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Pollen viability is essential for the sexual reproduction in plants. Genetic and environmental factors as well as plant age can influence this characteristic. In this work, pollen viability was studied in guava (Psidium guajava L.), a cross-pollination species. The genetic parameters for this characteristic were estimated considering 22 genotypes, two environments and different plant ages. For that, the pollen viability of the genotypes was evaluated for three years (2013, 2014 and 2015) in two experimental orchards (installed in randomized block design, with three blocks and two plants per plot) and at two different regions of the state of Espírito Santo, Brazil. The plants were analyzed at 19, 24 and 38 months of age in the years 2013 and 2014 in Mimoso do Sul (ES) and 2015 in Linhares (ES), respectively. The flower buds, at pre-anthesis stage, were collected, fixed in ethanol:acetic acid (3:1) and stored at -20°C. Pollen viability was obtained by colorimetric methods (Alexander's, Acetic Orcein and Lugol dyes) and the genetic parameters estimated by means of mixed models. The pollen viability of the genotypes was high, with an overall mean of 93.46% in the thr ee harvests. Mean heritability was lower in the harvests of 2013 (0.479) and 2014 (0.126) in relation to 2015 (0.583), indicating a slighter possibility of predicting genetic gains based on this characteristic. Altogether, these results provide information about pollen viability in commercial and superior genotypes of the guava crop used in this study, given that pollen-donor genotypes are reported to influence characteristics related to weight and fruit quality in this species. In addition, these genotypes showed good potential for cross-pollination, and can therefore be used as pollinators in orchards and crosses within breeding programs.

The tomato root-knot nematode is one of the main phytosanitary problems in crops. Chemical control is the phytosanitary method most used by farmers, and the study of alternative management of phytonematodes is crucial. The objective of this study was to evaluate the effect of silicon dioxide (SiO2) on the initial development of tomato plants, as well as to determine the best dose of SiO2 for inducing resistance to parasitism by M. incognita. This experiment was set up under a completely randomized design with ten treatments and five replicates in a 5×2 factorial arrangement consisting of five concentrations of SiO2 (0, 0.15, 0.3, 0.45 and 0.6 g dm-³ of soil) with the presence and absence of M. incognita, under greenhouse conditions. The following variables were evaluated: plant height; number of leaves; fresh and dry weight of shoot; percentage of shoot dry matter; root fresh weight; number of galls; final population of nematodes; and population per gram of root. The M. incognita infection affected plant height, number of leaves and shoot fresh weight, while the application of SiO2 negatively affected the formation of galls in the roots of the inoculated plants and the population per gram of root, reducing the final population of nematodes in the root system. SiO2 also provided greater development in the tomato plants, with a significant effect on plant height. The ideal dose was 0.34 g dm-3 of SiO2.

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Diploid and polyploid species derived from the euploid series x = 11 occur in the genus Psidium, as well as intraspecific cytotypes. Euploidy in the genus can alter the gene copy number, resulting in several “omics” variations. We revisited the euploidy, reported genomic (nuclear 2C value, GC%, and copy number of secondary metabolism genes) and epigenomic (5-mC%) differences in Psidium, and related them to essential oil yield and composition. Mean 2C values ranged from 0.90 pg (P. guajava) to 7.40 pg (P. gaudichaudianum). 2C value is intraspecifically varied in P. cattleyanum and P. gaudichaudianum, evidencing cytotypes that can be formed from euploid (non-reduced) and/or aneuploid reproductive cells. GC% ranged from 34.33% (P. guineense) to 48.95% (P. myrtoides), and intraspecific variations occurred even for species without 2C value intraspecific variation. Essential oil yield increased in relation to 2C value and to GC%. We showed that P. guajava (diploid) possesses two and P. guineense (tetraploid) four copies of the one specific TPS gene, as well as eight and sixteen copies respectively of the conserved regions that occur in eight TPS genes. We provide a wide “omics'' characterization of Psidium and show the outcome of the genome and epigenome variation in secondary metabolism.

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