Selection of experimental strawberry (Fragaria x ananassa) hybrids based on selection indices.

The strawberry (Fragaria x ananassa Dutch.), is the only vegetable belonging to the rosacea family. All strawberry species have now emerged from wild species and belong to the genus Fragaria, being that this genus presents more than 45 described species, and only 11 are considered natural species. Due to the octoploid nature of strawberry and its variability after hybridization, selecting one or more characters may result in unfavorable genotypes and even the exclusion of promising ones, because negative genetic correlations have been observed among them that cause inefficient selection. Therefore, the objective of this study was to verify the efficiency of selection indices in selecting experimental strawberry hybrids for in natura consumption and processing. Seven commercial cultivars and 103 hybrids were used, which were obtained from populations derived from their crossings. The experiment was conducted in augmented blocks, in which four agronomical traits (total mass, amount of commercial fruit, amount of noncommercial fruit, and average fruit mass) and seven physical-chemical traits (soluble solids, soluble solids:titratable acidity ratio, total sugars, total pectin, vigor, and internal and external coloration) were evaluated. For hybrid selection, the following indices were used: Mulamba and Mock (1978), Smith (1936), Hazel (1943), and genotype-ideotype, which selected 20% of the genotypes evaluated. The three indices selected about 9% of the hybrids. The selection of two experimental hybrids (89 and 495) and the use of selection indices resulted in larger estimates of selection gains. The Mulamba and Mock (1978), Smith (1936), and Hazel (1943) indices had the highest percentage of gains on selection, and are therefore recommended for the selection of strawberry clones.

Prediction of industrial tomato hybrids from agronomic traits and ISSR molecular markers.

Heterosis is a highly relevant phenomenon in plant breeding. This condition is usually established in hybrids derived from crosses of highly divergent parents. The success of a breeder in obtaining heterosis is directly related to the correct identification of genetically contrasting parents. Currently, the diallel cross is the most commonly used methodology to detect contrasting parents; however, it is a time- and cost-consuming procedure. Therefore, new tools capable of performing this task quickly and accurately are required. Thus, the purpose of this study was to estimate the genetic divergence in industrial tomato lines, based on agronomic traits, and to compare with estimates obtained using inter-simple sequence repeat (ISSR) molecular markers. The genetic divergence among 10 industrial tomato lines, based on nine morphological characters and 12 ISSR primers was analyzed. For data analysis, Pearson and Spearman correlation coefficients were calculated between the genetic dissimilarity measures estimated by Mahalanobis distance and Jaccard's coefficient of genetic dissimilarity from the heterosis estimates, combining ability, and means of important traits of industrial tomato. The ISSR markers efficiently detected contrasting parents for hybrid production in tomato. Parent RVTD-08 was indicated as the most divergent, both by molecular and morphological markers, that positively contributed to increased heterosis and by the specific combining ability in the crosses in which it participated. The genetic dissimilarity estimated by ISSR molecular markers aided the identification of the best hybrids of the experiment in terms of total fruit yield, pulp yield, and soluble solids content.

Acyl sugars and whitefly (Bemisia tabaci) resistance in segregating populations of tomato genotypes.

The wild tomato, Solanum pennellii, is an important source of resistance genes against tomato pests. This resistance is due to the presence of acyl sugars (AS), which are allelochemicals that have negative effects on arthropod pests. There are no commercially available tomato cultivars that exhibit significant levels of resistance to arthropod pests. Therefore, this study evaluated resistance to whitefly (Bemisia tabaci) in F2 and F2RC1 tomato genotypes with high AS levels from a cross between Solanum lycopersicum 'Redenção' and the S. pennellii accession, LA-716. Plants were exposed to B. tabaci biotype B at the pre-flowering stage. In both generations, there were significant, negative correlations between AS content and oviposition preference and nymph development. Whitefly exhibited a lower preference for oviposition and produced fewer nymphs in genotypes with high AS levels and the wild parent S. pennellii than in the low AS-level genotypes and Redenção cultivar, demonstrating that the breeding program was effective in transferring resistance to the F2 and F2RC1 generations. RVTA-2010-pl#31 and RVTA-2010-pl#94 in the F2 population are promising genotypes that produced materials with high AS levels in the F2RC1 generation (RVTA-2010-31-pl#177 and RVTA-2010-94-pl#381).

