Abstract
A total of 96 winter and 10 summer growing chilli (Capsicum annuиm L.) genotypes of Bangladesh were
studied to identify diversity in sensitivity to drought and waterlogging with their bio-molecular markers
involved in tolerant mechanism during October, 2016 to December, 2019. In this study, 39 and 8 SSR
markers were used to characterize 96 winter and 10 summer chilli genotypes, respectively. Аll
microsatellite markers were found to be polymorphic, revealing a total of 123 and 30 alleles with an average
3.154 and 3.750 alleles in analysis of 96 and 10 chilli genotypes, respectively. Variability also found in Nei's (1973) еxреcted heterozygosity, Gene flow estimated, Genetic differentiation and Shannon's Information
Index. According to PIC values 12 out of 39 and 6 out of 8 markers were very informative with higher PIC
values (>0.6). Higher PIC values might be the result of diverse genotypes. All of winter and summer chilli
genotypes in this study showed unique and differential DNA banding patterns across at least one and/or
combination of two to five primers. The genotypes had distinct status in the dendrogram, because there
might have effect of different genetic distance (GD) which might be designated through morphological
traits and geographical sources. According to Nei's (1972) genetic distance, higher values (>0.6) generated
in participation of 55 among 96 winter genotypes, while all of 10 summer chilli genotypes exhibited higher
GD (>0.6) values. Hence, morphological characterization was determined in these diverse 55 winter and 10
summer chilli genotypes. Thirty qualitative characters were recorded to study on morphological traits.
According to diversity index, 15 and 11 out of 30 characters showed high phenotypic diversity (H≥0.75) in
winter and summer chilli genotypes, respectively. Many genotypes were found distinct morphologically
from others due to different traits and their combination. Variation in phenotypic characters separated the
genotypes in different clusters of the dendrogram. Dendrogram showed that eight winter chilli genotypes
closely related with other genotype in respective cluster. Hence, 47 among 55 genotypes were selected for
further study. On the other hand, all of 10 summer chilli genotypes were selected for further study due to
their different cluster position with distinct phenotypic variation. Overall, a relationship between genotypic
and phenotypic markers was determined. Forty seven winter genotypes were evaluated for their genetic
potential to drought tolerant at germination stage using 12.5% polyethylene glycol (PEG, 6000). Based on
aggregated score of RGE, RGR, RGI and RVI parameters top 10 genotypes on ranking position were
selected as tolerant. While, lowermost 10 genotypes in the rank of drought tolerant 38-47 position were
selected as susceptible to drought stress. In dedrogram, tolerant genotypes grouped in cluster I. RGI
showed comparatively strong and positive correlation with all tested parameters. Hence, these 20
genotypes were used to further screening of drought tolerance performance at seedling stage. Besides,
seedling of 10 diverse summer chilli genotypes was evaluated to find out their tolerance performance under
waterlogging. Based on their survival performance under deficit water stress, two genotypes viz., BD-10906
and BD-10912 were selected as tolerant and the genotypes BD-10902 and RT-20 as susceptible to drought
stress. Similarly, two genotypes viz., SRC-517 and BARI morich-2 was selected as tolerant while AHM-206
and RI-1(6) as susceptible to waterlogging stress. Distinct phenotypic difference was observed between
tolerant and susceptible genotypes in stress and recovery condition. Growth and chlorophyll (Chl a, Chl b
and Chl a+b) were also inhibited in both tolerant and susceptible under both stress, but the inhibition was
high in susceptible genotypes. Higher carotenoid in stress induced tolerant genotypes play important role
in reducing reactive oxygen species (ROS) like 102 as well as beta-oxidation. Relative water content and
better osmotic adjustment maintained by accumulating more osmolytes, were mainly responsible to make
tolerant genotypes. Stomatal limitation occurred in tolerant genotypes to maintain leaf water potential and
relative water content. The formation of aerenchyma cells in tolerant genotypes under flooding conditions
can be considered as tolerance mechanism for long-term survival. Both drought and waterlogging stress
caused oxidative stress in chilli seedlings through lipid peroxidation, loss of plasma membrane integrity, higher ROS and methylglyoxal (MG) formation. ROS like O2*- and H2O2 were significantly higher in that susceptible genotypes. Higher ascorbate and glutathione redox system also help tolerant genotypes by scavenging overproduced ROS under water stresses. However, antioxidant defense especially superoxide
dismutase (SOD), catalase and non-chloroplatic peroxidase (POD) was found significantly higher in
tolerant genotypes, which play one of the most important role for scavenging oxidative stress. In gel activity, SOD2 and SOD3 play important roles to defense in O2- mediated oxidative damage. Similarly, POD1 can be important for ROS metabolism in recovery as well as to provide higher specific activity. Activity of other antioxidant like ascorbate peroxidase, glutathione peroxidase, glutathione reductase,
dehydroascorbate reductase and monodehydroascorbate reductase was also higher in tolerant genotypes. Higher glyoxalase I and glyoxalase II activities in tolerant genotypes help to convert the potential MG to
non-toxic hydroxiacids