Sugars levels of four sugarcane genotypes in different stem portions during the maturation phase

ABSTRACT Maturation is a characteristic of sugarcane plant (Saccharum spp.) and even when grown under the same soil and climate conditions the varieties differ on the maturation curve. Thus, studies that allow establishing maturation curves of different sugarcane genotypes in the local soil and climate may indicate the proper harvesting period to ensure better quality of the raw material. This study aimed to analyze the levels of soluble sugars during the maturation phase and assess the technological and productivity indexes of four irrigated sugarcane genotypes in the region of Rio Largo, Alagoas. The experiment was conducted in randomized blocks in a 4 x 2 x 5 factorial: four genotypes (RB92579, RB98710, RB99395 and RB961003), two stem portions (internodes 1-4 and internodes 5-8) and five seasons (82, 49, 25, 13 and 3 days before harvesting), each treatment with three replications. Internodes 1-4 showed the highest levels of reducing sugars, while the largest accumulation of sucrose and total soluble solids occurred in internodes 5-8. RB99395 genotype showed more stability in the sugar levels during sugarcane maturation, which can indicate early maturation and high agricultural yield.

La disminución de la población de Gluconacetobacter diazotrophicus en caña de azúcar, después de la fertilización nitrogenada, está relacionada con la fisiología de las plantas en experimentos de raíz dividida / The decrease in the population of Gluconacetobacter diazotrophicus in sugarcane after nitrogen fertilization is related to plant physiology in split root experiments

It has been established that a decrease in the population of Gluconacetobacter diazotrophicus associated with sugarcane occurs after nitrogen fertilization. This fact could be due to a direct influence of NH4NO3 on bacterial cells or to changes in plant physiology after fertilizer addition, affecting bacterial establishment. In this work, we observed that survival of G. diazotrophicus was directly influenced when 44.8 mM of NH4NO3 (640 mg N/plant) was used for in vitro experiments. Furthermore, micropropagated sugarcane plantlets were inoculated with G. diazotrophicus and used for split root experiments, in which both ends of the system were fertilized with a basal level of NH4NO3 (0.35 mM; 10 mg N/plant). Twenty days post inoculation (dpi) one half of the plants were fertilized with a high dose of NH4NO3 (6.3 mM; 180 mg N/plant) on one end of the system. This nitrogen level was lower than that directly affecting G. diazotrophicus cells; however, it caused a decrease in the bacterial population in comparison with control plants fertilized with basal nitrogen levels. The decrease in the population of G. diazotrophicus was higher in pots fertilized with a basal nitrogen level when compared with the corresponding end supplied with high levels of NH4NO3 (100 dpi; 80 days post fertilization) of the same plant system. These observations suggest that the high nitrogen level added to the plants induce systemic physiological changes that affect the establishment of G. diazotrophicus.

La población de Gluconacetobacter diazotrophicus asociada a la caña de azúcar disminuye después de la fertilización nitrogenada, lo cual podría ocurrir por la influencia directa del NH4NO3 sobre la supervivencia bacteriana, o por cambios en la fisiología de las plantas, que impiden el establecimiento bacteriano. En el presente trabajo se observó que en experimentos in vitro la supervivencia de G. diazotrophicus fue influenciada por 44,8 mM de NH4NO3 (640 mg N/plant). Además, G. diazotrophicus fue inoculado en plántulas micropropagadas de caña de azúcar, que fueron usadas para realizar experimentos de raíz dividida, en las que ambos extremos de los sistemas se fertilizaron con un nivel basal de NH4NO3 (0,35 mM; 10 mg N/planta). A los 20 días posteriores a la inoculación (dpi), la mitad de plantas fueron fertilizadas en uno de sus extremos con una dosis elevada de NH4NO3 (6,3 mM; 180 mg of N/plant). Este nivel fue menor al que afectó directamente a las células de G. diazotrophicus; sin embargo, provocó una disminución de la población bacteriana en comparación con plantas testigo fertilizadas con niveles basales de nitrógeno. La disminución de la población fue mayor para raíces fertilizadas con un nivel basal de nitrógeno en comparación con las raíces fertilizadas con altos niveles del mismo sistema de plantas (100 dpi; 80 días posfertilización). Estas observaciones indican que el alto nivel de nitrógeno añadido a las plantas inducen cambios fisiológicos sistémicos que afectan el establecimiento de G. diazotrophicus.

