Seleção de genótipos de tomateiro visando tolerância ao estresse por deficiência hídrica

Abstract

The tomato crop adapts to different climatic conditions however it is sensitive to the lack of water which can damage its development and productivity. This study aimed to select tomato genotypes tolerant to stress by water deficiency from the deficit induction in seeds and plants in the field. The research was divided into two moments. In the first moment the selection was done in the laboratory with tomato seeds of the Santa Cruz group. A completely randomized design was used with four replications. 17 genotypes were evaluated in the generation F2BC2, which were obtained from an interespecific cross between Solanumpennellii and Solanum lycopersicum L. and three check treatments, one resistant [wild access LA-716 (S.pennellii)] and two susceptible (cv. Santa Clara and precommercial line UFU-650). After subjected to the osmotic potential of -0,3 MPa, the genotypes were evaluated for: germination percentage, standard germination percentage, first counting percentage, germination velocity index, average time of germination and initial and final length of radical. In fact, the wild access, S. pennellii, was better than the susceptible check treatment. The genotype UFU102/F2BC2#71115 was highlighted when compared to the others F2BC2 genotypes and in relation to the three check treatments, susceptible (cv. Santa Clara and UFU-650) and resistant (S. pennellii). Analyzing the genetic diversity, 8 different groups were obtained, thus being an indicative of genetic variability between the evaluated genotypes. The variable %G (percentage of germination) contributed with 33,9% in the diversification of the genotypes, presenting itself as the most important criterion, to be evaluated. In the second moment the selection was in mini tomatoes. We used a completely randomized design with three replications and eight treatments in which there were five F2BC1 genotypes from the interspecific cross between the pre-commercial strain UFU-222 (S. lycopersicum) versus wild accession LA-716 (S. pennellii), and three genotypes used as check treatments, two susceptible (UFU-222; cv Santa Clara.); and one resistant (S. pennellii). The experiment was conducted in a greenhouse with monitoring of the flux density, solar radiation, air temperature, relative humidity and the matric potential in the substrate. The collected physiological characteristics were: leaf temperature, internal CO2, transpiration, stomatal conductance and CO2 assimilation, determined by portable gas analyzer infrared - IRGA; Chlorophyll levels a and b by using a hand-held chlorophyll meter clorofiLOG (CFL- 1030, Falker) and leaf water potential using a pressure chamber type Scholander (SoilMoisturemodel3000). All parameters evaluated showed significant values among genotypes. The water stress tolerance of wild Solanum pennellii is not solely determined by morphological and anatomical characters, it can be characterized by gas measurements and leaf water potential. The instantaneous efficiency in water use is possibly the main variable response that characterizes this access. Genotypes from the population UFU22/F2BC1#2 were highlighted among the others as the most promising featuring high photosynthetic rates associated with low stomatal conductance and transpiration.