Gabriel Mascarenhas Maciel

Herança do formato do fruto em tomateiro do grupo cereja

The tomato fruit shape is a result of action of various gene loci that can act in several ways: alone, with pleiotropic effects or interacting with each other or with genes responsible for the fruit weight. According to this, the study of the inheritance of this characteristic, very important for the improvement of the species, is complex and difficult to implement. This work was carried out at the Horticultural and Experimentation Section of Jose do Rosario Vellano University, during the period of July 2003 through March, 2005 with the objective to determine the fruit shape of the cherry tomato plant. Two wild genotype contrasting tomato plants were utilised with the fruit shape: long fruit shape (LF) and round fruit shape (RF). Reciprocal crosses and backcross were realised and the fruit shape was evaluated in the generations origininated from these crosses. All plants of the F1 generation produced round shape fruit. In the F2 generation, 111 plants produced round fruit shape and 47 plants produced long fruit shape. On the backcross generation (F1 x LF) 47 plants produced round fruit shape and 42 plants produced long fruit shape. These results when analysed by chi square, confirmed Mendelian segregation 3:1 and 1:1 respectively. It was concluded that the studied fruit shape has monogenic inheritance. The allele that determines fruit round shape has complete dominance over the allele that determines elongated shape fruit with possible action of the sun locus.

Mini tomato genotypes resistant to the silverleaf whitefly and to two-spotted spider mites

The mini tomato production has expanded, becoming an amazing alternative for enterprise. Despite all commercial potential, the cultivation has the occurrence of pests as main obstacle during the crop development. Nowadays, there are no researches that aimed obtaining genotypes with high acylsugar content, capable of providing a broad-spectrum resistance to pests. This study aimed the selection of mini tomato genotypes, with high acylsugar content, and checking the resistance level to the silverleaf whitefly [Bemisia tabaci (Gennadius)] and to the two-spotted spider mites (Tetranychus urticae Koch). Sixteen genotypes were evaluated, from which 12 were on the generation F2BC1, originated from the interespecific cross between Solanum pennellii versus Solanum lycopersicum L. and 4 were check treatments, being three of cultivated tomatos (cv. Santa Clara, UFU-02, and UFU-73) and the wild accession LA-716 (S. pennellii). The variables analyzed were acylsugar content, repellency to the silverleaf whitefly, repellence to the two-spotted spider mites, and density of glandular trichomes. The genotypes UFU-22-F2BC1#9 and UFU-73-F2BC1#11 have high acylsugar content and both are resistant to the pests that were evaluated. New studies must be conducted seeking for inbred lines, obtained from the selected genotypes, aiming to get commercial hybrids with high acylsugar content.

Gas exchanges and water use efficiency in the selection of tomato geno-types tolerant to water stress.

Water stress can affect the yield in tomato crops and, despite this, there are few types of research aiming to select tomato genotypes resistant to the water stress using physiological parameters. This experiment aimed to study the variables that are related to the gas exchanges and the efficiency in water use, in the selection of tomato genotypes tolerant to water stress. It was done in a greenhouse, measuring 7 x 21 m, in a randomized complete block design, with four replications (blocks), being five genotypes in the F2BC1 generation, which were previously obtained from an interspecific cross between Solanum pennellii versus S. lycopersicum and three check treatments, two susceptible [UFU-22 (pre-commercial line) and cultivar Santa Clara] and one resistant (S. pennellii). At the beginning of flowering, the plants were submitted to a water stress condition, through irrigation suspension. After that CO2 assimilation, internal CO2, stomatal conductance, transpiration, leaf temperature, instantaneous water use efficiency, intrinsic efficiency of water use, instantaneous carboxylation efficiency, chlorophyll a and b, and the potential leaf water (Ψf) were observed. Almost all variables that were analyzed, except CO2 assimilation and instantaneous carboxylation efficiency, demonstrated the superiority of the wild accession, S. pennellii, concerning the susceptible check treatments. The high photosynthetic rate and the low stomatal conductance and transpiration, presented by the UFU22/F2BC1#2 population, allowed a better water use efficiency. Because of that, these physiological characteristics are promising in the selection of tomato genotypes tolerant to water stress.

Agronomic performance of mini-tomato hybrids from dwarf lines

Little is known about the commercial potential of mini-tomato hybrids obtained from one dwarf parent. Thus, our objective was to evaluate the agronomic performance of mini-tomato hybrids obtained by crossing a dwarf line (A) with normal lines with indeterminate (I), determinate (D) and semi-determinate (SD) growth habits. The experiment was conducted in a greenhouse at the Estacao Experimental de Hortalicas at the Universidade Federal de Uberlândia-UFU in Monte Carmelo, Brazil. The experiment was completely randomized with 17 treatments and four repetitions. The genetic material consisted of 16 experimental mini-tomato hybrids from the tomato germplasm bank at UFU, and a commercial hybrid (Mascot) as a control. The following variables were used to evaluate agronomic performance: fruit weight (g); number of fruits plant-1; productivity (kg plant-1); number of bunches plant-1; number of fruits bunch-1; stem diameter (mm); distance between first bunch and soil (cm); internode length (cm) and total soluble solids (°Brix). The growth habit of the parents influenced the performance of the hybrids. In general, the mini-tomato hybrids from dwarf lines differed from the control with respect to all variables except number of fruits plant-1, number of fruits bunch-1 and stem diameter. On average, hybrids from dwarf lines showed higher productivity (20%), shorter internodes (11%) and a shorter distance between the first bunch and the ground (30%), relative to the control. Using dwarf lines to obtain mini-tomato hybrids was shown to be viable since the hybrids demonstrated better agronomic performance.