Induction of insect plant resistance to the spittlebug Mahanarva fimbriolata Stål (Hemiptera: Cercopidae) in sugarcane by silicon application

Changes in the agroecosystem with the increase of green cane harvesting in Brazil affected the insect populations associated to this crop, and secondary pests like the spittlebug Mahanarva fimbriolata Stål, became much more important. Many studies have demonstrated the active role played by silicon in plant defense against herbivory. The objective of this study was to evaluate the effects of silicon applications on the biology of the spittlebug reared on two resistant (SP79-1011 and SP80-1816) and one susceptible (SP81-3250) sugarcane cultivars. Sugarcane plants were grown under greenhouse conditions and submitted to different treatments: with and without silicon fertilizer in two different soil type (sandy and clay soil). The newly hatched nymphs were transferred to sugarcane roots and placed into boxes with lids, to keep a moistened and dark environment favoring their growth and maintenance of the root system, providing food access to the developing nymphs. After emergence, adult males and females were placed in cages for mating and oviposition. The silicon absorbed and accumulated in the plant caused an increase in nymphal mortality, and depending on the sugarcane cultivar tested this element also provided an increase in the duration of the nymphal stage and a decrease in the longevity of males and females. 'SP79-1011' presented the highest silicon content in leaves, and M. fimbriolata had the highest nymph mortality and the shortest female longevity. The pre-oviposition period, fecundity and egg viability were not affected by the silicon content in plants or the cultivar used.

Efeito fisiológico do inseticida thiamethoxam na cultura da cana-de-açúcar / Physiological effect of the insecticide thiamethoxam on sugarcane

Com a finalidade de avaliar o efeito fisiológico de thiamethoxam no desenvolvimento inicial de plantas de cana-de-açúcar, foram realizados dois experimentos. O primeiro conduzido em caixas plásticas do tipo gerbox (3,5 x 11 x 11 cm) contendo substrato, aplicou-se thiamethoxam em toletes de cana-de-açúcar, nas doses: 0, 100, 150 e 200 g de ingrediente ativo (i.a.).ha-1. O segundo experimento foi realizado em tubos de PVC (0,2 x 1,20 m), preenchido com solo, utilizaram-se seis doses de thiamethoxam (0, 50, 100, 150, 200 e 250 g i.a.ha-1) em mudas de duas variedades (RB867515 e SP80-1816). Avaliou-se a parte área e o sistema radicular das plantas aos 30 dias após a aplicação do inseticida, no primeiro experimento e aos 130 dias no segundo. Observou-se que no primeiro experimento as características altura, diâmetro e massa seca da parte área não foram alterados em razão da aplicação do inseticida nos toletes de cana-de-açúcar, porém, nos tratamentos com thiamethoxam houve um incremento na massa seca das raízes de até 3,7 vezes mais. No segundo experimento, thiamethoxam proporcionou aumento no diâmetro das plantas e incremento na massa seca das raízes da variedade RB867515 de até 72,69%. No entanto, o comprimento do sistema radicular e a massa seca da parte aérea não foram alterados pela aplicação do inseticida nas mudas.

With the purpose to evaluate the physiological effect of thiamethoxam on the initial development of sugarcane, two experiments were carried out. In the first, carried out in Gerbox-type plastic boxes (3.5 x 11 x 11 cm) containing substrate, thiamethoxam was applied on sugarcane cuttings at the doses of 0, 100, 150 and 200 g of active ingredient per hectare (a.i.ha-1). The second experiment was carried in PVC pipes (0.2 x 1.20 m), filled with soil. Six doses of thiamethoxam (0, 50, 100, 150, 200 and 250 g a.i.ha -1) were used on two cultivars (RB867515 and SP80-1816).Roots and shoots were evaluated 30 days after the insecticide application in the first experiment and after 130 days in the second one. In the first experiment it was observed that the height characteristics, diameter and dry mass of shoots did not change through the use of the insecticide on sugarcane cuttings, however, in the treatments with thiamethoxam there was an increase on roots dry mass up to 3.7 times more. In the second experiment, thiamethoxam increased the diameter of shoots and the root dry mass of RB867515 cultivar up 72.69%. However, the length of the root system and the shoot dry mass were not changed by insecticide application in seedlings.