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Journal of Cereal Science 57 (2013) 398e404

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Journal of Cereal Science

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Heat and drought stress on durum wheat: Responses of genotypes, yield,and quality parameters

Yun-Fang Li a,b,c, Yu Wu a, Nayelli Hernandez-Espinosa b, Roberto J. Peña b,*

aChengdu Institute of Biology, Chinese Academy of Sciences, Chengdu, Chinab International Maize and Wheat Improvement Center (CIMMYT, Int), Apdo Postal 6-641, 06600 Mexico D.F., MexicocGraduate University of Chinese Academy of Sciences, Beijing, China

a r t i c l e i n f o

Article history:Received 22 October 2012Received in revised form10 January 2013Accepted 14 January 2013

Keywords:Drought and heat stressDurum wheatFlour yellownessGluten strength

Abbreviations: FP, flour protein content; FY, flourcontent; LARC, lactic acid retention capacity; MPT, mixsedimentation volume; SIG, swelling index of glutweight; TW, test weight; Y, yield.* Corresponding author. Tel.: þ52 55 5804 2004; fa

E-mail address: j.pena@cgiar.org (R.J. Peña).

0733-5210/$ e see front matter � 2013 Elsevier Ltd.http://dx.doi.org/10.1016/j.jcs.2013.01.005

a b s t r a c t

Heat and/or drought stress during cultivation are likely to affect the processing quality of durum wheat(Triticum turgidum L. ssp. durum). This work examined the effects of drought and heat stress conditionson grain yield and quality parameters of nine durum wheat varieties, grown during two years (2008e09and 2009e10). Generally, G and E showed main effects on all the parameters whereas the effects of G � Ewere relatively small. More precipitation in Y09e10 may account for the large differences in parametersobserved between crop cycles (Y08e09 and Y09e10). Combined results of the two crop cycles showedthat flour protein content (FP) and SDS sedimentation volume (SDSS) increased under both stress con-ditions, but not significantly. In contrast the gluten strength-related parameters lactic acid retentioncapacity (LARC) and mixograph peak time (MPT) increased and decreased significantly under droughtand heat stress, respectively. Drought and heat stress drastically reduced grain yield (Y) but significantlyenhanced flour yellowness (FY). LARC and the swelling index of glutenin (SIG) could be alternative teststo screen for gluten strength. Genotypes and qualtiy parameters performed differently to drought andheat stress, which justifies screening durum wheat for both yield and quality traits under these twoabiotic stress conditions.

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1. Introduction

Durum wheat (Triticum turgidum L. ssp. durum) is cultivatedmainly in the Mediterranean Basin and North America, in irrigatedand rainfed environments. It possesses harder kernel, considerablyhigher yellow pigment content, and relatively higher grain proteincontent than common wheat (Triticum aestivum L.). Durum wheatgenerally has inextensible gluten (Ammar et al., 2000; Liu et al.,1996) and therefore, most of the durum wheat produced world-wide is milled into semolina to make a compact and stiff dough tomanufacture alimentary pasta. In West Asia and North Africa,durum wheat is used extensively to prepare regional foods such ascouscous, frekeh, and bulgur. Dense durum wheat breads arepopular in the Mediterranean Basin, partly due to their unique

yellowness; GP, grain proteinograph peak time; SDSS, SDSenin; TKW, thousand kernel

x: þ52 55 58047558.

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texture and flavor (Liu et al., 1996). Yellow pigment content, proteincontent, and gluten strength play a critical role in determining thepasta-making quality of durum wheat (Edwards et al., 2003; Peñaet al., 2002).

