Research ArticleReceived: 7 December 2013 Revised: 16 April 2014 Accepted article published: 26 April 2014 Published online in Wiley Online Library:

(wileyonlinelibrary.com) DOI 10.1002/jsfa.6709

Effects of drought after pollination on grainyield and quality of fresh waxymaizeDalei Lu,† Xuemei Cai,† Junyu Zhao, Xin Shen andWeiping Lu*

Abstract

BACKGROUND: Waxy maize is consumed as a vegetable when harvested at fresh stage (23–26 days after pollination) in China.Fresh waxy maize is normally grown under rain-fed conditions and suffers drought frequently during plant growth. The effectof drought on grain development of fresh waxymaize is not known.

RESULTS: Two years of pot trials showed that drought decreased fresh grain number and weight, which consequently reducedfresh ear and grain yields, especially in Yunuo7. Moisture and starch contents in grains were not affected but protein contentwas increased under drought treatment in both varieties. Grain soluble sugar content response to drought was not affectedin Suyunuo5 but was decreased in Yunuo7. Pasting and gelatinization temperatures, trough viscosity, final viscosity, setbackviscosity, gelatinization enthalpy and springiness of grain were little affected by drought. Drought decreased peak viscosity,breakdown viscosity and adhesiveness (absolute value), whereas it increased hardness. The retrogradation percentage wasincreased in both varieties in both years.

CONCLUSION: Drought after pollination decreased the fresh waxy maize yield. Grain quality was reduced through decreasedpeakviscosityandadhesiveness (absolutevalue),while itshardnessandretrogradationpercentagewere increased,whichmightbe due to the increased protein content.© 2014 Society of Chemical Industry

Keywords: fresh waxy maize; drought; yield; protein content; grain quality

INTRODUCTIONWaxy maize (Zeamays L. sinensis Kulesh) is a special maize mutantwidely consumed as a vegetable in China because of its goodstickiness. The stickiness is attributed to its endosperm starchcomposed of nearly 100% amylopectin because of a wx genemutation. With the improvement in the national living standard,the plant area of fresh waxy maize has become the largest amongspecial commercial crop areas.1

Maize, one of the most important food crops, is grown underrain-fed and irrigated conditions worldwide. Under rain-fed con-ditions, developing grains of maize are frequently exposed todrought during the grain development stage. The annual maizeyield loss due to water stress dominates all natural causes, andthe degree of influence of water stress is gradually increasing withglobal climate change and environmental deterioration.2,3 Maizeis sensitive to water stress, and numerous studies have focused onthe influence of water stress on grain yield and relative physiolog-ical indices.3–7

Drought can produce changes in grain quality for differentfood applications as well as reduce the grain yield. It has beendemonstrated that drought could decrease the starch contentand increase the protein content in many crops.8,9 In sweet maizegrain, although the protein content increased, the Fe, Zn and Cuconcentrations in the kernels decreased with increasing waterdeficiency.10 In addition, drought after pollination decreases theamylose and lipid contents and increases the percentage of largegranules, resulting in higher peak viscosity and lower gelatiniza-tion temperatures in wheat starch.11 Other research also revealed

that water stress after flowering decreased the protein content ofrice flour, while its swelling power, peak viscosity, gel hardness andcohesiveness increased.12 However, the changes in the grain yieldand quality of fresh waxy maize in response to water deficit afterpollination have yet to be determined. This study investigated theeffects of drought after pollination on the grain yield and qualityof fresh waxy maize.

MATERIALS ANDMETHODSMaterialsTwo varieties of fresh waxy maize, Suyunuo5 and Yunuo7, wereused in this study. These samples are the control varieties in theChina south fresh waxy maize regional test and have large plantareas in southern China.

Experimental designThe experimentwas conducted at the farmof YangzhouUniversityin 2011 and 2012. Seeds were sown on 1 July and transplanted to

∗ Correspondence to: Lu Weiping, Key Laboratory of Crop Genetics and Phys-iology of Jiangsu Province, Yangzhou University, Yangzhou, 225009, China.E-mail: wplu@yzu.edu.cn

† These authors contributed equally

Key Laboratory of CropGenetics and Physiology of Jiangsu Province, YangzhouUniversity, Yangzhou, 225009, China

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plastic pots on 5 July (two plants per pot, with one plant left at thejointing stage) in both years. Each treatment included eight potsas replicates. Each pot was 30 cm in height and 30 cm in diame-ter. Each pot was filled with 15 kg of sieved sandy loam soils. Theplants were given a basal dressing of 10 g per pot (commercial fer-tilizer, N/P2O5/K2O= 15:15:15%) during transplantation and a topdressingof 6.6 gper pot (commercial urea, N concentration= 46%)during the jointing stage.A negative-pressure water supply and controlling pot device

