FORAGE DRY-MATTER YIELDS AND PSYLLID RESISTANCE OF 31 LEUCAENA SELECTIONS IN HAWAII

Forage yields of L. leucocephala (Lam). de Wit have been reduced as the result of psyllid damage since Heteropsylla cubana Crawford invaded the Hawaiian Islands in 1984. The forage productivity and psyllid resistance of 31 Leucaena species and interspecific hybrids were assessed from 5 harvests in Hawaii during 1991 and 1992. The trial consisted of an augmented randomized complete block with 22 Leucaena selections in all 4 replicates, 2 selections in 3 replicates and 7 selections in 1 or 2 replicates. Forage (leaves and stems < 6 mm diam.) dry matter (DM) biomass yield over a 13-month period ranged from 1.4 to 34 Mg ha(-1) from total DM ranging from 1.9 to 63.7 Mg ha(-1). Percent forage fractions ranged from 49 to 78% (forage DM/total DM). The 10 selections in this trial of either L. pallida Britton & Rose, and its hybrids with L. leucocephala consistently produced both the highest forage and total DM yields averaging 22 and 40 Mg ha(-1) respectively. This represented a three-fold increase in forage production when compared to L. leucocephala K636 (a standard around the world). The excellent performance of the L. pallida lines was attributed to high psyllid resistance and seedling vigor. All L. pallida selections with the exception of K953 exhibited good psyllid resistance. Leucaena diversifolia Benth. K749, L. pallida K376, and L. esculenta (Moc. & Sesse) Benth. K950 had the highest psyllid resistance (p < 0.05). Psyllid damage was negatively correlated to forage DM yield at both harvest 2 and 5 (r = -0.55, p < 0.01, n = 94). Forage DM was positively correlated to seedling vigor for the first harvest (r = 0.83, p < 0.001, n = 74) and combined harvests (r = 0.88, p < 0.001, n = 74).