Processo infeccioso de Pseudocercospora musae e severidade da Sigatoka Amarela da bananeira em função do silício, potássio e cálcio em solução nutritiva

Yellow Sigatoka leaf spot, caused by Pseudocercospora musae (Mycosphaerella musicola), is one of main threats to banana production around the world. However, information regarding the infection process of P. musae and the influence of mineral nutrition on the disease severity could help with cultural control strategies and increase the fruit yield. Therefore, this work aimed to characterize the infectious process of P. musae in banana leaves, to study the effect of silicon (Si) and the interaction between potassium (K) and calcium (Ca) on the Yellow Sigatoka leaf spot severity. In the first study, samples were inoculated on the abaxial leaf surface with P. musae and analyzed at 12, 24, 36, 48, 72, 96, 120, 144, and 168 hours after inoculation (HAI) as well as 36 and 50 days after inoculation (DAI). The conidia germinated between 24 and 36 HAI and penetrated through the stomata between 96 and 120 HAI, or usually from 144 HAI. P. musae colonized intercellularly the spongy parenchyma at 36 DAI and inter- and intracellularly the palisade parenchyma at 50 DAI. The sporulation occurred at 50 DAI on the adaxial leaf surfaces. In the second study, banana plants grown in nutrient solution with 0; 0.5; 1.0; 1.8 and 3.6 mmol L -1 of silicic acid (H 4SiO 4) were inoculated with conidial suspension. The disease severity was assessed and data were integrated in the area under the disease severity progress curve (AUDSPC). The lower AUDSPC was 49.27% for the concentration of 3.05 mmol L -1 of H 4SiO 4 compared to plants grown without Si addition. Regarding silicon accumulation, at 3.6 mmol L -1 H4SiO 4, leaf Si content was 23.53% higher compared to the control. In the third study, plants grown in nutrient solution with 5 K concentrations (1, 2, 4, 6, and, 8 mmol L -1 ) combined with 5 Ca concentrations (1, 3, 5, 7, and, 9 mmol L -1 ), forming 25 treatments, were inoculated with conidial suspension. The disease severity was assessed and the data were integrated in the AUDSPC. There was no interaction between concentrations of K and Ca for AUDSPC, although the AUDSPC increased with the increase of K concentrations from 1 to 6 mmol L -1 . The K increase led to a reduction in chlorophyll a and b contents and in the N, P, Mg, B, Cu, Zn, and, Mn nutrients as well as increased the total plant dry weight.

Metodologias para a avaliação do potencial fisiológico de sementes de tabaco

Despite tobacco being a culture propagated by seeds, there is little information concerning tests that allow the distinction of similar germination lots in different levels of vigor. The diversity of cultivars available in the market, and a few peculiarities of the species, such as uneven maturation of the flowers, fruits and seeds, small size and seed dormancy, are considered obstacles for obtaining lots of tobacco of high physiological potential. Thus, this research was developed with the objective of adapting feasibility and vigor tests for evaluating the physiological potential of tobacco seed lots. We used nine lots of tobacco seeds of cultivar CSC 447 and nine lots of seeds of cultivar BAT 2101, belonging to variety groups Virginia and Burley, respectively. Initially, germination test was conducted to characterize the profile of the lots. For determining the feasibility and vigor of the tobacco seeds, germination tests were conducted in distinct temperatures, controlled emergence conditions, electric conductivity, artificial aging and in tetrazolium. For determining the isoenzymatic marker for seed quality, analyses were conducted with enzymes catalase, esterase, malate dehydrogenase and alcohol dehydrogenase. In conclusion, the emergence tests at 25oC and artificial aging at 41oC for 72 hours, are efficient in discriminating the lots of tobacco seeds in different levels of vigor. The electric conductivity and germination tests in different temperatures have distinct responses in relation to the genotype of the tobacco seeds. The tetrazolium test using the methodology with pre-conditioning in 3.5% sodium hypochlorite solution and subsequent emersion in 1.0% tetrazolium solution for 18 hours is efficient for the quick evaluation of the feasibility of tobacco seeds. The analysis of the profiles of enzymes catalase, esterase, malate dehydrogenase and alcohol dehydrogenase is efficient as markers for tobacco seed quality.