Line × Tester Analysis for Identifying Turcicum Leaf Blight (TLB) Resistant Maize Genotypes and Developing Superior Hybrids

Abstract

Maize (Zea mays L.) is globally recognized as the "queen of cereals" and is essential for food, livestock feed, and industrial raw material. Despite its importance, maize is vulnerable to numerous pathogens, with Turcicum Leaf Blight (TLB), caused by Exserohilum turcicum, posing a major global threat. This disease can result in severe yield losses, documented between 25% and 90% in various regions of India. Exploiting host plant resistance is recognized as the most effective and sustainable strategy for management, necessitating the evaluation of germplasm and identification of resistant genotypes through breeding techniques like line × tester analysis. The present study, conducted in Rabi 2024 at MRU, Hyderabad, utilized 5 lines and 10 testers to generate 50 F₁ crosses. The genotypes were subjected to artificial inoculation using the whorl drop method at 32 DAS to ensure consistent exposure to Exserohilum turcicum. Disease severity was recorded on a standard 1-9 scale at three crucial stages: tasseling, 20 days after tasseling, and maturity, followed by the calculation of the Per cent Disease Index (PDI). Evaluation revealed a marked decline in foliar disease resistance over time. While all 50 F₁ hybrids were classified as resistant (R) at tasseling, only 38% remained resistant by physiological maturity, with others shifting to intermediate or susceptible ratings. The inbred lines JLML-01888 and JLML-94333, along with testers JLSN-34 and JLSN-73, demonstrated the most stable and durable resistance across all stages, suggesting they harbor strong resistance genes or quantitative resistance loci (QTL). This temporal decline in resistance underscores the necessity of multi-stage screening to accurately capture hybrid performance. The identified resistant parental lines are critical germplasm for future breeding efforts focused on incorporating durable, multi-gene resistance to enhance stability.