Durum wheats frequently experience drought and/or heatstress in the SEWANA region (South Europe, West Asia, and NorthAfrica), where they are mainly grown under rainfed conditions.Heat and drought stress, particularly during the grain fillingperiod, often limit the expression of yield potential, may enhancegrain protein content, and may improve or deteriorate processingquality. It is therefore very important to determine the effects ofthese environmental factors on durum wheat yield and quality. Afew studies (Ames et al., 1999; Mariani et al., 1995; Rharrabtiaet al., 2003a) have investigated the effects of genotype (G), envi-ronment (E), and their interaction (G � E) on durumwheat quality.In general, it has been seen that G � E effects are smaller thanthose of G and/or E. In addition, variations in the relative contri-butions of G, E, and G � E on different quality parameters, mainlydue to different genotypes and environments studied, have beenobserved.

Studies of heat stress onwheat have been focusing on the periodof grain filling (Borghi et al., 1995; Corbellini et al., 1997,1998; Stone

Y.-F. Li et al. / Journal of Cereal Science 57 (2013) 398e404 399

and Nicolas, 1995), and have shown that two typical heat stressesare common during wheat grain filling. “Heat shock” is charac-terized by sudden, extreme high temperatures (>32 �C) for a shortduration (3e5 days), while“ chronic heat stress” consists of mod-erately high maximum temperatures (20e30 �C) for a longerduration. Heat shock takes different forms, which are characterizedby timing (days after anthesis) and by duration, which may alsogave rise to different effects on the durumwheat quality (Corbelliniet al., 1997). A “strengthening” effect has been observed withchronic heat stress whereas heat shock may have a “weakening”effect, both in common and durum wheat (Borghi et al., 1995;Wardlaw and Wrigley, 1994; Wrigley et al., 1994).

When compared with heat stress, there is limited literature onthe effects of drought caused by erratic or deficient rainfall orlimited irrigation on durum wheat quality. Flagella et al. (2010)found that technological quality and protein composition wereaffected by water scarcity, but that the severity was dependent onwhen the stress occurred. Moisture stress caused an increase inprotein content and a reduction in thousand kernel weight(Rharrabtia et al., 2003a). Limited water input during grain fillingdecreased grain quality by reducing test weight and SDS sed-imentation volume, and by increasing ash content (Rharrabtia et al.,2003b).

Heat stress experiments can be achieved by late sowing in thefield, by plots covered with tunnels, or by transferring pots into thegreenhouse during grain filling. For studies comparing the variationin timing and duration for different stress types, the tunnel orgreenhouse methods are preferable (Corbellini et al., 1997), thoughdifferences in results may occur between the two methods them-selves (Borghi et al., 1995). The fact that heat stress occurs in thefield should promote more field-based research on the effects ofstress on wheat quality. Although it has been shown that the re-sponses of durumwheat genotypes to heat stress vary regardless ofthe timing and duration treatment (De Stefanis et al., 2002; Marianiet al., 1995), no research focusing on genotype responses to droughtstress in durum wheat is available. Therefore, more attentionshould be given to the selection of cultivars showing adaption toboth heat and drought conditions.

In order to breed for acceptable durum wheat quality underdrought and heat stress, it is necessary to screen hundreds of linesin the early segregating stage, using rapid and reliable small-scaletests. When breeding for durum wheat quality, the SDS-sedimentation (SDSS) test is commonly used to predict glutenstrength (Brites and Carrillo, 2001; Peña et al., 1994). Other rapidgluten strength-related screening tests exist but these are appliedmainly to common wheat. The lactic acid retention capacity(LARC) test was designed to estimate gluten strength of soft wheat(Gaines, 2000), and it was highly positively associated with glutenstrength parameters of Farinograph and Mixograph (Ram et al.,2005). The swelling index of glutenin (SIG) was recently devel-oped for estimating insoluble glutenin content, and can be usedfor predicting gluten strength (Wang and Kovacs, 2002a,b). LARCand SIG both meet the requirements (rapid small-scale tests) forscreening in the early stages of breeding; therefore, these twomethods may be good options, alternative to the SDSS test, torapidly estimate gluten strength. These two tests were evaluatedwith respect to their performance in drought and heat stressconditions for common wheat (Li et al., 2013), but how thesesmall-scale tests may perform to heat and drought stresses indurum wheat is unknown.

