Evaluation of agronomic traits in rice mutant groups from different generations under water deficit during the reproductive stage

Abstract

This research aimed to select rice mutant genotypes tolerant to water deficit stress during the reproductive stage, using different experimental designs and selection strategies. The thesis is structured into five chapters, in addition to the introduction and literature review, and focuses on the evaluation of mutants derived from the BRS Pampeira cultivar, obtained through gamma radiation induction (⁶⁰Co). The experimental set consisted of mutants generated under two radiation doses (250 and 300 Grays), integrated into the rice breeding program at the Center for Genomics and Plant Breeding of the Federal University of Pelotas (UFPel), in collaboration with FAO/IAEA. The experiments described in Chapters 1 to 4 were conducted at the experimental field of the Estação Terras Baixas of Embrapa Clima Temperado (Capão do Leão, RS, Brazil), while Chapter 5 was carried out in a greenhouse at the Capão do Leão Campus of UFPel. Water deficit stress was induced during the reproductive stage by suspending irrigation and monitored using tensiometers installed at 10 and 15 cm depths. In Chapters 1 and 2, an augmented block design was employed, involving repeated checks (reference cultivars) and additional treatments (non-repeated mutants). These trials explored, in addition to experimental design principles, the application of mixed models, variance component estimates, genetic gain, principal component analysis (PC), cluster analysis, and Pearson correlation. Chapter 1 addressed the estimation of genetic parameters in 149 mutant lines exposed to 250 Grays and 150 lines exposed to 300 Grays (M 4 generation), evaluated under water deficit conditions. Chapter 2 evaluated the M 5 generation under the same environmental conditions, focusing on the selection of tolerant genotypes through multiple regression and multivariate analysis. Chapter 3 dealt with the evaluation of agronomic traits in M 6 families under two contrasting environments (with and without water deficit), aiming to identify the most resilient materials. Chapter 4 assessed physiological responses related to chlorophyll a and b content, measured at 15, 30, and 45 days after stress induction, under the same conditions as Chapter 3. Chapter 5 explored physiological and agronomic responses using an infrared gas analyzer (IRGA LI-6400XT, LI-COR Biosciences) equipped with a leaf fluorescence chamber, comparing plants under control and water deficit conditions. In general, the results provide relevant information on the adaptive behavior of mutants derived from the BRS Pampeira cultivar, highlighting their potential to be integrated into future breeding programs.