Repellent effects of various cherry tomato accessions on the two-spotted spider mite Tetranychus urticae Koch (Acari: Tetranychidae).

Several studies have been conducted on resistance sources to improve the genetic resistance of farm-grown tomatoes to arthropod pests, including phytophagous mites. In the present study, we evaluate the behavior of the two-spotted spider mite on different cherry tomato accessions to identify possible sources of resistance (repellent effect) to this pest. Sixty-four accessions of cherry tomatoes, Solanum lycopersicum var. cerasiforme (Dunal), were tested. In addition, a commercial cultivar of cherry tomato cv. Sweet Grape (susceptible pattern) and the wild tomato accession Solanum pennellii Correll LA-716 (multiple pest resistance) were evaluated as well. The distance traveled by mites on the leaflet surface over time varied largely among cherry tomato accessions. The wild genotype, S. pennellii LA-716, showed the smallest traveled distance on the leaflet surface (0.8 to 1.1 mm over time), and the variety cv. Sweet Grape was one of the genotypes with highest traveled distance (16.2 to 16.4 mm over time). The cherry tomato accessions 2298-42, RVTC-03, and 6889-53 showed a decrease in the traveled distance by mites over time, similar to that as observed in the wild tomato accession LA716. These accessions showed mite repellence levels similar to those of the wild genotype and may, therefore, be good candidates for breeding programs dealing with resistance to mites.

Indirect selection of industrial tomato genotypes rich in zingiberene and resistant to Tuta absoluta Meyrick.

Obtaining tomato cultivars resistant to pests through interspecific crosses between commercial cultivars and wild accessions is an important tool in integrated pest management. The aim of this study was to select tomato genotypes with high zingiberene (ZGB) levels that are resistant to the South American tomato moth (Tuta absoluta Meyrick) and to estimate genetic parameters of ZGB inheritance from the interspecific cross Solanum lycopersicum cultivar 'Redenção' x Solanum habrochaites var. hirsutum (PI-127826 accession). F2 plants with different ZGB contents were selected and submitted to a tomato moth resistance test. ZGB content exhibits high broad sense heritability, with incomplete dominance of lower ZGB content. Furthermore, the level of ZGB in leaflets was estimated to be controlled by two genes. These results show that high ZGB levels are effective at conferring resistance to the South American tomato moth.

Indirect selection of industrial tomato genotypes that are resistant to spider mites (Tetranychus urticae).

Acyl sugars present in the tomato Solanum lycopersicum 'LA-716' accession confer good levels of resistance to arthropod pests. The objective of the present study was to select F2 plants from the interspecific cross Solanum pennellii 'LA-716' x Solanum lycopersicum 'Redenção' to assess resistance to spider mites (Tetranychus urticae) based on the leaf acyl sugar content and repellence tests. Four genotypes were selected with high leaflet acyl sugar content (RVTA-2010 pl#31, RVTA-2010 pl#75, RVTA-2010 pl#83, and RVTA-2010 pl#94), and an additional three genotypes with low acyl sugar content were also selected (RVTA-2010 pl#33, RVTA-2010 pl#39, and RVTA-2010 pl#73). The results from the in vivo tests used to confirm the selection of plants resistant to mites indicated that the genotypes with high acyl sugars content did not differ from the resistant parent LA-716. The negative correlation between acyl sugar content and the distance run by the mite along the leaflet surface confirmed the association between high and low allelochemical content and resistance. The medium degree of dominance (MDD) was estimated (MDD = -0.83), indicating that the high acyl sugar content was due to incomplete dominance of a recessive allele. A value of 81.85% was found for the broad sense heritability estimate, which suggests that most among-plant variation in the F2 generation is genetically based. Furthermore, 0.69 genes were estimated, which presumably confirms monogenic inheritance. Thus, indirect selection was an efficient method used to obtain industrial tomato plants that are resistant to spider mites.

Establishment and molecular characterization of a sweet potato germplasm bank of the highlands of Paraná State, Brazil.

