Variabilidade genética e caracterização morfológica, produtiva e qualitativa de acessos de Desmanthus spp

Abstract

Knowing the genetic variability, production characteristics and nutritive values of Desmanthus species is essential to identifying promising germplasm within this genus. The objective was to study the genetic variability of Desmanthus spp., namely the morphological, production, and evaluation of plants submitted to moisture stress as well as evaluate of plants submitted to 75 or 120-day cutting intervals. To study the genetic variability we used four accesses native species D. pernambucanus (L.) Thellung (7G, 100C, 43F e 89F) from the Federal Rural University of Pernambuco germplasm bank in Serra Talhada-PE, and Desmanthus pubescens AusTRC, from Embrapa Tabuleiros Costeiros –Sergipe. Through amplified fragment length polymorphism (AFLP), 38 primers were tested, 32 combinations amplified 707 fragments, of which 436 (62%) were polymorphic and 271 (38%) monomorphic, indicating a wide variability among the five accessions. NEI genetic distance matrix indicated that 89F and AusTRC, distinct species collected from different locations (Bom Jardim and Saint Croix, USA, respectively), had less genetic distance (33.5%) compared to 43F and 100C belonging to D. pernambucanus but collected in Bom Jardim and Sertania, with 57% distance. The geographically closest D. pernambucanus accessions, 43F and 89F, had the greatest genetic distance (63%). We submitted three Desmanthus spp. accessions to moisture stress, in a greenhouse: two native species D. pernambucanus (43F e 89F) and one accession, Desmanthus spp. (AusT), from Embrapa Tabuleiros Costeiros –Sergipe, were submitted to moisture stress 7 and 21-day. The 43F accession showed a decrease (P≤0.05) in growth rate of 0.03 cm day-1 in diameter, Aust and 89F accessions showed (P≤0.05) growth rate average of 8.40 and 4.27 cm, respectively in water suspension of 21 days. We also observed reductions (P≤0.05) in the number of branches, number of leaves, length of leaves and stem diameter. However, 89F and Aust accesses showed an increase (P≤0.05) in width of water hanging on leaves after 21 days. Occurred proline accumulation in moisture stress 21-day of 90.22 mg kg-1, and greater 43F shown (P≤0.05) accumulation of 89.46 mg kg-1 differing from 89F (24.91 mg kg-1) and AusT (45.01 mg kg-1) accesses. Accumulation of total soluble carbohydrates were observed in leaves of plants submitted to moisture stress 21-day in 43F (32.62 g kg-1) and 89F (33.07 g kg-1), AusT showed accumulation lower of 13.64 g kg-1. AusT presented in leaves, the higher (P≤0.05) crude protein (229.03 g kg-1), higher (P≤0.05) carbon (390.52 g kg-1), the lower (P≤0.05) C:N ratio (10.65) and higher (P≤0.05) chlorophyll a (25.33 μg g-1) and b (10.48 μg g-1) submitted to moisture stress 21-day compared to D. pernambucanus. accesses. It was observed that SPAD is not suitable for evaluating chlorophyll content in Desmanthus spp. submitted to moisture stress 21-day. As such, 43F and 89F were more susceptible to water 21 day moisture stress. Accession AusT is indicated for cultivation under water suspension of 21 days, with better morphological and chemical behavior. The third study included D. pernambucanus accessions 6G, 7G and AusTR. The field trial took place at the Experimental Cane Sugar Carpina, Federal Rural University of Pernambuco, Carpina City. The accessions were submitted to two cutting of 75 and 120-days intervals, between March and October 2015. 6G exhibited greater growth in the rainy season at 75-day intervals (53.01 cm) compared to the dry season 120-day interval (11.01 cm). The 120-day interval resulted in 0.36% greater stem diameter (2.29 cm), 41% greater leaf DM content (484.87 g kg-1), 17.37% less leaf crude protein (CP; 202.07 g kg-1), with 194.45% greater binding to condensed tannins (CT), where 78.27 g kg-1 protein precipitable phenols (PPP) were measured plants cut at 75-day intervals. Compared to 6G and 7G which did not differ from each other, AusTR had 14% greater DM (450.87 g kg-1). The 6G and 7G access not differ from each other, with 397.87 and 393.03 g kg-1 values, respectively. Higher (P≤0,05) CP was found in AusTR (233.91 g kg-1) with PPP of 36.85 g kg-1, as the 6G (214.44 g kg-1) and 7G (210.54 g kg-1) access had lower (P≤0,05) CP (214.44 g kg-1 and 210.54 g kg-1, respectively) and PPP 50.93 g kg-1 and 69.50 g kg-1, respectively. AusTR C:N ratio was 11.05, indicating greater N liberation during leaf decomposition compared to 6G with 12.37, and 7G with 12.48. In vitro DM disappearance for 6G was 651.67 g kg-1, 614.32 for 7G, and 666.71 for AusTR at 75-day intervals and 586.09, 617.11 e 580.75 g kg-1, respectively, for 120-day intervals. Seventy-five-day cutting intervals for these Desmanthus species resulted in the best nutritional values and yields compared to 120-day intervals. Compared to the D. pernambucus accessions, AusTR had greater regrowth and nutritive value.