Genetic parameters estimate for plant characters of a particular carrot population in two different agroecologic cultivation systems / Parâmetros genéticos estimados para caracteres de planta de uma população particular de cenoura em dois sistemas de cultivo agroecológico diferentes

Carrots are among the most planted vegetables in Brazil, which represents importance in the national market. This crop can be grown in conventional and agroecological systems, and studies to improve productivity, disease resistance and root quality in agroecological cropping systems are important. The aim of the present work was to estimate genetic parameters that provide a breeding strategy in the search for the development of new varieties of carrot adapted to the conditions of Distrito Federal's agroecology cultivation. Considering data from tests performed in areas of agroecology cultivation (Natural Agriculture-NA and Organic Agriculture-OA), the following characteristics were evaluated: incidence of leaf blight-LB, incidence of root cracking-CRACK, root length-COMP, format of root tip-TP, format of root shoulder-TO, measure of the color of the a* xylem parameter-a*X, measure of the color of the a* phloem parameter-a*F. Traits were evaluated in 100 half-sib progenies derived from Brasília cultivar, using a completely randomized block design. For the characters COMP, a*X, a*F, TP and TO, the treatment X environment interaction was significant according to the results from test F. The values of the individual variance analyses presented significant effect for the following characteristics: COMP, a*X, TP, TO, LB for NA system, and COMP, a*X, a*F, TP for OA system. In NA system, the values of heritability estimates-ha² for the plant characters fluctuated from 65.66 to 25.52% and, in the OA system, the ha² of the characters a*X, was 81.13%. Estimates of genetic gain per cycle for the characters a*X and a*F were lower in NA system than the estimates observed in OA system.

A cenoura está entre as hortaliças mais plantadas no Brasil, o que representa importância no mercado nacional. Essa cultura pode ser cultivada em sistemas convencionais e agroecológicos, sendo importante o desenvolvimento de estudos para melhorar características de produtividade, resistência a doenças e qualidade de raiz em sistemas com base agroecológica de cultivo. O objetivo do presente trabalho foi estimar parâmetros genéticos que fornecem uma estratégia de melhoramento na busca pelo desenvolvimento de novas variedades de cenoura adaptadas às condições do cultivo agroecológico do Distrito Federal. Considerando dados de testes realizados em áreas de cultivo agroecológico (Agricultura Natural - NA e Agricultura Orgânica - OA), foram avaliadas as seguintes características: incidência de queima das folhas - LB, incidência de rachadura radicular - RACH, comprimento de raiz - COMP, formato de raiz -TP, formato do ombro -TO, medida da cor do parâmetro a * do xilema ­ a*X, medida da cor do parâmetro a *do floema ­ a*F. As características foram avaliadas em 100 progênies de meios-irmãos derivadas da cultivar Brasília, usando um delineamento de blocos inteiramente casualizados. Para os caracteres COMP, a*X, a*F, TP e TO, a interação tratamento X ambiente foi significativa de acordo com os resultados do teste F. Os valores das análises de variância individuais apresentaram efeito significativo para as seguintes características: COMP, a*X, TP, TO, LB para o sistema NA e COMP, a*X, um a*F, TP para o sistema OA. No sistema NA, os valores de estimativa de herdabilidade - ha² para os caracteres da planta variaram de 65,66 a 25,52% e, no sistema OA, o ha² da característica a*X foi de 81,13%. As estimativas de ganho genético por ciclo para os caracteres a*X e a*F foram menores no sistema NA do que as estimativas observadas no sistema OA.