(Chinese Patent 200510123976) was used to control the differentrelative soil moisture contents (SMCs) by setting the water supplytension of the device at different values.13 The pot device was con-nected to a negative-pressure water control device by permeableand airtight ceramic irrigation emitters. The irrigation emitter wasembedded in the pot base and could adjust the SMCby setting thevalue of the negative-pressure water supply. The emitter ensuredthe continuous and accurate control of the water supply. The keytechnology was based on the theories of soil water potential bal-ance and water pressure control as well as on the different valuesof negative pressure corresponding to different SMCs.Plant growth under the relative SMC was about 75% before

flowering stage. The plants were subjected to stress treatmentsafter artificial pollination until harvest at fresh stage (23 daysafter pollination for both varieties). The pollination/harvest datesfor Suyunuo5 were 29 August/21 September in 2011 and 28August/20 September in 2012. The corresponding dates forYunuo7 were 2 days later than those for Suyunuo5. The SMCs forcontrol and drought treatments were 75 and 60% respectively.14

A transparent waterproof canopy at a height of 5m aboveground was used to avoid the influence of rainfall. The meanday/night temperature, humidity and light intensity during grainfilling were 26/18 ∘C, 75%, 1404 μmolm−2 s−1 and 29/18 ∘C, 69%,1523 μmolm−2 s−1 in 2011 and 2012 respectively.

Grain yield determination and flour productionThe grain numbers per ear were counted and the fresh ear weight(g per plant) was obtained (mean of three ears), then the grainswere manually stripped from the cobs and fresh grain yield (g perplant) and freshgrainweight (mg)weredetermined (meanof threeears). After grain yielddetermination, 100grains (three tofive lines)were dried in a hot air oven at 100 ∘C for 12 h for moisture con-tent analysis (triplicates). The moisture content was calculated as:moisture content (g kg−1)= 1000× (1−dry weight/fresh weight).The other grains were oven dried at 40 ∘C for 5 days, ground usinga grinder (FW100, Taisite, Tianjin, China) and passed through a100-mesh (0.149mm) sieve for sample determination.

Proximate analysisThe soluble sugar and starch contents (g kg−1) in the flour weredetermined by ICC Method 123/1.15 The nitrogen content (g kg−1)was determined using the Kjeldahl method (AACC Method46–10).16 The protein content was evaluated by measuring thenitrogen content (protein content=nitrogen content× 6.25). Allmeasurements were made in duplicate.

Pasting propertiesThe flour pasting properties (28 g total weight; 10% w/w, drybasis) were evaluated using a rapid viscosity analyzer (Model3D, Newport Scientific, New South Wales, Australia) following themethod we described previously.17 All measurements were madein duplicate.

Textural propertiesTwo fresh waxy maize ears in each treatment were boiled(immersed fully in water) in an electric cooker for 30min. Thetextural properties of the fully cooked grains that were cut offfrom the mid-section of the ear (five kernels per ear) were imme-diately measured using a TA-XT2i texture analyzer (Stable MicroSystems, Godalming, UK) coupled with a 35mm diameter alu-minum plate probe. Some parameters of the compression modewere set as follows: pre-test speed, 1mms−1; test speed, 2mms−1;post-test speed, 2mms−1; trigger force, 5 g; distance, 70% ofinitial sample height. A force–time curve was obtained from thetest, and the textural results discussed below determined.17 Allmeasurements were repeated ten times.

Thermal propertiesThe flour thermal characteristics were studied using a differentialscanning calorimeter (Model 200 F3 Maia, NETZSCH, Bavaria, Ger-many) according to themethod described by Sandhu and Singh.18

All measurements were made in duplicate.

Statistical analysisThe data were subjected to analysis of variance by the leastsignificant difference test at 5% probability level using thedata-processing system (DPS 7.05).19

RESULTS ANDDISCUSSIONGrain yieldTwo years of pot trials showed that drought decreased grainnumber and weight, which consequently reduced plant ear andgrain yields, in both varieties in both years (Fig. 1). The yield losswas due primarily to the decrement of grain number (r= 0.99 and0.92 for ear yield and grain yield respectively), followed by grainweight (r= 0.52 and 0.80 for ear yield and grain yield respectively),indicating that the grain number was the vital yield componentdirectly associated with increased grain yield in cereal crops.20 Itwas also the most important trait considered to estimate droughttolerance in maize.21 Similar results were also reported for normalmaize,22 barley23 and wheat.24 The decrement of fresh ear andgrain yields in plants exposed to drought was more severe inYunuo7, indicating that it was more sensitive to water stress thanSuyunuo5 (Fig. 1).