The objectives of this study were: to examine the influence of G,E, and G � E on ten parameters of nine durum wheat cultivarspossessing contrasting quality attributes, and to determine howgenotypes and parameters will respond under heat and droughtstress relative to optimum growing conditions.

2. Materials and methods

2.1. Materials and field experiment

Seven Mexican durum wheat (T. turgidum L. ssp. durum) culti-vars (Banamichi, Samayoa, Jupiter, Aconchi, Yavaros, Cocorit, RioColorado), one USA cultivar (Mohawk), and one advanced exper-imental line (CMH83.2578) from the CIMMYT durum wheatbreeding program were used. All the materials were planted withtwo replicates over two crop cycles, 2008e09 (Y08e09) and 2009e10 (Y09e10), in Ciudad Obregon, Sonora, northwestern Mexico,with a randomized complete block design. Two 80 cm wide and2.5 m long rows per cultivar were planted. In all the trials, N wasapplied (pre-planting) at a rate of 200 kg/ha, using a seed rate of80 kg/ha. Weed, diseases, and insects were all well controlled. Theenvironmental conditions establishedwere: E1, optimum irrigation(one pre-planting and 4 auxiliary); E2 drought stress (irrigation:one pre-planting and one auxiliary 30 days after planting); E3, heatstress (irrigation: one pre-planting and 5 auxiliary throughout thecrop cycle). Planting dates were November 28, 2008 and 2009 forthe E1 and E2 treatments, and January 15, 2009 and 2010 for the E3treatment. Irrigation was applied when 50% available water hasbeen depleted in the top 60 cm of the soil profile.

The meteorology data of the experimental station in CiudadObregon was characterized by almost no precipitation during thewhole wheat growing season, with maximum temperatures be-tween 34 and 35 �C in early-May, which was the harvesting time forE1 and E2 treatments, andmaximum temperatures above 36e38 �Cin mid-June, which was the harvesting time for the heat-stresstreatment (E3). Flowering time and physiological maturity inmost of the cultivars used occur at similar times, due to the fact thatthese genotypes were bred for the same growing area. The excep-tion may be Mohawk and Rio Colorado, which flower a few dayslater, depending onwater supply andmorning temperatures duringthe crop season. According to the general growing stages of durumwheat in Ciudad Obregon, drought stress was continuous fromstem elongation to grain ripening while heat stress started in thegrain filling stage and remained until ripening. Therefore, drought(E2) and heat stress (E3) could be achieved through less irrigationand late-planting, respectively, allowing comparison of yield andquality performance among no stress environment (E1) and stress(E2; E3) conditions. Detailedmeteorology data, irrigation times andintervals of three treatments (E1, E2, and E3) of two crop cycles(Y08-09 and Y09-10) during the wheat growing season in CiudadObregon were previously reported (Li et al., 2013).

2.2. Grain physical parameters and quality parameters

Grain yield (Y), test weight (TW), thousand kernel weight (TKW)of all samples were evaluated using conventional means. Grainmoisture and protein content (PC) were determined by near-infrared spectroscopy (NIRS, Foss-NIRSystems), and then grainsamples were tempered and milled into flour using a BrabenderSenior mill. Flour moisture and flour protein content (FP) weredetermined by NIRS (INFRATEC 1255, Foss-Tecator). GP and FPwereexpressed at 12.5% and 14% moisture basis, respectively. Sodiumdodecyl sulfate sedimentation (SDSS) volume was measured ac-cording to a modified SDSS test using 1 g flour (Peña et al., 1990).Flour yellowness (FY, as the b value of a Minolta color meter,Minolta Co.), Mixograph (National Mfg. Co.) dough peak time (MPT,using 35 g flour samples), and lactic acid retention capacity (LARC)were determined according to AACC methods 14-22, 54-40A, and56-11A, respectively (AACC, 2000). Swelling index of glutenin (SIG)was determined according to the method of Wang and Kovacs(2002a), using the isopropanol-lactic acid variant.

