Avaliação agronômica e nutricional de híbridos de sorgo com capim-sudão normais e mutante bmr em quatro idades de corte

Abstract

The aim of this study was to evaluate the agronomic traits, nutritional value, in vitro fermentation kinetics and the effects of bmr mutation and cutting age on these parameters in sorghum x sudangrass hybrids BR 800, BRS 810 (bmr), BRS 802 and 156x2784 cut at 52, 61, 67 and 74 days after planting. The hybrids BRS 810 (bmr) and BRS 802 are isogenic pairs differing only by the presence of the bmr-6 mutation in the first one. Regarding the agronomic traits, the hybrid BRS 802 stood out due to its higher dry matter (DMY) and digestible dry matter (DDMY) yields (P<0.05), while the hybrid BR 800 stood out due to its higher leaf/stem ratio (P<0.05). The bmr-6 mutation caused an average reduction of 25% on DMY, 19% on DDMY (P<0.05) and did not affect plant stand and leaf/stem ratio (P>0.05). Regarding the nutritional value, the hybrid BR 800 stood out when compared to other conventional hybrids due to its lower levels of ADF and lignin and higher in vitro NDF digestibility (P<0.05). The bmr-6 mutation led to an increased nutritional value due to reductions in NDF, ADF and lignin levels and an increase in crude protein content and in vitro dry matter and NDF digestibility (P<0.05). Regarding the in vitro fermentation kinetics, at ages of 61, 67 and 74 days, the bmr-6 mutation caused an increase in cumulative gas production after an incubation time of 72 and 96 hours (P<0.05). At ages of 61 and 74 days the isogenic pair presented different in vitro fermentation kinetics (P<0.05) that were mainly characterized by higher gas production from the fibrous carbohydrates fraction by the mutant hybrid. The highest yield and good nutritional value presented by hybrids at 74 days indicate that they may be used at this age. The hybrid BRS 810 (bmr) showed higher nutritional value than its isogenic pair and other conventional hybrids and, although it presented lower yield potential than its isogenic pair, this potential was similar to that of other conventional hybrids. In this case, using the bmr-6 mutation can be interesting, especially when seeking for higher individual productivity rates.