Banca de DEFESA: ANDRE OLIVEIRA SANTOS

PROFILE OF CARBOHYDRATES AND LIGNIN IN THE BIOMASS OF CULTIVARS AND ECOTYPES OF GUINEA GRASS AIMING AT THE POTENTIAL IN ETHANOL PRODUCTION

Megathyrsus maximus. Cellulose. Fermentable sugars.

Plant species with high growth, high composition in fermentable sugars and low levels of lignin and ash are suitable sources for ethanol production. Forage grasses are considered appropriate for these purposes, due to their rapid growth and high biomass production. The objective of this work was to study such characteristics in commercial cultivars - Tanzânia (TA), Mombaça (MO) and Aruana (AR) - and ecotypes - Assaré (AS), Barbalha (BA) and Caririaçu (CA) – of guinea forage grass, collected from the Cariri region, Ceará. Seeds were collected, disinfected and sown in pots containing medium texture sand with an 80% field capacity. From the On fifteenth day, plants were irrigated alternately with Hoagland's nutrient solution of 1/3 ionic strength and distilled water. On 45 and 90 days after sowing, morphophysiological parameters (leaf length and width, number of tillers, stem caliber and transpiration) were analyzed. The shoots of the plants on 45 days were collected and divided into: primary leaf, secondary leaf, primary stem and secondary stem and the tissues were stored at -20 ° C for biochemical analysis. Levels of glucose, fructose, reducing sugars, sucrose, starch, cellulose and lignin were quantified. Total biomass did not show differences between the materials studied at 45 days; however, biomass of cultivar AR was the lowest at 90 days of cultivation. At 45 days, the glucose and fructose contents of total shoot was significantly higher in ecotypes AS and BA than in cultivar MO. Regarding fructose content, significant differences were found in primary and secondary leaves between cultivars and ecotypes, highlighting the high content in AS ecotype. Sucrose levels followed a heterogeneous accumulation pattern in each tissue of aerial part; however, when tissues were analyzed together, AS, TA and AR stood out. In general, cellulose content in tissues were higher in the cultivar MO and lower in cultivar AS, a pattern also observed when whole aerial part was analyzed. Regarding lignin, there were no differences in levels of primary leaves and secondary stems, however, in secondary leaves there were significant differences between the cultivars MO and TA and, and in primary stems BA stood out due to its low content. In total aerial part, CA ecotype showed lower levels of lignin. In general, total content of sugars resulted mainly from the contribution of cellulose. The AS ecotype did accumulate more high levels of soluble sugars and starch than structural sugars. It was concluded that the TA cultivar and CA ecotype would be suitable to produce ethanol.