Avaliação de pastagens de Brachiaria decumbens Stapf. consorciadas com leguminosas na Zona da Mata Seca de Pernambuco

Abstract

Aimed to evaluate the productive potential, the adaptability, the stability, the repeatability coefficient (r), the minimum number of measurements for the selection with greatest efficiency and reliability and to estimate genetic parameters of Pennisetum spp. genotypes (G), as a function of levels of nitrogen (N). The experiment was carried out in 2009 at the Itambé Experimental Station of Pernambuco, Agricultural Research Institute – IPA, Northeast Brazil, under randomized block in split plot design, being allocated in the main plot four nitrogen levels (control, 30, 60 and 90 kg ha-1 cut-1 ) and in the subplots, 16 Pennisetum spp. genotypes [10 new interspecific hybrids (IPA-1, IPA-7, IPA-8, IPA-A2, IPA-A4, IPA-A5, IPA-B1, IPA-B3, IPA-C8 and IPA-C9), one cultivated interspecific hybrid (HV 241) and five elephant grass cultivars (“Mineirão”, Taiwan A-146, “Elefante B”, IRI 381 and “Pioneiro”)]. The genotypes were evaluated in six cycles (CY), with evaluations in 2010 (04/21, 07/19 and 09/28) and 2011 (01/06, 04/07, 08/03). The variables forage mass (FM), leaf length (LL), leaf width (LW) and internode length (IL) presented triple interaction (G x N x CY). The new hybrid, IPA-7 (“Pioneiro” x IPA Bulk- 1), presented high adaptability (β1 = 1) and high stability (σ2 di = 0) for FM, was not influenced by the interaction, reaching average of 0.88 kg DM shoot-1 cut-1 , LL of 76.24 cm and IL of 78.79 cm. The coefficient of repeatability was of medium-high magnitude for all variables. For variables FM, plant height, LL, LW, stem diameter (SD), leaf chlorosis (LChl) and leaf area index, up to three evaluation cycles was enough to reach R2 of 90% by principal components method, based on the covariance matrix. The genetic parameters of variables FM (h2 = 96%, CVG = 38.19%), LL (h2 = 95%, CVG = 16.05%), LW (h2 = 96%, CVG = 16.17%, b = 1.04), SD (h2 = 93%, CVG = 16.43%) and LChl (h2 = 97%, b = 1.07) are of high magnitude, favoring the selection of superior Pennisetum spp. genotypes