Y.-F. Li et al. / Journal of Cereal Science 57 (2013) 398e404400

2.3. Statistical methods

Analysis of variance, multiple comparisons (Duncan test), andcorrelation analysis were performed using SAS software (SAS,2009). The relative contributions of variance sources (G, E andG � E) were their sum square (SS) percentage of the total SS of themodel.

3. Results and discussion

3.1. Influence of genotype (G), environment (E), andgenotype � environment (G � E) on quality traits

In this study, a combination of one treatment (E1, E2 or E3) andone crop cycle (Y08e09 or Y09e10) was regarded as a separateenvironment (E). Analysis of variance and the relative effects of G, E,and G � E on the quality parameters of the nine durum wheatcultivars are presented in Table 1. G, E, and G � E all had significanteffects on the ten parameters tested, with the exception of theinsignificant effect of G� E on Y. However, the effects of G� E weregenerally smaller than those of G and E. G and E showed similareffects on TW, FP, and SDSS. G showed much larger effect than E onFY (87%), SIG (53%), and MPT (54%), and on the contrary, E showedmuch a larger effect than G on Y (90%), TKW (73%), and GP (60%).This was in accordance with previous results in that quantitativeparameters, such as Y, TKW, and GP are generally strongly influ-enced by environmental factors while qualitative parameters, suchas FY and SDSS, are mainly controlled by genotype (Mariani et al.,1995; Rharrabtia et al., 2003a). In our previous study on commonwheat (Li et al., 2013), LARC was primarily determined by G;however, in this study, E showed a bigger effect than G, presumablypartly because in our study with common wheat, hard and softwheat cultivars with very contrasting gluten quality were included,while in the present study, all durum wheat cultivars present hardendosperm and not very contrasting gluten quality; these narrowdifferences in mainly gluten strength, may have diminished thegenotypic effects on LARC previously seen in common wheat.

3.2. Responses of genotypes and parameters to drought and heatstress

The mean values and coefficients of variance (CV) of the ninevarieties under the E1, E2 and E3 in relation to Y and quality pa-rameters are shown in Table 2. We used the CV of each parameteregenotype combination to examine in a broad way the relativestability of the cultivars across environmental conditions. Both,mean value and CV of the parameters under E1, E2, and E3 variedamong cultivars, with larger variations in CV values for Y, SDSS,

Table 1Analysis of variance and sum square percent of G, E and G � E of 10 traits for 9 durum g

Model Genotype (G) Environment (E)

Trait SS SS SS

Y 243,542,370 *** 17,543,292*** 219,661,495***TW 510.06*** 261.29*** 220.55***TKW 3350.66*** 593.93*** 2435.39***GP 115.78*** 26.41*** 69.47***FY 1730.83*** 1510.66*** 152.69***FP 80.59*** 32.62*** 34.25***SDSS 264.4*** 109.1*** 101.47***LARC 9097.52*** 2370.74*** 4434.96***SIG 15.85*** 8.33*** 5.94***MPT 32.32*** 17.47*** 7.3***

Significant level: ***, p < 0.0001; **, p < 0.01; *, p < 0.05.a Contribution (%) of variance sources ¼ SS of G (or E, or G � E)/SS of Model.

LARC, and MPT. Good stability across environments together withdesirable mean values (yield, for example, the higher the better) ishighly desirable in wheat breeding to impact commercial produc-tion positively. Therefore, the average of the CV of all the cultivarsfor each parameter was used to determine the magnitude of thevariation of each parameter under the E2 and E3 stress conditions.

