Tolerância à termoinibição em sementes de alface de híbridos recíprocos e gerações segregantes

Abstract

Lettuce is one of the most important leafy vegetables, being planted and consumed throughout the year, in all regions of Brazil. Meeting this constant demand becomes a challenge, as the occurrence of high temperatures is a limiting factor for the germination of lettuce seeds and temperatures above 30°C are common in several regions of the country. Lettuce seeds subjected to high temperatures during imbibition suffer a phenomenon called thermoinhibition, which consists of the temporary inhibition of germination, being reversible when the temperature is restored to optimal levels. There are lettuce cultivars considered tolerant to thermoinhibition, such as the Everglades cultivar, however, these materials do not have characteristics that suit Brazilian commercial standards. The objective of this work was to confirm the occurrence of maternal effect in lettuce seeds for the thermoinhibition tolerance trait, to determine the parameters involved in the genetic control of this trait, as well as the enzymatic expression related to this trait, in seeds of lettuce genotypes from crosses between Everglades and Luísa cutivars. For this purpose, reciprocal crosses were made between Everglades and Luísa cultivars, obtaining F1 reciprocal hybrids and, from self-pollination, the respective F2 and F3 generations. The cross between the Everglades and Verônica cultivars was also carried out as a control and the F1 reciprocal hybrids and the F2 and F3 generations of only one of the hybrids were obtained. The seeds of these 11 genotypes were submitted to germination tests at temperatures of 20 and 35°C, whose results were expressed as percentage of normal seedlings and root protrusion. The results obtained were subjected to generational analysis using the GENES software and estimated the genetic and phenotypic parameters. The activity of the catalase, ascorbate peroxidase and endo-β-mannanase enzymes in the seeds of each genotype was also evaluated. It is concluded that there is a maternal effect for the characteristic of tolerance to germination at elevated temperatures in lettuce seeds and that the cultivar Luísa can be considered moderately tolerant to thermoinhibition. It is also concluded that the enzyme catalase can be used as a marker for the selection of lettuce genotypes tolerant to thermoinhibition. Finally, it is concluded that the additive effects are more strongly expressed for the trait of tolerance to thermoinhibition in lettuce seeds, as well as the heritability in the broad sense is relatively high, allowing to predict the success with the selection of genotypes tolerant to thermoinhibition.