Genome-wide association study of drought tolerance in cassava

Despite being considered a drought-tolerant species, cassava (Manihot esculenta Crantz) exhibits reduced growth and productivity under prolonged water stress. Therefore, the objective of this study was to identify the genomic regions associated with water deficit in cassava using a genome-wide association study (GWAS). A total of 49 cassava genotypes were evaluated under two water conditions: irrigated (control) and water deficit. An additional set of 252 clones grown for several years under water deficit conditions were used to validate the GWAS. The following traits were evaluated: yields of storage roots (RoY), shoots (ShY), and starch (StY); root dry matter content (DMC); drought tolerance index (DTI) and drought tolerance stability index (DTSI). The GWAS was performed using a multiple mixed linear model with a kinship matrix and population structure for each trait and water condition. Broad-sense heritability (h2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${h}^{2}$$\end{document}) estimates were variable depending on the water conditions and characteristics under analysis. Overall, 62 single nucleotide polymorphisms (SNPs) were identified across all 18 cassava chromosomes. Additionally, it was possible to identify specific and stable markers across environments. The identified SNPs comprise approximately 160 transcripts, of which 119 were previously described and 41 have known functional annotations. Some of these transcripts are related to proteins involved in drought tolerance, such as APETALA 2 domain (AP2), photosystem II oxygen-evolving enhancer protein, PR5-like receptor kinase-related, beta-fructofuranosidase/saccharase, leucine zipper, and bZIP transcription factor. There is great potential for applying these SNPs in the marker-assisted selection of new cassava varieties that are tolerant of water deficit.