To see the trends in quality parameters of the specific cultivarsin relation to their response to both stress conditions, the perfor-mance of the cultivars as percent change in the value of their pa-rameters relative to E1is shown in Table 3. A drastic loss in Y wasobserved for all cultivars; being much larger under drought (42e54%) than under heat stress (24e35%). The best response to bothE2 and E3 corresponded to the recently developed cultivars Jupareand Samayoa, and the worst to the experimental line CMH83.2578.All cultivars showed the same trend (small change, if any) in TWand GP (96e101% and 95e104%, respectively) under E2 and E3. TheTKW of all cultivars showed no change or small differences (94e105% of E1) under E2, but tended to decrease (10e16% less thanin E1) in all but one cultivar (CMH83.2578) when exposed to E3.These results on TKW seem to indicate that, under the droughtstress conditions of Cd. Obregon (morning-dew environment), theplant tends to produce less numbers of grains per spikelet (and/orless tillers), maintaining grain size and density practically similar tothat under the no-stress condition, while, under heat stress (but nowater and N limitations), the plant tends to have a shorter grainfilling period, reducing grain size and maintaining relatively highTW (Yang and Zhang, 2006; for a review; Bennett et al., 2012). Mostcultivars showed practically no change in FP (97e105% of E1) underE2 and variable increases (4e16% higher than in E1) under E3, mostlikely related to the reduction in TKW observed in E3. The FY of allthe cultivars was similar or slightly higher (up to 9% higher than inE1) in both E2 and E3. Most of the cultivars showed similar trendsin LARC, SIG, and MPT, with equal to higher values under E2 andequal to lower values in E3 relative to E1, evidencing that glutenquality is a major factor influencing these parameters similarly. Inthe case of SDSS, several cultivars showed different trends in bothE2 and E3. Some presented no change relative to E1, while othersshowed increases higher than 10% (Table 3). The SDSS value reflectsmainly protein quality (gluten strength), but it can be influenced byprotein content. Considering that GP generally tends to increaseunder abiotic stress, in the present study it was reasonable toexpect changes in SDSS influenced by changes in protein content.However, the observed increases in SDSS could not be associatedwith changes in GP or FP. Therefore, the differences in the trends ofthe cultivars with respect to SDSS could have been mainly influ-enced by differences in the proportions of gluten proteins accu-mulated under the different environmental conditions(Labuschagne et al., 2009). In general, the results show that the

enotypes across 6 treatment-year combined environments.

G � E Contribution (%) of variance sourcesa

SS G E G � E

6,337,583 7 90 328.22* 51 43 6321.34** 18 73 1019.9*** 23 60 1767.48** 87 9 413.72*** 40 42 1753.83*** 41 38 202291.81*** 26 49 251.58* 53 37 107.56* 54 23 23

Table 2Meanof cultivareparameter-treatment combination and coefficient of variation of cultivars for cultivareparameter combination.

Trait Banamichi Samayoa Jupare Aconchi Yavaros Cocorit Rio Colorado Mohawk CMH83.2578

Y (ton/ha) E1 7143 7385 7685 6732 7367 6619 6991 6153 7146E2 3654 4049 4445 3655 3466 3351 3415 2977 3304E3 5328 5649 5833 4792 5468 4551 5147 4612 4680CVa 32.46 29.30 27.15 30.75 35.9 34.15 34.50 34.67 38.60

TW (kg/hl) E1 81.98 82.63 83.45 84.15 83.33 81.98 79.73 79.85 83.55E2 82.35 83.35 84.25 84.48 83.23 81.78 80.38 80.38 83.35E3 79.55 80.85 82.13 82.48 82.00 79.73 79.25 76.65 82.65CV 1.87 1.56 1.29 1.28 0.9 1.53 0.71 2.55 0.57

TKW (g) E1 47.46 50.77 50.99 50.26 55.16 55.10 55.33 52.88 50.52E2 47.92 50.69 53.02 50.18 52.69 51.69 54.92 55.61 47.33E3 40.94 45.93 44.18 42.26 48.14 49.32 49.77 46.07 54.71CV 8.59 5.65 9.38 9.66 6.8 5.59 5.81 9.54 7.29