The sweet potato (Ipomoea batatas L.) is a crop of great importance in developing countries, as a food staple, for animal feed, and potentially for biofuel. Development of cultivars adapted to specific regions within these countries would be useful. To start a breeding program, the first step is the establishment of a germplasm bank. We initiated a sweet potato germplasm bank with accessions collected from the highlands of Paraná State, Brazil. To establish this germplasm bank, we carried out numerous sweet potato-collecting expeditions in regions with an altitude above 700 meters in this region; 116 genotypes currently comprise this collection. The genetic diversity of this germplasm bank was estimated using inter simple sequence repeat (ISSR) markers. Polymorphic information content (PIC), marker index (MI), and resolving power (RP) were calculated to determine the viability of ISSR markers for use in sweet potato genetic studies. The correlation between PIC and MI (r(2) = 0.81) and between MI and RP (r(2) = 0.97) were positive and significant, indicating that ISSR markers are robust for sweet potato identification. Two ISSR primers, 807 and 808, gave the best results for all attributes, and thus could be used as representative ISSR primers for the genetic analysis of sweet potato. Cluster analysis and principal component analysis indicated high genetic variability (0.51 of similarity among all genotypes); genotypes collected from different counties grouped together.

Genetic divergence among Brazilian garlic cultivars based on morphological characters and AFLP markers.

Outside its centers of origin, garlic propagates only asexually. Since asexual reproduction leads to the absence of meiotic recombination, the main garlic cultivars available for cultivation have arisen from the accumulation of somatic mutations in early cultivars. Thus, it is common for a single clone to have different names in different regions. This study aimed to evaluate the genetic diversity of 20 garlic cultivars by using morphological characters and amplified fragment length polymorphism (AFLP) markers to identify possible duplicate cultivars. We assessed 28 morphological characters related to the leaves, bulbs, and bulbils of the garlic plant and divided them into two categories: quantitative and qualitative (14 characters each). For molecular marker-based analysis, we used three AFLP primer combinations. Genetic divergence was calculated using the Jaccard coefficient; the cultivars were grouped using unweighted pair-group mean analysis. The average genetic divergence detected using the morphological characters was 2.30 (range, 0.45-4.70). Plant height and coat adhesion exhibited the highest divergence among the cultivars. The average genetic diversity based on AFLP data was 43% (range, 0-79%). Dendrograms derived from both techniques divided the cultivars into two groups: noble and semi-noble. Together with the divergence within groups, the correlation between morphological and molecular data suggested that the cultivars in the noble group had greater phenotypic stability than those in the semi-noble group. Analysis of Jonas and Quitéria cultivars using these two techniques revealed only slight differences, suggesting that these cultivars may be clones or have a high degree of kinship.

Selection of processing tomato genotypes with high acyl sugar content that are resistant to the tomato pinworm.

Acyl sugars are allelochemicals present at high concentrations in leaves of accessions of the wild tomato Solanum pennellii; they confer resistance to a large number of arthropod pests, including the tomato pinworm, Tuta absoluta (Lepidoptera, Gelechiidae). Accession 'LA716', with high contents of acyl sugars in the leaves, was used as a source of resistance to start a genetic breeding program of processing cultivated tomato, S. lycopersicum. We selected plants of the F2 generation of an interspecific cross (S. lycopersicum cv. 'Redenção' x S. pennellii 'LA716') for extremes of concentrations (high and low) of acyl sugars in the leaves and evaluated the resistance of selected genotypes to the tomato pinworm, compared with plants of the parental and F1 generations. The concentrations of acyl sugars present in the genotypes selected for high contents were close to those of S. pennellii 'LA 716', while the genotypes with low concentrations of acyl sugars were close to cultivar 'Redenção'. The F1 hybrid ('Redenção' x 'LA716') had intermediate concentrations of acyl sugars, but was closer to Redenção, indicating that the inheritance of this type of character is due to a recessive major gene, along with minor genes with additive effects. There was a direct association between high contents of acyl sugars and non-preference for oviposition and suppression of larval development, indicating that the allelochemical acts through mechanisms of non-preference for oviposition and through antibiosis. Genotypes with high contents of acyl sugars were more effective in reducing the damage caused by the tomato pinworm. Genotypes RVTA-2010pl#94 and RVTA-2010pl#31, selected for high contents of acyl sugars, showed a good level of resistance to T. absoluta, similar to the wild genotype LA716. These genotypes are promising for use in a breeding program for developing commercial processing tomatoes.