Interspecific hybridization in the genus Leucaena produces hybrid vigor, resulting in highly adaptable varieties that expand the growth range of the genus. This study was conducted to test the total biomass (combined stem and forage fraction), total forage dry matter (DM) yield, psyllid (Heteropsylla cubana Crawford) damage, and phenolic concentration of Leucaena F-1 hybrids in comparison with species-level selections in two distinctly different environments. A total of 19 Leucaena spp. and hybrid selections were tested for 2 yr at the Waimanalo and Mealani Research Stations in Hawaii. Thirteen species and hybrid selections were replicated three times and included species selections from L. pallida Britton & Rose; L. leucocephala (Lam.) de Wit; L. diversifolia (Schlechtend.) Benth. (2n = 4x); and L. trichandra (Zucc.) Urban [syn. L. diversifolia (Schechtend.) Benth. subsp. trichandra (Urban) F.J. Pan] (2n = 2x). Additionally, five selections were interspecific F-1 hybrids and two were advanced-generation interspecific hybrids. Six other selections were augmented in the trials. Over 2 yr, L. pallida x L. leucocephala F-1 hybrids (K748 x K636 and K748 x K584) had the highest DM yield at both locations. At Waimanalo, K748 x K636 produced 53.4 Mg ha(-1) total DM biomass of which 24.6 Mg ha(-1) was forage, while at Mealani, K748 x K636 produced 29.4 Mg ha(-1) total DM biomass and 9.6 Mg ha(-1) forage. These yields were twice those of L. leucocephala at Waimanalo and eight times greater at Mealani. Leucaena leucocephala was the most susceptible to psyllid damage (P < 0.001), while the most resistant was L. trichandra (2n = 2x). Leucaena pallida hybrids had intermediate levels of psyllid resistance. Psyllid damage was negatively correlated with forage DM once at Waimanalo (r = -0.37, P < 0.05, n = 42). Forage phenolic concentration averaged 110 mg g(-1) for all treatments at both locations and was correlated once to psyllid damage (r = 0.32, P < 0.05, n = 42) at Waimanalo. Superior yield, psyllid resistance and cold tolerance of L. pallida x L. leucocephala hybrids was observed at low and high elevation sites.