GP (%) E1 12.85 12.23 12.15 12.60 11.63 12.50 12.05 13.28 13.20E2 12.83 11.83 12.18 12.63 12.15 12.63 12.55 13.35 13.20E3 12.58 12.45 12.10 12.55 11.73 12.23 11.48 13.65 13.00CV 1.19 2.60 0.31 0.30 2.4 1.64 4.47 1.48 0.88

FY (b value) E1 27.88 27.13 23.10 26.10 23.98 20.00 27.30 33.80 28.93E2 27.83 27.98 24.30 26.38 23.95 21.63 27.18 35.88 30.65E3 29.00 29.25 23.90 27.00 26.03 21.35 28.25 35.53 28.70CV 2.35 3.80 2.57 1.74 4.80 4.14 2.13 3.17 3.63

FP (%) E1 10.35 10.33 10.35 10.53 10.05 10.35 10.58 11.80 11.18E2 10.23 10.00 10.15 10.40 10.30 10.53 10.70 11.93 11.78E3 11.38 11.58 11.43 11.53 11.00 11.40 11.03 12.83 13.00CV 5.92 7.82 6.44 5.70 4.7 5.23 2.16 4.59 7.76

SDSS (ml) E1 10.63 8.38 10.38 9.13 9.25 9.00 9.25 11.50 12.00E2 10.50 9.38 10.38 9.63 10.50 10.13 9.75 11.50 12.13E3 10.88 9.00 10.75 10.13 10.13 11.00 9.25 13.00 12.25CV 1.79 5.67 2.06 5.19 6.4 9.98 3.07 7.22 1.03

LARC (%) E1 125.24 103.77 121.02 121.74 121.08 117.50 125.27 125.62 121.66E2 130.46 113.03 129.78 133.29 131.32 131.53 133.71 122.61 124.69E3 117.28 107.73 112.65 109.96 117.78 118.96 112.73 118.41 101.27CV 5.34 4.29 7.07 9.59 5.7 6.29 8.52 2.96 10.99

SIG E1 4.44 3.85 4.65 4.56 4.33 4.37 4.73 5.09 4.72E2 4.71 4.11 4.81 4.61 4.52 4.67 4.87 5.11 4.82E3 4.59 3.94 4.61 4.59 4.49 4.51 4.55 5.02 4.47CV 3.03 3.33 2.22 0.54 2.30 3.30 3.41 0.95 3.84

MPT (min) E1 3.42 1.94 2.93 3.36 2.43 2.63 3.15 3.33 3.00E2 3.93 2.19 3.27 3.42 3.13 2.43 3.15 3.09 2.89E3 2.96 1.82 2.53 2.67 2.74 2.67 2.81 3.23 2.12CV 13.98 9.46 12.72 13.29 12.7 4.92 6.39 3.83 17.97

E1: no stress; E2: drought stress; E3: heat stress.a CV, %, coefficient of variation.

Table 3Performance of cultivars as percent change of the parameter value under E2 and E3 relative to E1.

Trait % Relative to E1

Banamichi Samayoa Jupare Aconchi Yavaros Cocorit Rio Colorado Mohawk CMH83.2578

Y E2 51 55 58 54 47 51 49 48 46E3 75 76 76 71 74 69 74 75 65

TW E2 100 101 101 100 100 100 101 101 100E3 97 98 98 98 98 97 99 96 99

TKW E2 101 100 104 100 96 94 99 105 94E3 86 90 87 84 87 90 90 87 108

GP E2 100 97 100 100 104 101 104 101 100E3 98 102 100 100 101 98 95 103 98

FY E2 100 103 105 101 100 108 100 106 106E3 104 108 103 103 109 107 103 105 99

FP E2 99 97 98 99 102 102 101 101 105E3 110 112 110 109 109 110 104 109 116

SDSS E2 99 112 100 105 114 113 105 100 101E3 102 107 104 111 110 122 100 113 102

LARC E2 104 109 107 109 108 112 107 98 102E3 94 104 93 90 97 101 90 94 83

SIG E2 106 107 103 101 104 107 103 100 102E3 103 102 99 101 104 103 96 99 95

MPT E2 115 113 112 102 129 92 100 93 96E3 87 94 86 79 113 102 89 97 71

Y.-F. Li et al. / Journal of Cereal Science 57 (2013) 398e404 401

Table 4Multiple comparisons of mean parameter values of a group of 9 cultivars grown under 3 E treatments.

