Highlights of Dr. Brewbaker’s Leucaena Tree and Sweet Corn Breeding Programs

We were privileged to have Dr. James Brewbaker as a speaker at our annual conference in November 2007. As a plant breeder at the University of Hawaii, Dr. Brewbaker has devoted many years of scholarly research to the leucaena tree and to sweet corn. He has always had a strong interest in ways that his work can benefit smallholder farmers. This article will highlight seeds he donated to ECHO’s seed bank, along with key points from his presentations, his conversations with ECHO staff, and his publications.

Leucaena leucocephala, frequently referred to as ‘Leucaena’ (in Australia and the United States) and Ipil ipil (in the Philippines) is a long-lived, fast growing, leguminous, multi-purpose agroforestry tree. Uses include reforestation, fuel wood, shade crop for coffee and cacao, green manure, and fodder. As fodder, leucaena has nutritional value that can be comparable to that of alfalfa. It can be toxic to non-ruminant animals, and to ruminants (cows, goats) that do not have appropriate ruminant bacteria (Synergistes jonesii; often already present in ruminant animals in the tropics). The toxic effect is due to mimosine, an unusual amino acid present in the leaves and seeds.

Leucaena originated in Central America and Mexico. Early in the 16th century, Spanish traders brought what is now referred to as ‘common’ (also known as ‘Hawaiian’) leucaena to the Philippines. Common leucaena plants are shrubby and tend to be weedy. Nonetheless, the agroforestry potential of the plant was widely recognized and common leucaena spread to most of the tropics, thriving in low-elevation areas with slightly alkaline soils.

|

Leucaena plantings were mostly free of pests until late in 1982 when the leucaena psyllid (Heteropsylla cubana) began to spread beyond its native territory in Central America to parts of the world where there were no insect predators to keep it in check. There it caused major damage to existing plantings. Urgent research efforts led to new types of L. leucocephala that were selected from extensive collections at the University of Hawaii and other institutions. Types have been identified that are resistant to psyllids and are better suited to forage (Peru type) and timber [Salvador (Hawaiian giant) type] production. ECHO currently carries seed of K6 (Peru), K8 (Salvador), K67 (Salvador; heavy seeder), K500 (cross of Peru and Salvador types; excellent for forage), and K636 (Hawaiian giant; cold tolerant and psyllid resistant).

Dr. Brewbaker emphasizes that there are at least 21 other leucaena species besides L. leucocephala, and that some of these possess traits that provide plant breeders with even greater ability to address the problems mentioned above. L. diversifolia (ECHO carries seeds of K156 and K784), for example, provides genes for cold tolerance. L. pallida has resistance to psyllids and low seediness. Crossing L. leucocephala with L. pallida resulted in a hybrid (KX2 Hawaii) that tolerates cool weather, has psyllid resistance, and is low in mimosine. At the November 2007 conference, Dr. Brewbaker provided ECHO’s seed bank with KX2-Hawaii seeds. See the final paragraph of this article for information on how to request a trial packet of seed.

Concerning seed propagation of KX2, Dr. Brewbaker mentioned that the traits of this hybrid can be maintained over successive generations of seed saving as long as seed is collected from more than just two or three trees. He recommended establishing leucaena “orchards” as living seed banks, and suggested eliminating off-types. An off-type of KX2, for instance, would be a tree that is shrubby and produces numerous seed pods in large bunches. True-to-type, less-seedy KX2 trees produce just a few pods that usually occur singly in the tree canopy. (Leucaena trees can produce so many seeds that they become a weed problem. Consequently, types that produce much fewer seeds are desirable).

Dr. Brewbaker also spoke about his efforts to develop sweet corn varieties that perform well in the tropics. North American sweet corn varieties typically fail in the tropics, largely because day length in the tropics is shorter than an average summer day in the northern hemisphere. Pests such as earworms can also significantly harm the plants.

An open-pollinated sweet corn variety that Dr. Brewbaker developed is called ‘Hawaiian Supersweet’. He provided us with seeds of both a yellow and white kernelled form of this variety. ECHO has carried the yellow-kernelled type in the past; the type with white (also called silver) kernels is a new addition.

Brewbaker continually “massages” ‘Hawaiian Supersweet’ by growing it out and selecting ears from the best plants. The seeds he gave us during the 2007 conference are thus an improvement over seeds we have carried in the past. He also gave us seeds of ‘Sweet Sarah’, a hybrid with very tightly wrapped husks that prevent earworms from being able to find their way to the cobs and eat the kernels.

Members of our overseas network may request a packet of one or several of the leucaena or sweet corn varieties mentioned above. For more information on leucaena, request or download (www.echocommunity.org) a copy of our “Leucaena” Technical Note, written by Dr. Brewbaker.