Chapter 4 Assessment of drought tolerance in selected bread wheat
4.3 Results
4.3.2 Mean responses of genotypes for grain yield and drought indices
Table 4.4 presents mean values and mean comparison of genotypes for Yp, Ys and 9 drought tolerance indices of wheat genotypes evaluated under drought stress and non-stress conditions. Minimum and maximum values recorded for mean Yp were for genotypes SYM2016-047 and SYM2016-044 with values of 254.5 g.plot-1 and 705.9 g.plot-1, respectively.
The overall mean Yp recorded was 448.6 g.plot-1. Superior Yp was detected for genotypes SYM2016-044 and SYM2016-008 with values of 705.9 g.plot-1 and 627.5 g.plot-1, respectively.
The lowest and highest values of Ys were relatively poor compared to Yp with values of 283 g.plot-1 and 576.2 g.plot-1 for genotypes SYM2016-027 and SYM2016-016, in that order. Whilst mean Ys was recorded as 423.7 g.plot-1 and genotypes SYM2016-016 and SYM2016-012 presented above-average Ys with values of 576.2 g.plot-1 and 560.0 g.plot-1, respectively.
Table 4.4: Mean values for 15 wheat genotypes evaluated using grain yield and 9 drought tolerance indices under non-stress and drought stress conditions
Genotype Yp Ys DR HM MP SSI STI TOL YI YR YSI
SYM2016-004 436.7 abcde 416.1 abcd 3.7 f 219.2 abc 225.6 a -13.5 a 0.3 a -7.6 a 0.5 ab -0.1 a 1.1 a SYM2016-006 269.3 a 422.0 abcd 0.7 abcd 696.7 f 701.4 d 14.8 c 2.6 e -14.5 a 1.6 d 0.0 a 0.9 a SYM2016-008 627.6 ef 399.2 abcd 1.0 bcde 417.7 cd 555.4 bcd 12.8 abc 1.3 abc 516.7 a 0.7 ab 0.6 a 0.4 a SYM2016-010 508.1 cde 497.6 bcde 2.0 ef 343.2 abcd 346.2 abc 13.1 abc 0.7 ab -48.3 a 0.7 ab -0.1 a 1.1 a SYM2016-012 542.3 cdef 560.0 def 1.7 cdef 273.1 abcd 406.1 abc 14.0 abc 0.6 ab 166.6 a 0.7 ab 0.3 a 1.3 a SYM2016-014 296.7 ab 353.4 abc 2.6 ef 199.9 ab 237.0 a -13.7 a 0.3 a 78.0 a 0.5 ab 0.1 a 1.0 a SYM2016-016 443.5 abcde 576.2 def 0.6 ab 628.0 ef 674.1 d 14.1 abc 2.4 de 249.5 a 1.3 cd 0.3 a 0.7 a SYM2016-019 427 abcde 390.3 abcd 1.2 bcde 376.7 bcd 449.1 abcd -11.2 ab 1.0 abc 240.3 a 0.8 abc 0.3 a 1.0 a SYM2016-027 423.4 abcd 283 a 1.4 bcdef 144.5 a 298.1 ab 13.7 abc 0.3 a 366.3 a 0.4 a 0.3 a 1.0 a SYM2016-029 260.1 a 294.5 ab 1.6 bcdef 300.9 abcd 316.2 ab 10.5 ab 0.6 ab -65.7 a 0.8 abc -0.3 a 1.5 a SYM2016-037 544.2 cdef 350.1 abc 0.3 a 455.6 de 597.2 cd 13.3 abc 1.8 cde 341.3 a 1.0 bc 0.2 a 2.1 a SYM2016-038 441.9 abcde 439.8 abcde 2.3 ef 257.3 abcd 281.0 a -13.5 a 0.4 a 40.9 a 0.8 abc 0.1 a 1.1 a SYM2016-042 548.2 cdef 441.8 abcde 2.0 def 409.4 bcd 448.4 abcd 12.5 abc 1.0 abc 222.2 a 0.7 ab 0.4 a 0.5 a SYM2016-044 705.9 f 490.8 bcde 0.6 abc 448.4 de 604.3 cd 13.3 abc 1.523 bcd 424.9 a 0.9 abc 0.4 a 0.8 a SYM2016-047 254.5 a 440.8 abcde 2.1 ef 229.3 abc 386.5 abc 14.5 bc 0.5 ab 233.5 a 0.6 ab 0.4 a 1.2 a
Mean 448.6 423.7 1.3 360.0 435.1 13.2 1.0 182.9 0.8 0.2 1.0
CV (%) 2.6 2.6 28.6 13.4 12.3 9.2 20.7 19.8 4.9 8.4 23.3
l.s.d. (P < 0.05) 168.0 168.0 0.9 183 226.6 14.6 0.9 685.5 0.5 1.4 2.0
Key: DR - drought resistance index, HM - harmonic mean of yield, MP - mean productivity, SSI - stress susceptibility index, STI - stress tolerance index, TOL - tolerance index, YI - yield stability index, YSI - yield stability index, YR - yield reduction, Yp - yield for each genotype under non-stress, Ys - yield for each genotype under drought stress, Yp- mean grain yield of each genotype under non-stress, Ys-mean grain yield of each genotype under stress, CV (%) - coefficient of variation expressed as a percentage, l.s.d. (P <
0.05) - least significant difference at 5% probability level.
Means in a column followed by the same letter are not significantly different at the 5% probability level.