Y (kg/ha) TW (kg/hl) TKW (g) GP (%) FY (%) FP (%) SDSS (ml) LARC (%) SIG MPT (min)

Crop cycle Y08e09E1a 6754 a 82.18a 51.94a 12.88c 25.19c 10.56c 8.75c 117.26b 4.64c 2.98aE2 3307 c 82.30a 50.58b 13.30b 25.99b 11.16b 9.39b 128.24a 5.01a 2.97aE3 5348 b 78.44b 38.84c 13.61a 28.10a 11.96a 10.91a 118.01b 4.73b 2.99aCrop cycle Y09e10E1 7295a 82.40b 52.18a 12.11a 27.74b 10.66b 11.14a 123.39b 4.42a 2.83bE2 3874c 82.93a 52.55a 11.88a 28.62a 10.17c 11.47a 127.42a 4.37a 3.14aE3 4961b 82.26b 53.05a 11.29b 27.17b 11.29a 10.36b 109.79c 4.35a 2.33cCombined two crop cyclesE1 7025a 82.29a 52.06a 12.50a 26.47b 10.61b 9.94a 120.32b 4.53b 2.91aE2 3591c 82.61a 51.57a 12.59a 27.31a 10.67b 10.43a 127.83a 4.69a 3.06aE3 5144b 80.46b 46.37b 12.38a 27.61a 11.61a 10.62a 113.66c 4.53b 2.64b

Different letters within rows indicate significant differences (p < 0.05) between mean values.a E1: no stress; E2: drought stress; E3: heat stress.

Y.-F. Li et al. / Journal of Cereal Science 57 (2013) 398e404402

outcome of the comparison of Y and quality performance of durumwheat under no-stress and stress conditions was largely influencedby the genotypes used in the study, agreeing with those of DeStefanis et al. (2002) and Mariani et al. (1995) in that the re-sponses of genotypes to drought and heat stress vary greatly.

3.3. Effects of drought and heat stress in relation to year of testing

Multiple comparisons of effects of E1, E2, and E3 by crop cycle onthe mean of the quality parameters of the group of 9 genotypes areshown in Table 4.

Fig. 1. Relationship (correlation coefficients) between MPT and gluten strength-related smallconditions (E1eE3) in two crop cycles (Y08-09 and Y 09e10). MPT ¼mixograph peak time; Sindex of glutenin.

In crop cycle Y08e09 (Year 1), GP, FY, FP, SDSS, and SIG sig-nificantly increased while TKWand Y decreased under drought andheat stress, respectively. With the exception of SIG, the magnitudeof the change was larger in E3 than in E2. However, in crop cycleY09e10 (Year 2), with the exception of Y, the trends of the rest ofthe parameters were different to those observed in Year 1. Y, TW,TKW, and FY, showed higher values and GP and FP lower values inY09e10 than in Y08e09. SDSS was higher and SIG lower in Y09e10than in the previous crop cycle. The most likely explanation for thedifferences in trends between the two crop cycles was that therewas more precipitation in January and February of Y09e10

-scale parameters (SDSS; SIG; LARC) of 9 cultivars grown under 3 different environmentDSS ¼ SDS sedimentation volume; LARC¼ lactic acid retention capacity; SIG ¼ swelling

Y.-F. Li et al. / Journal of Cereal Science 57 (2013) 398e404 403

(16.6 mm and 6.8 mm, respectively) than in the same period(practically no precipitation) of Y08e09.

