Evaluation of Some Sugar Beet Genotypes Under Drought Stress Based on Selection Indices

This study was conducted to determine drought tolerant indices of some sugar beet genotypes under water stress and non-stress conditions. Nine sugar beet (Beta Vulgaris L.) genotypes were tested in a Split-plot experiment based on a randomized complete block design in three replications under three levels of water stress 100%, 75% and 50% from plant requirements at the experimental farm Faculty of Agriculture, Suez Canal University, Ismailia, Egypt during 2015/ 2016 and 2016 / 2017 seasons. Twelve drought tolerance indices were used in this study, stress sensitivity index (SSI), stress tolerance (TOL), mean productivity (MP), geometric mean (GMP), harmonic mean (HM),yield stability index (YSI), yield index (YI), stress tolerance index (STI), sensitivity drought index (SDI), relative drought index (RDI), drought response index (DI) and stress susceptibility percentage index (SSPI). GMP, MP and STI were more informative towards classification of better or superior genotypes with respect to tolerant and sensitive groups. The results showed that the genotypes with high STI, GMP and MP values were suitable for cultivation under drought stress and non-stress environments. Both Yp and Ys of root yield in the control-50% analysis had significantly positive correlated (P value<0.05) with MP, GMP, YI, HM and DI, This indicates that these indices were more effective in identifying high yielding genotypes under drought stress as well as non-stress conditions. Principal components analysis showed that the first two components in the control-50% analysis, genotype Bts 1237 and Temar were identified as the most stable high yielding genotypes in both environments. DOI : 10.14302/issn.2639-3166.jar-18-2083 Corresponding author: Salah A. Okasha, Agronomy, Dept, Faculty of Agriculture, Suez Canal University, Ismailia, Egypt, Email:Saok2006@yahoo.com

planted area and increasing productivity at the same time. Moreover, some cultivated area might be suffered from this shortage of water. Sugar beet crop is sensitive to drought, especially in seedling stage [8].
Variation in plant response to drought genetically manipulated enhanced preliminary for improving the appearance of the plant and increased production of stress [9]. There is little genotypic information on drought tolerance in sugar beet, and breeders are not equipped to make these selections. [10] measured drought sensitivity of each genotype as reduction in yield under drought stress, whilst the mentioned values are baffled with different yield potential of genotypes [11]. However difference in yield potential could cause by factors related to adaptation rather than to drought tolerance by itself [12]. Many studies used several drought indices to select stable genotypes according to their performance under favorable and stress conditions [13,14,15].
Accordingly, Stress tolerance (TOL) has been defined as the differences in yield between the stress (Ys) and non-stress (Yp) environments and mean productivity (MP) as the average yield of Ys and Yp [16].

Materials and Methods
Nine sugar beet (Beta Vulgaris L.) genotypes i.e.

Results and Discussion
Descriptive statistics of drought indices under 100% (favorable), 75% (moderate drought stress) and 50% (severe drought stress) of water stress are presented in Table (

1-Stress Sensitivity
Index (SSI) [28] The genotypes with SSI<1 are more resistant to drought stress conditions 2-Tolerance index (TOL) [29] The genotypes with low values of this index are more stable in two different conditions.

3-Mean Productivity
(MP) [30] The genotypes with high value of this index will be more desirable.

4-Geometric Mean
Productivity (GMP) [31] The genotypes with high value of this index will be more desirable.

5-Stress Tolerance
Index (STI) [32] The genotypes with high STI values will be tolerant to drought stress.
6-Yield Index (YI) [33] The genotypes with high value of this index will be suitable for drought stress condition.

7-Yield Stability
Index (YSI) [34] The genotypes with high YSI values can be regarded as stable genotypes under stress and non-stress conditions.

8-Harmonic Mean
(HM) [35] The genotypes with high HM value will be more desirable.

Correlation Analysis
To determine the most desirable drought The observed relationship between YP, MP, STI, YS, MP and STI are in consistent with those reported by [47] in sorghum and [48] in wheat crop. [49] Introduced STI, MP and GMP as the best indices for yield predicting.
[50] Reported that GMP, MP STI indices were significantly positive correlation with stress on yield. [51] Mentioned that, the validity of selection index for screening genotypes for stress conditions depends on its  (Tables 6 and 7). Therefore, the bi-plot was drawn based on the first two components (Figures 1 and 2).
For the moderate stress (75%) analysis (Table   6) In the severe stress conditions (50%) analysis (Table 7)  and 2 were classified as drought-sensitive genotypes ( Figure 1). In the control-75% analysis, the Genotypes 4 and 6 were more stable than the other genotypes; however, genotypes 1 and 9 were most sensitive ( Figure 2

Conclusion
Selection of drought-tolerant genotypes should be well adapted to stress and non-stress conditions.