Grain proximate compositionDrought did not affect the water-soluble sugar content inSuyunuo5 but decreased it in Yunuo7 in both years (Fig. 2).Brooks et al.25 observed that water deficit did not affect thesucrose content in wheat and barley, while other studies foundthat water deficit significantly decreased the sugar content inwheat26 and normal maize.27

The grain moisture and starch contents in both varieties werenot affected by water stress, indicating that the grain-fillingrate was similar between the control and drought treatments(Fig. 2). The similar starch content under both treatments maybe due to the decrement of grain weight (13.2%) being similarto that of starch (14.8%). A previous review summarized thatdrought decreased the starch content in many crops.8 NeSmithand Ritchie28 observed that water stress can shorten the durationof the linear kernel-filling phase but cannot reduce the rate ofsingle-kernel filling. Sala et al.29 also demonstrated that water

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Figure 1. Effect of drought after pollination on yield of fresh waxy maize.

stress cannot affect the grain moisture in plants until they reachphysiological maturity. Zhao et al.30 observed that mild droughtincreased starch content but severe water deficit decreased it.Water shortage increased protein content in both varieties in

both years (Fig. 2). The high protein content under droughttreatment was only a concentration effect, as the decrement ofgrain weight and starch accumulation was more severe than thatof protein accumulation (average values were 13.2 and 14.8 vs6.8%). Many studies have reported that water stress increasesprotein content, as reviewed by Thitisaksakul et al.9 Cai et al.31

and Gunaratne et al.12 observed that drought after pollinationincreased the protein content in rice flour. The results can beattributed to the increase in the activities of glutamine syn-thetase and glutamate synthase, which are involved in nitrogenmetabolism by promoting nitrogen accumulation and increasingthe protein content of grains.31

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Figure 2. Effect of drought on grain proximate composition (dry basis) offresh waxy maize.

Pasting propertiesThe pasting characteristics of fresh waxy maize flour were influ-enced by variety and drought treatment (Table 1). Compared withthe control, drought did not affect the trough and final viscosi-ties in all treatments, except for a decrement in Suyunuo5 in 2012.Peak and breakdown viscosities in both varieties were decreasedby drought in both years. Pasting temperature was only increasedin Suyunuo5 in 2012. In a study by Fofana et al.,32 peak and break-down viscosities were decreased by water deficit in the ripen-ing stage. However, several researchers found that water stressincreases peak viscosity.11,12 This discrepancy in results may bedue to the different experimental designs (simple restricted irri-gation in the previous studies) and variety-dependent responsesof different crops to water stress. The low value of setback

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Table 1. Effect of drought after pollination on pasting properties of fresh waxy maize floura

PVb TV BD FV SB Ptemp

Year Variety Treatment (cP) (cP) (cP) (cP) (cP) (∘C)

2011 Suyunuo5 Control 1144b 352 cd 792b 444 cd 93bc 72.7ab

Drought 1077b 410bc 668d 492c 83c 73.2a

Yunuo7 Control 1084b 271de 813ab 379de 109b 71.9b

Drought 988c 268de 721c 359ef 91bc 72.8ab

2012 Suyunuo5 Control 1415a 564a 852a 721a 157a 69.5c

Drought 975c 463b 512e 627b 164a 71.9b

Yunuo7 Control 955c 183ef 772b 288 fg 105b 69.9c

Drought 628d 166f 462f 243 g 78c 70.3c

a Mean values in the same column followed by different letters are significantly different (P≤ 0.05).b PV, peak viscosity; TV, trough viscosity; BD, breakdown viscosity; FV, final viscosity; SB, setback viscosity; Ptemp, pasting temperature.

Table 2. Effect of drought after pollination on textural properties of fresh waxy maize graina

Year Variety Treatment Hardness (g) Adhesiveness Springiness Cohesiveness Chewiness Resilience

2011 Suyunuo5 Control 10709b −21.5c 0.376a 0.288ab 1172ab 0.211b

Drought 10648b −11.0a 0.402a 0.301a 1288a 0.231a

Yunuo7 Control 7736d −16.0b 0.379a 0.261 cd 790 cd 0.203b

Drought 8380c −16.0b 0.336a 0.256d 723 cd 0.194b

2012 Suyunuo5 Control 10243b −37.5e 0.334a 0.277bc 951bc 0.170c

Drought 12085a −33.1d 0.371a 0.259 cd 1171ab 0.152 cd

Yunuo7 Control 7560d −37.4e 0.350a 0.234e 616d 0.138d

Drought 10397b −22.1c 0.341a 0.257d 930bc 0.157c

a Mean values in the same column followed by different letters are significantly different (P≤ 0.05).

