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Leucaena Cytogenetics in Relation to the Breeding of Low Mimosine Lines¹

Cytological and biochemical studies were conducted in the genus Leucaena in relation to the breeding of low mimosine, high yielding forage types of L. leucocephala (Lam.) de Wit. Meiotic and mitotic chromosomes were studied in the following species; L. leucocephala and L. pulverulenta (Schlecht) Benth. (2n = 56); L. trichodes Benth., L. lanceolata (S. Wats.), L. stenocarpa (Urban), and accessions designated "L. buitenzorg" (2n = 52) and "L. esculenta" (2n = 104).

All species of Leucaena hybridized freely, insofar as they were tested. The 80-chromosome hybrids of L. pulverulenta x L. leucocephala were grown and studied in detail. Seed recovery and yields of these hybrids were high, despite meiotic chromosome pairing of 26 bivalents and 28 univalents. F₂ plants ranged widely in chromosome numbers.

Assays for the toxic alkaloid, mimosine, were conducted on F₁, F₂, and backcross progenies from a cross of high x low mimosine strains of L. leucocephala. Despite the apparent polyploidy of the species, wide variations were observed in mimosine contents of the segregating generations, enabling the selection of plants with less than 30% of the normal mimosine values (ca. 4% dry weight) of tropical forage strains. The correlation between mimosine and protein contents for related F₂ segregants from high x low mimosine crosses was not significant (r = .60).

² Former graduate student (now Agronomist, Centro de Investigaciones Agronomicos, Venezuelan Ministry of Agriculture, Maracay), Professor, and Graduate Assistant, respectively, in the Department of Horticulture, University of Hawaii. The authors acknowledge the assistance of the New Crops Research Branch. USDA, in collection of materials, and of Dr. Gary Stringam and Miss Phyllis Bond in cytological studies.

Received for publication October 14, 1966.