Agronomic Potential of Leucaena Species and Hybrids in Hawaii

Abstract

A series of 10 experiments was conducted to evaluate Leucaena species and hybrids as forage and total biomass in Hawaii and to determine methods to vegetatively propagate this genus. Eleven Leucaena species comprising 84 selections (species and hybrids) were evaluated at Waimanalo, Maunawili and Mealani, Hawaii from 1991 to 1994. The best yielding forage varieties were hybrids of L. pallida x L. leucocephala. The best dry matter forage yields ranged from 18 to 22 Mg ha-1 yr-1 from 5 harvests yr-1 at Waimanalo and 4 to 5 Mg ha-1 yr-1 from 2 harvests yr-1 at Mealani. Total biomass from these trials averaged 40 Mg ha-1 yr-1 and 11 Mg ha-1 yr-1, respectively. Psyllid resistance was maximized in L. pallida varieties and hybrids with L. leucocephala. Other species with good psyllid resistance included L. esculenta, L. collinsii, and L. diversifolia K749. Cold tolerance maximized among Leucaena pallida x L. leucocephala hybrids and among L. diversifolia species and their hybrids with L. leucocephala. Wood yields maximized in the L. leucocephala K636 cultivar with peak mean annual increment yields ranging from 12 to 38 Mg ha-1 yr-1 • Hybrids of L. diversifolia x L. leucocephala KX3 produced 15 to 16 Mg ha-1 yr-1• Heritability values were derived from studies of psyllid resistance and vigor. Heritability of psyllid resistance ranged from 0.37 to 0.90 for self-and open-pollinated F4 lines of L. pallida x L. leucocephala KX2. Heritability for vigor ranged from 0.25 to 0.86. Heritability of psyllid resistance and vigor for L. diversifolia x L. leucocephala KX3 was 0.64 and 0.70, respectively, reflecting a high degree of self-fertility. Vegetative propagation of Leucaena is often difficult to achieve. Sterilization procedures for micropropagation developed clean explants from field-grown plant material. Contaminated explants ranged from o to 40 % depending on the method used. The best results came from a 3 second dip in 90 % EtOH followed by a 7 minute dip in 20 % v/v chlorox bleach and a 7 minute dip in 0.1 % mercuric chloride. Rooting of coppiced field-grown plant material using 6 to 10 cm long one-leaf cuttings dipped in rooting hormone was successful, with 66 % of tested genotypes rooting to some degree. Rooting percentage within lines ranged from 7 to 60 %. Survivors were transplanted to the field to develop seed production orchards.