# Testcross Analysis of Pl-1 Marker Expression and Seedling Vigor in Thai Maize Germplasm for Doubled Haploid Breeding Applications

## TL;DR

This study evaluates the Pl-1 marker in Thai maize for doubled haploid breeding, finding it more reliable than other markers in tropical germplasm.

## Contribution

The study confirms allelic absence of Pl-1 in Thai maize and its potential as a marker for DH breeding in tropical conditions.

## Key findings

- 99.3% of Thai maize genotypes showed complete absence of Pl-1 expression.
- Testcross F1 progeny exhibited intermediate Pl-1 expression, indicating allelic absence.
- Seedling vigor traits showed significant genetic diversity independent of Pl-1 status.

## Abstract

Doubled haploid (DH) technology accelerates maize breeding by generating completely homozygous lines within two generations, but its efficiency depends on reliable haploid identification markers. The Purple plant 1 (Pl-1) root pigmentation marker has emerged as a promising alternative to R1-Navajo (R1-nj), which suffers from frequent suppression in tropical germplasm. This study evaluated Pl-1 expression and seedling vigor in 298 diverse Thai maize genotypes across four market classes under controlled growth chamber conditions (24 ± 1 °C, 85–90% humidity, and standardized lighting), followed by testcross analysis with 89 representative genotypes crossed with BHI306 to distinguish between allelic absence and epistatic suppression mechanisms. Complete absence of Pl-1 expression was observed in 99.3% of Thai genotypes, contrasting with consistent expression in the temperate-derived control (BHI306). Testcross F1 progeny from 89 Thai × BHI306 crosses exhibited intermediate expression levels (1.57–2.05) across all market classes, confirming allelic absence rather than suppressor-mediated inhibition. Substantial genetic diversity was detected in seedling vigor traits independent of Pl-1 status, with root length varying 43-fold and fresh weight 20-fold, showing highly significant genotypic effects. The uniform lack of Pl-1 expression across Thai germplasm eliminates background interference, highlighting its utility as a complementary marker when introgressed from inducer lines. These findings establish the genetic foundation for implementing optimized DH breeding strategies in tropical maize through marker-assisted backcrossing approaches.