Mean value for drought tolerance indicator DR was 1.3, whilst DR values ranged between 0.3 and 3.7 for genotypes SYM2016-037 and SYM2016-004, respectively (Table 4.4). Genotypes identified with superior DR values were SYM2016-004 and SYM2016-014 with values of 3.7 and 2.6, in that order. The mean value detected for drought selection index HM was 360.0 and values ranged from 144.5 for genotype SYM2016-027 to a maximum of 696.7 for genotype SYM2016-006. Genotypes which expressed superior HM values were SYM2016-006 and SYM2016-016 with values of 696.7 and 628.0, in that order. Conversely, drought tolerance index MP was detected with a mean of 435.1, whilst minimum and maximum values were 225.4 and 701.4 for genotypes SYM2016-004 and SYM2016-006, in that order. The highest values for MP were 701.4 and 674.1 for genotypes SYM2016-006 and SYM2016-016, respectively. For drought tolerance indicator SSI, mean SSI, minimum and maximum values were 13.2 and -13.7 for genotype SYM2016-014 and 14.8 for genotype SYM2016-006, in that order. Superior SSI values were realised for genotypes SYM2016-014 as well as SYM2016- 004 with values of -13.7 and -13.5, respectively. For STI drought tolerance indicator, values ranged between 0.3 for genotypes SYM2016-004, SYM2016-014, SYM2016-027 and 2.6 for genotype SYM2016-006, whilst the mean STI was recorded as 1.0. The highest values for drought selection index were 2.6 and 2.4 for genotypes SYM2016-006 and SYM2016-016, respectively (Table 4.4).
Conversely, minimum and maximum values for TOL drought tolerance index were -65.7 and 516.7 for genotypes SYM2016-029 and SYM2016-008, respectively. TOL mean value was 183.0. Genotypes with lowest values were SYM2016-029 and SYM2016-010 with values - 65.7 and -48.3, respectively. For drought tolerance index YI, the detected mean value was 0.8. Minimum and maximum values were for genotypes SYM2016-027 and SYM2016-006 which had YI values of 0.4 and 1.6, in that order. On the other hand, the highest values were for genotypes SYM2016-006 and SYM2016-016 with 1.6 and 1.3, in that order. Drought tolerance index, YSI, the mean value was 1.0 and values ranged from 0.4 for genotype SYM2016-008 to 2.1 to SYM2016-037. Superior genotypes detected were SYM2016-037 and SYM2016-029 with values of 2.1 and 1.5, respectively. The mean value detected for drought tolerance index YR was 0.2, whereas values ranged from -0.3 to 0.6 for genotypes SYM2016- 029 and SYM2016-008, in that order. Whist genotypes recorded with superior YR values were SYM2016-029 and SYM2016-010, respectively (Table 4.4).
4.3.3 Mean rank, rank sum and standard deviation of ranks for wheat genotypes assessed through drought selection indices
Results of Spearman’s rank of wheat genotypes based on 9 drought indices and grain yield are presented in Table 4.5. Wheat genotypes detected with low values for rank mean, standard deviation of ranks and sum of ranks were regarded as superior. Lowest values for mean rank were 6 for genotypes SYM2016-010 and SYM2016-016, whereas highest values were detected for genotypes SYM2016-027 and SYM2016-047 with values of 12 and 10, respectively. The genotypes with lowest for standard deviation of ranks, both with a value of 2, were SYM2016-019 and SYM2016-027. Maximum values were detected for genotypes SYM2016-006 and SYM2016-016 each with a value of 6. On the other hand, lowest values for sum of ranks were 68 and 70 for genotypes SYM2016-010 and SYM2016-006, whilst maximum values were 134 and 108 for genotypes SYM2016-027 and SYM2016-047, respectively. Overall, genotypes were ranked differently for each of the variables.
Table 4.5: Spearman ranks for 15 wheat genotypes using 9 drought selection indices and grain yield under drought stress and non-stress conditions
Genotype Yp Ys DR HM MP SSI STI TOL YI YR YSI Mean rank Std dev rank Sum of rank
SYM2016-004 9 9 1 13 15 2 14 4 13 3 5 8 5 88
SYM2016-006 13 8 12 1 1 15 1 3 1 4 11 6 6 70
SYM2016-008 2 10 11 5 5 7 5 15 11 15 15 9 5 101
SYM2016-010 6 3 5 8 10 8 8 2 9 2 7 6 3 68
SYM2016-012 5 2 7 10 8 12 9 7 8 8 3 7 3 79
SYM2016-014 12 12 2 14 14 1 15 6 14 6 8 9 5 104
SYM2016-016 7 1 14 2 2 13 2 11 2 10 13 7 5 77
SYM2016-019 10 11 10 7 6 4 6 10 6 9 10 8 2 89
SYM2016-027 11 15 9 15 12 11 13 13 15 11 9 12 2 134
SYM2016-029 14 14 8 9 11 5 10 1 5 1 2 7 5 80
SYM2016-037 4 13 15 3 4 9 3 12 3 7 1 7 5 74
SYM2016-038 8 7 3 11 13 3 12 5 7 5 6 7 3 80
SYM2016-042 3 5 6 6 7 6 7 8 10 14 14 8 4 86
SYM2016-044 1 4 13 4 3 10 4 14 4 13 12 7 5 82
SYM2016-047 15 6 4 12 9 14 11 9 12 12 4 10 4 108
Key: DR - drought resistance index, HM - harmonic mean of yield, MP - mean productivity, SSI - stress susceptibility index, STI - stress tolerance index, TOL - tolerance index, YI - yield stability index, YSI - yield stability index, YR - yield reduction, Yp - yield for each genotype under non-stress, Ys - yield for each genotype under drought stress, std dev ranks - standard deviation of ranks
.