2 seem t be cnsistent with thse fr NIl in Experiment 1 (cf igure 2). In bth cases, with stalks, pl % cane and mass pl per stalk were at a maximum in September and had apparently begun decreasing by Octber. With AV stalks there was little increase in pl % cane after September in either experiment. Mass pl 'per stalk fav stalks remained apprximately cnstant after September in Experiment 2 and the trend f the pltted pints (igure 2) is cnstant, with mass pl f Nil reaching a maximum in abut Octber in Experiment 1. Table 2 Quality and yield f flwered () and artificially vegetative (AV) stalks f Nll in trial 2 Date f Type f Dry matter ibre % Pl % Tns cane Tns sugar Sampling stalk % cane cane cane Iha Iha 29,1 13, 15,3 74,4 11,4 September AV 29,2 13,1 15,1 1,6,4 LSD (,5) 2,1,5 3,6 5,1 2,6 13,, 73,9,9 Octber AV 2,7 13,1 15, 5,, LSD (,5) 2,2,9 31,6 4,3 2,3, 13,4 73, 9,9 Nvember AV 29,6,3,6 77,7 11,3 LSD (,5) 1,6 1,3 2,5 3,7 27, 13,7 13,2 74,1 9, December AV 29,9,4,9 4,,7 LSD (,5),4 1, 15,,6 The measurements made frm September t Nvember n stalks divided int bases and tps shw (Table 3) that the fall in pl % cane and in sugar yield f plts stemmed mainly frm lsses f sugar frm the upper part f the stalk. N samples were taken in December because eldana brer had infested the trial; 77% f stalks were damaged by 13 Cnclusin In Suth Africa flwering is nt nrmally prfuse in mst varieties. In the weeks fllwing anthesis, in partially flwering fields, mass f sucrse in stalks with flwers is greater than that fvegetative stalks. After anthesis flwering stalks gain weight faster than nn-flwering stalks, prbably until early summer (say Nvember) in mst varieties. Where there is n flwering (prevented with lights) stalks usually gain weight mre slwly than d flwering stalks; rather they gain weight at a similar rate t r smewhat faster than nnflwering stalks in partially flwering fields. By early summer, hwever, in varieties where senescence f leaves n flwering stalks is cmparatively rapid, the mass f sucrse per stalk in nn-flwering fields may catch up with that f flwering stalks in partially flwering fields. Accrdingly, yield f sucrse per hectare is generally little affected by flwering at least until early summer (see igure 3). In certain varieties, hwever, if flwering is heavy, yield f sucrse is likely t fall if harvesting is delayed until mid t late summer. Experiment I was terminated t sn (in any case flwering in it was generally sparse) t shw whether yield in a range f varieties is likely t be affected if the harvesting f heavily flwering fields is delayed until late summer. In Zimbabwe there was a substantial fall in pl % cane f flwered stalks fnc376 when the crp was carried ver fr harvesting in the fllwing seasn (Lng'),

4 Whle stalk Tp f stalk 2 NC <, "' 5-15 ~ <, ~ 5 - NC3..,/,fII",/ :::: AV ~.. ",,'," /. NV ' /-_/ + _ 6 4 ~ NC3 6 4,.. ~ AV ' ",,",---- tj" " "",--_/ " /"NV ;,'.." -"". /". -,~---- "AV / ~..P NV / ----'.,.."..",.."..-. /.. / 2-t ~ "' 5 - Nll,,,,, ",.y,, _.-._.-', AV -NV /:;:-'",,,,,/- ~,y' '--" 6 4 2""t N52/219 2-r Nll ~ _--_~AV 6 4 May June July Aug Sept Oct June July Aug Sept Oct IGURE 2 Mass f pl (g/stalk) f flwered () natural vegetative (NV) and artificial vegetative (AV) stalks and tps f five varieties sampled frm May t Octber. 14

5 " REERENCES I. Gsnell, GM and Lng, AC (1973). A cmparisn f yield and quality between flwered and nn-flwered cane. Prc S AfrSug Technl Ass47: Julien, MHR and Spramanien, GC (1976). The effect f flwering n yield in sugarcane. Rev agric et suer l/e Maurice 55: Julien, MHR; Delaveau, P; Spramanien, GC and Matine, J (1977). Age, time f harvest and envirnment as factrs influencing differences in yield between flwering and vegetative canes. Prc int Sc Sug Cane Technl16: Julien, MHR; Spramanien, GC; Martine,J and Medan,H (19). The rle f side shts in flwered stalks f sugarcane. Prc int ScSug Cane Technl17: Lng, AC (1976). A large varietal difference in cane deteriratin due t flwering. Prc S Afr Sug Technl Ass 5: Mre, PH and Nuss, KJ (197). lwering and flwer synchrnizatin. In Heinz, DJ (ed) Sugarcane Imprvement thrugh Breeding, pp Elsevier, Amsterdam. 7. Ra, PS (1977). Effects f flwering n yields and quality f sugarcane. Ex Agric 13: IGURE 3 Changes with time in estimated mean pl yield (g/stalk) f lighted (LP=nn flwering) and flwering (P) plts f five varieties. 15