Responses of leaf anatomy, growth, and physiology in backcross 1 progeny from <i>Saccharum</i> spp. hybrids and <i>S. spontaneum</i> under drought stress at early growth phase

A deeper understanding of the anatomical, physiological, and morphological responses of interspecific hybrid sugarcane to water deficit conditions could enhance the efficiency of developing drought-resistance varieties. This study aimed to investigate the responses of anatomical characteristics of backcross (BC) 1 interspecific hybrids, produced by crossing commercial cane with wild-type sugarcane, under drought and well-watered treatment. A two-factorial pot experiment in a completely randomized design (CRD) with three replications was conducted. Soil volume water contents were 12.34% prior to the start of drought treatment. Two water regimes, field capacity (FC) and drought stress (DS), were tested, with the DS treatment involving water withholding for 51 st to 110 th days after planting (DAP). Fifteen sugarcane genotypes were evaluated, including ten BC1 interspecific hybrids, two commercial varieties (F152 and UT5), the wild type (ThS98-94), the F1 interspecific hybrid male parent (F4-19), and KK3 as a drought resistance check. Anatomical, physiological, and morphological traits were measured at 110 DAP; results indicated that BC1-1-7, BC1-1-44, and BC1-1-50 exhibited superior traits than the other BC1 interspecific hybrids in this study. These genotypes had a high morphological drought resistance index (DRI) for tiller height and tiller number, and the anatomical leaf had low leaf thickness (% reduction from FC by 14.0%, 10.0% and 3.9%, respectively) and vertical length of bulliform cells (% reduction from FC by 26.2%, 23.9% and 4.9%, respectively) but high cuticle thickness (an increase from FC by 10.7%, 18.3% and 19.7%, respectively) and stomatal crypt depth (an increase from FC by 21.0%, 12.9% and 13.4%, respectively), resembling those of the wild type and F1 interspecific hybrid. Additionally, BC1-1-7 demonstrated greater drought resistance, characterized by low stomatal conductance (% reduction from FC by 90.6%), reduced transpiration rates (% reduction from FC by 89.9%), and high water use efficiency (% gain from FC by 76.1%) compared to BC1-1-44 and BC1-1-50. These results highlight the importance of genetic diversity in breeding programs, as interspecific hybrids like BC1-1-7 combine traits from wild and cultivated relatives, enhancing drought stress performance. Future research should evaluate BC1 hybrids under drought stress in the field, focusing on agronomic performance and final yields.