Daucus carota as a novel model to evaluate the effect of light on carotenogenic gene expression

Carotenoids are synthesized in prokaryotic and eukaryotic organisms. In plants and algae, these lipophilic molecules possess antioxidant properties acting as reactive oxygen species scavengers and exert functional roles in hormone synthesis, photosynthesis, photomorphogenesis and in photoprotection. During the past decade almost all carotenogenic genes have been identified as a result of molecular, genetic and biochemical approaches utilizing Arabidopsis thaliana as the model system. Studies carried out in leaves and fruits of A. thaliana and tomato determined that light regulates carotenoid biosynthesis preferentially through the modulation of carotenogenic gene transcription. In this work we showed for the first time that light induces accumulation of psy 1, pds and zds2 transcripts in leaves of Daucus carota (carrot), a novel plant model. In addition, modified roots of carrots exposed to light accumulate zdsl, whereas the pds gene is highly repressed, suggesting that some carotenogenic genes, which are expressed in roots, are regulated by light. Additionally, light negatively regulates the development of the modified carrot root in a reversible manner. Therefore, this suggests that light affects normal growth and carotenogenic gene expression in the modified root of carrot plants. The molecular insight gained into the light-regulated expression of carotenoid genes in this and other model systems will facilitate our understanding of the regulation of carotenoid biosynthesis to improve the prospects for the metabolic engineering of carotenoid production in plants.

Path analysis suggests phytoene accumulation is the key step limiting the carotenoid pathway in white carrot roots

Two F2 carrot (Daucus carota L.) populations (orange rooted Brasilia x very dark orange rooted High Carotene Mass - HCM cross and the dark orange rooted cultivated variety B493 x white rooted wild carrot Queen Anne's Lace - QAL cross) with very unrelated genetic backgrounds were used to investigate intrinsic factors limiting carotenoid accumulation in carrots by applying phenotypic correlation and path analysis to study the relationships between major root carotenes, root color and several other morphological traits. Most of the correlations between traits were close and agreed in sign between the two populations. Root weight had a moderate to highly significant positive correlation with leaf length, root length and top and middle root diameter. Although phenotypic correlations failed to identify the order of the substrates and products in the carotenoid pathway the correct order of substrates and products (phytoene -> zeta-carotene -> lycopene) was identified in the causal diagram of beta-carotene for the Brasilia x HCM population. Path analysis of beta-carotene synthesis in the B493 x QAL population suggested that selection for root carotenes had little effect on plant morphological traits. Causal model of beta-carotene and lycopene in the B493 x QAL population suggested that phytoene synthesis is the key step limiting the carotenoid pathway in white carrots. Path analysis, first presented by Sewall Wright to study quantitative traits, appears to be a powerful statistical approach for the identification of key compounds in complex pathways.

Genetic parameter estimates and efficiency of three selection procedures in carrot breeding, variety Campinas

The potential for genetic breeding of the carrot variety "Campinas" was assessed through estimates of the genetic-statistical parameters of 16 traits of agronomic importance. The parameters were obtained from 102 half-sib progenies, harvested in a seed production field. Two experiments were carried out in Randomized Complete Blocks in the fall-winter and spring-summer planting periods. To compare the three selection methods, usually employed in population breeding genetics the expected genetic gains were estimated considering each blockor plot as strata, and mass selection between and within the half-sib progenies. Samples of 15 marketable roots per plot were evaluated at the individual level for the characters root length (RL) and root shape index (SI). A joint analysis of variance, weighted for the differences in number of replications between the experiments was performed for the six common traits. The results of the genetic parameter estimates of the single variance analysis indicated that the variety Campinas was best adapted to the fall-winter planting period. Heritabilities greater than 60 per cent were observed for the majority of traits assessed at the plot level. The selecction against the trait premature flowering (PF) may result in satisfactory genetic gain in the two environmental conditions because of the high genetic variability coefficients obtained. The percentage of marketable cylindrical roots (MCR) demonstrated an expected genetic gain per cycle of only 4.82 per cent in the fall-winter period, probably because it had already been selected, for various cycles, under these environmental conditions. On the other hand, in the spring-suminer planting period, the genetic gain was estimated to be 14.44 per cent. Total and marketable yields were high in the fall-winter period and low in the spring-summer period. For the traits RL and SI, assessed at the individual level, the stratified mass selection, considering each plot as strata, was less efficient in relation to the other proposed selection methods. Therefore it is concluded that breeding of the variety Caampinas, based on the performance of the half-sib progenies for root quality and yield is fairly promising within each planting period, but simultaneous selection for both periods is difficult.