The influence of heat and drought on the quality parameters ofthe group of all 9 cultivars was also examined eliminating year ef-fects (Table 4, the results of the two crop cycles combined). Incomparison to the optimum condition (E1), both drought and heatstress caused a large reduction in Y and a slight but significantincrease in FY. Rharrabtia et al. (2003b) also reported that the pig-ment content (main compositional factor defining FY) in the grainincreased in high seasonal temperature, and may be partly due tothe reduced TKW. Regarding physical grain parameters, althoughdrought increased the values of TW, GP and FP it decreased thevalues of TKW although the effects were not significant. However,heat stress caused significant reductions in TW, TKWand significantincreases in FP. These latter results are in agreement with previousstudies (Flagella et al., 2010; Singh and Jain, 2000).

As for gluten strength related parameters, the SDSS values underE2 and E3 both increased but not significantly. The values of LARCand SIG significantly increased in drought stress (E2) while thevalues of LARC and MPT significantly decreased in heat stress (E3).Although the value of SIG in E3 and the value of MPT in E2 were notsignificantly different from the same in E1, they showed similartrends as LARC. Generally, the values of LARC and SIG showed betterrelationship than SDSS with gluten strength, as measured by MPT(Fig.1). As far aswe know there are no previous studies on the use ofLARC to estimate gluten strength in durum wheat; our resultsindicate that this is possible. The method of SIG using an SDS-lacticacid solution was used in durum wheat by Wang and Kovacs(2002b), showing that gluten index, a time-consuming method,was significantlycorrelatedwithbothSIGandSDSS. Therefore, thesetwo parameters show potential as additional (or alternative) rapidsmall-scale tests to select for gluten strength in durum wheat.Overall, the results indicate that in durumwheat, drought tends toenhance gluten strength whereas heat stress tends to reduce it. Incomparison with our previous study on common wheat (Li et al.,2013), the multiple comparison results across E1, E2 and E3 onLARC, SIG and MPT, were the same in this study on durum wheat.Therefore, drought and heat stress showed almost opposite effectson gluten-related parameters when compared with no stress envi-ronment in both common wheat and durum wheat. In previousstudies a “weakening” effect of heat stress on the gluten strength ofdurum wheat was reported (Borghi et al., 1995; Corbellini et al.,1998). Although the parameters tested were different, our resultsalso show a weakening effect associated with heat stress. Like incommonwheat, the effects of drought and heat stress on the glutenstrength of durum wheat may function through changes in thecomposition and distribution of gliadins, soluble and insolubleglutenin (insoluble polymeric protein) as reported by several in-vestigators (Corbellini et al., 1997, 1998; De Stefanis et al., 2002;Flagella et al., 2010; García del Moral et al., 2007).

4. Conclusions

In general, when compared to the effect of G and E, the effects ofG� E on the tested parameters were smaller. AlthoughG and E havemajor effects, their relative effects ondifferent parametersmayvary.G had a major effect on FY, SIG, and MPT, whereas the relativelylarger effects of E were on Y, TKW, and GP. Therefore, quantitativeparametersmaybe determinedpredominantly byE,whereas glutenstrength (MPTand SIG in this study) appearedmore influenced byG.

In general drought stress tends to enhance gluten strengthwhereas heat stress tends to reduce it.

The trends and stability of durum wheat cultivars with respectto quality parameters vary across environments, with a stronggenotypic influence. Therefore, in order to succeed when breeding

concomitantly for yield and quality, selection pressure for both,yield components and quality traits should be applied under thetargeted stress conditions. LARC and SIG showed strong relation-ship with MPT, showing their potential to select for gluten strengthin durum wheat.

Acknowledgments

This project was partially funded by State-Sponsored Post-graduates Study Abroad Program of the China Scholarship Council,Main Direction Program of Knowledge Innovation of ChineseAcademy of Sciences (No.KSCX3-EW-N-02-2) and The "TwelfthFive-Year" National Key Technology Research and DevelopmentProgram (No.2011BAD35B03). Editing assistance was received fromEmma Quilligan (CIMMYT).

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