viscosity in the present trial (≤164 cP) indicates that waxy maizestarch forms a weak gel during cooling because its starch com-prises 100% amylopectin.33

Textural propertiesGrain springiness was not affected by drought in both vari-eties in both years, hardness was increased by drought, exceptfor Suyunuo5 in 2011, and adhesiveness was also increased bydrought, except for Yunuo7 in 2011. Cohesiveness and chewinesswere not affected by water deficit, except for Yunuo7 in 2012.Resilience response to drought was dependent on variety andyear: it was not affected in Yunuo7 but increased in Suyunuo5 in2011, while the contrary tendency was observed in 2012 (Table 2).The high values of hardness and adhesiveness under droughttreatments indicate that the grain stickiness was decreased andthe grain rigidity was increased. As a result, the quality of freshwaxy maize was reduced. The low adhesiveness (absolute value)under drought observed by texture analyzer was consistent withthe low peak viscosity value observed by rapid viscosity analyzer.Gunaratne et al.12 reported that water stress increases gel hard-ness and adhesiveness in rice flour. Cai et al.34 also observed thatcooked rice grain presents high hardness and low adhesivenessunder water stress, thus resulting in poor eating and cooking qual-ities. Compared with Yunuo7, Suyunuo5 presented higher hard-ness and chewiness but lower adhesiveness. This information canbe used in selecting fresh waxy maize varieties according to taste,softness or stickiness.

Gelatinization propertiesTable 3 shows the effects of water stress on the gelatinizationcharacteristics of fresh waxy maize flour. The ΔHgel of both vari-eties was not affected by water stress in both years. To, Tp and Tc

were affectedbywater stress. However, the variable coefficients forthese three characteristics were 2.0, 1.9 and 1.3 respectively, indi-cating that the differences were insignificant. Gunaratne et al.12

also observed that gelatinization temperature is slightly affectedby water stress.After the gelatinized samples were stored at 4 ∘C for 7 days,

retrogradation occurred. The %R was increased by water stress inboth varieties in both years, indicating that fresh waxymaize grainis easily retrograded under water stress conditions. Gunaratneet al.12 also observed that the %R of rice flour was increased bywater stress. The high %R under water stress may be primarily dueto high protein content in flour, because the denatured protein ingelatinized grain increases aggregation.35

CONCLUSIONSTwo years of pot trials showed that drought after pollinationresulted in the loss of fresh ear and grain yields by decreasing grainnumber and grain kernel weight, with the loss being more severein Yunuo7. Drought did not affect starch and moisture contentsbut increased protein content in both varieties. The soluble sugarcontent response to drought was only decreased in Yunuo7 inboth years. Drought little affected trough, final and setback viscosi-ties but decreased peak and breakdown viscosities. Water deficit

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Table 3. Effect of drought after pollination on thermal properties of fresh waxy maize floura

ΔHgelb To Tp Tc ΔHret

Year Variety Treatment (J g−1) (∘C) (∘C) (∘C) (J g−1) %R

2011 Suyunuo5 Control 9.4a 69.4c 74.7d 82.1c 3.3a 35.1 cdDrought 9.0a 69.1c 74.3e 81.6d 3.4a 37.4bc

Yunuo7 Control 8.2bc 69.4c 74.1f 81.1e 2.7b 33.0deDrought 8.1c 69.0c 74.4e 81.7 cd 3.4a 42.1a

2012 Suyunuo5 Control 8.8ab 71.3b 76.4c 83.1b 2.4b 27.4fDrought 8.9a 72.5a 77.5a 84.0a 3.5a 39.7b

Yunuo7 Control 8.1c 71.7b 77.2b 84.0a 2.5b 30.6eDrought 8.1c 71.6b 76.4c 83.0b 2.6b 32.5de

a Mean values in the same column followed by different letters are significantly different (P≤ 0.05).b ΔHgel, gelatinization enthalpy; To, onset temperature; Tp, peak gelatinization temperature; Tc, conclusion temperature; ΔHret, retrogradationenthalpy; %R, retrogradation percentage.

increased adhesiveness and hardness but did not change springi-ness. Gelatinization enthalpy and temperature were little affectedby water stress. %R was increased by drought in both varieties inboth years. Significant differences in grain yield and quality werealso observed between the two varieties.

ACKNOWLEDGEMENTSThis study was supported by the Chinese Natural Science Foun-dation (Grant Nos. 31271640 and 31000684) and the Priority Aca-demic ProgramDevelopment of Jiangsu Higher Education Institu-tions.

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